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i.-- -- -V DRAFT DETAILED PROJECT REPORT and ENVIRONMENTAL STATEMENT GARAPAN FLOOD CONTROL Saipan, Northern Marianas COASTAL ZONE I N-FORMATION CENTER TC 423 U55 1980 United States Army Corps of Engineers ...SmIng the Army -@lng the Naa@n Honolulu Clistriot DEPARTMENT OF THE ARMY U. S. ARMY ENGINEER DISTRICT, HONOLULU BUILDING 230 FT. SHAFTER. HAWAII 96858 PODED-PJ 28 July 1980 Pacific Region Manager Office of Coastal Zone Management 3300 Whitehaven Street, N.W. Washington, D.C. 20235 Dear Sir: A Draft Detailed Project Report with Environmental Statement has been completed for the Garapan Flood Control Study, Saipan, Northern Marianas. Comments on this document are requested by 15 September 1980 so that they may receive full consideration In the final report. Sincerely, '."" All I Inc] /@@-SUK CHEUNG Re port Chief, Engineering Division ERRATA SHEET GARAPAN FLOOD CONTROL STUDY SAIPAN, CNMI MAIN REPORT 1. Page 18, paragraph 2, line 8: "a million dollars" should read."ten million dollars". ENVIRONMENTAL STATEMENT 1. Page 4, paragraph 3.2a.(2), line 4: Revised line should read "Mean sea level at its seaward end, sloping upward to -2.7 feet at its con-". APPfiNDIX C, ENGINEERING INVESTIGATIONS, DESIGN AND COST ESTIMATES 1. Page C-5, Table C-3. Summary of First Costs: The culvert installation cost for.Plan I should read $669,000, not $669,999. to US Deparbmwt of Commerce NOAA Coastal Savices Center Library 2234 South Robson Avenue Charleston. SC 29405-2413 DETAILED PROJECT REPORT AND ENVIRONMENTAL STATEMENT A STUDY TO DETERMINE THE FEASIBILITY,OF PROVI-DING FLOOD CONTROL IMPROVEMENTS FOR GARAPANj SAIPANj COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS U,S. ARMY ENGINEER DISTRICTj HONOLULU BUILDI.NG 230 FORT SHAFTER, HONOLULU 96858 JULY 1980 GARAPAN FLOOD CONTROL SAIPAN, CNMI MAIN REPORT TABLE OF CONTENTS MAIN REPORT PAGE INTRODUCTION 1 STUDY AUTHORITY I SCOPE OF THE STUDY 1 STUDY PARTICIPANTS AND COORDINATION 2 PERTINENT STUDIES 3 STUDY PROCESS 3 THE REPORT 3 PROBLEM IDENTIFICATION 4 NATIONAL OBJECTIVES 4 PROFILE OF BASE CONDITIONS 5 Physical Setting 5 Human Resources 5 Development and Economy 6 CONDITIONS WITHOUT FEDERAL PROJECT 7 Land Use 7 Economy 7 PROBLEMS AND NEEDS 8 The Flood Problem 8 Analysis of the Flood Problem 9 Related Problems and Needs 10 PLANNING OBJECTIVES 10 FORMULATION OF PRELIMINARY PLANS 11 INTRODUCTION 11 PLANNING GUIDELINES AND CONSTRAINTS 11 Institutional Policies of the Corps 11 Institutional Policies of the Local Government 11 Existing and Proposed Flood Control Improvements 12 of Other Agencies Design-Criteria, Level of Protection 13 00 Environmental Considerations 13 TABLE OF CONTENTS (Cont) PAGE MANAGEMENT MEASURES 13 Nonstructural Measures 13 Flood Warning and Temporary Evacuation 14 Floodproofing 14 Permanent Evacuation and Relocation 14 Floodplain Regulation 14 Structural Measures 14 Ponding 14 Levees and Channel Improvements 14 PRELIMINARY SCREENING 15 Applicable Nonstructural Measures 15 Applicable Structural Measures 15 PLAN FORMULATION RATIONA.LE 16 Technical Criteria 16 Economic Feasibility 16 Environmental and Social Acceptability 17 Preliminary Plans 17 ANALYSIS OF PRELIMINARY PLANS 17 Description of Plans 1, 2 and 3 17 Description of Plan 4 17 Impact Assessment and Comparison of Preliminary Plans 17 SCHEDULED WORK 18 Main Report 19 Appendices 19 LIST OF TABLES TABLE PAGE 1 Summary of Damages Following Typhoon Carmen, August 1978 9 2 Screening of Possible Measures 16 3 Summary Comparison and System of Accounts l8a-c LIST OF FIGURES FIGURES Follows Page I The Pacific Area 1 2 Project Location Map 2 3 Existing and Proposed Land Use 6 4 Land Tenure (Generalized) 6 5 Flood Damage Reaches 8 6 Flood Limits 14 7 Alternative Plan 1 18 8 Alternative Plan 2 18 9 Alternative Plan 3 18 10 100-Year Plan 18 11 Typical Cross Sections, Plans 1, 2, 3 18 12 Typical Cross Sections, 100-Year Plan 18 LIST OF APPENDICES APPENDICES A Hydrology B Geology and Soils C Engineering Investigations, Design, and Cost Estimates D Economics E Social and Cultural Resources F Public Involvement G Recreation and Natural Resources H Compliance Documents INTRODUCTION STUDY AUTHORITY By letter dated-9 May 1978, the Northern Marianas Commonwealth Legislature requested assistance for flood control improvements in the Garapan area. The purpose of this report is to evaluate the extent of the flood problem and to determine the feasibility and justification of Federal participation in providing flood mitigation measures in the Garapan area. The study and report were accomplished under the authority of Section 205 of the 1948 Flood Control Act, as amended: "The Secretary of the Army is authorized to allot from any appropriations heretofore or hereafter made ifor flood control, not to exceed $30,000,000 for any one fiscal year, for the construction of small projects for flood control and related purposes not specifically authorized by Congress, which come within the provisions of Section I of the Flood Control Act of June 22, 1936, when in the opinion of the Chief of Engineers such work is advisable. The amount allotted for a project shall be sufficient to complete Federal participation, in the project. Not more than $2,000,000 shall be allotted under this section for a project at any single locality, except that not more than $3,000,000 shall be allotted under this section for a project at a single locality if such project protects an area which has been declared to be a major disaster area pursuant to the Disaster Relief Act of 1966 or the Disaster Relief Act of 1970 in the five-year period immediately preceding the date the Chief of Engineers deems such work advisable. The provisions of local cooperation specified in Section 3 of the Flood Control Act of June 22, 1936, as amended, shall apply. The work shall be complete in itself and not commit the United States to any additional improvement to insure its successful operation, except as may result from the normal procedure applying to projects authorized after submission of preliminary examination and survey reports." Section 502 of the Covenant Act to establish the Commonwealth of the Northern Marianas (PL 94-241) provided that the U.S. Army Corps of Engineers, con- tinuing authorities for small projects are also applicable to the islands of the Northern Marianas. SCOPE OF THE STUDY The Northern Mar Iiana Islands are a chain of 16 islands in the Western Pacific approximately 3,800 miles west of Hawaii (Figure 1). Saipan, the capital and population center, is the largest island in the Northern Mariana Islands. The island is about 13 miles long,, between 1-112 and 7 miles wide and has an area of 48 square miles (Figure 2). PEKING do SAN OKYO FRANCISCO c'--JT 0 JMANILA HONOLULU) SA PAN HAWAII COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS THE'PACIFIC AREA 4 (STATUTE MILES) FIGURE I The purpose of this draft document is to present the results of engineering and economic analyses which will serve as the basis for the selection of a feasible plan for alleviating the flood problem in Garapan. The study focused on an evaluation of this flood,problem development of conceptual measures for protecting the flood-pron*e areas and preventing flood damages, and the costs, benefits and environmental'impacts associated with implementing these measures. STUDY PARTICIPANTS AND COORDINATION The US Army Corps of Engineers, Honolulu Engineer District, was responsible for conducting the overall study and preparing the report. Studies and investigations were performed with the assistance of the Department of Public Works and the Mariana Islands Housing Authority (MIHA), both of the Government of the Northern Marianas. Initial coordination meetings and a public,workshop were conducted in March 1979. These meetings focused on an identification of the flooding problem and solicitation of the needs and desires of the general public as well as local officials. Boo COMMON WEAL' NORTHERN M@ FARALLON DE PAJAROS- @MAUG ASUNCIO; AGRIMAN PAGAN -o -ALAMAGAN GUGUAN ;ZEALANDIA BANK N OARIGAN *ANATAHAN FARALLON DE MADINILLA- TINIA g SAIPAN %ZJAN ROTA- #*GUAM (USA) NORTHERN MARIANA ISLANDS NO SCALE SAN ROQUE TANAPAG PA CIFIC 0 C E A N GARAPAN PROJECT r SITE ISLAND OF SAIPAN 1 0 1 2 i EEEE@a SCALE IN MILES usu CHALAN SAN VINCENTE KANOA 0 LAKE SUSUPE GARAPAN DRAINAGE BASIN SAN ANTONIO SAIPAN GARAPAN FLOOD CONTROL INTERNATIONAL SAIPAN, CNMI IRPOR PROJECT LOCATION MAP U.S. ARMY ENGINEER DISTRICT, HONOLULU FIGURE 2 PERTINENT STUDIES A reconnaissance report, recommending that detailed studies be undertaken to determine the feasibility of providing flood control improvements for Garapan, was completed in November 1978 by the Corps of Engineers. As a result, this detailed study was authorized. In order to prepare for Commonwealth Government, the Office of Transition Studies and Planning (OTSP) was created to assess social, cultural, governmental, and physical development needs of the Northern Mariana Islands, and to recommend directions and areas of effort which should be emphasized under the newly elected Commonwealth government. Three documents were prepared by the OTSP: (1) The Socioeconomic Plan, finalized in October 1977, investigated the natural, human, and economic resources in the Northern Mariana Islands; and presented goals and strategies for economic growth. (2) The Government Plan presented the necessary government structure and organization plan in preparation for Commonwealth government. (3) The Physical Development Master Plan translated the policies, objectives, and funding targets developed in the Socioeconomic Development Plan into specific capital improvement programs with emphasis on the 1978-1985 period. The Plan'also presented recommended zoning and building regulations and possible implementation procedures. In May 1979, the Coasta 1 Resources Management Office of the Co@monwealth of the Northern Mariana Island completed a draft of the Coastal Land and Water Use Plan (CLWUP) of the Commonwealth. Its purpose was to present a comprehensive land and-water use plan which would encompass previous planning efforts with an emphasis on wise conservation and use of the Northern Marianas' resources. STUDY PROCESS This study follows the guidelines of the Principles and Standards for Planning Water and Related Land Resources, prepared in 1973 by the US Water Resources Council and related Corps 67 FEngineers regulations. The planning process involves plan selection based on increasingly detailed investigations by reiteration of the four interactive tasks of problem identification, formulation of alternatives, impact assessment, and evaluation. Under the Section 205 authority, the Detailed Project Report (DPR), serves as the feasibility, design, and construction authority document. THE REPORT This document consists of a main report which includes the environmental statement, and a series of supporting appendices. The main report is a self-contained docume.nt which describes the planning effort and includes the 3 Environmental Impact Statement. The appendices contain technical detail information and backup data to support the information presented in the main report: The appendices are: Appendices Title A Hydrology B Geology and Soils C Engineering Investigations, Design and Cost Estimates D Economics E Social and Cultural Resources F Public Involvement G Recreation and Natural Resources H Compliance Documents PROBLEM IDENTIFICATION The purpose of problem identification is to develop planning objectives which will guide the formulation of alternative plans. Public concerns which relate to water and related l.and resource problems are identified and then refined based on national and local policies and the study authority. To identify the resource management problems, the base condition.of the study area is defined. The base condition is the existing.economic, social, and environmental chracteristics of the area. Future conditions are then projected and analyzed to determine the "most probable future" which would prevail over the area without any changes to the exist,ing resource management . plans. This analysis produces the without condition criterion. Planning objectives are then established based on the problems and needs of the area as related to the without condition criterion and national and local planning policies. NATIONAL OBJECTIVES The Principles and.Standards (P&S) for planning water and land resources define the national.objectives of National-Economic Development and Environmental Quality. The national objectives provide the basis for formulation and analysis of alternative plans. The National Economic Development (NED) objective is achieved by increasing the value of the nation's output of goods and services and improving national efficiency. The Environmental Quality (EQ) objective provides for the management, conservation, preservation, or improvement of the quality of certain natural and cultural resources and ecological systems in the study area. P&S also require that the impacts of a proposed action be measured in terms of Regional Development (RD) and Social Well-Being (SWB). Contributions to the RD account are determined by establishing a proposal's effects on the region's income, employment, population, and economic base. Contributionsto the SWB account are determined by esiabli'shing a proposal's effects on real income, security of life, health and safety, education, and emergency preparedness. 4 PROFILE OF BASE CONDITIONS Physical Setting. The study area (Figure 2) is located on the west-central coast of Saipan. The 1.9 square mile rectangular-shaped basin is about 1-112 mile long and averages about 1-1/4 mile in width. Garapan Village is located on the western coastal plain. This relatively flat coastal plain varies from 1,000 to 3,000 feet in width and is composed essentially of limesand or artificial fill over limesand. Upland of the coastal belt are steep axial uplands, characterized by a succession of nearby flat benches and vertical scarps of limestone. Slopes in the uplands vary from about 30% to nearly vertical. The climate of Saipan is tropical marine characterized by warm and humid conditions throughout the year. Wind and rainfall are the most variable elements with humidity, temperature, and barometric pressure remaining fairly constant. Average temperature in Saipan is 81.50F (27.50C) and humidity averages 83 percent. During nineteen years of recorded data, annual rainfall extremes recorded at Garapan ranged from 59.8 inches to 115.1 inches. Annual rainfall over this same period averaged about 83 inches. Records indicated that the heaviest rainfall occurs from July through October. Tradewinds are the dominant feature of the wind regime on Saipan. Tradewinds are pronounced from January through May, blowing from the northeast and east-northeast direction more than 90 percent of the time. Wind directions are far more variable during the remaining months. Average wind velocity throughout the year is 10.5 miles per hour. Two principal kinds of storms contribute to the climatic character of Saipan: localized thunderstorms and squalls, and cyclonic tropical storms and typhoons. Saipan is located in a part of the western Pacific that is frequently crossed by tropical storms and typhoons. These low pressure systems are accompanied by high winds (sometimes in excess of 150 miles per hour) and heavy rains. Historically, the heaviest rains have occurred during tropical storms and typhoons. During Supertyphoon Pamela in 1976, 27 inches of rainfall were recorded in a 24-hour period in Guam, located about 120 miles south of Saipan. Although the recorded frequency of typhoons affecting Saipan is irregular, statistics show that one typhoon a year affects Saipan significantly. Human Resources. The present population of Garapan represents about 11 percent of the total island population of 14,800. Today, Chamorros, Carolinians, and Micronesians comprise over 80 percent of the total island population. Alien labor, U.S. expatriates and tourists comprise the remainder of the population. Since western discovery by Magellan in 1521, Saipan has come under various rules. Saipan was originally inhabited by Chamorros who mirgrated from southeast Asia in approximately 500 BC. Under Spanish rule (1521-1898), the Chamorros were forced to relocate to Guam but later resettled on Saipan during 5 the 1800's. It was also during the 1800's that several hundred Carolinians established settlements in Saipan. Following the Spanish-American War in 1898, Germany obtained administration of the island. By World War 1, Japan, which dominated trade in the region during the German rule, had obtained administration of Saipan. By 1930, the total population of Saipan was about 45,000 of which less than 10 percent were native (Chamorro and Carolinian). Under the Japanese administration, sugar production was developed on a large scale. Garapan-became the center of population and commerce. Saipan was captured by the U.S. during World War II and in 1947 the United Nations granted trusteeship to the U.S. Until recently the Northern Marianas were part of the Trust Territories of the Pacific Isiands. On 9 January 1978, under the terms of the Covenant Act (Public Law 94-241), the President of the United States approved establishment of the Commonwealth of the Northern Mariana Islands. Development and Economy. Approximately 50 percent of the total labor force on Saipan is employed by the Government. The most significant industries in the terms of employment and wage distribution are: personal services (tourism and tourism-related); wholesale and retail trade; and transportation and public utilities. Tourism is and will continue to be a significant economic base. In 1977, more than 58,000 tourists visited Saipan, with the bulk of them being Japanese. It is estimated that in 1976, $5.6 million was added to the economy through the visitor industry. Presently, there are six first class hotels on. Saipan with, approximately 780 rooms. Three of these hotels are located in the study area. The 30th Annual Report of the Trust Territory indicates that total exports for the Northern Marianas Islands in 1978 amounted to $4,398,000 which included $756,000 worth of goods; $3,600,000 in tourist goods; and $130,000 in marine products. Existing land uses in the Garapan study area include residential development along both sides of Beach Road, an elementary school, and three of Saipan's largest hotels Figure 3. Just north of the study area is the American Memorial Park, which is a 133-acre area set aside for public use as a memorial to American and Marianas people who were killed or wounded in the Marianas Campaign during World War II. Also, located north of the study area are the island's only dock and port facilities and an industrial area. Because of the various governmental administrations on Saipan over the years, land records are extremely complex. Land and land ownership play a major role in the culture and values of the people of the Northern Mariana Islands. Land ownership is closely tied with family solidarity and a sense of group responsibility. It is often considered solemn duty to retain land within the family, especially among those of Carolinian heritage. This reluctance to sell land has created a high mark*et valuation of land. Figure 4 illustrates the generalized land-tenure for the study area. 6 PA CIFIC 0 C E A N PUNTAN MUTCHOT A MICRO BEACH CONTINENTAL AMERICAN HOTEL MEMORIAL PARK PU LIC RESERVE INTER- CONTINENTAL HOTEL R++ _41% APAN LEME Y C H L ROP)O JUN 10 HAFA ADA[ HOTE HIGH H 0 ttltt .............. PROPOSED__K HOSPITAL LOCATION L E G E N D al AGRICULTURE -GRAZING CONSERVATION RESIDENTIAL HOTEL-RESORT COMMERCIAL PUBLIC FACILITY Ns INDUSTRIAL GARAPAN FLOOD CONTROL SAIPAN, CNMI 0 0.1 0.2 0.3 0.4 0.5 EXISTING AND i PROPOSED LAND USE SCALE IN MILES U-S. ARMY ENGINEER DISTRICT, HONOLULU FIGURE 3 PA CIFIC 0 C E A N ............ PUNTAN MUCHOT MICRO BEACH ...... CONTINENTAL ............ ..... ... .. ....... ... E;Rf'C-AN.::::::.-.- ......... .........I.... ... ..... ........... HOTEL .................... ........... MEMQ JA . ..... .......... .R ............................................... ...... INTER- CONTINENTAL HOTEL ........... .............. ................ .................. ..... ..... .......... ............. ..... .... .... HAFA ADAI NOT E ........... ... ... .............. ll..*.- ...... .............. ..................... .................... .............. ......... . 'A 0- '0*:::::: ..... ...... ........... N ........................ ........... ........ ............. ...... ........ .......... ........... ........... ............. LEGEND PUBLIC PRIVATE PPIVATE VILLAGE tttt SOURCE: PHYSICAL DEVELOPMENT MASTER PLAN FOR THE COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS, JANUARY, 1978. GARAPAN FLOOD CONTROL SAIPAN, CNMI 0 0.1 0.2 0.3 0.4 0.5 LAND TENURE SCALE IN MILES (GENERALIZED) U.S. ARMY ENGINEER DISTRICT, HOMOLULU FIGURE 4 CONDITIONS WITHOUT FEDERAL PROJECT Land Use. The Physical Development Master Plan presents a proposed land use plan for the Garapan area (Figure 3). The proposed plan is based on the concept that Garapan will grow as an independent urban community. It should be recognized that Garapan is already experiencing the fastest residential growth in Saipan. Many factors contribute to Garapan being an ideal site for growth. These include the availability of easily developable land, the presence of water, sewer, and power service, and the probable development of a number of public facilities in the area. The Master Plan presents a number of proposals for public facilities on the Garapan study area. These are: (1) Construction of a junior high school at the intersection of Navy Hill Road and West Coast Highway. (2) Construction of an acute care hospital on Navy Hill Road. (3) Reconstruction of the Garapan Sugar Dock into a fishing village complex. In conjunction with the proposed fishing village, the Legislature of the Commonwealth of the Northern Mariana Island requested the US Army Corps of Engineers to study the feasibility of providing a small boat harbor in this area. Presently, the harbor study is scheduled for completion in late 1980 under the authority of Section 107 of the Rivers and Harbors Act of 1960, as amended. (4) New residential construction. Garapan is undergoing rapid residential growth. The Garapan Estates, for low to moderate income families, is being constructed under the auspices of the Mariana Islands Housing Authority (MIHA). Site development for phase I of the Sugar King II subdivision is presently being conducted by MIHA. Ultimately, this develop- ment will add more than 200 new houses in the study area. In addition, the Physical Development Master Plan suggests the possible expansion of tourist accommodations by the construction of another hotel in the coastal strip between the Hafa Adai Hotel and Saipan Intercontinental Hotel. A community commercial center, to be located just north of the junior high school site, is also proposed. Commercial activities will be limited to personal service uses, such as banks, grocery stores, insurance offices, laundromats, barber shops, bakeries, restaurants, and other similar uses. In conjunction with the commercial center, a multiple family residential area is proposed in the area surrounding the commercial center. Other proposals for the near vicinity but not within the study area are port and dock facilities improvements and upgrading of the industrial park, both located north of Garapan in Tanapag. Economy. Tourism and agriculture are expected to play major roles in the development of the Commonwealth. Construction is also expected to increase significantly. A more limited role is projected for manufacturing and services and trade. Government is still expected to employ the majority of the work force even with the relocation of the Trust Territory Government headquarters to Ponape by 1981. 7 The visitor industry is expected to be the leading industry for development in the immediate future. By 1985, it is estimated that 200,000 persons will visit the northern Mariana Islands annually, which represents almost a four-fold increase over the present visitor count. With the expanding tourist industry, related services such as restaurants, tourist agencies, sports fishing, car rental, and souvenir shops should be enhanced. Garapan, because of its beautiful beaches, will remain a popular tourist destination. Popular hotels, such as the Saipan Continental, the Saipan Intercontinental, and the Hafa Adai are located within the project area. Construction of another hotel should add to the economy, both in terms of construction and tourism. PROBLEMS AND NEEDS The Flood Problem. Although their history has not been documented, floods are a common occurrence in the lower Garapan area. Many long time residents have stated that flooding is experienced almost yearly. Because of the relatively flat terrain in the lower basin and the lack of a suitable outlet channel, severe ponding problems occur following moderate as well as heavy rainfall. Developments within the basin which are subject to flooding include an extensive number of residential structures, some small "mom and pop" stores, and moderate sized commercial establishments. Photographs of flooding in Garapan on file with MIHA were reviewed by members of the Honolulu District during a field investigation in February 1979. The photos included floods of August 1976, September 1977, and August 1978. Although the Garapan area is frequently plagued by flooding problems, detailed records of past floods are not available except for the flood of August 1978 resulting from Tropical Storm Carmen, the worst flooding in Garapan in recent years recalled by local residents. Flooding from this storm caused an estimated $2.0 million dollars in damages to private dwellings, public facili- ties, and agricultural crops in Saipan. In the Garapan area, damage records revealed that total damages exceeded $200,000. Most of the damage were to newly-built private dwellings in the Annex I, Annex II, and Puntan Muchot subdivisions (Table 1 and Figure 5). The maximum flooded area was about 90 acres. Depths of inundation ranged up to 1-112 feet of essentially non-velocity flooding. The bulk of damages resulted when silt.-laden stormwaters entered houses and damaged home contents. Furthermore, stormwaters remained ponded over a period of days within the housing areas, hindering cleanup efforts and daily activities. On 18 August 1978, President Carter, acting on a request from Governor Carlos Camacho, declared the Commonwealth of the Northern Marians a federal disaster area. The August 1978 flood is estimated to have a recurrence interval of 30 years. 8 LEGEND: ANNEX I LIMIT OF FLOOD DAMAGE ANNEX 11 PUNTAN MUCHOT DRAINAGE BOUNDARY PUNTAN LIMIT OF FLOOD DAMAGE, MUCHOT Q ANNEX I A X. AN IEX It ?E 2, CV cj@, zo '/ 17 IN -I c ikl* cl Flo ABAWN .2 -LIMIT OF FLOOD DAMAGE brAINAG (J.4. U f cc GARAPAN FLOOD CONTROL SAIPAN, CNMI FLOOD DAMAGE REACHES -4 U.S@ ARMY ENGINEE4 OIST., HONOLULU FIGURE 5 Table I SUMMARY OF DAMAGES FOLLOWING TROPICAL STORM CARMEN, AUGUST 1978 tuamage in $1,00UT No. of Damages Subdivision Structures Content Structural Miscellaneous To_t__aT_ Annex 1 31 $ 51.50 $23.96 $ 6.12 $ 81.58 Annex 11 19 4.13 13.81 .02 17.96 Puntan Muchot 35 96.94 21.30 4.86 123.10 r5 $TTT.-57 $_59.07 P -1.0 $_222.64 Analysis of the Flood Problem. Flooding in lower Garapan can be attributed to two primary factors. The first factor is the lack of a suitable outlet channel to effectively convey runoff to the ocean. Under Japanese rule prior to World War II, shallow open drainage channels conveyed runoff from the As Rapugan and As Felipe hills, through Garapan, to the ocean. However post-World War II residential and commercial developments obliterated most of the channels, causing storm runoff to flow overland as sheetflow. The second factor, which is the relatively flat topography in the area, compounds the flood problem. The elevation range of the lower Garapan area is approximately 3 to 8 feet above mean sea level. Consequently runoff which enters lower Garapan spreads over the coastal plain and remains ponded in lowlying areas. Furthermore, construction of the Saipan Continental and Saipan Intercontinental Hotels on fill added to the problem by preventing water from flowing to the ocean and keeping stormwaters confined within the subdivision area. The existing flood control measures consist of ponding basins which are grossly inadequate. The most critical area is located between the hotel resort area (Continental and Intercontinental Hotels) and the West Coast Highway. The area is designated Area 3A on Plate A-1 of Appendix A. Area 3A is the site of the residential subdivision developed by MIHA. There is no natural drainageway in Garapan. The only remaining drainageway constructed by the Japanese occupa- tional forces is an earth,, grass-lined ditch which runs from the West Coast Highway to the ocean along the Island Power Road. It has an estimated capacity of 190 cubic feet per second (cfs), a 2-year recurrence interval. Due to the land slopes and the lack of drainageways, floodwaters flow essentially in a northwestern direction. Discharges from Area I (see Plate A-1) would flow along the highway towards Area 2. However, because of the limited culvert and swale capacities, dis- charges greater than 25 cfs generally overflow across the highway and flow into Area 1A. Discharges from Area 2 would concentrate at a culvert crossing at the West Coast Highway, where seven 24-inch diameter pipes are located. The crossing feeds water into the Japanese built ditch. Discharges from Area 3 flow over the low point of West Coast Highway in that vicinity and into the problem Area of 3A. The drainage system in Area 3A consists of a ponding area west of the highway and an open concrete ditch 9 below the Beach Road. According to MIHA, the pond has the capacity of containing localized runoff but not flows originating from the upstream area east of the highway. The concrete ditch outlet.is normally blocked by sand at the shorel ine. Related Problems and Needs. Two related water resource problems have been identified in conjunction with this flood control study: offshore water quality and interior drainage. Saipan Lagoon is located on the western side of Saipan, enclosed by a barrier reef located approximately 800 to 1500 yards offshore. Within the lagoon, water depths range from a few inches to about 30. feet. Water clarity and water quality, for the most part, are excellent. Based upon recent public input, water quality of the lagoon and its effects on the beaches are of concern to the community. The Coastal Land and Water Use Plan also emphasizes the aesthetic and recreational value of Saipan Lagoon. The second related problem is interior drainage. While a plan of improvement would convey most of the basin runoff through Garapan, resolution of interior drainage problems is primarily a local responsibility and is not within the scope of this study. In May 1978, the Commonwealth Legislature requested the U.S. Army Corps of Engineers to investigate the feasibility of the federal government assistance in alleviating flooding in the lower Garapan area. At the March 1979 public workshop, local residents stated their concern over the severity and frequency of flooding that they had experienced in the past, and they expressed the need and desire to see an end to the flooding problem. PLANNING OBJECTIVES Based on the analysis of social, economic, and environmental aspects of the study area, and an identification of problems and needs, the following planning objectives have been developed to guide the formulation and evaluation of alternative plans of improvement for reducing flood damages in Garapan. a. Contribute to the reduction in floodwater damages in Garapan during the 1985-2035 period of analysis. b. Preserve (or minimize detrimental effects to) the naturalresources of the area during the 1985 to 2035 period of analysis. 10 FORMULATION OF PRELIMINARY PLANS INTRODUCTION The formulation portion of the study involves the development and evaluation of management measures which best fulfill the previously defined planning objectives. The initial step in the formulation process is the identification of a study constraints and criteria. Then a full range of possible management measures is identified which address the problems and needs of the study area. The next step involves a preliminary screening of the measures based on an examination of the technical adequacy, economic efficiency, environmental management, and social acceptability of each solution. The remaining measures are eveloped further to determine and compare their beneficial and adverse contributions for the purpose of selecting a plan. This draft report is intended to be a plan formulation document, meaning that a number of different alternatives is analyzed and presented for review and comment by local and federal agencies as well as the general public. PLANNING GUIDELINES AND CONSTRAINTS Several criteria and constraints are identified which affect the plan formulation process of the study. These considerations are categorized and described in terms of institutional policies of the Corps, institutional policies of local government, existing and proposed improvements of other agencies, design criteria, and environmental guidelines. Institutional Policies of the Corps. Various Corps of Engineers, regulations on flood control will affect the magnitude of design and the ultimate decision for local and federal participation in terms of costs and responsibilities. The Corps may participate in studies leading to construction of urban flood damage reduction measures. Interior drainage facilities, which consist of structures designed to collect and convey runoff from rainfall in urban areas, are the responsibility of the local government. Flood damage reduction works must conform to regulations on cost sharing and responsibilities between federal and nonfederal interests. The federal government, under applicable statutes of the Corps of Engineers, authorities, will fund all work (up to the statutory requirement of the authority) except for acquisition of land, easements, and rights-of-way, relocations (including utilities and bridges), and associated administrative costs which will be funded by the nonfederal sponsoring agency. In addition to costs indicated above, the local sponsor must agree to certain items of local cooperation. These items will be spelled out and agreed to by the local sponsor in a letter of compliance prior to construction. Institutional Policies of the Local Government. As mentioned previously, the Physical Development Master Plan presents a land-use plan for the Garapan area (Figure 3). Among the major developments proposed for Garapan are a junior high school, a hospital, and two residential subdivisions (Sugar King I and Sugar King 11). Implementation of any of these proposals are ultimately contingent upon funding and priorities of both the Commonwealth and the 11 federal goverment. At the time of this report only the Sugar King II subdivision is under construction. Thus, of the proposed improvements, only Sugar King 11 is assumed existing in the base condition. However, based on conversations with local government officials, the proposed improvements can be realistically assumed to be implemented in the near future. The construction plans for the Sugar King II subdivision show that a 100-foot greenbelt has been provided between the West Coast Highway and the sub- division. Conversations with local government officials indicate that this 100-foot easement could be used for flood control purposes. A preliminary draft of the Coastal Land and Water Use Plan (CLWUP) was prepared by the Coastal Resources Management Office of the CNMI government in May 1979. The document will serve as the basis of conservation and development policies within the context of the Physical Development and Socio-Economic Development Plans. In the CLWUP, various Areas of Particular Concern (APC's) are delineated. The APC1s are defined as unique areas requiring special management considerations. In Garapan, a combined wetlands, flood zone, and mangrove APC is identified. The CLWUP proposes, in part, that attempts should be made to "assist in the relocation of persons in this area, both to reduce damages to the resource values and risk to people's lives, homes, and property in times of floods," and "nonstructural methods of reducing flood damages to property and buildings shall be given preference over structural measures." This study will investigate a number of nonstructural measures including relocation as possible flood control measures. In addition, the CLWUP identifies some historical/archeological site APC's which consist of all identified historic and archeological site which should not be disturbed and should be protected from destruction. Within the Garapan area, historic sites located within the Sugar King Historic Park include the Japanese Jail, Sugar King Monument, German Steps, Shinto Shrine, and Japanese Hospital. In addition, the historic Japanese Lighthouse is located inland, to the east of American Memorial Park (Figure G-1). Existing and Proposed Flood Control Improvements of Other Agencies. At the present time, there are no facilities to convey basin runoff effectively through Garapan. The only existing flood control measures consist of small ponding basins which were constructed by MIHA to handle runoff from the Annex I and Annex II subdivision. However, these ponding basins are small and overflow during moderately-sized storms. The Physical Development Master Plan for Saipan discusses drainage problems and recommendations to solve these problems. Garapan is identified as one area having "acute, chronic drainage problems.." The Plan recommends that a solution to the problem could involve "intercepting and diverting upland storm flows away from existing and proposed residential, commercial and industrial areas and either ponding in conservation area or channeling to the sea or throu h a combination of both methods." The Plan further recommends that "a detailed drainage study be conducted and a facilities plan be prepared for the combined regions of Lower Base, Garapan and Puntan Muchot, including Puerto Rico, the coastal area between Lower Base and Garapan." 12 Design Criteria, Level of Protection. In considering the desired level of protection for both structural and nonstructural alternative plans, the following procedure was used in the determination of various appropriate levels of protection: a. Formulate plans and determine the level of protection afforded by maximizing net economic benefits. b. Formulate plans for higher or lower degrees of protection based on the planning objectives established for the study and other factors, such as desires of local interests, environmental or social considerations, or design considerations. C. Consider the chance and risk of exceeding various floods and the consequences of.exceeding those floods. Based on preliminary benefit maximization studies, net benefits are maximized approximately at the 50-year level of protection. The 2 percent or 50-year flood corresponds to a 87 percent risk that it will be exceeded one or more times in:a 100-year period. It was recognized that alternative structural and nonstructural plans need not afford the same level of protection; however, in view of the benefit maximization studies, the 50-year level is considered the minimum acceptable level. This implies there is still a fair risk of exceeding such a flood level; however, residual damages are not expected to be signifi- cant. Flood limits of the Garapan area are shown on Figure 6. Environmental Considerations. There are a number of statutory and regulatory Te-quirements of the federargovernment which must be complied with during the planning process. The required coordination is largely related to the evaluation and assessment of potential project implementation and impacts on the environmental resources of the area. These requirements are depicted in Table 1 of the environmental impact statement. MANAGEMENT MEASURES Possible management measures for flood mitigation in the Garapan area can be separated into two broad categories, nonstructural measures and structural measures. The effectiveness of these measures in alleviating the flood problem and their economic feasibility and compatibility with existing and desired socioeconomic and environmental conditions in Garapan are discussed in the following paragraphs. The alternative of "No Development" would result in continued damages from flooding and restriction of land use in the flood plain. This action would not be responsive to the study area's needs and was therefore eliminated as an alternative. Nonstructural Measures. Nonstructural measures would not reduce or eliminate the occurrence of floods. They are intended to minimize loss of life and damages when floods occur through implementation of various programs. These include flood warning and evacuation, floodproofing, relocation, and regulation of future development in flood plain areas through zoning ordinances an d building codes. 13 a. Flood Warning and Temporary Evacuation. Flood forecasting can be consider-ec7-useful in two ways: the preparaMon of temporary protection to minimize damage from an impending flood and the evacuation of floodplains anticipated to be inundated. Reliable and timely forecasts of potential flooding and flood stages are necessary to provide adequate warning for effective implementation of this measure. - b. Floodproofing. This measure consists of adjustments to structures and building contents which are designed or.adapted primarily to reduce flood damages. Floodproofing includes, but is not limited to: (a) raising existing buildings, ,(b) providing floodwalls to protect structures and content, (c) providing flood shields for all openings, and (d) providing waterproof coatings to reduce seepage. c. Permanent Evacuation and Relocation. This measure for reducing potential damages in flood-prone areas is the physical removal of all damageable structures located in the floodplain and converting the land to a use that is compatible with the-deigree of flood risk. d. Floodplain Regul.ation. Floodp*lain regulation and management p rograms are designed to control development of flood-prone areas to lessen the damaging effects of floods. Fl6odplain regulation relies on local government's adoption and use of legal tools to control the extent and typeof development which would be permitted.in these areas. The Federal Flood Insurance Program gives residents the opportunity to purchase flood insurance to cover losses from flooding. However, Saipan is not presently under the Flood Insurance Program but indications are that it will be in the near future. Structural Measures.. A variety of structural measures exists for managing resources, reducing flood.damages, and minimizi 'ng or preventing the occurrence of floods. These measures which confine and channel harmful floodwaters include ponding basins, levee and channel improvements, and combinations of these measures. The various structural measures were examined with respect to the study area. a. Ponding. The function of ponding basins is to store a portion of the floodflow in such a way as to reduce the flood flows in the areas to be protected. Ideally, ponding basins should have high permeability for effective infiltration, b. Levees and Channel Improvements. The occurrences of floods and their, damaging effects can be controlled by the construction of levee and channel improvements which are designed to conta 'in floodflows. These types of improvement include realigning the channel to eliminate restrictive bends, enlarging the channel capacity, lining the channel to prevent bank erosion, and constructing structures to confine, divert, or control floodwaters in a designated floodway. 14 1. SUMMARY 1.1 Major Conclusions. Plan 1 is designated the NED plan because of the largest net economic benefits among the plans considered. Plan 4 is designated the least environmentally damaging because it does not affect the wetlands and historic sites in the Garapan area and preserves the floodplain. However, the plan causes the greatest amount of social disruption. All the structural plans have the potential of degrading water quality in the lagoon due to the discharge of stormwater runoff and the water in the outlet channels is expected to be lower in quality than the lagoon waters. The discharge of fill material to line the channels is specified through the application of the US Environmental Protection Agency Section 404(b)(1) guidelines. No endangered species or their critical habitat are likely to be jeopardized by any of the alternatives. All channel plans involve the potential loss of an archaeological data and may require archaeological salvage to mitigate the loss. Similarly all channel plans may involve work and alteration.of wetland areas and will require mitigative measures to avoid the wetlands or to protect the wetlands from physical alteration. 1.2 Areas of Controversy. None known. 1.13 Unresolved Issues. None. 1.4 Relationshi.p to Environmental Requirements. See Table 1. 2. NEED FOR AND OBJECTIVES OF THE ACTION. 2.1 Study Authority. The Garapan Flood Control Study was conducted under the authority of Section 205 of the Flood Control Act of 1948, as amended. The Flood Control Act authorized federal assistance in providing flood protection to a limit of $2,000,000, but $3,000,000 if the area has been declared a major disaster area. 2.2 Public Concerns. a. The study was requested by the Legislature of the Commonwealth of the Northern Mariana Islands. The request indicated a desire to alleviate flooding problems in the Garapan village area of Saipan. Investigations were performed with the assistance of the Commonwealth Department of Public Works and Mariana Islands Housing Authority. b. Flood occu'rrences are common in the coastal areas of Garapan. Factors contributing to the flood problems experienced in Garapan include extensive urban development in a flood prone area, lack of gradient which prevents adequate drainage, and the lack of drainage outlets. While records of past flood damages on Saipan are lacking, tropical storm Carmen, August 1978, caused an estimated $2,000,000 in damages on Saipan to residences, public facilities and crops. In the Garapan area the total damage was about $200,000, involving 85 newly constructed private dwellings in the Annex I, 1 TABLE I RELATIONSHIP OF PLANS TO ENVIRONMENTAL REQUIREMENTS Plan 1 Plan 2 Plan 3 Plan 4 National Environmental Policy Act of 1969 All plans are in full compliance. National Historic Preservation Act of 1966 Partial compliance. Historic Preserva- tion Officer coordination required. Scenic and Wild River Act of 1969 Not Applicable National Trails System Act Not Applicable Federal water Project Recreation Act of 1965 All plans are in full compliance. Water Resources Development Act of 1974 All plans are in full compliance. Coastal Zone Management Act of 1972 In partial compliance. The Common- wealth has no approved CZH plan. Resource Conservation and Recovery Act Not Applicable of 1976 President's Water Policy Initiatives Water Conservation Not Applicable Groundwater Supply and Instream Flows All plans are in full compliance. E.O. 11988 Flood Plain Management All plans are in full compliance. Plan 4 pre- serves the floodplain. Clean Water Act of 1977 Water quality certification Not Applica required. Partial comoliance. Noise Control Act of 1972 All plans are in in full. coispliance. Clean Air Act of 1976 All plans are in full compliance. Pesticide Control Act of 1972 Not Applicable Fish and Wildlife Coordination Act of 1959 7artial compliance. Fish and Wild- life report needed. Endangered Species Act of 1973, as amended All plans are in full compliance. Marine Mammal Protection Act of 1972 Not Applicable Migratory Bird Treaty Act. All plans are in full compliance. Estuaries Protection Act of 1972 Not Applicable Marine Protection, Research and Not Applicable Sanctuaries Act of 1972 E.O. 11990 Protection of Wetlands Partial compliance. Plans may in full affect wetland, but limits of compliance wetland not accurately defined. E.O. 11987 Exotic Organisms Not Applicable Annex II and Pun,tan Muchot subdivisions of Garapan (See Figure 5 of Main Report). On 18 August 1978, President Carter declared the Commonwealth area a disaster area as a result of the storm. At a public workshop held on Saipan in March 1979, local residents indicated their concern over the severity and frequency of flooding and expressd a desire to see an end to their flooding problems. 2.3 Plannin@ Objectives. The following planning objectives were employed in plan formulation. . a. Contribute to the reduction of floodwater damage during the 1985-2035 period of analysis. b. Preserve (or minimize detrimental effects to) the natural resources of the area during the 1985-2035 period of analysis. 3. ALTERNATIVES INCLUDING THE PROPOSED ACTION. 3.1 Plans Eliminated from Further Study. a. Non-Structural Alternatives. Non-structural alternatives involved those alternatives which would reduce flood damages and losses without major construction. These alternatives included floodproofing, floodplain management and flood insurance. (1) Floodproofing. Most of the homes in the floodprone areas are built on concrete slabs laid on the ground-making it expensive to raise the homes above the flood elevations. Constructing berms or floodwalls around each home is not practical and is unacceptable to individual land owners. Other floodproofing measures include flood shields and waterproof coating. (2) Floodplain Management. Floodplain ordinances have not been developed b-y-fne local government. If a program was developed it would apply to the future home construction and does not alleviate flood hazards for existing homes in the floodprone area. The local government is attempting to provide interior drainage to alleviate flooding, but it is not using any specific design criteria in the construction of the drainage structures. However, the local government is aware of the flood hazards and is attempting to alleviate flood damage potential in new developments requiring interior drainage as part of any housing development. Under US Department of Housing and Urban Development funding, interior drainage for a subdivision is required, but the drainage design does not require consideration of upland flows which enter the subdivision. (3) National Flood Insurance Program. The CNMI does not participate in the National Flood Insurance Program. The program enables property owners to buy flood insurance for their homes and its contents at reasonable cost. However, the local government must develop floodplain management measures to protect lives and to regulate new construction in the 100-year floodplain in order to remain in the program. Flood boundary hazard maps have not been developed for Saipan and no floodplain management program is in effect. While the insurance offsets flood losses, damages and losses will continue to occur without structural measures to reduce the flood hazard. 3 (4) Interior Drainage. The local government is improving interior drainage in areas frequentiy damaged by floods associated with rainstorms of short intensity. These measures are required in conjunction with grants from the US Department of Housing and Urban Development, and will not accommodate floodwaters associated with rainstorms of long duration. b. No Action. Flooding and flood damages will continue to occur if nothing is done by any one agency. Residents may be forced to design new homes or redesign existing homes so that they can be raised above anticipated flood elevations. Since most existing homes are constructed on concrete slabs, the homeowner will be forced to undertake major and expensive structural modifications to raise his house, or tolerate periodic flooding and property loss and damage. 3.2 Plans Considered in Detail. a. Channelizing (Plans 1 to 3). The design concept involves a diversion channel above the West Coast Highway that will divert water from the upland portions of the drainage basin and into an outlet channel which will convey the waters through the flat coastal area into Saipan Lagoon. The diversion channel location and alignment remains the same for three alternative outl*et channel alignments but the outlet channel location will vary. The diversion channel alignment follows the West Coast Highway for approximately 3,500 feet (See Figures 7 to 9), along a 100-foot rights-of-way. The channel invert will be 10-20 feet wide, and 7-11 feet below existing ground level. The channel will have a trapezoidal cross-section and will be lined with grass. Where flow velocities are erosive, riprap lining will be provided. The diversion channel may pass close to a wetland and an archaeological site. The exact location of both resources is not known, but methods to avoid the resources and to mitigate their losses will have to be considered if the channel does affect the resources. Aligning the channel to avoid the wetland and historic site will infringe on lands planned for junior high school use. (1) Plan 1. For this alternative, the outlet channel empties into Saipan Lago-on--a-Fo-ut 300 feet south of Hafa Adai Hotel and follows an existing 21-foot-wide drainage channel. The channel will be riprap lined with a 35-foot base width and will have a trapezoidal cross-section. The channel depth will be -6.0 feet below MSL at its mouth, sloping upward to +0.2 feet MSL at the West Coast Highway connection with the diversion channel. The channel will be about 1,700 feet long and will be tidal for the majority of its length. A 120-foot rights-of-way passes through private and government property. The outlet channel would divide the diversion channel into a north and south branch. The south branch will have to be lined with rock. The alignment involves obtaining 5.0 acres of private land and the possible displacement or relocation of four homes. (2) Plan 2. For this alternative, the outlet channel alignment passes around a wetland in the proposed American Memorial Park and discharges into Tanapag Harbor. The channel will be 1,800 feet long and will be 8 feet below mean sea level at its seaward and sloping upward to -2.7 feet at its con- nection with the diversion channel. The channel will be tidal for its entire 4 length. The channel will have a base width of 30 feet, will have a trapezoidal cross-section, and will be lined with riprap. A 110-foot rights-of-way through the park will be required. With this alternative the diversion channel will be grass-lined. (3) Plan 3. For this alternative, the outlet channel alignment passes next to Garapan Elementary School and empties into Saipan Lagoon about 1,000 feet north of the Hafa Adai Hotel, adjacent to the Intercontinental Hotel property. Embankments will be kept low to prevent ponding of water in the floodpron 'eareas.. In order to contain floodwaters, the channel width will be wider than the other alternatives being considered. The channel base w-idth will be 40 feet and will have a trapezoidal cross-section. The channel will be 2,500 feet long and lined with riprap. The channel depth will be 8 feet below MSL at its mouth and slope upward to 2-3 feet below the existing ground level at its connection with the diversion channel. The south branch of the divers.ion channel will be lined with riprap to protect the channel against streamflow erosion. The outlet channel alignment passes,through 4.8 acres of private land and may possibly force relocation of four homes. b. Plan 4, Relocation. Relocation involves removing damageable contents from floodpFo-nestructures and resettling contents and occupants in a flood-free location. Approximately 340 structures would need to be relocated to a flood-free area involving an estimated cost of more than $10 million. This alternative would significantly disrupt the community by relocating families and upsetting traditional values. Those persons who place a high value on land ownership, because of its association with family solidarity and a sense of family responsibility and participation, will be reluctant to leave traditional family owned lands. Those who view land as an economic commodity to be bought or sold for monetary gain will ask a high price for their landholdings. Since there is a lack of housing on Saipan, the local government may have to construct additional housing units to resettle dislocated families or individuals. The alternative also involves terrestrial habitat modification of unknown size and extent and unknown effects on cultural properties. The alternative avoids wetland alterations and possible degradation of coastal water quality due to point source stormwater discharges associated with channel construction. 3.3 Comparison of Alternative Impacts (see Table 2). 4. AFFECTED ENVIRONMENT. 4.1 Environmental Conditions. Garapan village lies in the central coastal area of western Saipan (See Figure 2, Main Report). The present population of the village is 1,700 persons representing about 11% of the total population on Saipan. However, the Garapan region also includes Saipan's only deepwater port facility and concentration of industry at Tanapag and the villages of Tanapag, San Roque, Capital Hill, and Navy Hill. The population of these areas including Garapan village represents about 40% of the total population on Saipan. The vill'age of Garapan is located in an area adjacent to Puntan Muchot Peninsula, and is presently undergoing population growth more rapid than any other village on Saipan. Garapan estates and two Sugar King subdivisions are expected to double population in the Garapan area. Two of 5 COMPARISON OF ALTERNATIVE IMPACTS Diversion Outlet Channel Channel* Plan I Plan 2 Plan Length of Channel (feet) 3500 1700 1800 250 Base width of channel (feet) 10-20 feet 35 30 40 Channel depth at mouth (feet) None -6msl -8msl -8m Channel shape Trapezoid Trapezoid Trapezoid Tra Channel lining Grass. South branch Riprap. Riprap Rip riprap with Plans 1 & 3. Rights-of-way width 100 feet 120 feet 110 feet 130 Flood protection provided 50 year 50 yr 50 yr 50 Local flooding Not Applicable Reduced Reduced Red Wetland destruction Yes No Possible No Terrestrial Habitat Lost 0 1.9 ac. 2 ac. 3.4 Terrestrial Habitat Modified 8 ac 0 0 0 Lagoon Habitat Excavated N/A 300 ft2 400 ft2 480 Volume of Material Removed N/A 1030 CY 1330 CY 163 Intertidal Habitat Created 0 0.19 ac 0.20 ac 0.2 Total Water Volume in Channel N/A 20940 CY 31600 CY 350 Tidal Prism N/A 17000 CY 25930 CY 285 Migratory bird habitat Increased Increased Increased Inc Channelized storm water Yes Yes Yes Yes discharge Littoral drift interruption None Probable Not Probable Pro Diversion channel is same for all 3 structural plans. 0 TABLE 2 COMPARISON OF ALTERNATIVE IMPACTS (Contd) Diversion Outlet Channel Channel* Plan I Plan 2 Pla Threatened/Endangered Species No No Probable Nc Recreation' No effect Increase recreational fishing. Interrupt pedestrian move- ment along the shoreline. Historic resources Potential for destroy- None Channel passes N( ing an archaeological through the site. American Memorial Park, has potential for unearthing WWII artifacts. No. of structures relocated 0 4 0 4 Private Lands Taken 0 5.0 ac None 4 Diversion channel is same for all 3 structural plans. Saipan's most modern hotels and Saipan's best beaches are located at Garapan. The Physical Development Master Plan for Saipan assumes that Garapan will remain a desirable location for new residential growth because of the availability of easily developable land. The plan also provides for a resort-tourist related industry, memorial park, historical park, port and industrial facilities, a new junior high school and elementary school, and a new hospital in the Garapan area. Figure 3 illustrates future land uses in the Garapan area. 4.2 Garapan may have been either a Chamorro or Spanish village prior to the removal of the native Chamorro population by Spain in 1660. Carolinians resettled Saipan in the 1800's and reestablished Garapan before the Chamorros returned to Saipan. During the Japanese occupation of Saipan, Garapan became the center of government, economy and population on Saipan, and the Japanese population far outnumbered the native population. During World War II, portions of Garapan were destroyed and later rebuilt as a fighter strip and as a naval port supporting US military operations. The native population was relocated to Chalan Kanoa/Susupe, but were later allowed to reestablish other villages including Garapan. 4.3 The Garapan coastal area consists of filled land and beach material. Alluvial material overlies hardened limestone at the foot of the limestone hills. Vegetation in the Garapan area reflects previous disturbance by man and is basically identified as coastal strand vegetation, urban vegetation (consisting of a mixture of strand, cultivated and upland vegetation), and the tangan tangan vegetation (cultivated during the war to control erosion). The upland hill areas consist of a mixture of tangan tangan and limestone forest vegetation. Wildlife in the area is dominated by introduced birds. No national shoreline or beach parks, wildlife sanctuaries or refuges, municipal water supply, harvestable shellfish beds, or prime agricultural lands are designated in the Garapan project area. SIGNIFICANT ENVIRONMENTAL RESOURCES. 4.4 Floodplain. The Garapan drainage area is about 1.9 square miles with steep gradients in the hills and a relatively flat coastal plain. Flood problems in the coastal area where the majority of residences are located are caused by severe ponding in the relatively flat coastal area. The lack of a suitable outlet channel contributes to the problem. During the Japanese occupation of Saipan, shallow open channels conveyed runoff through the Garapan area into the ocean. Post World War II construction obliterated the channels causing storm runoff to flow overland as a sheet flow in the low-lying areas. Construction of the Saipan Continental and Intercontinental Hotels on fill raised the ground elevation along the shoreline inhibiting water flow to the ocean, forcing floodwaters into the low-lying subdivision. Essentially, damageable properties are located in a depression between the hills and the fill areas along the shoreline. The construction of roads above the elevation of the ground i'n the low-lying area aggravates flooding because the roads cause waters to pon-d.. 4.5 Groundwater. No municipal groundwater supply sources are located in the area, and the close proximity to the ocean suggests that the water is not 8 potable. Sewerage systems in South Garapan consist of cesspools and septic tanks. The leaching of wastewaters into the groundwater probably occurs. It is not known whether nitrogen laden waters are leaching into the lagoon along the shoreline. In Hawaii the leaching of wastewaters from cesspools into coastal waters along sandy areas has been identified as a water pollution problem. Coastal water quality data is insufficient to determine whether cesspools and,septic tanks in the South Garapan area have any effect on coastal water quality. When floods occur, cesspools and septic tanks overflow, creating a health hazard in the community. 4.6 Littoral Processes. No information on littoral processes is available for the Garapan area. Aerial photographs and information concerning dredged areas at Garapan indicate that a predominant littoral drift is not present on the shoreline. The Garapan Dock area dredged during World War II still has a 12-foot depth despite the lack of any maintenance dredging. Old pier structures perpendicular to the shoreline do not appear to interrupt any along shore sand movement. Another dredged channel north of the Garapan Dock is still evident in aerial photographs. The aerial photographs also indicate that a strong current flow may exist in mid-lagoon where sand movement may be more prominent in the mid-lagoon area. Current surveys indicate that water in the lagoon flows seaward over the barrier reef at Garapan. A sand berm presently blocks the existing drainage channel suggesting that there may be an onshore/offshore movement of sand related to significant storm events. 4.7 Water Quality. No data are available for the Garapan area. No significant pol n sources are present along the shoreline, except for a boat launching ramp at Garapan Dock and an intermittent drainage ditch which discharges into Saipan Lagoon near the Hafa Adai Hotel. Water quality measurements were made in the Unai Sadog Tase area by the University of Guam. Salinity values ranged from 24.4 to 35.5 parts per thousand. Water temperatures ranged from 26.8 to 27-50C. Dissolved oxygen levels ranged from 7.02 to 8.73 milligrams per Titer indicating 109 to 136% oxygen staturation. Nitrate values ranged from 0 to 0.20 microgram-atoms nitrate per liter, and phosphate values ranged from 0.06 to 0.16 microgram-atoms phosphate per liter. The measurements indicate that water quality is relatively good with low concentration of nutrients, high levels of dissolved oxygen and water salinity reflecting some freshwater input. No wastewater discharges are located at Unai Sadog Tase, although the Puerto Rico dump is located just north of the area. 4.8 Wetlands. Two or three wetlands are located in the Garapan area (see Appendi-TIJ-.The larger wetland is located in the proposed American Memorial Park area and two smaller wetlands are located in a residential area in Garapan Village. Grasses dominate the wetland areas, and the wetlands were previously disturbed and modified during World War II. The wetland in the proposed park area was once part of an airfield and is crossed by an eroded, overgrown asphalt road. The area was being used as a dump by the local population. The smaller wetlands are bordered by roads, some of which pass through the wetland. The wetlands provide habitat for a variety of upland birds and migratory shorebirds (see Appendix G). Seventeen species of birds were found in the wetland areas. Six species were found in the small wetlands and 12 species were found in the large wetland. The Chinese least bittern was 9 common to both wetlands. In general, birds found in one wetland were not found in the other. The most abundant birds in the small wetland were the Chinese least bittern and ruddy turnstone. Birds common to the larger wetland were the Philippine Turtle Dove, Marianas Gallinule, White Tern, Cardinal Honeyeater and the Bridled White-Eye. A conceptual plan for the proposed American Memorial Park shows the wetland in the park developed as a Nature Study area and pond. The smaller wetlands are located in an area to be urbanized. The Unai Sadog Tase shoreline of the American Memorial Park is overgrown with mangroves forming a wetland area. No information about this wetland area is available. 4.9 Migratory Shorebirds. The US Fish and Wildlife Service (see Appendix G) observed the White Tern, Lesser Golden Plover, Whimbrel and Wandering Tattler in the urban and beach area of Garapan. The Cardinal Honeyeater, Eurasian Tree Sparrow, Philippine Turtle Dove and the Bridled White-Eye were the most abundant birds observed in the same area. If Garapan is developed in accordance to the Physical Master Development Master Plan, the presence of the migratory shorebirds may possibly decrease. However, the open.beach and park space will also serve as resting and feeding areas for the migratory shorebirds. No nesting sites were found by the US Fish and Wildlife Service. 4.10 Lagoon Resources. A survey of fishery resources in Saipan Lagoon identified 24 fishery habitats and 249 species of fish, recommended preservation of 21 fishery habitats, and identified roughly 24 species of fish of economic importance. The habitats along the Garapan shoreline and Memorial Park shoreline were not identified as the habitats with the most significant fish diversity. The richest fish habitats were those associated with the barrier reef, reefs around Managaha Island and the Acropora thicket in Garapan channel. However, both the Garapan shoreline and American Memorial Park shoreline habitats were recommended for preservation and conservation based on the densities of economically valuable fish. The habitat along the Garapan shoreline fronting Hafa Adai Hotel, Garapan Dock and Mico Beach was described as a Enhalus acoroides seagrass habitat having a fine sand substrate and mixed with other seagrasses and algae. Rabbitfish were abundant in the habitat, while goatfish and snappers were relatively abundant. The mid-lagoon habitat further offshore consisted of sand and rubble dominated by algae with few economically important fishes. The boat harbor within the Memorial Park is a dredged habitat consisting of a silty rubble substrate littered with wreckage that provides unique marine habitats by providing shelter and hard substrate above the bottom. While the highest counts of silversides were made in the habitat, the abundance of silversides was judged by the investigators to be low. Schools of juvenile jacks were also seen in the dredged channels. The habitats were not identified as important fish egg and larvae areas. 4.11 Endangered Species. The US Fish and Wildlife Service Endangered Species Office indicated that the threatened Green Sea Turtle and endangered Nightingale Reed Warbler have been seen in the project area. The status of 10 rare bird species and 2 mammalian species (bats) on Guam is being reviewed for possible inclusion on the Endangered Threatened Species list. The official status of the species on Guam does not necessarily correspond to the status of 10 the species in the Commonwealth. The Guam list did include the Cardinal Honeyeater, Marianas Gallinule, White-throated Ground Dove, and the Bridled White-Eye, which were seen on Saipan. The Nightingale Reed-Warbler, which is endangered in the Trust Territory and Mariana Islands was also seen in the American Memorial Park wetland. 4.12 Recreation. The beaches along the lagoon shoreline provide water- contact recreation opportunities. Boating facilities are located at the Garapan dock and in the proposed American Memorial Park. Micro beach park, the beach fronting the Intercontinental and Continental and the Hafa Adai Hotels, and the Beach Drive beach park also provide recreational resources. Fishing occurs all along the shoreline and underwater tour operators utilize the lagoon for recreational diving and snorkeling. Surfing is not known to be a significant recreational diversion. Physical Development Master Plan for Saipan proposes the development of a Sugar King Historic Park and the develop- ment of the American Memorial Park. School grounds in the Garapan Village also serve recreational needs. A new junior high school is planned on the upland side of the intersection of the Navy Hill road and the Coastal Highway. 4.13 Historical Resources. The American Memorial Park land was set aside in 1978 for development as a park honoring those American and Commonwealth citizens who died during World War II. The proposed Sugar King Historic Park includes structures constructed during the German and Japanese occupation of Saipan. A lighthouse on-Navy Hill and a lighthouse on the barrier reef off- shore from Garapan dock were also constructed by the Japanese and are considered eligible for inclusion to the National Register of Historic Places. A cultural reconnaissance survey-!/ of the proposed channel alignments in Garapan reported one potential archaeological site on the east- side of the Coastal Highway at the intersection of the Navy Hill road in a recently constructed sewer line trench. The outlet channel alignment through the American Memorial Park would avoid significant historic sites found by the National Park Service. 4.14 Social Resources. Approximately 340 structures are located in the flood prone ir-easof Garapan. The majority of residents in the area are native to Saipan and own the land on which their homes are built. They also view landownership as a commodity which can be bought, and as a vehicle of family solidarity and responsibility. The desire to own land is strong and results in a high market valuation of land on an island with limited land area. Many conflicts and confusion regarding landownership exist because the various land law systems which were imposed by non-native rulers created complex and contradictory sets of land records. Thus, many titles to private parcels are in dispute. A government study in 1977 indicated that there were about 3,500 homes on Saipan of which 2,000 were substandard and needed to be replaced. About 150 new homes a year were needed to meet housing demands on Saipan. 5. ENVIRONMENTAL EFFECTS. 5.1 Floodplain. The intercept of stormwater runoff from the upland areas and conveying the Waters through flood prone areas in a channel would not be judged to have an adverse effect on the floodplain. The floodplain is a l/ Pacific Studies Institute, Cultural Resources Reconnaissance for the Garapan Flood Control Study7'-Area, March 1980. 11 developed area highly modified by previous activities, especially those related to World War II. Historic, wildlife, vegetation and water supply resources found in the floodplain are not dependent upon the floodplain for their existence. Relocating damageable properties from the floodplain affords an opportunity to preserve the floodplain possibly encouraging development uses compatible with the floodplain, such as open space parks and agriculture. 5.2 Groundwater. The groundwater in the Garapan area is not potable, and no municipal water supplies are located in the floodplain. All outlet channel alternatives will extend tidal waters inland, but will not affect potable water resources on Saipan. The relocation alternative does not modify waterways or tidal waters, and should not affect groundwater resources. 5.3 Water Quality. Water in the outlet channel will be lower in quality than water in tFe7agoons. The channel will be intermittent, flowing only when rainfall is significant enough to create runoff, and will be.receiving waters for interior and upland drainage. Thus, the channel will accumulate trash, sediment, and a variety of urban stormwater pollutants, which will eventually be discharged into the lagoon. The length of the channel will tend to act as a sediment trap and will require periodic dredging to maintain the channel depth. However, some of the finer sediment will remain suspended and carried into the lagoon when the channel is discharging. The turbid plume may be unnoticeable when the channel is flowing because rainfall over the island area will result in a large discharge of stormwater into Saipan from other village areas around Garapan. Sediment discharged from outlets located in Plans 1 and 3 will be carried northward in the lagoon, then offshore over the barrier reef at Puntan Muchot. Stormwater discharged in the American Memorial Park area may be confined to the area, minimizing its spread to other areas. Flow into Saipan Harbor and dredged areas around the Park is anticipated. Salinity stress is expected to be confined to the nearshore area. Mixing should be adequate to prevent significant salinity variations on the barrier reef. Less than 50% of the water volume in the channel will be exchanged during each tidal cycle. This assumes that all the water within the tidal prism can exit the channel, and once out of the channel does not reenter the channel during the incoming tide. Under no flow conditions, water in the channel will be higher in temperature than lagoon waters, will contain higher levels of nutrients, particularly nitrogen, and will contain a high concentration of phytoplankton. Eutrophic conditions will most likely develop with oxygen levels increasing during daylight hours and decreasing during the night. Periodically, high volume rainfall will create flows strong enough to flush nutrient laden waters from the channel, essentially purging the channel. Plan 1 has the possibility of allowing cesspool and septic tank leachates into the channel, a condition that will contribute to eutrophic development in the outlet channel and possibly create a health hazard. Plan 2 has the potential of being a debris trap. The direction of the prevailing surface drift in Saipan Harbor is toward Puntan Muchot. Any floating trash from the harbor, which drifts into the Unai Sadog Tase area, may also drift into the channel and be trapped there. The direction of surface drift may also impede tidal flow out of the channel, further limiting water exchange in the channel. 12 LEGEh lot' Mill ------ ........... Z@x ell CEO 4%6 qt) IF cz? Z?l 4D k@x SCALE 0 400 0 PRELIMINARY SCREENING Applicable Nonstructural Measures. Because the existing use and proposed zoning (Figure 3) of the Garapan floodplain are primarily residential, preliminary analysis indicated that an essentially nonstructural plan is possible and would partially meet the planning objectives. A nonstructural plan consisting of relocating all existing damageable structures together with a program for local floodplain management has been carried out in the analysis. This plan is discussed further in subsequent sections. Analyses of other nonstructural measures showed that application of these measures would not provide a practical solution to the problems and needs (Table 2) of the Garapan area. Flood prediction, warnings, preparation of temporary flood protection measures and temporary evacuation would help to decrease the flood damages. Because of the uncertainty of predicting hydrologic variables over a small drainage area, these methods of damage reduction for Garapan are not considered suitable. Floodproofing was found to be impractical in view of the large number of homes (nearly 300) of which the majority is the concrete block and slab type. Raising these structures to flood-free levels would require reconstruction of these structures on higher home site elevation which may be accomplished by filling. The concept of floodproofing therefore, was assessed on the basis of providing floodwalls, floodshields, and waterproofing coatings for these structures. The large number of property owners in the affected area, @ogether with other nonstructural steps such as preparation to minimize inundation damages, temporary evacuation and reoccupation, would present many social and economic problems for the affected residents. Although floodplain regulation would control future development and thereby eliminate or reduce damages, this approach will not alleviate the existing flood problems in the developed areas. Applicable Structural Measures. Various structural methods for alleviating the flood threat and preventing flood damages were considered. These included detention ponding; creating channelways and combinations of the above. Preliminary assessments indicated that due to the limited lands, ponding could not provide the necessary capacity and protection without channel or levee improvements. Consequently, alternative flood protection plans for Garapan consisting of diversion and outlet channels were developed for further consideration. 15 TABLE 2 - SCREENING OF POSSIBLE MEASURES Measures Preliminary Findings Flood Warning/Temporary Evacuation Predictions untimely and unreliable for small drainage areas. Flood Proofing Not practical. Adverse socioeconomic impact. Permanent Evacuation and Relocation High cost and adverse housing and social impact, but being considered further. Floodplain Regulation Does not alleviate the existing flood problems in developed areas. Ponding Basins Less favorable than other structural measures. Channel-Levee Improvements Has merit, should consider further. Combination Nonstructural and Less desirable than structural measures Structural from the equity standpoint. PLAN FORMULATION RATIONALE As defined earlier, flood mitigation is the primary objective of this study and the principal benefit values are considered generally basin-wide. Possible measures evaluated include nonstructural, structural and likely combinations of the two. Certain measures were subjected to preliminary investigations only because they were obviously less favorable than other measures in solving the flood problems. Some measures which have implemen- tation possibilities were subjected to more studies to define their technical and economical feasibility, environmental impacts, and social acceptability. These factors are discussed in the following paragraphs. Technical Criteria. Technical criteria established for plan formulation include consideration of alternative plans that can effectively reduce the flood problem or flood damage potential in the Garapan floodplain. The alternative plans should have dimensions adequate to provide a level of protection consistent with design and safety requirements. Economic FeasibiliLy. The alternative plans must be examined for economic feasibility. First, the quantifiable benefits should exceed project economic costs. Second, the project scope and scale should be formulated so that each alternative would maximize its net benefit effects. The economic analysis should be based on current prices, the adopted 50-year period of analysis, and at an interest rate of 7-1/8 percent. 16 Environmental and Social Acceptability. Environmental and social acceptability involved the identificit-ion, assessment, and evaluation of environmental resources and social effects which might be affected by a plan's implementation. Emphasis should be placed on avoidance of plans with severe natural resources, social, and health impacts. The views of the general public, particularly those of the Garapan residents, should be given careful consideration. Support from the public is a necessary item for plan implementation. Preliminary Plans. In view of the lack of existing flood control improvements, and as a result of the preliminary screening of applicable measures, four preliminary alternative plans that could fulfill the planning objectives were developed. One is a nonstructural plan consisting of permanent,relocation, and the other three are levee-channel alternatives. ANALYSIS OF PRELIMINARY PLANS Description of Plans 1, 2 and 3. Three structural channel plans which would provide protection for Garapan were investigated. Under each of these plans, a diversion channel located above West Coast Highway would be provided to convey floodwaters to an outlet channel which would discharge the flow into the ocean. These alternative'plans are shown on Figures 7 through 9. Total length of channel improvements varies from 5,200 feet for Plan 1 to 6,000 feet for Plan 3. Common to all three plans is the 10 to 20 feet base width of the diversion channel. The outlet channel base width for Plan 1 would be 35 feet, Plan 2 at 30 feet, and 40 feet for Plan 3. In addition to relocation of existing utilities such as water and sewer lines, new culvert crossings will be required for all three plans. Plans 1 and 2 will require four new culverts, while Plan 3'requires five. Depending on the exact channel alignment, both Plans 1 and 3 may require relocating four residential structures. Description of Plan 4. In view of the type of existing structures (mostly concrete blocks and slabs) discussed earlier, where elevating work will require substantial reconstruction, Plan 4 provides an alternate nonstructural possibility by permanent evacuation and relocation of residences to a flood-free area. Within the Garapan area, there are approximately 340 structures. This plan would necessitate the development and construction of new homes elsewhere, while the vacated lands would be retained for other passive use consistent with the flooding potential. In compliance with Section 73 of the Water Resources Development Act of 1974 (PL 93-251) which requires that consideration shall be given to nonstructural measures for flood damage prevention, and the President's water policy initiatives on non- structural alternatives, this permanent evacuation and relocation plan has been assessed and is presented in this document. Impact Assessment and Comparison of Preliminary Plans. The structural alternative plans differ with respect to the outlet channel alignment and their impact on factors such as area of construction, location of floodwater discharge, concerns on natural, archaeological, and historic resources which might be affected and construction costs. Plan 1 provides for a shorter length of total channel improvements, and Plan 3 being the longest. No federal or local designated wildlife refuge, marine sanctuary will be affected 17 by any of the channel plans. Potential impact on wetlands would be the greatest under Plan 2, especially within the proposed American Memorial Park site. Plan 2 may also affect or unearth World War 11 artifacts in the proposed park area. Due to the creation of the waterway, all structural plans will benefit migratory bird habitat. Since the outlet channel of Plan 2 does not traverse through the residential area, there will be no acquisition of privately-owned lands and relocation of residential structures will not be necessary. The economic factors, major environmental and social impacts are presented in Table 3 - Summary Comparison and System of Accounts. An evaluation of the discharge of dredged or fill material based on requirements of Section 404 of the Clean Water Act of 1977 is included in Appendix H - Compliance Documents. Plan 4 would have the least environmental impact. Investigations of permanent evacuation and relocation indicate that it is neither practicable nor economically feasible to move the residences of Garapan to another area on Saipan. Because of the shortage of available lands on a small island, high infrastructure development costs and social and cultural considerations associated with relocation, Plan 4 would present economic as well as social problems that cannot be justified. Preliminary cost estimate for evacuation and relocation Is established at more than a million dollars. However, consistent with Corps planning requirements, this nonstructural plan is being carried through the study process and its significant beneficial and adverse impacts are displayed on Table 3. On the basis that exceedence of the design flow would not endanger human lives in view of the low velocity and short-duration flows, no consideration was given to the standard project flood protection level. However, in compliance with engineering regulations, a detailed plan with protection against the 100-year is presented in Figures 10 and 12. The alignment for the 100-year plan is similar to Plan 2 with the outlet channel 11"n the American Memorial Park area. To convey the higher flows and velocities, a major portion of the channel would be concrete-lined, in lieu of the grass-lined section utilized for the 50-year alternative plans. The average annual benefits and costs would be $267,000 and $476,000, respectively. The benefit to cost ratio is 0.6. Of the four plans shown onTable 3, only Plans I and 2 are economically feasible. Plan 1, because of its larger net benefits, has been designated as the National Economic Development (NED) plan. Plan 4 appears to best meet the Environmental Quality (EQ) aspects by preserving the floodplain, and does not impact upon the wetlands and historic sites in the Garapan area. Accordingly, Plan 4 has been designated as the least environmentally damaging (LED) plan. SCHEDULED WORK The final selection of the most suitable and desirable plan will involve further comparison, tradeoffs, and public input. This work will be accomplished following the plan formulation public meeting scheduled for 30 July 1980, and review comments on this draft document. Additional sections to complete this Detailed Project Report are: 18 P A C / F / C 0 C E A N PUNTAN MUCHOT P, X4;,? lk '501k ,A -k MICRO BEACH CONTINENTAL AMERICAN HOTEL MEMORIAL PARK INTER- CONTINENTAL HOTEL EtfEMENTARY 'SCHOOL -TYPE "B"CHANNEL SUGAR HAFA ADAI HOTEL@ XING R Ik OUTLETCHANNEL RIGHT DIVER- OAD SION CHANN CULVERT "B" CULVERT 01cgo 11 TYPE B"CHANNEL "CULVERT "Do' 0 SUGAR KINGI TYPEW'CHANNEL t ExS SWA E cl "IT \,LEFT 4(/ DIVERSION CHANNEL GARAPAN FLOOD CONTROL SAIPAN, CNMI 0 0.1 0.2 0.3 0.4 0.5 ALTERNATIVE PLAN I SCALE IN MILES U.S. ARMY ENGINEER DISTRICT, HONOLULU FIGURE 7 PACIFIC 0 C E A N PUNTAN MUCHOT MICRO BEACH TYPE 'W'CHANNEL CONTINENTAL AMERICAN CULVERT "E" HOTEL MEMORIAL PARK OUTLET INTER- CHANNEL TYPE "A!'CHANNEL CONTINENTAL HOTEL CULVERT F ELEMENTARY SCHOOL SUGAR HAFA ADAI HOTEL KING X DIVERSION 44 CHANNEL TYPE "d CHANNEL CULVERT "G" --TYPE "B" CHANNEL CULVERT "H" 0 SUGAR XING I a: EXST TYPE "C" CHANNEL SWALE UJI co Ill GARAPAN FLOOD CONTROL SAIPAN, CNMI 0 0.1 0.2 0.3 0.4 0.5 --------4 - ALTERNATIVE PLAN 2 SCALE IN MILES U.S. ARMY ENGINEER DISTRICT, HONOLULU FIGURE 8 TYPE 'W'CHANNEL PA CIFIC 0 C E A N CULVERT"I" TYPE 'VCHANNEL CULVERT'V TYPE 'W'CHANN PUNTAN MUCHOT A MICRO BEACH CONTINENTAL MERICAN HOTEL MEMORIA PARK INTER- CONTINENTAL HOTEL RIGHT DIVERSION CHANNEL OUTLET CHANNE qEME Ry rcl ---TYPE "B" CHANNEL HAFA ADAI HOTEL@ CULVERT Iflel SSUGAR KI 3X CULVERT "L" LEFT DIVERSION 4 CHANNEL '-4:-'---TYPE "B" CHANNEL CULVERT "d' TYPE "B" CHANNEL 11 to 0 SUGAR KING I CULVERT N N EXST SWALE TYPE "C!'CHANNEL w co w 31t GARAPAN FLOOD CONTROL SAIPAN, CNMI 0 0.1 0.2 0.3 0.4 0.5 ALTERNATIVE PLAN 5 SCALE IN MILES U.S. ARMY ENGINEER DISTRICT, HONOLULU __j FIGURE 9 PA CIFIC OCEA A( PUNTAN MUCHOT A MICRO BEACH TYPE "A 11 CHANNEL CONTINENTAL AMERICAN CULVERT go0 HOTEL MEMORIAL PARK INTER- .,,--TYPE "A" CHANNEL CONTINENTAL HOTEL CULVERT P ElefEMENTAR 'SCHOOL HAFA ADAI HOTE SUGAR KING.M OAD TYPE I'D" 4 CHANNEL CULVERT go0It TYPE "E" CHANNEL CULVERT "R" 0 SUGAR KING I TYPE it D"CHANNEL TYPE "W'CHANNEL SUGAR KING MONUMENT CID 0 U) GARAPAN FLOOD CONTROL SAIPAN, CNMI 0 0.1 0.2 0.3 0.4 0.5 SCALE IN MILES 106-YEAR PLAN U.S. ARMY ENGINEER DISTRICT, HONOLULU __j FIGURE 10 SYMMETRICAL ABOUT 4- 15' PERMANENT R/W VARIES DESIGN WATER SURFACE EXISTING 2/2 GRASSING GROUND 2.5 FREEBOARD FI AS REQUIRED BEDDING VARIES RIPRAP VARIES VARIES TYPE 11 A11 RIPRAP CHANNEL 15' - eO' PERMANENT R/W 100- FILL,AS 2'FREEBOARD REQUIRED EXISTING GROUNOZ [WEST COAST H VL@j le 10. 15 FILL, AS 2v2 21/2 REQUIRED GRASSING TO MNNW VARIES 5* - ?d TYPE 11 B 11 GRASS LINED CHANNEL PERMANENT R/W 100' --------u2'FREEBOARD rWWT-COAST HWLJ 'ARIES 25* VARII k VARIES BEDDING VARIES RIES RIPRAP VARIES ic V IV- 25' TYPE Ifc 11 RIPRAP CHANNEL SECTIONS NOT TO SCALE GARAPAN FLOOD CONTROL SEE TABLE I SAIPAN, CNMI 15 1/2 L 4 L UT ""I GR A.3' NG @D@ESIGN I@ATER SIJ@RRFAC-E S 2 @5-FREE@BOARD LL, AS REQ UIRED 2 BEDDING VAR IES EXISTING GROUND T HW I k VAR 'ES EDDIIG VARIES R I @E ALTERNATIVE PLANS 1-3 TYPICAL CHANNEL SECTIONS U.S. ARMY ENGINEER DISTRICT, HONOLULU SYMMETRICAL ABOUT PERMANENT R/W EXISTING Is' GRASSING DESIGN WATER SURFACE GROUND ir 2.5' FREEBOARD v 71q- FILL REQUIRED' 2 Y2 BEDDING VARIES RIPRAP VARIES TYPE A RIPRAP CHANNEL PERMANENT RIW 10 21/2 15, GRASSING DESIGN WATER SURFACE EXISTING GROUND E) ISTING ir- F 2.5'-3.0'FREEBOAND al OUND yf@ a [WEST COAST HWY FILL, AS EQUIRED BEDDING CONCRETE VARIES 20'-30 TYPE "D," TRAPEZOIDAL CONCRETE CHANNEL PERMANENT R/W DESIGN WATER SURFACE] CHAINLINK FENCE 10, @ 2V2 15, GRASSING 15, Irl 4' -r- 2.5' JWEST COAST HWY = FILL,:S@R @QU51RE@@ CONCRETE BEDDING VARIES 20'- 45' TYPE Es' RECTANGULAR CONCRETE CHANNEL SECTIONS NOT TO SCALE GARAPAN FLOOD CONTROL SAIPAN, CNMI 100-YEAR PLAN TYPICAL CHANNEL SECTIONS @t sT im.3 @/2 '0@ 1,2 U, ----------- ----------- ----------- ----------- ----------- U.S. ARMY ENGINEER DISTRICT, HONOLULU FIGURE 12 TABLE J. SUNMARY'COMPARISON AND SYSTEM OF ACCOUNTS W I T H C 0 N D I T 1 0 N PLAN 1 PLAN 2 PLAN 3 CHANNEL 41TH SAIPAN Cukun WITH CHANNEL WITH GARAPXK WITHOUT CONDITtONS IAGOON OUTLET MEMORIAL PARK OuTurf __SCHDOL OUTLET A. PLAN DESCRIPTION 90 PROJECT 1,700-FODT-:LONG CHARNRL.. 1,800-FOOT-LONG CHA M L 2,500-FOOT-IDNG CHANN CHANNEL DEPTH -6.0 FEET MSL PASSES THROUGH PARK AND DISCHARGES INTO SAIPA AT MOUTH. DISCHARGES INTO TAKAPAG LAGOON NEAR SCHOOL. HARBOR. CHANNEL DEPTH CHANNEL DEPTH -8 FEET -8.0 FEET MSL AT MOUTH. MSL AT MDUNTH. ALL CHANNEL PUNSHAVR TRAPEZOIDAL CROSS-SzcrION, RIPRAP OR GRASS LINING AND PROVI IN ADDITION TO THE OUTLET CHANNEL SHOWN A3OV-z FOR EACH CHANNEL PLAN, A 3,50r,-FOOT B. SIGNIFICANT IMPACTS WOULD ALSO BE PROVIDED. & PLAN RELATIONSHIPS TO NATIONAL ACCOUNTS 1. ECONOMIC (NED) a. PROPERTY VALUES INCREASING AT PREVAILING -SAME AS WITHOUT CONDITIONS. SAME AS PAIN 1. SAM AS PLAN 1. RZ4L:BSTATE MARKET RATR. (2'6'9) b. PUBLIC FACILITIES DAMAGES TO FACILITIES AND NO SIGNIFICANT IMPACT WITH PLAN 1, 2, or 3 (2, 6, 9) INTERRUPTION OF SERVICES DURING FLOODING as c. DESIRED REGIONAL ADVERSE EFFECT IN FLOOD- BENEFICIAL IMPACT IN FUW'-@ BENEFICIAL, BUT DISRUPT SAME AS PLAN 1. GR93WTH PLAIN. PLAN. (2, 6, 9) PARK DEVELOPMENT. (2, 6, 9) d. SuskHass/umsTaTAT DisaurrioN DURING FLOODING. K=azE5 DISRUPTION DVRING SAME AS PLAN 1. SANE AS PLAN 1. ACTIVITIES FLOOD FLOW ON ROADS. (2, 6, 9). e. FARM DISPLACEMENT DISRUPTION DURING FLOOD ING . NONE NONE NONE f. QUANTITATIVE ANALYSIS (1) ARNEFICIAL IMPACTS ($1,000) REDUCTION IN FLOOD DAMAGES 0 229.0 229.0 229.0 (b) EDA BENEFITS 0 .5.0 5.0 5.0 (cy AFFLUENCE FACrOR 0 10.0 10.0 10.0 (d) EMERGENCY SAVINGS 0 -16.0 16.0, 16.0 (e) TOTAL NED BENEFITS 260.0 260.0 260.0 (2) ADVERSE IMPACTS LOCAL 1,4 00 1,500 1,700 REST OF THE NATION 1,800 1,900 2,000 O&M (LOCAL) 5.0 5.0 5.0 TOTAL ANNUAL COSTS 241.0 255.0 277.0 ..(3) NET NED BENEFITS L40CAL (ASSUME ALL -BENEFITS ACCRUE TO LOCAL) 152.0 145.C 130.0 NATION (-)133.0 (-)140.0 (-)147.0 NET NED BENEFITS 19.0 5.0 (-)17.0 (4) B/C RATIO 1.08 1.02 0.94 2. ENVIRONMENTAL. (EQ) A. TERRESTRIAL INSIGNIFICANT CHANGE. 9.9 AC. MODIFIED' 10 AC. MODIFIED 11.4 AC. MODIFIED ENVIRONMENT b. MARINE ENVIRONMENT INSIGNIFICANT CHANGE. @1.9 AC CREATED 2 AC. CREATED 3.4 AC. CREATED 300 S.F. DREDGED 400 S.F. DREDGED 480S.F. DREDGED c. ENDANGERED SPECIES INSIGNIFICANT CHANGE. NO EFFECT. NO EFFECT. NO EFFECT. Go d. WATER QUALITY INSIGNIFICANT CHARGE. TEMPORARY TURBIDITY AND SAME AS PLAN 1. SAME AS PLAN 1. SUSPENDED SEDIMENTS DURING CONSTRUCTION. WATER QRALITY IN THE OUTLET CHANNEL WILL BE LOWER THAN IN THE LAGOON. (1, 6, 9). e. HISTORIC INSIGNIFICANT CHANGE. POSSIBLE DAMAGE To PREHISTORIC MIDDEN SITE. (1, 5, 9) f. WETLANDS INSIGNIFICANT CHANGE. yOSSISLEENCROACHMENT ON WETLAND AREAS. (1, 5, 9) g. RECREATION INSIGNIFICANT CHANGES. FISHING OPPORTUNITIES SAME AS PLAN 1. SAME AS PLAN INCREASE. (3, 6, 9) 3. SOCIAL (SWB) HEALTH, SAFETY, & DEGRADED DURING AND AFTER Fi.OOD-RELATED HEALTH AND SAME AS PLAN 1. SAME AS PLAN 1. COMMUNITY WELL.- FLDODING- SEWAGE OVERFLOW SAFETY IMPROVED.COM MUN ITY BEING OCCURS. WELL-BEING ENHANCED. (2, 6, 9). b. AESTHETIC VALUES DEGRADATION OF LAND AND NEW VISUAL ELEMENTS ADDED SAME AS SAME AS PLAN 1. WATER QUALITY DURING AND CHANGING AESTHETIC CHARACTER AFTER FLOODING. OF AREA. (2, 6, 9). C. AIR AND NOISE INSIGNIFICANT CHANGE. TEMPORARY DURING CONSTRUC- SAME AS PLAN 1. SAME AS PLAN 1. TION. (1, 6, 9) d. DISPACEMENT DISPLACEMENT OF FAMILIES FOUR HOMES DISPLACED; 5.0 NO DISPLACEMEM OF HOMES. FOUR HOMES DISPLACED: IN FLDODPIAIN DURING FLOOD. AC. PRIVATE LAND PURCHASED 4.8 AC. OF PRIVATE LA (1-51 9). PURCHASED. (1, 5, 9) e. CONMUNITY COHESION INSIGNIFICANT CHANGE. NO CHANGE. SAME AS PLAN 1. SAME AS PLAN 1. 4. REGIONAL DEVELOPMENT ADVERSE EFFECT ON DEVELOP- IN CONFORMANCE WITH SAME AS PLAN 1; SAME AS PLAN 1. (COMMUNITY GROWTH) XW WITH FLOODPLAIN. REGIONAL DEVELOPMENT PLAN (2, 5, 8, 9). C. PLAN EVALUATION 1. CONTRIBUTION TO PLANNING OBJECTIVES a. CONTRIBUTE TO THE CONTINUED FLOODING AND REDUCTION IN FLOOD DAMAGES SAME AS PLAN 1. SAME AS PLAN 1. REDUCTION OF FLOOD- FLOOD DAMAGES. TO RESIDENTIAL STRUCTURES. WATER DAMAGE DURING THE 1985-2035 PERIOD OF ANALYSIS. b. PRESERVE THE NATURAL NO CONTRIBUTION. PARTIALLY CONTRIBUTION. PARTIAL CONTRIBUTION. PARTIAL CONTRIBUTION. RESOURCES OF THE AREA DURING THE 1985-2035 PERIOD OF ANALYSIS. 2. RESPONSE TO ASSOCIATdD EVALUATION CRITERIA a. ACCEPTABILITY N/A TO BE COMPLETED FOLLOWING PUBLIC REVIEW OF DOCUMENTS AND PUBLIC MEETINGS. b. EFFECTIVENESS N/A MODERATELY HIGH MEDIUM MODERATELY HIGH c. EFFICIENCY N/A LEAST COST MEDIUM LOW d. NED B/C RATIO N/A SHE ITEM B.I.f(4) e. STABILITY NiA YODERATE MODERATE MODERATE I/ SPECIFIC CRITERIA OF COMPLETENESS, CERTAINTY, GEOGRAPHICAL RELEVANCY, AND REVERSIBILITY NOT CRUCIAL TO DECI SION- MAKING. 3. IMPLEMENTATION N/A CORPS OF ENGINEERICNEI SAME AS PLAN 1. SAME AS PLAN 1. INDEX OF FOOTNOTES FINING EXCLUSIVITY 1. IMPACT IS EXPECTED TO OCCUR PRIOR TO OR DURING IMPLEMENTATION OF THE PLAN. 7. OVERLAPPING ENTRY: FULLY MONETIZED IN NED AC 2. IMPACT IS EXPECTED WITHIN 15 YEARS FOLLOWING PLAN IMPLEMENTATION. 8. OVERLAPPING ENTRY: NUI FULLY MONETIZED IN NE 3. IMPACT IS EXPECTED IN A LONGER TIME FRAM@E(15 OR MORE YEARS FOLLOWING IMPLEMENTATION). ACTUALIT UNCERTAINTY 9. IMPACT WILL OCCUR WITH IMPLEMENTATION. 4. THE UNCERTAINTY ASSOCIATED WITH IMPACT IS 507 OR MORE. 10. IMPACT WILL OCCUR ONLY WHEN SPECIFIC ADDITION 5. THE UNCERTAINTY IS BETWEEN 107. AND 50%. IMPLEMENTATION. 6. THE UNCERTAINTY IS LESS THAN 10%. 11. IMPACT WILL NOT OCCUR BECAUSE NECESSARY ADDIT *ITEMS REQUIRED BY SECTION 122, PUBLIC LAW 91-611 AND ER 1105-2-240. 1. Main Report. a. Assessment and Evaluation of Detailed Plans. b. Plan Implementation and Public Views. c. Conclusion (including Statement of Finding and Recommendations). 2. Appendices. a. Subsurface investigations, laboratory tests, and design values in Appendix 8 - Geology and Soils. b. Detailed hydraulic designs and cost estimated in Appendix C Engineering, Investigations, Design and Cost Estimates. c. Economics of the selected plan in Appendix D - Economics. d. Draft report and environmental statement review, and report comments and responses in Appendix F - Public Involvement. e. Fish and Wildlife 2(b) report in the Environmental Statement. f. Compliance certification and evaluation reports as required in Appendix H - Compliance Documents. 19 0 GARAPAN FLOOD CONTROL SAIPAN, CNMI ENVIRONMENTAL IMPACT STATEMENT 0 DRAFT ENVIRONMENTAL STATEMENT GARAPAN FLOOD CONTROL PROJECT, GARAPAN SAIPAN, COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS The responsible Commonwealth agency is the Coastal Resources Management Office. The lead federal agency is the US Army Corps of Engineers, Honolulu District. The cooperating federal agency is the US Fish and Wildlife Service, Pacific Islands Office. Abstract: Saipan is the main island in the Commonwealth of the Northern Mariana Islands. The Honolulu District, US Army Corps of Engineers, has investigated public concerns regarding flood protection in the village of Garapan on Saipan. Channelizing the floodflow and permanent evacuation and relocation are the alternative concepts being studied. The channel alignments all include a channelized section along the eastern edge of the West Coast Highway, involving one of three different outlet alignments. The alignment for Plan I involves the discharge of stormwater into Saipan Lagoon near the Hafa Adai Hotel. The alignment for Plan 2 conveys water through the proposed American Memorial Park. The outlet alignment for Plan 3 is adjacent to an existing roadway alongside Garapan Elementary School. A relocation plan, Plan 4, involves the physical removal of all damageable structures located in the floodplain. No area for relocation has been identified. SEND YOUR COMMENTS TO THE DISTRICT ENGINEER BY 15 SEPTEMBER 1980. If you would like further technical information about this statement, please contact: Dr. James E. Maragos, Chief Environmental Resources Section US Army Engineer District, Honolulu Bldg 230 Fort Shafter, HI 96858 Telephone: (808) 438-2263 LIST OF PREPARERS PROFESSIONAL NAME EXPERTISE EXPERIENCE DISCIPLINE Mr. Michael T. Lee Biology BA, Biology; I year Environmental (EIS Preparer) Biologist US Navy; Biologist 8 years EIS studies, US Army Corps of Engineers, Honolulu, District Dr. James E. Maragos Marine BS, Zoology; PH D, Supervisory (EIS Coordinator) Ecology Oceanography; 2 years Environmental Post-Doctoral Research; Biologist 10 years Environmental Consultant; 5 years EIS studies, US Army Corps of Engineers, Honolulu District Mr.David G. Sox Historical BA, MA Geography; Social & Cultural 6 years Research; Environmental Geography 5 years EIS studies, Specialist US Army Corps of Engineers, Honolulu District Mr. Harvey Young Engineering BS, Civil Engrg; Project (Project Manager) 5 yrs civ engrg; Engineer 13 yrs planning and hydraulic engrg. Tom Hablett MA, General 2 yrs University Fish and (US Fish and Aquatic Biology Teacher; Wildlife Wildlife Service) Biology 2 yrs Park Naturalist, Biologist National Park Service; 6 yrs Fisheries Research and Habitat & EIS Studies, US Fish and Wildlife Service. TABLE OF CONTENTS TITLE PAGE COVER SHEET LIST OF PREPARERS TABLE OF CONTENTS SUMMARY NEED FOR AND OBJECTIVE OF THE ACTION ALTERNATIVES INCLUDING THE PROPOSED ACTION 3 AFFECTED ENVIRONMENT 5 SIGNIFICANT ENVIRONMENTAL RESOURCES 8 Floodplain 8 Groundwater 8 Littoral Processes 9 Water Quality 9 Wetlands 9 Migratory Shorebirds 10 Lagoon Resources 10 Endangered Species 10 Recreation 11 Historical Resources. 11 Social Resources 11 ENVIRONMENTAL EFFECTS 11 Floodplain 11 Groundwater 12 Water Quality 12 Littoral Processes 13 Wetlands 13 Migratory Shorebirds 14 Lagoon Resources 14 Endangered Species 14 Recreation 14 Historical Resources 14 Social Resources 15 PUBLIC INVOLVEMENT 15 INDEX 17 The intertidal mudflats created in the channel may create an odor nuisance within the community. Plan 2 located in the park has the least possibility of affecting residential areas, but will degrade park aesthetics. Waters exiting the channel will create a localized area of nutrient enrichment in Saipan Lagoon, possibly invigorating the growth of seagrass at the channel outlet. Approximately 300 square feet of lagoon habitat will be dredged at the mouth of the channel. The excavation of about 1,200 cubic yards of sand and coralline material will contribute to a temporary increase in water turbidity in the lagoon. The extent of the effect is grossly estimated by the length of time necessary to complete the dredging and the quantity of material to be removed. In all cases, the material to be removed consists of coralline fines, sand and rubble.. The relocation alternative does not directly affect water quality. Urban stormwater runoff will be increased from the developed site once the developed site is paved, and sediment eroded from open areas will eventually find its way to manmade or natural drainageways. The new urban area will most likely be sewered, improving sanitation conditions as well as eliminating health problems related to overflowing or flooded cesspools or septic tanks. 5.4 Littoral Processes. Longshore sand movement is not evident at the Garapan shoreline. Garapan Dock still has 12-foot depths around it and a channel north of the harbor near Puntan Muchot is still evident in aerial photographs. This indicates that the channel mouth does not 'and probably will not shoal at a fast rate or interrupt littoral drift. Although a sandbar has formed at the mouth of the existing drainage ditch next to the Hafa Adai Hotel, the bar may have 'be formed by onshore and offshore sand movement during signi.ficant storm events. Shoaling in the channel due to sedimentation from upland sources is anticipated and will require periodic maintenance dredging of the channel. If a bar does form across the channel mouth, the water trapped behind the bar will stagnate, and periodic clearing will be required to maintain the channel. Plans 1 and 3 may have a greater possiblity of shoaling at the channel mouth than Plan 2, where the channel outlets into Unai Sadog Tase (Unai Sadog Tase is a quiet water cove in the harbor formed by the filled shoreline and dredged causeways). The relocation alternative does not affect littoral processes. 5.5 Wetlands. The diversion channel alignment has the potential of destroying a portion of a wetland which was identified during an ornithological survey of Saipan wetlands. The location of the wetland is uncertain in that it conflicts with the location identified by a wetland survey conducted by the University of Guam. The diversion channel will be excavated in a portion of the wetland converting the wetland to a dry habitat. The wetland is already divided by the West Coast Highway and may be formed by a lack of drainage past the highway. The channel alignment through the American Memorial Park passes around the park wetland and avoids the wetland. However, the.channel section passing the wetland area will be made impervious to prevent the exchange of water between the wetland and channel, or the drainage of the,wetland. The relocation alternative avoids any construction in the wetlands. 13 5.6 Migratory Shorebirds. Migratory shorebirds may profit by the creation of more intertidal area within the channels. Cleared, grassed open areas within the channel will provide resting and feeding areas for some of the birds. The riprap outlet channel and channel intertidal area will also provide feeding and resting habitat. The relocation alternative is not expected to affect migratory shorebirds. 5.7 Lagoon Resources. The outlet channel requires excavati 'on of a small area near the sho-r-eTi-ne in the lagoon. The area disturbed for each plan is estimated on Table 2. Dredging will result in the loss of some Enhalus seagrass. Nutrients exiting the channel during tidal flushing a-nJ -periods of flow may stimulate a growth of seagrass and algae at the mouth of the channel. Fish will colonize the outlet channel and the channel may become a nursery area for fisheries resources. The amount of new marine habitat created by each plan is estimated on Table 2. The relocation alternative does not affect Saipan Lagoon. 5.8 Endangered Species. None of the alternatives are likely to jeopardize the continued existence of the threatened Green Sea Turtle which has been seen in Saipan Lagoon. The shoreline areas and the-lagoon are not known to be nesting or breeding habitats for the turtle. Loss of the American Memorial Park wetland will most likely force the Nightingale Reed Warbler into other wetland areas on Saipan. 5.9 Recreation. The channel alternatives will create an 8-foot water depth along the shore].ine which will interrupt pedestrian movement along the beach. The channel alignment through the park will divide the parklands into two sections inhibiting free movement between the two sections. The channel may attract fishermen and children who want to catch fish. The outlet channel alignment in Plan 3 passes alongside Garapan Elementary School and may create a nuisance to the school. The channel will be about 2 feet deep at that point and will have a side slope of 1 vertical to 2.5 horizontal and thus should not create a hazard at the school. The diversion channel will be a grass swale along the boundary of the proposed site of the junior high school and is not expected to interfere with recreation activities at the school. The relocation alternative opens up more coastal land for potential park development and increased recreational areas, provided that the relocation area is not located within a potential recreation area. 5.10 Historic Resources. The channel alternatives involve a diversion channel upland of the West Coast Highway. An archaeological midden site was found along the channel alignment in an area recently excavated for a sewerline construction near the Navy Hill Road intersection with the West Coast. The Commonwealth Historic Preservation Officer was asked to determine if the site was destroyed by the sewerline construction and for his opinion regarding the eligibility of the site to the National Register of Historic Places. The site is the first prehistoric site found in the Garapan area, and, if still present, has the potential of yielding scientific data important to understanding the prehistory of Saipan and the Garapan area. Excavation of the channel may destroy the site, resulting in the loss of scientific data. Plan 2 outlet channel alignment passes through the Memorial Park which was set aside in commemoration of those who fought and died in the Marianas Campaign during World War II. The channel is not expected to disturb historic sites in the park found by the National Park Service's survey, but war artifacts could 14 be uncovered during construction. Since the location of the relocation site has not been identified, the impacts of relocation on historic sites cannot be discussed. 5.11 Social Resources. The relocation alternative involves approximately 340 structures. Social di ruption would be significant, especially for those families who see landownership as a family bond. Those persons, who view landownership as a commodity to be bought and sold, will ask an extremely high price for their land and homes. The complex and contradictory set of land records and titles may make settlement with landowners a long and tedious process with many disputes. The government would have to find a relocation site that could be developed to provide homes and land for displaced families. The proposed Sugar King subdivision on the hillside overlooking Garapan may be a likely location for resettlement. However, relocating residents from Garapan into the new subdivision reduces the number of housing units the government is trying to make available to families who do not own their own homes and live in substandard structures. 6. PUBLIC INVOLVEMENT 6.1 Public Involvement Program. Project detailed design investigations were performed with the assistance of the Commonwealth Coastal Resources Management, Department of Public Works, and Mariana Islands Housing Authority. A survey of damageable property within the flood prone area was conducted on Saipan by Corps personnel. A public notice advising the public of the study and announcing a public workshop was circulated on Saipan in February 1979. The public workshop was held on Saipan in March 1979 and approximately 20 persons participated in the workshop. 6.2 Required Coordination. The following coordination needs to be completed prior to finalizing the report and environmental impact statement. Coordi- nation to be satisfied by circulation of the EIS for review and comment is identified by an asterisk. a. Section 404. A water quality certification must be obtained from the Commonwealth, Div'ision of Environmental Quality. An evaluation of the discharge of dredged or fill material was completed using the US Environmental Protection Agency Section 404 (b)(1) guidelines (see Appendix H) and is provided for agency review. b. Endangered Species Coordinator. US Fish and Wildlife Service and the NationaT -Marine Fisheries ServTc-ewill have an opportunity to review and comment on the Draft EIS. Formal consultation will not be initiated under Section 7 of the Endangered Species Act of 1978. C. Fish and Wildlife Coordination. The US Fish and Wildlife Service, National Marine Fisheries Service, and the Commonwealth Department of Natural Re sources will have an opportunity to review and comment on the report/EIS. The US Fish and Wildlife Service will prepare a report under Section 2(b) of the Fish and Wildlife Coordination Act expressing their opinion regarding the project and the conservation, preservation or protection of fish and wildlife resources. The report will be included in the final report/EIS. d. Historic Preservation. The results of the archaeological reconnaissance survey of the project site are being coordinated with the 15 Commonwealth Historic Preservation Office. The Historic Preservation Officer will provide his opinion about the eligibility of the archaeological site and may provide a determination of effect under the National Historic Preservation Act of 1966. e. Coastal Zone Management. The Office of Coastal Zone Management will have an opportunity to review and comment on the draft report/EIS. An approved Coastal Zone Management Plan is not in effect in the Commonwealth; thus a federal consistency certification is not required until the Common- wealth Coastal Management program is approved. f. Floodplain Management. The public will have an opportunity to review and comment on the effects of the project on the floodplain. An evaluation of the project on the floodplain will be included in Appendix H after a tentative recommended plan has been selected. 6.4 Statement Recipients. The following agencies and individuals were provided copies of the draft Detailed Project Report and Draft Environmental Statement for.review and opportunity to comment. a. Federal. U.S. Environmental Protection Agency (Washington & Region IX) U.S. Department of Commerce National Marine Fisheries U.S. Advisory Council on Historic Preservation U.S. Department of Interior National Park Service U.S. Fish and Wildlife Service U.S. Department of Housing and Urban Development U.S. Department of Health, Education and Welfare U.S. Department of Transportation Federal Highway Administration U.S. Coast Guard U.S. Department of Energy b. Commonwealth. Office of the Governor Department of Public Works Mariana Islands Housing Authority Commonwealth Historic Preservation Officer Department of Natural Resources Officer of Planning and Budget Mayor of Saipan Division of Marine Resources Development Division of Environmental Quality Office of Coastal Resources Management Marianas Public Land Corporation Department of Public Health 6.5 Public Views and Responses. To be completed following the review period for the Draft ETS-. 16 7. INDEX GARAPAN FLOOD CONTROL STUDY SAIPAN, COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS Subject Environmental Statement Main Report & Appendices Affected environment Para 4, PP 5-8 PP 5-7 Alternatives Para 3, PP 3-5 PP 13-14 Areas of Controversy Para 1.2, P 1 Comparative Impacts of Alternatives Table 2, PP 6-7 P 17, Table 3 Cover Sheet P i Environmental Conditions Para 4, PP 5-8 PP 5-7 Environmental Effects Para 5, PP 11-15 P 17 List of Preparers P ii Major Conclusions and Findings Para 1.1, P 1 P 17 Need for and Objective of the Action Para 2, PP 1-3 P I Planning Objectives Para 2.3, P 3 P 10 Plans Considered in Detail Para 3.2, PP 4-5 PP 15-17 Plans Eliminated From Further Study Para 3.1, PP 3-4 P 15 Public Concerns Para 2.2, PP 1-3 P 2 Public Involvement Para 6, PP 15-16 Appendix F Public Involvement Program Para 6, PP 15-16 Appendix F Public Views and Responses Para 6.5, P 16 Relationship to Environmental Requirements Table 1, PP 2-3 P 13, Appendix H 17 GARAPAN FLOOD CONTROL STUDY SAIPAN, COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS Subject Environmental Statement Main Report & Appendices Required Coordination Para 6, PP 15-16 Appendix F Significant Resources Para 4.4 - 4.14, PP 8-11 PP 5-7, Appendices E & G Community Cohesion and Para 4.14, P 11 Social Well-Being Para 5.11, P 15 Appendix G Historic Sites Para 4.13, P 11 Para 5.10, P 14 Appendix G Land Ownership'and Land Use Para 4.1, P 5-8 P 7 Statement Recipients Para 6.4, P 116 Appendix F Study Authority Para 2.1, P 1 P 1 Table of Contents P iii Precedes Main Report Unresolved Issues Para 1.3, P 1 Without Conditions Para 3, PP 5-8 P 7 (No Action) 18 8-LIST OF REFERENCES* 1. Amesbury et al., A Survey of the Fish Resource in Saipan Lagoon, prepared for the Office of Coastal Zone Management, CNMI, University of Guam Marine Lab., Technical Report No. 50, March 1979 (Contract #579-02) 2. Coastal Zone Management office, Preliminary Draft Natural Resources Study, Commonwealth of the Northern Mariana Islands, Office of Planning Buaget, GNMI, Feb 19/9 3. Cloud et al., Geology of Saipan, Mariana Islands, U.S. Geological Survey Professional paper 280A, Parts 1-4, 1955 and 1959 4. Cloud et al., Military Geology of Saipan, Mariana Islands Vols 1-3, Pacific Geological Mapping Program, U.S. Army and U.S. GeoT-ogical Survey, 1955 and 1958 5. Doty, J. and J. Marsh, Jr., Marine Survey of Tanapag, Saipan: The Power Barge 'Impedance', University of Guam Marine Laboratory, Technical Report No. 7 March 1977 6. Juan C. Teno.rio and Associates, Inc., Ornithological Survey of Wetlands in Guam, Saipan and Pagan, prepared for the U.S. Army Corps of Engineers, ific Ocean Division, 19/9 7. M&E Pacific, Inc., Facilities Plan for the Island of Saipan, Mariana Islands, prepared for the Department of Public Works, GNMI, March 1979 8. Moore, et al., Inventory and Mapping of Wetland Vegetation in Guam, Tinian, Saipan, Mariana Islands, University of Guam (Bio Sciences), prepared U.S. Army Corps of Engineers, Pacific Ocean Division, June 1977 9. Office of Planning and Statistics, Bulletin of Statistics, Vol 1, No. 3, Trust Territory of the Pacific Islands, Dec 1978 10. Pacific Planning and Design Consultants, Physical Development Master Plan, Vol. II Saipan, prepared for the Office of Transition Studie s and Planning, GNMI, Jan 1978 11. Pacific Studies Institute, Cultural Resources Reconnaissance, for the Garapan Flood Control Study Area, Commonwealth of the Northern Mariana T-Slands, prepared for U.S. Army Corps oT-En--g"lneers, Pacific OceaiT 'Division, March 1980, Contract No. DACW84-79-C-0028, and Archaeological Reconnaissance of the Armerican Memorial Park, Saipan, Commonwealth of the Northern Mariani Islands, f-o-r-The National Park SeFTI-ce, November 1979. 12. Robert R. Nathan Associations, Inc., Socio-economic Development Plan for the Northern Mariana Islands, 1978 to 1985, Vols 1, 11, and III, prepared for the Office of Transition Studies and Planning, GNMI, Oct 1977 For EIS and Appendix G, Recreation and Natural Resources 19 GARAPAN FLOOD CONTROL SAIPAN, CNMI -HYDROLOGY APPENDix A HYDROLOGY APPENDIX Title Page INTRODUCTION A-1 Scope A-1 Alternative Flood Control Plans A-1 GENERAL DESCRIPTION A-1 Hydrologic Data A-1 Methodology A-1 SPF FLOOD.HYDROGRAPH DERIVATION A-2 Unit Hydrographs A-2 Unit Hydrographs for Future Conditions A-6 Rainfall A-6 Infiltration Losses A-7 Local Drainage A-7 Flood Routing A-7 Standard Project Flood (SPF) A-7 DISCHARGE-FREQUENCY ANALYSIS A-8 Streamgage Data A-8 Regression-Correlation Analysis A-8 Discharge-Frequency Curves A-12 Discharge-Frequency Curves at Shoreline A-12 FLOODPLAIN ANALYSIS A-12 General A-12 Flood Limits A-13 VERFIFICATIOh OF HYDROLOGIC INVESTIGATION A-13 LOCAL DRAINAGE - WITH PROJECT CONDITION A-13 TABLES Table Page A-1 Unit Hydrograph Parameters A-3 A-2 Unit Hydrograph for Local Drainage A-5 A-3 Summary of Peak Discharges A-9 A-4 Streamgages on Guam and.Saipan A-11 Plate PLATES A-1 Drainage Areas A-2 10-Minute Unit Hydrographs Peak Increased by 50%, Existing Condition A-3 10-Minute Unit Hydrographs for Local Drainage, Existing Condition A-4* Unit Hydrograph Peaks versus Widths A-5 10-Minute Non-Increased Unit Hydrographs, Existing Condition A-6 Peaked 10-Minute Unit Hydrographs, Future Condition A-7 Depth-Duration Curve, PMP A-8 Depth-Area Curve for Probable Maximum Precipitation A-9 2-Year Storm Hyetograph A-10 100-Year Storm Hyetograph A-11 SPF Hydrographs, Existing Conditions A-12 SPF Hydrographs at Shoreline (Area 2-2A) A-13 SPF Hydrographs at Shoreline (Area 3-3A) A-14 100-Year Flood Hydrograph at Shoreline (Area 2-2A) A-15 2-year Flood Hydrograph at Shoreline (Area 2-2A) A-16 100-Year Flood Hydrograph at Shoreline (Area 3-3A) A-17 2-Year Flood Hydrograph at Shoreline (Area 3-3A) A-18 Streamgage and Study Area Location A-19 Streamgage Location A-20 Discharge Frequency Curves at West Coast Highway, Existing Condition A-21 2-Year Flood Hydrographs, Future Project Condition A-22 100-Year Flood Hydrographs, Future Project Condition A-23 Discharge Frequency Curves, Future Project Condition A-24 Discharge Frequency Curves at Shoreline, Future Condition (Area 3-3A) A-25 Discharge Frequency Curves at Shoreline, Future Condition (Area 2-2A) HYDROLOGY GARAPAN AREA, SAIPAN COMMONWEALTH NORTHERN MARIANA ISLANDS INTRODUCTION 1. Scope. This appendix contains descriptions of studies made to determine the runoff process for various selected concentration points within the Garapan watershed which has a total drainage area of 1.89 square miles (Plate A-1). There are four objectives of this appendix: (a) to present the basic meteorologic and hydrologic characteristics of the study area; (b) to outline the methods and techniques used to determine the runoff process; (c) to present discharge frequency values for the present and future (project and no-project) conditions; and (d) to provide standard project flood, 100-year, and 50-year design discharges for the alternative flood control plans. 2. Alternative Flood Control Plans. Four conceptual schemes were investigated, three plans are structural alternatives and the other a nonstructural alternative. All structural alternatives consist of a diversion channel system above West Coast Highway and an outlet channel in various locations. While all the schemes were hydrologically analyzed, only the results for alternative 1 are discussed and displayed graphically. The design concepts for all alternatives are stated in the main report. GENERAL DESCRIPTION 3. Hydrologic Data. Due to a paucity of hydrologic information on the Garapan watershed and the island of Saipan, a reliable investigation was deemed possible only with the use of data from other areas which were judged to be hydrologically similar to Saipan and the Garapan watershed. The nearest source of dependable hydrologic information is the island of Guam. Both of the islands belong to the Mariana Island formation, with Guam located 120 miles south of Saipan. Both islands also lie within the same band of typhoon and tropical storm exposure according to the report prepared by the Bureau of Planning, Government of Guam, entitled "Typhoons: Their Nature and Effects on Guam," December 1977. These typhoons ahd tropical storms produce intense rainfalls and are the primary storm events of the rainy season which occurs from July through October. Since there are similarities between drainage area sizes, topography, geology, and meterology of the Garapan watershed and the watersheds in Guam, it was assumed that they would also be hydrologically similar. 4. Methodology. Areas 1, 2. and 3 (plate A!-.l) are topographically similar to the Guam and Saipan watersheds having recorded hydrologic data. Therefore these areas were analyzed by the direct use of the results obtained A-1 in the hydrologic analysis of the recorded data. Discharge-frequency curves were developed by the application of regression equations which were developed from a regression-correlation analysis of peak discharge-frequency data. The Standard Project Flood was constructed by applying unit hydrographs described by Snyder's Unit Hydrograph Parameters to the Standard Project Storm hyetograph. 5. Areas IA, 2A and 3A are unlike the gaged watershed. They are relatively developed and lie on the flat coastal plain which is marked with many depressions. To account for the differences, modificatons were made to the analytic computations of the gaged watersheds. The primary changes made vlqre the recomputation of the time of concentration and lag time. These changes were incorporated in determining the discharge-frequency curves and the SPF. hydrographs for areas 1A, 2A and 3A and are described in greater detail in Paragraph 13. SPF FLOOD HYDROGRAPH DERIVATION 6. Unit Hydrographs. Snyder's Unit Hydrograph Parameters, used for the Garapan@ -watershed analysis, were obtained from a report entitled, "Survey of Harbors and Rivers in the Territory of Guam, Ugum River - Derivation of Probable Maximum Flood," 17 November 1978, which was prepared by the US Army Corps of Engineers, Pacific Ocean Division (POD). The report derived a unit hydrograph for the 4 December 1963 flood in the Umatac River watershed, the only watershed in Guam with a recording rain gage and a continuous water-stage recorder. This unit hydrograph was assumed to be representative of the hydrologic response of the watersheds in Guam, and therefore, Saipan. The 1963 storm data were analyzed by HEC-1, a flood hydrograph computer program developed by the Hydrologic Engineering Center (HEC), US Army Corps of Engineers. The following Snyder's Unit Hydrograph Parameters, were computed: CP = 0.64, and Ct = 0.34. Regional curves defining the unit hydrograph widths, W75 and W50,.were developed by drawing lines parallel to the standard curves shown in EM 1110-2-1405 through points described by the computed unit hydrograph (Peak Q = 2,100 cfs, D.A. = 2.11 square miles, Peak Discharge per square mile = 995 cfs per square mile, W75 = 0.38 hours, and W50 = 0.60 hour). By applying the Guam based unit.hydrograph data to the physical dimensions of the Garapan drainage areas, 10 minute unit hydrographs for Garpan were developed. A 10-minute time interval was chosen since it provided adequate description of the unit hydrographs. In accordance with EM 1110-2-1405, the peaks of the unit hydrographs were increased to account for differences noted in past analyses of minor and major floods. A 50 percent increase was selected in this study. Plates A-2 and A-3 shows the unit hydrographs used to develop the SPF for the Garapan watershed. Plate A-4 depicts the regional W75 and W50 curves used to shape the unit hydrographs. Tables A-] and A-2 summarizes the unit hydrograpb calculations. The applicability of the derived unit hydrographs to model the Garapan watershed is discussed in Paragraph 25; "VERIFICATION OF HYDROLOGIC INVESTIGATION." A-2 TABLE A-1. UNIT HYDROGRAPH PARAMETERS WATERSHED CHARACTERISTICS DA L LCA Ct 640CP (SQMI) (MILE) (MILE) Area 1 0.68 1.85 1.03 0.34 410 Area 2 0.28 0.99 0.49 0.34 410 Area 3 0.50 1.42 0.70 0.34 410 10-MINUTE UNIT HYDROGRAPH Q t W-75 W-50 pr pr (cfs) (Minute) (Minutel (Minute) Area 1 640 26.1 22.8 40.8 Area 2 380 18.0 16.3 25.8 Area 3 560 21.9 20.0 31.6 PEAK INCREASED BY 50 PERCENT 10-MINUTE UNIT HYDROGRAPH Qpr tpr W-75 W-50 (cfs) (Minute) (Minute). (Minute) Area 1 960 17.4 15.9 25.2 Area 2 570 12.2 10.8 17.1 Area 3 840 14.6 12.9 20.7 PEAK INCREASED (FUTURE CONDITION) 10-MINUTE UNIT HYDROGRAPH Qpr tpr W-75 W-50 (cfs) (Minute) (Minute) (Minute) Area 1 640 26.1 22.8 40.8 Area 2 500 13.7 12.0 19.2 Area 3 650 18.8 16.8 27.0 A-3 TERMINOLOGY DA: Drainage area of the watershed L: Length of the longest watercourse from the outflow point to the upstream watershed boundary. LCA: Length along the longest watercourse from the outflow point to the point nearest the centroid of the watershed. Ct and 640CP: Regional coefficients which represent the basin slopes, stream patterns, basin shape, and other properties. Q Peak discharge of the unit hydrograph. "pr t Time between the mid-point of I inch rainfall excess and the 'PrI peak discharge of the unit hydrograph. W-75: Width of the unit hydrograph at the ordinate that equals 75% of the peak discharge. W-50: Width of the unit hydrograph at the ordinate that equals 50% of the peak discharge. A-4 TABLE A-2. UNIT"HYDROGRAPH FOR LOCAL DRAINAGE EXISTING CONDITION 'WATERSHED CHARACTERISTICS DA L LCA SLOPE Tc (SQ MI) (MILE) (MILE) (FT/FT) (MINUTES) Area 1A 0.15 0.25 0-12 0.0263 14 Area 2A 0.09 0.34 0.17 0.0045 20 Area 3A 0.19 0.54 0.27 0.0028 34 10-MINUTE UNIT HYDROGRAPH tpr 640C p Qpr W-75 W-50 (MINUTES) (cfs) (MINUTES) (MINUTES) Area IA 8.5 410 435 7 12 Area 2A 12 410 185 11 17 Area 3A 20 410 235 18 28 TERMINOLOGY SLOPE: Slope of the longest watercourse. Tc: Time of concentration, i.e., the time of travel of rainfall runoff from the most distant part of the watershed to the outflow point. Other terms are defined in Table A-1. A-5 7. Unit Hydrographs for Future Conditions. To determine the impact of urbanizaton on peak discharges (see Main Report for Future Land Use Map), unit hydrographs and rainfall runoff hyetographs were first developed for the existing condition and then modified to reflect the future condition. The unit hydrographs for the existing condition are identical to the non-increased unit hydrographs developed for the SPF and are shown on Plate A-5. The non-increased unit hydrographs were used for all flood frequencies to provide a uniform basis of comparison. And since the drainage areas are small, the unit hydrographs for the minor and major floods are not expected to vary considerably. The increased peak for the SPF unit hydrograph was a conservative estimate. For the future condition, the lag times of the unit hydrographs were recomputed and determined by the relationship, Lag = 0.6 X Time of Concentration, where the Time of Concentration represents the time of travel of rainfall runoff from the most distant part of the watershed to the outflow point. The Time of Concentration was determined from the Soil Conservation Service publication entitled, "Urban Hydrology for Small Watersheds," January 1975. The unit hydrographs for the future condition were constructed based on the changes made to the lag time and are shown on Plate A-6. 8. Rainfall. The Probable Maximum Precipitation (PMP) for Garapan was also obtain-e-d 7roFthe Ugum River report. Subsequent review of the report by the Office of the Chief of Engineers recommended that a PMP of 48 inches for a 24-hour period be used for the Ugum River watershed. In accordance with the recommendation, a 24-hour PMP rainfall of 48 inches was selected for the Garapan watershed. The depth-duration curve and depth-area curve for the PMP are shown on Plates A-7 and A-8, respectively. 9. Since the Standard Project Storm-(SPS) rainfall has not been established for either Saipan or Guam, the SPS was assumed to be 50 percent of the PMP. The assumption is within the guidelines of EM 1110-2-1411.and is somewhat justified by past rainfall data on Guam. Super Typhoon Pamela (21 May 1976) produced Guam's highest recorded 24-hour rainfall of 27 inches at the NWS Taguac site. Prior to "Pamela," the highest 24-hour recorded rainfall of 24.5 inches occurred at the Agana Agricultural Experimental Station during the 1 October 1924 typhoon. Although SPS determinations are made using various meteorological factors, the primary governing factor is the highest recorded rainfall (except for very unusual events). A detailed investigation for the SPS rainfall is beyond the scope of this study, but nevertheless, the assumption of a 24-hour SPS rainfall of 24 inches (50 percent of PMP) for the Garapan watershed is deemed reasonable. 10. Rainfall intensity-duration-frequency curves for Guam or Saipan have not been previously developed. Consequently, storm hyetographs, arranged to produce maximum discharges, were derived using available information. For the existing condition, the peak discharges for various flood frequencies were determined by the regress ion-correl ation analysis and the unit hydrographs for the drainage areas were derived in the SPF analyses. The relationship between the two knowns - peak discharge and unit hydrographs - were analyzed to produce the storm hyetographs. The storm hyetographs were determined by a A-6 trial and error method which applied various proportions of the SPS hyetograph to the unit hydrograph to match the peak discharges of the regression- correlation equations. Although the computed hyetograph is theoretical in its derivaton, it does compare favorably with the intensity-duration-frequency curves for the Hawaiian Islands. The computed hyetographs for the 2-year and 100-year floods are illustrated on Plates A-9 and A-10, respectively, and are divided into two categories - Rainfal] Losses and Rainfall Excesses. 11. Infiltration Losses. Infiltration losses were assumed to be uniform and were estimated by the Soil Conservation Service method of relating Soil types and land use to curve numbers from which rainfall losses can be determined. From an estimation of the soil types of the Garapan watershed, an infiltration loss rate of 0.6 inches per hour for the SPS was used. 12. For the future condition in the watershed (see main Report for Future Land Use Map), the SPF was calculated using a reduced infiltration loss rate due to the increased imperviousness associated with development. A loss rate of 0.4 inches per hour was used. 13. Local Drainage. Due to the dissimilar topography, the low flat areas of Garapan (areas 1A, 2A and 3A) were analyzed differently than the upstream areas. Peak discharges for the various flood frequencies and the SPF were determined by the use of unit hydrographs and storm hyetographs. Unit hydrographs were derived by calculating the time of concentration and using the following relationship; Lag = 0.6 x Time of Concentration. Other Snyder's Unit Hydrograph Parameters were assumed to equal those used for the upstream watersheds. The storm hyetographs were assumed to equal those derived in the analysis of the upstream watersheds; changes were made to the rainfall loss rates. The unit hydrographs for Areas 2A and 3A are shown on Plate A-3. Table A-2 summarizes the local drainage characteristics. 14. Flood Routing. Flood hydrographs were routed by the Modified Puls Method using HEC-1. The outflow-discharge relationship was derived using the HEC-2 computer program. The number of routing steps equaled the travel time of the flood wave divided by the routing time step. Routing time steps were made equal to the flood hydrograph time interval of 10 minutes. The travel time of the flood wave was determined by the flood wave celerity method described in EM 1110-2-1408, "Routing of Floods Through River Channels." The ratio of the wave celerity to the mean velocity (Vw/V) of 1.67 (for a wide rectangular channel) was selected. Mean velocities were obtained from HEC-2 computer runs. 15. Standard Project Flood (SPF). The SPF was developed in accordance with the directions and criteria contained in EM 1110-2-1411. Derivation of the SPF was made by applying the unit hydro raphs (Plate A-2) to the rainfall excesses of the Standard Project Storm (SPST The rainfall intensity patterns were structured to produce the maximum runoff for the SPF. The SPF hydrographs for the Garapan watershed are shown on Plate A-11. A-7 16. Peak discharges for the various flood frequencies and the SPF at the shoreline were determined by routing the flood hydrographs of the upstream areas (Areas 1, 2 and 3) and combining the routed flood hydrographs with the local drainage flood hydrographs. Plates A-12 through A-17 show the combined hydrographs at the shoreline. SPF and peak discharges for the subbasins and various concentration points are shown on Table A-3. DISCHARGE - FREQUENCY ANALYSIS 17. Streamgage Data. Discharge-frequency curves were developed by analyzing imum annual peak discharge streamgage data obtained from U.S. Geological Survey (USGS) publications and employing the Log - Pearson Type III criteria described in the U.S. Water Resources Council's Manual, "Guidelines for Determining Flood Flow Frequency, "Bulletin 17A. in accordance with the guidelines of Bulletin 17A, only streamgages with 10 or more years of record were used in the analysis. Nine Guam streamgages and two Saipan streamgages, a total of 11 gages having an average of 20 years of record, were examined. Plates A-18 and A-19 show the streamgage locations. Peak discharges were analyzed by using the "Flood Flow Frequency Analysis" computer program developed by HEC. A summary of the frequency analysis and a brief description of the streamgages are shown on Table A-4. 18. Regression-Correlation Analysis. A regression-correlation investigation, relating known hydrologic characteristics of the gaged watersheds in Guam and Saipan to the calculated peak discharge of various frequencies, was made to develop regional peak discharge equations. The data were analyzed by using the "Multiple Regression" computer program developed by HEC. The selected equations relate peak discharges to drainage area sizes and are listed below: Q - 2 year = 635 x DAO.948 Q - 10 year = 1265 x DAO.933 Q - 50 year = 1915 x DAO-924 Q - 100 year = 2215 x DAO.922 Q - 500 year = 2975 x DAO-915 Where Q is in CFS and DA in square miles. The unadjusted determination coefficients (R2) for the 2, 10, 50, 100 and 500 year peak discharge equations are 0.828, 0.834, 0.800, 0.782, and 0.737, respectively. The standard error in Log for the 2, 10, 50, 100 and 500 year peak discharge equations are: 0.219, 0.212, 0.235, 0.248 and 0.278, respectively. 19. The independent variab@es used in the analysis but deleted in the final analysis included the mean annual precipitation (AP), slope of the main channel (SL), length of the main channel (CL), mean elevation (EL), forest A-8 TABLE A-3. SUMMARY OF PEAK DISCHARQES EXISTING CONDITION - (NO PROJECT) AT WEST COAST HIGHWAY Peak Discharges (cfs) Flood Area I Area 2 Area 3 2-year 510 190 330 10-year 1,160 390 670 50-year 2,000 660 1,120 100-year 2,400 820 1,400 500-year 3,800 1,400 2,400 SPF 3,800 1,700 2,900 EXISTING CONDITION - (NO PROJECT) AT THE SHORELINE Peak Discharges (cfs)** Flood Area 1 & 1A Area 2 & 2A Area 3 & 3A 2-year 400 150 200 10-year 1,100 380 640 50-year 2,150 720 1,300 100-year 2,800 940 1,700 500-year 5,000 1,600 3,100 SPF 5,100 1,650 3,100 FUTURE PROJECT CONDITION AT WEST COAST HIGHWAY Peak Discharges (cfs) Flood Area 1* Area 2 Area 3 Area 2&3*** 2-year 510 250 410 640 10-year 1,160 470 760 1,150 50-year 2,000 760 1,250 1,800 100-year 2,400 920 1,550 2,250 500-year 3,800 1,500 2,600 3,750 SPF 3,800 1,750 3,000 4,600 *Developments are not planned-for Area 1. "Combined and routed discharges at the shoreline. ***Discharges used for Plan 1. A-9 LOCAL DRAINAGE EXISTING CONDITION Peak Discharges [lcfs) Flood Area IA Area 2A Area 3A 2-year 120 65 115 10-year 320 180 320 50-year 600 340 620 100-year 750 440 800 500-year 1,250 760 1,350 SPF 1,000 560 1,050 COMBINED DISCHARGE (FUTURE CONDITION) - NO PROJECT Peak Discharges (cfs) Flood Area 1 & IA Area 2 and 2A Area 3 & 3A 2-year 450 190 240 10-year 1,150 460 720 50-year 2,200 830 1,450 100-year 2,850 1,050 1,900 500-year 5,000 1,700 3,400 SPF 5,100 1,700 3,200 A-10 TABLE A-4 STREAMGAGES ON GUAM AND SAIPAN LENGTH DRAINAGE PEAK DISCHARGE (cf STATION OF RECORD AREA NUMBER STATION NAME (Years)- (Sq. Miles) Q2 2LO- Q100 8083 Finile Creek 17 0.28 215 328 464 at Agat 8160 Umatac River 23 2.11 2,480 5,200 9,520 at Umatac 8210 Geus River 22 0.93 729 2,060 4,780 near Merizo 8400 Tinaga River 25 1.89 795 2,020 4,330 near Inarajan 8470 Imong River 17 1.95 1,950 2,870 3,940 Near Agat 8480 Almagosa Springs 19 0.70 203 442 832 near Agat 8550 Ugum River 19 7.13 2,650 6,350 13,000 Near Talofofo 8580 Ylig River 24 6.48 3,090 4,630 6,430 near Yona 1 8650 Pago River 25 5.67 4,230 7,020 10,600 near Ordot 8010 South Fork 10 0.69 720 2,450 6,660 Talofofo Stream (Saipan) 8015 Middle Fork 11 0.35 214 620 1,480 Talofofo Stream (Saipan) cover (FC), shape factor (SF), and 1-hour rainfall for the 10, 50, and 100 year storm event OF). The linear regression equation used in the investigation was of the following form: Q = Cp DAa Apb CLc SO ELe FCf SF9 RFh It was ultimately reduced to the selected equations which reflected the best combination of correlation, application, and conformance to hydrologic principles. 20. Discharge-Frequency Curves. From the equations selected in the regression-correlation analysis, the peak discharges were computed for various frequencies and then plotted on probability paper. The best fit line of the computed discharges was adjusted to the expected probability curve. The adjustment was made by using N = 20 (the average number of years of record for the streamgages used in the regress ion-correl ation study) in the P versus P Table shown in "Statistical Methods in Hydrology", Leo R. Bearl, January 1962. Plate A-20 shows the discharge-frequency curves at the West Coast Highway. 21. Peak discharges for the future condition were determined by applying the computed hyetographs, modified by lesser infiltration rates to reflect increased imperviousness, to the unit hydrographs developed for the Future Condition. A 33% increase in imperviousness was used and was based on the area planned for future development and the anticipated impervious factors of the future development. Plates A-21 and A-22 depict the 2-year and 100-year floods, respectively. The peak discharges of the flood hydrographs were used to develop the discharge-frequency curves which were drawn to the expected probability curve by adjusting the exceedance frequency plotting positions. The adjustment was made using N = 20 (the average number of years of record for the stream gages used in the regression-correlation analysis) in the Pn versus Poo Table shown in "Statistical Methods in Hydrology." Plate A-23 shows the discharge-frequency curves for the future condition. 22. Discharge-Frequency Curves at Shoreline. The discharge-frequency curves were developed by the same procedures described in previous paragraphs. The discharge-frequency curves at the shoreline are shown on Plates A-24 and A-25. FLOODPLAIN ANALYSIS 23. General. The probable overflow area is defined as that area most susceptible to overflow based on the areas inundated by historical flood events and existing conditions. Probable overflow limits for the 100-year and standard project flood and the limits of possible overflow were prepared for use in the economic determination of flood damages caused by each return period flood. These limits are delineated for purposes of evaluating potential flood damages for benefit analysis and constitute no assurance that shifting debris would not cause overflow to move to other locations within the gros,s area subject to inundation. A-12 24. Flood Limits. Flood elevations associated with the peak discharges were determined by t e HEC-2 computer program. Manning's Roughness Coefficient, n, of 0.04 to 0.08 was used for overland flow. Garapan is subject to shallow flooding with flood flows in the s.ubcritical flow regime. Velocities are low, ranging from I to 4 feet per second for the 100-year flood. Due to the flat topography of the Garapan area, the flood discharges will cause flood limits of irregular boundaries intermixed with adjacent flood plains. The flood limits for various floods are shown in the Main Report (Figure 6). VERIFICATION OF HYDROLOGIC INVESTIGATION 25. A study to substantiate the computed results of the hydrologic investigation with observed data is impossible due to the absence of flood data for the Garapan watersheds. The only reliable known flood data for the area are the high water marks surveyed by the USGS for the 8-12 August 1978 flood. Compared against flood elevations computed by the HEC-2 computer program using peak discharges derived in the hydrologic investigation, the 1978 flood was estimated to range between a 10-year and a 30-year flood. The range of flood frequencies is not very significant since the flood elevations of the 10-year and 30-year floods vary by an average of only 0.25 to 0.3 foot. Perhaps the primary reason that the 1978 flood cannot be exactly matched with a flood frequency is the inability of the HEC-2 computer program to accurately model the subtleties of overland flow where local obstructions, dividing flows, intermixing flows, actual flood hydrograph, and splash waves add to its complexity.* The surveyed high water marks attest to the irregular nature of overland flow in the Garapan area. In one instance, a difference of 0.4 feet between high water mark elevations was measured in a residential lot. In another, the upstream high water mark elevation was slightly lower than a downstream mark. Surveying errors are very possible and would further distort comparisons between actual and computed flood surface elevations. The 1978 flood was remembered as the most severe flood encountered in the Garapan area by many long-time residents, an account which favors a 30-year flood classification for the 1978 flood. Other flood data such as rainfall intensities, flood stages and peak discharges for the Garapan watershed are not known to exist. Thus, the results of this investigation are without verification due to the absence of data. LOCAL DRAINAGE - WITH PROJECT CONDITION 26. The exact local drainage discharge contribution, i.e., the discharge and its inflow location, have not been determined for the structural alterna- tive plans discussed in the main report and Appendix C. Local agencies, especially MIHA, have been contacted and made aware of the possible use of the structural alternatives as a means of also serving the local drainage system. Earlier statements from MIHA indicated that they were planning to install an improved drainage system not connected to any of the structural alternative plans. However, it is very likely that should a structural (channel) plan be A-13 approved and constructed, the local agencies will use the channel to carry local drainage discharges. Since, the local drainage system is not a major contributor to the design flows, accommodation for local discharges can easily be made to the structural alternative plans, the local agencies have not shown any desire for including specific local drainage plans and tie-ins to the structural alternative plans, and the local drainage system is the responsi- bility of the local government, approximate estimations of additional local drainage discharges to the structural alternative plans were made. These estimations were made using the results and general procedures of the detailed hydrologic investigation. After a plan is selected, a detailed hydrologic and hydraulic analyses will be made to accommodate the local drainage system. The drainage system will be coordinated with the local agencies. A-14 T- --7-6-7 - 6 e.p.-y 53 41 dredge Gs. 4 "rtd 14 b,1 1jj dl@cgFd t. It felt 't Gasoline 21 2 0 4 1 '1 4 1 la Q) 4 Punt n M@'ch 3A 4 ARE 4 A S PA L/A Q S, N fit N AREA 3 AREA 2A. to 0 ollo Foll 0 .0 10 AREA 1A AREA 2 4 tie '34 92, 4 Qua/ AREA I VO 4 1 2 Z c) To Y '9 2 A pt 40 GARAPAN FLOOD CONTROL SAIPAN,CNMI 10 METER CONTOUR INTERVAL SCALE 0 1/2 IM ILE @/ 4e'' 62 0 DRAINAGE AREAS U.S. ARMY ENGINEER DISTRICT, HONOLULU m PLATE A-1 I INCH RAIN EXCESS IN 10 MINUTES w 0 w 14 0-0 1330 CPS 13 AREA 2133 DA = 0.78 SOMI LAG= 14.5 MIN (SEE N TE BEL)W) I I 10 -969 CFS ARLJ k I DAz0.68 SQjMI 9 LAG =17.4 MIN I 8 W3FS U. DA - 0 r. - I @ I'Am, 0 7 w 570 CFS 0 6 AREA DA = 028 S 3: LAG= 12 2MIRNII 5 4 3 2 10 20 30 40 50 60 70 80 - TIME IN MINUTES GARAPAN FLOOD CONTROL SAIPAN, CNMI NOTE: 10 MINUTE UNIT HYDROGRAPHS AREA 2 AND 3 IS DEVELOPED FOR PLAN I PEAK INCREASED BY 50% (SEE APPENDIX Q AND REPRESENTS A WITH EXISTING CONDITION PROJECT CONDITION. US. ARMY ENGINEER DISTRICT, HONOLULU PLATE A-2 z cr 0 c/) -1 INCH RAIN EXCESS IN TEN MINUTES W x LAG w 9 kv U) w a. 5 435 OFS AREA IA DA=O.'5 SO MI LAG=8.5 MINUTES 3- AREA 3A DA= 0.19 So MI LAG=20 MINUTES cf) LL. 0 185 CFS 0 V- AREA 2A z DA= .09 SO MI -LAG=12 MINUTES- w (9 ck: 0 0 10 20 30 40 50 60 70 TIME IN MINUTES GARAPAN FLOOD CONTROL SAIPAN, CNMI LOCAL DRAINAGE 10 MINUTE UNIT HYDROGRAPHS EXISTING CONDITION 1U.S. ARMY ENGINEER DISTRICT, HONOLULU PLATE A-3 10,000 9,000 8,000 7,000 6,000 5,00 4,000 2 100011%, 2,000 0 1,000 900 Soo 700 600 500 CD 400 *N. N@o 300 ci w 200 100 NJ .2 3 .4 .5 .6 .7 .8.9 1 2 3 4 5 6 7 WIDTH OF UNIT HYDROGRAPH IN HOURS FLOOD CONTROL SAIPAN,CNMI UNIT HYDROGRAPH PEAKS VERSUS WIDTHS U.S. AMY ENGINEER DISTRICT, HONOLULU PLATE A-4 I INCH RAIN EXCESS IN 10 MINUTES w (D Ix LAG. w n ;n- 14 15 12 11 890 CFS 10 /-.AREA & a 3 SEE INOTE ON A z 0.78 IRA PLA1 E A-2 FAG =21.6 M f 640 CWS AREA I DA=0.6 3 SQ MI J LAG--2(.1. MIN U. 0 560 CFS 0 7 A AREA A DA = 0.50 SQMI LAGz21 9 MIN w (9 .4 Ix 6 5 380 CFS 4 AREA 2 DA = 0.28 SWI AG=18.0 MIN 2 10 20 30 40 50 60 70 so TIME IN MINUTES GARAPAN FLOOD CONTROL SAIPAN, CNMI NON-INCREASED 10 MINUTE UNIT HYDROGRAPHS EXISTING CONDITION F.S. ARMY ENGINEER DISTRICT, HONOLULU PLATE A-5 IINCH RAIN EXCESS IN 10 MINUTES w 2 LAG XX 14 13 12 1030 CFS I I AREA ? 81 3 SEE NOTE DA = 0.78 SOM ON PLATE A-2 LAG= 18 6 MIN 10 9 8 0 650 CFS 0 AREA 3 7 DA - 0.'50 SOMI Le LAG= 18.8 MIN w 6 500 CFS 5 -AREA P_ DA x 0.28 SOMI LAG= 13.7 MIN 3 10 20 30 40 50 60 70 so TIME IN MINUTES GARAPAN FLOOD CONTROL SAIPAN, CNMI NOTE: PEAK INCREASED UNIT HYDROGRAPH FOR AREA I IS THE 10 MINUTE UNIT HYDROGRAPHS FUTURE CONDITION SAME FOR BOTH EXISTING AND FUTURE CONDITIONS SINCE NO DEVELOPMENT IS PLANNED FOR THE AREA. (SEE PLATE A-5) JU.S. ARMY ENGINEER DtSTRIC@% HONOLULU PLATE A-6 50 '40 w 30 z _j 20-- 0 3 6 9 12 15 TIME IN HOURS GARAPAN FLOOD CONTROL SAIPAN, CNMI DEPTH-DURATION CURVE PROBABLE MAXIMUM PRECIPITATION US. ARMY ENGINEER DISTRICT, HONOLULU 100 80 9 6-HOUR 60 z .3-Hol,R 0 a. 40 U- 0 w w CL 20 IJR Ol 1 5 to GARAPAN FLOOD CONTROL SAIPAN, CNMI DEPTH-AREA CURVE DRAINAGE AREA IN SQUARE MILES FOR PROBABLE MAXIMUM PRECIPITATION m > LU.S. ARMY ENGINEER DISTRICT, HONOLULU NOTE: 24-HOUR PMP RAINFALL= 48 INCHES C6 w 0 z =7 77 7 v 7 7 7m717',-7-,'77777Y77"J z RAINFALL, LOSSES 0.5 1 6 HR. RAINFALL 3.7 INCHES RAINFALL EXCESS 6 HR. RAINFALL EXCESS 1. 5 INCHES 1.01 6 '510 CFS AREA I u- 0 4 330 CFS AREA 3 0 z 3 w 190 CFS (D cr AREA 2 < 2 ot 0 2 3 4 5 6 TIME IN HOURS U.S. AR 0 i RAINFALL LOSSES z z 0.5 6HR RAINFALL= 8.6 INCHES z I 6 HR RAINFALL EXCESS= 5.6 INCHES RAINFALL EXCESS 1.01 20 2,000 CFS AREA I 1170 CFS AREA 3 15 0 685 C@S AREA 2 0 z to w CD cr x 0 cn 5 G 0 3 4 2 5 6 TIME IN HOURS U.S. ARM w 0 z z I 6 HR RAINFALL= 16.4 INCHES 6 HR RAINFALL EXCESS= 12.8 INCHES RA 2 4 2 Ix GARAPAN FLOOD CONTROL SAIPAN, CNMI SPF HYDROGRAPHS EXISTING CONDITION 1 2 3 4 TIME IN HOURS U.S. ARmy ENGINEER DISTRICT, HONOLULU 20 1,700 CFS COMBINED HYDROGRA@7H 16 LL 240 CFS 0 1, o 12 AREA 2 - 0 ROUTED FLOOD HYDROGRAPH z ILI U) 560 CFS AREA 2A FLO OD HYDROGRAPH GARAPAN FL 0 -u 0 2 3 4 5 6 r s TIME IN HOURS AT m FUTURE U.S. ARMY E COMBINED HYDROGRAPH 30 24 cn LL 0 CFS 0 AREA 3 0 ROUTED FLOOD HYDROGRAPH 18 w (D ct: m 6 12 1,050 CFS AREA 3A FLOOD HYDROGRAPH OF 1.000, GARAPA N FLO s 0 0 1 2 3 4 5 6 AT FUTUR TIME IN HOURS U.S. ARMY E 1 -1 870 CFS COMBINED HYDROGRAPH 10 600 CFS AREA 2 ROUTED FLOOD HYDROGRAPH U. 0 0 z 6 w cr. 4 370 CFS AREA 2A FLOOD HYDROGRAPH 2 GARAPAN FLO 0 FLO 2 3 4 5 6 AT m FUTURE > TIME IN HOURS U. S. ARMY E 200 190 CFS COMBINED 155 C 150 ROUTE U. z 100 cl) 50 OF 0 0 2 3 4 5 TIME IN HOURS GARAPAN FIL r FLC AT rn FUTUR U.S. ARMY E 20 1520 CFS COMBINED HYDROGRAPI 16 1040 CFS AREA 3 u- ROUTED FLOOD HYDROGRAPH C-) 0 12 0 W- z w (9 a: x a 660 AREA 3A FLOOD HYDROGRAPH 4 '00, GARAPAN FL( 0 -4 0 2 3 4 5 6 -u r- TIME IN HOURS FL( AT m FUTUR 0@1 U.S. ARMY E 250 240 C@S COMBINED HYDROGRAPH 225 CFS AREA 3 ROUTED FLO OD i 200 z LLI (D 150 cr 115 CFS AREA 3A 100 FLOOD H 50 100 .400, .0e dol GARAPAN F 0 FL AT m FUTUR > TIME IN HOURS U. S. ARMY SAIPAN MT. MARPI SCAL E 0 1 2 3 MILES MT DOGAS 8015 STUDY AREA GARAPAN 8010 MT TAGPOCHAU 'H,@'WLAKE f X-'fSUSUPE LAULAU BAY LEGEND A GAGING STATION f GARAPAN FLOOD CONTROL SAIPAN,CNMI STREAM GAGE AND STUDY AREA LOCATION LU.S. ARMY ENGINEER DISTRICT, HONOLULU PLATE A-18 N 31 V. AGANA PRA HARBOR'-- 8650 8083 8580 8480 TALOFOFO t 8470 8550 UMATAC 8400 LEGEND 8160 8210 A GAGING STATION U GARAPAN FLOOD CONTROL GUAM SAIPAN, CNMI SCALE I 0 1 2 3 4 5 STREAM GAGE LOCATION 1 1 J- IN MILES U.S. ARMY ENGINEER DISTRICT, HONOLULU PLATE A-19 EXCEEDANCE FREQUENCY PER HUNDRED YEARS 70 60 50 40 30 20 10 5 2 1 0.5 o SPF PEAK DISCHARGE or 100" 0" OF AREA I el_*100' 0.0@ .1-00 -1000 GARAPAN FLOOD CONTROL SAIPAN, CNMI AREA 3 - AT WEST COAST HIGHWAY DISCHARGE -FREQUENCY CURVES 0'0@ (EXPECTED PROBABILITY ) ooo@ EXISTING CONDITION AREA 2 uU.S. ARMY ENGINEER DISTRICT, HONOLULU I ooo@l w 0 x 0 z z 0.5 NOTE: -1 6 HR RAINFALL= 3.7 ANCHES FLOOD HYDROGRAPH FOR 6 HR RAINFALL EXCESSz 1.9 INCHES RAI@ 1.01 1 AREA I (FUTURE PROJECT z CONDITION) IS SAME AS ;a SHOWN ON PLATE A-9 SINCE NO DEVELOPMENTS ARE PLANNED FOR AREA I 8 640 CFS- AREA2a3 7 6 U) 5 0 0 4 w 3 co 2 GARAPAN FLOOD CONTROL SAAPAN, CNMI 777 2-YEAR FLOOD HYDROGRAPHS FUTURE PROJECT CONDITION 2 3 4 US ARMY ENGINEER DISTRICT, HONOLULU TIME IN HOURS U) w 0 0 z 7-7 NOTE z 0.5 -j 6 HR RAINFALL= 8.6 INCHES FLOOD HYDROGRAPH FOR 6 HR RAINFALL EXCESS= 6.2 INCHES RAIN AREA I (FUTURE PROJECT 1.0 CONDITION) IS SAME AS .0, SHOWN ON PLATE A-10 SINCE ir NO DEVELOPMENTS ARE PLANNED FOR AREA 1 2000 Cl AREA 2 20 15 LL. 0 0 0 10 9 w M cr 5 GARAPAN FLOOD CONTROL SAIPAN, CNIMI 100-YEAR FLOOD HYDROGRAPHS FUTURE PROJECT CONDITION 2 3 4 US. ARMY ENGINEER DISTRICT, HONOLULU TIME IN HOURS EXCEEDANCE FREQUENCY PER HUNDRED YEARS 70 60 50 40 30 20 io 5 2 0.5 AREA I - AREA 2 8k 3---__ AT SHORELINE SEE NOTE ON PLATE A-2 AREA 2 a 3- op '00or 110000 0@ AT WEST COAST HWY e000- AREA 3 '001, 00, GARAPAN FLOOD CONTROL SAIPAN, CNMI ;00@ 'u DISCHARGE- FREQUENCY CURVES AREA 2 EXPECTED PROBABILITY FuTURE CONDITION U.S. ARMY ENGINEER DISTRICT, HONOLULU EXCEEDENCE FREQUENCY PER HUNDRED YEARS 6,000 60 50 40 30 20 10 5 2 1 0.5 0.2 0.1 5,000 4,000 3,000 0 2,000 LL OF 0 AREA 3-3A z III 1,000 U) 900 Soo 700 001, ILI 91 600 500 400 oor 300 200 GARAPAN FLOOD CONTROL SAIPAN, CNMI DISCHARGE- FREQUENCY CURVE (EXPECTED PROBABILITY AT SHORELINE) FUTURE CONDITION-NO PROJECT U.S. ARMY ENGINEER DISTRICT, HONOLULU PLATE A-24 EXCEEDENCE FREQUENCY PER HUNDRED YEARS 60 50 40 30 20 10 5 2 1 0.5 0.2 0.1 4,000 3,000 2,000 AREA 2-2A U- 0 1,000 z 900 001, 800 700 600 cl) '500 le 400 iL 300 oor 200 OF,z 100 GARAPAN FLOOD CONTROL SAIPAN, CNMI DISCHARGE- FREQUENCY CURVE (EXPECTED PROBABILITY AT SHORELINE) FUTURE CONDITION-NO PROJECT U.S, ARMY ENGINEER DISTRICT, HONOLULU PLATE A 25 GARAPAN FLOOD CONTROL SAIPAN, CNMI GEOLOGY AND SOILS APPENDix B APPENDIX B GEOLOGY AND SOILS TABLE OF CONTENTS Paqe REGIONAL GEOLOGY GEOMORPHOLOGY B-1 SEISMICITY B-2 SUBSURFACE CONDITIONS B-2 PRELIMINARY SOIL VALUES B-3 DESIGN CONSIDERATIONS AND ANALYSIS B-3 CONSTRUCTION CONSIDERATIONS B-4 SPOIL DISPOSAL SITES B-5 SOURCES OF CONSTRUCTION MATERIALS B-5 REFERENCES B-7 GEOLOGY AND SOILS APPENDIX REGIONAL GEOLOGY 1. The island of Saipan is small in size, 13 miles long, four miles wide, comprises 48 square miles of dry land and has considerable geographic diversity. The dominant topographic feature is an axial ridge, or highland that extends through the northern three fourths of the island and reaches 1,555 feet elevation near the center of the island. A coral limestone barrier reef and lagoon (1/4 to 2 miles wide) borders the island on the west. The barrier reef changes to a fringing reef at both ends of the island. A narrow fringing reef encircles much of the rest of the island. 2. Closely spaced and generally deep valleys dissect and fissure most of the central portion of the axial ridge to expose volcanic and other igneous rock. Elsewhere the exposed rocks include tuffs and other pyroclastic fragmental rocks which have been reworked into sandstones and conglomerates. 3. The island consists of a series of limestone benches and scarps off- lapping on the volcanic rock basement. Three principal sets of benches or terraces are recognized according to elevation and intervals of terrace formation: An upper set of terraces with surfaces around 500 feet and higher elevation, an intermediate set of terraces with surfaces between 100 and 500 feet elevation, and the late or lower set of terrace surfaces below 100 feet elevation. A solution notch five to eight feet above present sea level is recognized as the six-foot eustatic stand of the sea that may correlate with the late post glacial warm period. Cloud, et al (Reference a) gives carbon-14 determinations that suggests an age order of 19,000 to more than 30,000 years for the most recent limestone formations. The oldest rocks are estimated to be about 58 million years old. 4. The terraces that dominate the terrain pattern of Saipan are nearly horizontal or slightly sloping benches, separated by seaward facing scarps or steeply sloping surfaces. The terraces below 100 feet are attributable to shifts of sea level, caused by melting and accretion of Pleistocene ice. The many changes in the relative position of land and sea that resulted in bench cutting at higher elevations may be tectonic effects, or even in part actual sea-level changes due to factors other than glacial. Nearly everywhere the surfaces of the limestone are pitted, pinnacled, creviced, cavitated (sinks and karst topography) and ridged from the action'of water, aided by organic acids from the dense vegetation. Caves and sinks are formed from solvent ground water. Rain that falls on the porous and pervious limestone beds moves almost directly downward either to underlying impervious layers or to a water table which is in hydrostatic balance with the sea in accord with the principles of the Ghyben-Herzberg lens. GEOMORPHOLOGY 5. Saipan has been divided (Reference a) into six principal geomorphic divisions and 25 distinct smaller parcels of terrain. The six major land forms are: B-1 the terraced limestone uplands the low limestone platforms the lower terraced benches the east central (Donni) clay hills the south eastern coastal fault ridges the western coastal plain 6. The proposed flood control project is located on the Western Coastal Plain which extends along the entire west side of the island. The western coastal belt ranges from 3,000 feet to less than 1,000 feet wide, and includes a total area of about four square miles of limesand (also classified as coral limestone sediments predominately sand sizes) and artificial man-made sanitary fills, heterogeneous mixtures of all kinds of coral and man-made debris. Filled terrain ranges from dredged marine sediments, random land fills, sanitary land fills, area and landscape grading to limited selected fills with controlled compaction. The so called limesands range from very fine to very coarse grained, are gravelly at some places and contain many mollusk shells and Foraminifera. They resemble present beach lagoonal sands except that they extend to altitudes as high as 15 feet or more. The sands rest upon a westward-sloping, limestone platform that is part of the low limestone plat- form, the hilly terrain on the east side of the Coastal Plain. The low, sloping limestone platform was once continuous with the Tanapag bench along the south side of Saipan. However, it was faulted downward about 20 feet to the west in late Pleistocene or early Recent time. The fault movement observable in the hills took place about 3,000 years ago (Reference a). The sandy beach and bar deposits forming the dry-land beach deposits around the marsh accumulated in the last 3,000 years by normal intertidal factors, water, wind and storm all contributing to some degree in the production of a genetically complex but physically rather simple blanket of limesand. 7. Carbon-14 analysis of a pelecypod shell collected from 1.5 feet below the surface of undisturbed limesands gives a corrected age of 1730 years (Refer- ence a). SEISMICITY 8. Saipan is in a most active seismic area on the eastern edge of the Philippine Plate between the Marianas and Japan trenches on the Cicum Pacific seismic belt. Many earthquakes of low magnitudes occur throughout the year with sufficient energy to cause settlement and consolidation in loose, low- density sediments. The earthquake history of Saipan since 1800 records two major disasters (actual magnitude not available) in 1849 and 1902. The Guam observatory lists 83 earthquakes since 1902 with magnitude of six or greater on the Richter scale. Because the area is seismically active, it is reasonable to assume that earthquakes of this magnitude or greater will occur again. Government design manual TM 5-809-10 dated April 1973 shows Saipan located in seismic probability Zone 3 with a design maximum acceleration of 0.33g. and a corresponding approximate magnitude of 7 on the Richter scale. SUBSURFACE CONDITIONS 9. Subsurface explorations will be performed at a later date pending a preliminary determination of project feasibility. Based on the logs of test B-2 pits 10 and 11 contained in Geo-Engineering and Testings 18 December 1978, a soil investigation report for the 48-unit Mihaville Housing Project (Refer- ence e) located east of West Coast Highway, foundation materials along the diversion channel consist of approximately I-foot of reddish-brown silt (MH) underlain in turn by silty sandy coral gravel (GM), silty gravelly coral sand (SM) or gravelly silt (MH), and coral limestone. Top elevations of the test pits are shown at (+)2.5 and (+)2.4 mean sea level, respectively. However, recent conversations with Geo-Engineer's principal indicated that the eleva- tions shown are not reliable since no topo survey was available at the time of the explorations. Consequently, top elevations of (+)6.0 mean sea level were assumed for the two test pits to agree with topo surveys now available. 10. Based on borings and test pits performed by the Government in the Susupe- Chalan Kanoa area and other borings performed by Geo-Engineering in the Garapan fishing harbor area (Reference c), foundation materials along the outlet channel are assumed to consist of loose to medium dense limesands (SM to GP) overlying coral limestone. 11. Coral limestone may or may not exist within the limits of required excavation of the outlet channel. Vertical and lateral limits of coral limestone if present along the outlet channel will be determined by future subsurface explorations. PRELIMINARY SOIL VALUES 12. This project will be primarily in excavation (cut) with minimal fill for freeboard requirements. For preliminary design purposes, foundation materials can be taken as cohesionless and the following soil parameters assumed. Soil parameters will be subject to review and revision upon completion of future subsurface explorations and laboratory soils testing. SAT = 120 pcf M = 110 pcf 0 = 300 C = 0 psf DESIGN CONSIDERATIONS AND ANALYSIS DIVERSION CHANNEL 13. Based on available soils data and in keeping with Geo-Engineering's recommendations on the MIHA housing project, preliminary side slopes (cut and fill) of IV on 2H are recommended for the trapezoidal concrete diversion channel. Side slopes will be subject to verification by detailed stability analysis upon completion of future subsurface exploration and laboratory soils testing work. A 121, layer of bedding material should be provided for drainage beneath the concrete slope and invert lining. Weepholes should be provided at minimum 81-01, on-centers along the base of the slope lining for positive relief of excess hydrostatic pressures. Unlined portions of cut and fill slopes above the groundwater table should be grassed for erosion protection. B-3 OUTLET CHANNEL 14. Based on available sub-surface data, the outlet channel will be excavated through limesands and possibly coral limestone. Pending verification by detailed stability analyses upon completion of future subsurface exploration and laboratory soils testing, preliminary side slopes of IV on 2.5H are recom- mended for the outlet channel. Slope and invert protection consisting of 18 inches of riprap over 9 inches of bedding are recommended for erosion protec- tion in accordance with EM 1110-2-1601, Hydraulic Design of Flood Control Channels and ETL 1110-2-120, Additional Guidance for Riprap Channel Protection. Riprap design was based on a specific gravity of 2.3 for coral limestone rock, discharge of 2,950 cfs and velocity ranging from 7.0 to 8.9 fps. 15. Riprap will be provided for all channel slopes and invert situated on limesands. Should competent coral limestone be encountered in the lower limits of the cross sections, slope riprap will be terminated and keyed into the underlying coral limestone at the point of contact. Similar to the diversion channel, unlined portions of cut and fill slopes above the groundwater table will be grassed-for erosion protection. CONSTRUCTION CONSIDERATIONS SITE PREPARATION AND FILL COMPACTION 16. Areas to be graded should be cleared of vegetation, grubbed and stripped to remove weak organic surface soils, large roots and other organic debris or trash. Areas to receive fill should be benched into firm soils or rock wh ere slopes prior to grading exceed a steepness of IV on 4H. Pockets of unusually soft or compressible soils should be removed in the process of benching. . 17. Following site preparation, fills should be placed in lifts no thicker than nine inches loose thickness, moisture conditioned as necessary and compacted to minimum 95 percent of ASTM D 1557, Method D maximum density for cohesionless materials and minumum 90 percent of maximum density for cohesive materials. CHANNEL EXCAVATION AND RIPRAP CONSTRUCTION 18. Dewatering will not be mandatory for channel excavation and riprap place- ment. However, if caving of loose foundation limesands becomes a problem during excavation, the contractor may elect to dewater to facilitate excava- tion. Riprap stone protection should be installed as the channel excavation progresses to minimize the exposure of the unprotected open excavation to unexpected flood flows. To the extent feasible, excavation and riprap place- ment should begin at the upstream end of the project and proceed downstream to minimize sediment accumulation in previously completed sections. Installation of a silt curtain or other structure across the mouth of the outlet channel will be required to minimize contamination of offshore waters during the excavation of the channel outlet. B-4 DEWATERING FOR CONCRETE PLACEMENT 19. Dewatering will be required for concrete placement for portions of structures lying below the groundwater table. Where practical, consideration should be given to use of precast units to eliminate the need for dewatering. PHASE CONSTRUCTION 20. Phase construction will be necessary for construction of the various culvert structures across Beach Road, West Coast Highway and other local streets. Since Beach Road and West Coast Highway are parallel roadway systems only 1,000' to 1,5001 apart, local diversion of traffic from one roadway to the other could be used effectively to permit construction of the culvert structures. Alternatively, a temporary bypass could be provided immediately alongside each highway. Existing local streets could be incorporated into the temporary bypass'system where possible. 21. Use of precast culvert sections would expedite construction of the roadway crossings, minimize interruption of vehicular traffic and eliminate problems associated with dewatering. SPOIL DISPOSAL SITES 22. The volume of excess excavated materia ls on this project is between 150,000 and 200,000 cubic yards. Two possible sites are being considered by the Department of Public Works, Commonwealth of the Northern Marianas Islands for disposal of cleared and grubbed material and excess excavated materials. They are: 1) a low area east of West Coast Highway across from the American Memorial Park and 2) a proposed sanitary landfill site east of West Coast Highway, approximately one-quarter of a mile south of the Sugar Train. Both sites are within three miles of the project. The presence of numerous large trees which must be protected against damage at the first site may preclude its practicability as a disposal site. Since the Department of Public Works has no firm timetable for opening the sanitary landfill at the second site, its availability is also uncertain at this time. A definite disposal site will be designated during the plans and specifications stage. SOURCES OF CONSTRUCTION MATERIALS EXCAVATED MATERIALS 23. Fills for this project are minimal and only required to the extent of providing the necessary freeboard allowance. Excavated mateials will be suitable for fill construction. The volume of material from the required excavations will be more than ample to satisfy fill requirements. QUARRIES AND BORROW PITS 24. More than 50 quarries and borrow pits were opened on Saipan during World War II. Most of the sites have been abandoned and are now overgrown with vegetation or obscured by subsequent development. Reopening these abandoned quarries will require considerable investigations and development work. B-5 25. All borrow pits and quarries on Saipan are controlled by the Commonwealth of the Northern Marianas and are leased for a fixed period (normally five years) on a competitive bid basis. Two quarries presently in operation on Saipan are the Black Micro Quarry at Marpi and the Sablan Quarry on Capital Hill in Tanapag. The limestone at these two quarries varies from rubble to well-bedded-coral limestone breccia. The limestone is white to tan and yellow in color, poorly indurated, fossiliferous and crumbly, requiring only a small amount of blasting for removal. The limestone has been irregularly dissolved by water leaving pinnacled solution surfaces. Fresh rock is overlain by residual red or brown clay of high plasticity in thickness ranging from a few inches to more than ten feet. There is a sharp contact between the clay and the underlying bed rock. A description of materials available at each of the above quarries are described below. (a) Black Micro Quarry at Marpi. This operating quarry is presently the best source for riprap or armor stone on Saipan. It produces a dense coral limestone rock with specific gravity (BSSD) in the order of 2.6. A stockpile of approximately 500 pieces of stone, 31 to 51 in nominal diameter were observed'at the site in December 1979. Approximately 15 percent of the stone in the stockpil'e ranged in size from 4' to 5' and the remaining 85 percent ranged in size from 31 to 4'. Quarry personnel said approximately 200 to 300 pieces of stone in sizes ranging,from 31 to 5' are recovered each month of operation. A higher rate of recovery could be obtained by changing the drill- ing and blasting pattern which is presently tailored for production of concrete aggregate. Stones less than 3' in nominal diameter comprise the bulk of the stone recovered from the quarry. Stones of this size are readily accommodated by the crusher in the production of concrete aggregate. A crushing/screening plant and a concrete plant are located at the site. Concrete aggregate produced meets the requirements of ASTM C-33. However, washing and scrubbing will be required to remove adhered fines. (b) Sablan Quarry in Tanapag. This quarry produces coral limestone aggregate for concrete and asphaltic concrete. A crushing/screening plant, concrete plant and asphalt plant (temporarily out of operation) are located at the site. Quarry personnel said concrete aggregate produced meets the requirements of ASTM C-33. Stone sizes available at this quarry are generally less than 3 feet. A small stockpile of stone was observed at the site during May and December 1979. Specific gravity of the stone ranges from 2.1 to 2.5. Quality of the rock varies widely and handling costs involved in sorting out the few acceptable pieces may rule out consideration of this quarry as an economical source of riprap or armor stone. B-6 REFERENCES a. Cloud, et al, Geology of Saipan, Mariana Islands, Part 1, General Geology, U.S. Geological Survey Professional PaFer -28OA, pp 1-123, 1956. b. Cloud, et al, Military Geology of S-aipan, Mariana Islands Vols 1-3, T- Pacific Geological apping Program, U.S.Army and U.S. Geological Survey, 1955 and 1958. c. Geo-Engineering and Testing, Soils Investigation - Preliminarz Phase, Proposed Saipan Fishing Center, Saipan, GNMI, prepared for Frederick E-77. Sun Architects, AIA, Guam, 30 Oct 79. d. Geo-Engineering and Testing, Proposed Permanent Powerplant, Saipan, CNMI, prepared for the Department of Pu-blic Works, GNMI, 17 Dec-7T.- e. Geo-Engineering and Testing, Proposed 48 Unit Mihaville Housing Project, West Coast Highway, Garapan, Saipan, GNMI, prepared for ARIZALA, COSTINIANO, VTM-F-eal and Associates, 18 Dec 78. f. Kobayashi, Teiichi, Topography, Geology and Coral Reefs of Saipan, Japanese Journal of Geology and Geography, Vol 16, No. 1-2, 1939. g. Tayama, Risaburo, Geomorphyology, Geology and Coral Reefs of Saipan Island, Nettai Sangyo Kenkyusho Iho, Tropical Industry Institute, Pa South 3-e-a--Ts-land Bulletin, No. 1, p. 1-62, July 1938. h. Tayama, Risaburo, Report on Ground Water in Saipan Isl and, Tropical Industry Institute Bulletin, Palau, South Sea Island,--N-o-.-T,-p. 1-40, April 1939. i. U.S. Defense Mapping Agency, Hydrographic Center, Hydrographic Map of Saipan Harbor, DMA Stock Number 81AHA81076, Scale 1:12000, 4th edition, 25 MarcF7977. B-7 GARAPAN FLOOD CONTROL SAIPAN, CNMI E %INEERING INVESTIGATIONS, DESIGN AND COST ESTIMATES APPENDIX C APPENDIX C ENGINEERING INVESTIGATIONS, DESIGN AND COST ESTIMATES Table of Contents Page HYDRAULIC DESIGN C-1 GENERAL HYDRAULIC CRITERIA C-1 Guidance C-1 Computations C-1 Level of Protection C-1 HYDRAULIC PARAMETERS C-1 ,Hydraulic Cross Sections C-1 Roughness C-1 Culvert and Bridge Piers C-3 Permissible-Velocities C-3 Freeboard C-3 Superelevation and Bend Radii C-3 Transitions C-3 Baseline Elevation C-5 COST ESTIMATES C-5 List of Tables Table Title Page C-1 Hydraulic Parameter Values C-2 C-2 Culvert Sizes C-2 C-3 Summary of First Costs C-5 List of Plates Follows Plate Title Page C-1 Alternative Plan 1 C-5 C-2 Alternative 1 Profile C-5 C-3 Alternative Plan 2 C-5 C-4 Alternative 2 Profile C-5 C-5 Alternative Plan 3 C-5 C-6 Alternative 3 Profile C-5 ENGINEERING INVESTIGATIONS, DESIGN AND COST ESTIMATES APPENDIX HYDRAULIC DESIGN GENERAL HYDRAULIC CRITERIA I. Guidance. The hydraulic design follows the US Army Corps of Engineers' En ineering Manual 1110-2-1601, "Hydraulic Design of Flood Control Channels," daled I July 1970. 2. Computations. Standard hydraulic theories were applied in the analysis. Descriptions available in standard hydraulic texts and handbooks. The computational procedure generally follows Method 1, Engineering Manual 1110-2- 1409, "Backwater Curves in River Channels," dated 7 December 1959. The actual computations were performed utilizing principally the Corps' generalized computer program HEC-2 "Water Surface Profiles," dated November 1976. 3. Level of Protection. A major consideration in the determination of a suit le level of protection is the potential effect on the health and safety of the community. For potential measures in urban areas with high levees, floodwalls or high velocity channels subject to potential catastrophic effects, the standard project flood may be the recommended level of protection. Lower levels of protection may be recommended for less urbanized areas or areas not subject to a catastrophe resulting from floods exceeding the design flood. 4. In the alternative designs developed, the average channel velocities are less than 10 feet per second (fps). Overtopping of the embankments would produce a low velocity sheet flow over the surrounding areas with no potential catastrophic results. Therefore, the standard project flood is not considered a suitable design discharge for the project. The channel design, however, must also provide a technically feasible degree of protection. For this reason, discharges less than the two percent discharge are not considered at this stage of the study. Flooding in the lower Garapan area is a result of low velocity flows and localized ponding. Based on preliminary benefit maximization studies, and in view of the nature of the type of flooding problem involved, the two percent frequency flow was adopted as the tentative design flood. HYDRAULIC PARAMETERS 5. Hydraulic Cross Sections. The typical sections'utilized in the design are shoWn-on appropriate figur@_s of the main report. The sections were selected based upon the stability characteristics of the natural ground, and of the lining materials, the constraints in available rights-of-way, and the costs in potential construction and maintenance. The sections are intended to confine and convey flowing waters up to the specified design discharge. 6. Roughness. The conservation of energy principle states that the total ener@*g_y head at a upstream location equals the total energy head at the down- stream location plus energy losses. Energy losses include frictional losses estimated by Manning's roughness coefficient (n). Values utilized in the analysis are shown on Table C-1. C-1 TABLE C-1. HYDRAULIC PARAMETER VALUES Cross Section Type of Mannings Type & Material Channel Special Condition/Location Side Slope "n" Value Veloci Trapezoidal Riprap "All Alternative 1-3 outlet channels and IV on 2.5H .035 100-year plan diversion channel south of Island Power Road. Grass "B" Alternative 1-3 diversion channels. IV on 2H .030 Riprap 11C11 Alternative 1-3 diversion channels IV on 2.5H .035 south of Island Power Road, IV on 3H .035 IV on 4H .035 Concrete "D11 100-year plan diversion channel. IV on 2H .014 Rectangular Concrete All culverts. Vertical .014 Concrete "Ell To contain hydraulic jump in area Vertical .014 south of Island Power Road. *See Table C-2 7. Culvert and Bridge Piers. At new culvert (Table C-2) locations, computations were performed using the HEC-2 bridge routine. Flow parameters utilized are as follows: Class Flow Parameter Value A Pier shape coefficient, XK 1.05 A, C Pier shape coefficient, XK 0.0 (No piers) A Effective obstructed pier width Actual width +1.0 feet on each side A, C Pressure flow orifice loss 1.6 coefficient, K 8. Permissible Velocities. The range in acceptable mean velocities is based on accepted hydraulic standards. Velocities in excess of limiting values may cause scour, damage, and excessive maintenance to the channel. Channel velocities in the areas with riprap lining are therefore, limited to 15 fps and to 8 fps in grass-lined channel areas. The flow velocities for the alternative plans are also shown on plates C-5 through C-8. 9. Freeboard. Freeboard is the computed vertical distance between the design water surface to the top of the channel wall or embankment. The freeboard considered in the design is dependent on the flow regime (rapid or tranquil), uncertainty in hazard (special physical conditions) and the lining material (concrete or rock). In most areas, a minimum freeboard of 2.0 feet is required except in high velocity flow areas where a 3.0-foot freeboard is recommended. These values of freeboard appear to be consistent with the above-mentioned parameters and the nature of the flood control system. Freeboard allowances for various channel sections are summarized in Table C-1. 10. Superelevation and Bend Radii. The rise in water surface as a result of centrifugal and gravitational forces on curved sections is based on guidance in EM 1110-2-1601. Simple circular curves are used in the design. The manual recommends that for subcritical flow channels, the centerline curve radius be a minimum of three times the design water surface topwidth. All channel curves in the design follow this minimum criteria. The superelevation coefficient "c" of 0.5 is utilized for tranquil flows. 11. Transitions. Transition in the channelized portions of the proposed improvements (including certain culvert locations) follow the recommended con- vergence and divergence wall flare rates. For mean channel velocities of less than 10 feet per second, the ratio of horizontal to longitudinal distance for each wall is held at a minimum 1:5. For velocities in the 10 to 15 feet per second range, the ratio is increased to a minimum of 1:10. There are no transitions where channel velocities exceed 15 feet per second. 12. At other culvert locations, wedge type transitions involving vertical wingwalls and sloped transitions to the trapezoidal channel section are being considered. These are generally less costly to construct, but the abrupt change in channel configuration results in additional flow disturbance and increased head losses. The coefficients for contraction and expansion losses are as follows: C-3 TABLE C-2. CULVERT SIZES (See Plates C-1 to C-6) Dimensions Avg. Invert Freeboard Alternative Culvert Station H_(Ft) X W (Ft) Elev (Ft) (Ft) I A 7+20 to 7+60 Two Cells: -6 3.1 11 x 17 11 x 17 1 B 1+20 to 2+10 (RT) 9 x 30 0.3 4.5 1 C 1+30 to 2+00 (LT) 9 x 15 0.5 4.0 1 D 4+70 to 5+00 (LT) 7.5 x 25 1.4 1.5 2 E 5+30 to 5+60 12 x 30 -7.3 3.7 2 F 20+90 to 21+90 9 x 30 -2.7 3.3 2 G 45+20 to 45+50 9 x 30 0.7 1.7 2 H 49+70 to 50+00 7.5 x 25 1.4 1.0 3 1 13+00 to 14+00 Two Cells: -4.8 2.0 9 x 20 9 x 20 3 1 22+40 to 23+00 Two Cells: -1.9 1.0 7 x 20 7 x 20 3 K 1+70 to 2+00 (RT) 8 x 20 -0.1 2.5 3 L 1+70 to 2+00 (LT) 8 x 25 -0.3 2.5 3 M 12+70 to 13+00 (LT) 9 x 20 0.7 2.4 3 N 17+20 to 17+50 (LT) 7.5 x 25 1.4 1.4 C-4 Contraction Expansion Flow Regime Coefficient Coefficient Gradual Subcritical 0.30 0.50 (Wall Flare 1:10) Supercritical 0.10 0.30 Gradual Subcritical 0.30 0.75 (Wall Flare 1:5) Supercritical 0.2o 0.50 Abrupt Subcritical 0.30 0.75 (450 angle wingwalls) Supercritical 0.30 0.70 13. Baseline Elevation. All computations are performed on existing topo- graphic survey data. Elevations are based on mean sea level (MSL) datum. Backwater computations for sizing the outlet channels, start at an elevation equal to mean higher high water (MHHW) plus one-half foot for wind and wave set-up (0.8 feet plus 0.5 feet = 1.3 feet). Channel stability computations are based on an initial water surface elevation of (-)1.4 feet, which is equal to mean lower low water (MLLW). COST ESTIMATES 14. Quantity computations for the alternative plans were determined from topographic maps completed in September 1979. The sources of construction materials are discussed in Appendix B - Geology and Soils, under "Sources of Construction Materials." A Guam-based contractor to do the work was assumed. Unit prices and wage rates are based on July 1980 price levels in Saipan. 15. Table C-3 summarizes the estimated costs for Plans 1 through 3. TABLE C-3. SUMMARY OF FIRST COSTS Item Plan 1 Plan 2 Plan 3 Mobilization and Demobilization $197,000 $197,000 $197,000 Clearing/Excavation 659,000 697,000 734,000 Channel Construction 691,000 .1,176,000 1,053 ,000 Culvert Installation 669,999 542,000 740,000 Lands, Relocations, and Indirect Costs 309,000 90,000 197,000 Subtotal $2,525,000 $2,702,000 $2,921,000 Contingency (20%+) 505,000 540,000 584,000 Engineering and Design 89,000 89,000 89,000 Supervision and Administration 106,000 111,000 119,000 Total Project First Cost $3,225,000 $3,442,000 $3,713,000 C-5 ........... .............. --------------- ------------------ --------------- N- - T TTI 11 1 NOTES: 7 T ---- ---------- ------- ------ 4 1. TYPICAL CHANNEL SECTIONS IN MAIN REPORT "A ----------- 2. CULVERT DIMENSIONS ON TABLE C-2 3. VERTICAL DATUM IS BASED ON MEAN SEA LEVEL (MSL) -- ----------- ---- iMf - ----- --- --- ------ ---------- --- ------- LEGEND'. - ----- -- ----- - ----- e ----- ------------ CHANNEL CENTERLINE CENTERLINE TOP OF LEFT AND RIGHT BANK &D Q7 ---------- -- ---------- - ---------- 0 o ----------- L@ 0 F I ----------- -------------- ------ -------- tit it ou CV G?j El E, 0 @c. Z@. b z (7s, Din rj 1-13 6& zl- D. it w E30, W @,o o j @j -414p, 73 /* tit El 7,40 ---------- :1 0-@t ------------ ----------- ----- ------------- ------ ------------ ------------------ 200 400 48 SCA 0 + CULVERT "A" !0 MSL 0 4. V m 3.7 Vz 3.8 V c 4.6 5;-@, -10 0 1800 cfs 19*50 18+00 16+00 14+00 12+00 104-00 8+00 6+00 4+00 2+00 0+00 RIGHT 04-oo LEFT 0+00 OUTLET CHANNEL CULVERT" 10 tow MSL 0 Vz 2.6 V-3.0 V- 4.3 -10 IQ= 40 cfs I L Q 440 cf s I 10=790cfs I Q= 1070 cfs I it+00 22+00 20+00 18+00 16+00 14+00 12+00 104-00 8+00 6+00 4+00 24+50 RIGHT DIVERSION CHANNEL x 0 ow W+) !u 6, 40 Z-j - - - - - EXISTING G Q 500 cfs Q = 760 cfs U) WATER SUR DESIGN CHA 30 CHANNELVE 20 VERT SCAL vz8.0 CULVERT" C HOR SCALE 10 Vz 6.4 VERT "Do' --vl"---l---@ G v - 3. V.3.2 MSL 0 10+00 8+00 6+00 4+00 2+00 0*w 10.1-40 LEFT DIVERSION CHANNEL U.S. ARM @4 )Affl,! ----------- CULVERT E -------- --- ---------- `7 ---------- - - -------- 7-1 z P T F t4) NZ5 ..WON= ---------- -------- C T'YPE C '"N EL b 30, b 0 20 - ---------- ----------- -------- ------- cov @p CU LVEf 7 v C@.<j @11 J-1 R7. V cz@ z -.a r 1@1" 0@, ION il 77L-1@- -------- -- -------- El 400 200 A *AA ------- - P==4 SCAL - - ------- -. ..... j 2 - --------- --------- ---- - CULVERT E ------ ----------------- - of- (I -------- - ---- ----- - --- 14 cj ------------------- ci z RT F 00 +: z @z ----------- 6 vz 14\ 4 -------- - - ---- - - ------- ----------------- TYPE CHAIVMEL ------- 301 b= ao ---------------- own ------------- ---------- ZJ ..... ...... ? VE 13. k,-/ :P3. 7"7/ - ------------ it ja 400 200 . .......... .... P==4 r- SCAL .......... CY CULVERT F C LVERT E to MSL 0 V=9.2 v=KA -V=43 V=3.6 1 1 - I I I -101 - FQ7 18C'''),cfs - - - I I -- 22+00 20+00 18+00 16+00 14+00 IZ+00 104-00 8+00 64-00 4+00 2+00 w 0 OUTLET CHANNEL z0 -J 10 MSL 0 V 3.4 V =,4.2 V 5.1 Q= 930cfs Q tZ50 cfs 10=1500cfs -,Q=1740ctsT- 44+00 42+00 40+00 38+00 36+00 34+00 32+00 30+00 28+00 26+00 24+00 DIVERSION ,,CHANNEL KE 0 -1 0 X + - - - - EXISTING GROU It WATER SURFACE 30 DESIGN CHANNE CHANNEL VELOCI 20 CULVERT"Gkl VERT SCALE: I' CULV@RT"H" HOR SCALE: I" to V=2 9 60cfs Q 930 cfs V=4 a @027( V=4.8 MSL 0 V=8.1 0 C @ V=2.9 V=3.4 , fftS V=7@2 Q=50 1 0-=71 c@ 554,40 54*00 524*0 504-01 48+00 46+00 444@00 DIVERSION CHANNEL U. S. AR ---------- -------------------- --- -- ---------- -- -- NOTE -- - --- ------- -------- --------------- :--Z- ---------- 1. TYPICAL CHANNEL SECTIONS IN MAIN REPORT -2 2. CULVERT DIMENSIONS ON TABLE ------ V." C 3. VERTICAL DATUM IS BASED ON MEAN SEA LEVEL (MSL) 6 ---------- 0 LEGEND: ------ ------------ CHANNEL CENTERLINE ------- -- ------- --- b", ------ ----------- ------ CENTERLINE TOP OF LEFT AND RIGHT BANK ------- 5@@ -- -------- A ----------- ---- - --------- - --- ----------------- ------------------ .t@c. A, --------------- Ro --E5--- 0 Q@ ----------- --------- ------------- .. ... ........ 61 Q4 N, 7, 0 @4 Eln C1 Z@ CD '(7 0 -- - --------- A., v's 6 Z:; z 10C% 41/ ?o it t' -00 _0 It t it I A- 21@ I I; Lj - - ----- - --- C3 El NN I ---- A @--3 A I IJ 400 200 SCALE w z + CULVERT "J" CULVERT "J." to MSL 0 V=5 Vz 5.6 V=8.0 V= 6.7 -4-1 1800 cfs 74-00 26-6-00 24400 22+00 204-00 18+00 164-00 14+00 12+00 10+00 8400 6400 RGHT 0+00 LIEFT 0+00 OUTLET CHANNEL 30 20 10 CULVERT "N" CULVERT' CULVERT "Ll' V 8.0 V= 4.3 MSL 0 - V=6.1 V= 3.3 V= 3.2 V= 3.8 V=4.5 V=7.2 -101 1 Q 500 cfs Q=750efs I Q=, 860 cfs Q 970'cfs Qz 1@ IOOcfs @=1250( 22-1-90 22+00 204-00 184-00 16+00 14+00 12+00 104-00 8400 6+00 4+00 2+00 LEFT DIVERSION CHANNEL - Z- 8 -- -- EXISTING GROUND PRO j4 m1 WATER SURFACE PROM 10 co DESIGN CHANNEL INVER CHANNEL VELOCITY, V, IN FT/SEC MSL 0 CULVERT "K"-/ I VERT SCALE I" = 20' 1 HOR SCALE I"= 300' V 0.5 V 1.7 V 2.9 V = 6.4 V 6.7 -10 Q= 40cfs Q 225 cfs Q=,415 Q = 700 cfs j 14+00 124-00 104.00 84-00 6+00 4+00 2400 0+00 RIGHT DIVERSION CHANNEL U.S. AR GARAPAN FLOOD CONTROL SAIPAN, CNMI ECONOMICS APPENDIx D APPENDIX D ECONOMICS TABLE OF CONTENTS Page Methodology D-1 National Economic Development Objective D-1 Condition of Project Area D-1 Project Costs D-1 Benefit Components D-1 Evaluation Process D-1 PROJECT BENEFITS D-2 General Description of Study Area D-2 Development of Depth - Percent Damage Curves D-2 Structure and Content Values D-3 Damage and Benefit Categories D-4 Damages Average Annual Damages D-4 Emergency Costs D-4 Average Annual Flood Reduction Benefits D-12 (Existing Development) Business and Financial Losses D-13 Affluence Factor D-13 NED Employment Benefits (EDA) D-13 Intangible Benefits D-14 Summary of Benefits D-14 APPENDIX D ECONOMICS LIST OF TABLES Table Title Page D-1 Damages Reported by Principal Subdivisions During D-2 August 1978 Flood D-2 Comparison of Actual and Predicted Damages D-3 D-3 Building Type and Structure Values D-4 D-4 Stage Damage Data D-5 D-5 Basin Stage - Exceedence Probability Data D-8 D-6 Emergency Relief Cost Data D-10 D-7 Average Annual Damages D-12 D-8 Average Annual Flood Reduction Benefits by Alternative D-13 D-9 Projected Per Capita Income and Contents Value D-13 D-10 Summary of Benefits D-14 ECONOMICS APPENDIX METHODOLOGY National Economic Development Objective. Floodplain management (including flood control and prevention) contributes to the National Economic Development (NED) objective by improving the net productivity of flood prone land resources. This occurs either by an increase in output of goods and services and/or by reducing the cost of resources. Condition of Project Area. Each floodplain management plan under considera- tion is evaluated on a "with and without" project basis. The without condition is that most likely to occur without the specific plan and gives proper recognition of the effect of the flood hazard on the probable course of development. The adoption and enforcement of appropriate land use regulations pursuant to the Flood Disaster Protection Act of 1973 (PL 93-234) is assumed, both with and without a Corps plan. For purposes of evaluating structural components of a plan, rational economic use of the floodplain is assumed. Economic rationality assumes that users of the floodplain will attempt to maximize returns, and take actions with full knowledge of the flood hazard. Project Costs. The total project NED costs include the first construction , contingency, indirect costs, and rights-of-way costs. The sum total is amortized over a 50-year economic life at 7-1/8 percent discount rate. The discount rates utilized are the prevailing rate established by the Water Resources Council for major water development projects. Added to the amortized first cost is the Operation, Maintenance, and Replacement (OM&R) costs. The sum of these two values is the average annual costs. This time stream of annual costs is compared to corresponding benefit values. Benefit Components. The principal benefits for flood control facilities are inundation reduction benefits. These "benefits" are the net loss in income to the nation as a result of flooding, commonly measured as the physical damages, business losses, and emergency costs. The inundation reduction benefit is the value of reducing flood losses to activities which would use the floodplain without any plan. It is measured as the reduction in the amount of damages or related costs. The component elements are the economic life, the discount rate, the base year, and price level all related to the annual values of benefits and costs. The economic life of the alternatives evaluated will be fifty (50) years. This period is consistent with projects of this scope and type. The discount rate for current FY 1980 Federal water resources projects is 7-1/8 percent. The base year is the year any evaluated plan is expected to be operational. The base year for the analysis is 1982. All benefits and costs are evaluated in constant (1980) dollars and extrapolated to the base year. The July 1980 price level is the date of the relative price of goods and services evaluated. Evaluation Process. Each evaluated condition may include potential land use changes, additional development and similar modifications which will alter the hydrologic response and potential economic damages. The benefit analysis involves interrelationship between hydrologic, hydraulic, and economic data and characteristics. Because of the variable nature of hydrologic events, the D-1 benefits are reflected in a time stream of damages prevented. The future stream of benefits is estimated by the multiplication of potential damages by corresponding flood frequencies and deducting the residual damages not prevented by the project. PROJECT BENEFITS General Description of Study Area. Garapan is undergoing rapid growth as mentioned in the main report. Developments within the study area is well underway; large tracts of open space for subdivision in the immediate future are no longer available. There are 338 buildings within the area and about 97 percent are residential. The remaining 3 percent consist of "neighborhood" type business and a police station. In addition, a nine-building elementary school sits in the heart of the area, and three multi-story hotels are located along the shoreline. Few smaller parcels of vacant land scattered throughout the area are zoned residential. The most recent flood of 18 August 1978, a 10- ear to 30-year flood frequency had reported residential damages of $19y,000 and commercial loss of $27,000, for a total of $222,000. None of the hotels were affected. There are no documents of damages from earlier floods within the study area. Development of Deeth - Percent Damage Curves. The records of damages from the flood of August 1978 are nly available source of damage .data in Saipan and were used in deriving depth-percent damage relationships for structures and contents (see Table D-2). Damage data from the 82 residents in Garapan who completed a flood damage questionnaire was used in this tabulation. Table D-1 shows damages reported by principal subdivision in Garapan. Flood damage reaches are shown on Figure 5 of the main report. TABLE D-1. DAMAGES REPORTED BY PRINCIPAL SUBDIVISIONS DURING AUGUST 1978 FLOOD Structure Content Yard Area Damage Damage Damage Total Annex 1 $24,000 $51,500 $6,100 $81,600 Annex 11 $13,800 $4,100 $17,900 Puntan Mutchot $21,000 $69,800 _$4,900 $95,700 $58,800 $125,400 $11,000 $195,200 It was not possible to correlate damage versus depth of flooding on a house-to-house basis. Consequently, representative percent structure or content versus depth curves were derived using the area totals. Pacific Ocean Division's urban damage computer program was used to calculate stage damage curves for residential units by reach. Index stages in each reach were selected as representative of the actual water surface that produced the reported damages. Percent damage curves were developed such that the predicted damages matched those reported as closely as possible. The actual and predicted values are shown in Table D-2. D-2 TABLE D-2. COMPARISON OF ACTUAL AND PREDICTED DAMAGES is Actual Damage Predicted Damage Index Stage ($1,000) ($1,000) Area Reach (Feet, Msl) Struc. 5_nt. Struc. Cont. Annex 1 2 6.25 7.0 13.2 (Basin 3) 3 6.5 6.3 11* 6 4 6.75 7.7 15.2 SUBTOTAL 24.0 51.5 21.0 40.0 Annex II (Basin 3) 3 6.5 .0 .0 4 6.75 5.1 7.7 5 7.0 5.8 10.1 SUBTOTAL 13.8 4.1 10.9 17.8 Puntan Mutchot 1 5.75 (Basin 3) SUBTOTAL 21.0 69.8 28.0 74.2 TOTAL 58.8 125.4 59.9 132.0 The unexplainable low content value loss in Annex II accounts for the major part of the discrepancy in actual versus predicted damages. The derived percent damage curves are comparable to values suggested by the 1975 revised Flood Insurance Administration (FIA) damage curves for one-story structures without basements. Commercial and public percent damage curves were based on two sources. The structure portion developed for residences was used since the many small commercial buildings are built to the specifications of houses. Commercial and public building contents percent damage curves were based on those utilized by POD for similar types of establishments elsewhere. Sufficient commercial losses were not experienced in the August 1978 flood to present a good statistical basis for developing new curves. Structure and Content Values. The predominant type of structure in Garapan is a concrete block house bu on a slab. There are a few older wooden homes using post and beam foundations. Values (see table D-3) for different building types were obtained from the Mariana Islands Housing Authority for individual blocks in the study area. Content values were based on linear regression relationships between content and structure value developed from sample data for similar homes in comparable communities elsewhere in POD. This data covers the range of structure values encountered in Garapan. Commercial and public structure values were based on $38 to $40 per square foot for lar e buildings and $22 per square foot for small buildings. Content values were gased on comparable establishments in similar communities elsewhere in POD, scaled down to reflect smaller inventories in Saipan. D-3 TABLE D-3. BUILDING TYPE AND STRUCTURE VALUES Basin - Reach Building Type Structure Value Range 3 1 Concrete $24,300 - $27,000 Wood on Post & Beam $14,400 - $19,000 2-5 Concrete $24,300 - $36,000 2 1-2 Concrete $24,300 - $27,000 (North of Wood on Slab $19,000 Island Power 3-6 Concrete $24,300 - $27,000 Road) Wood on Post & Beam $14,000 - $19,000 Wood on Slab $11,000 2 2-5 Concrete $30,000 (South of Wood on Post & Beam .$3,000 Island Power Wood on Slab $11,000 Road) Damage and Benefit Categories. Flood damages occur to residential, commercial, and public properties. In addition to property damage, flood disasters necessitate large expenditures by relief agencies such as the American Red Cross. Private and public utilities and roads are frequently damaged. Benefits are based on inundation damage preventation and emergency relief cost saving with alternatives. Damages. In computing estimated damages to existing developments, water surface elevations and the floodplain area were first determined for various flood magnitude by reach. Water surface elevation by reach and the exceedence probability is shown in table 5. The estimated damages for each development by depth of flooding were determined by correlating the floor elevation and the depth percent damage curve to value of structure and content. Stage damage information was prepared for residential, commercial, and public property using the derived percent damage curves. The calculations were made using the POD urban damage computer program (URBOAM). Stage damage data are tabulated in table D-4. The range of elevations is relatively small because the stages do not increase very much over the probability range of flood events. Average Annual Damages. The frequency data in table D-5 and the damage data for residential, commercial and public property in table D-4 were intergrated by URBDAM computer program io derive average annual damages. Average annual damages thus computed totaled $236,000, and are summarized by reach in table D-7. Emergency Costs. Emergency costs were based on analysis of operations during the past flood. They include expenditure for Territory emergency crews, Red Cross relief work, Territory and Federal investigating teams, police, and rescue crews. The August 1978 flood resulted in the expenditure of $212,500 for relief basically by the American Red Cross. This total is the amount for the entire island; actually some 645 households were served. Roughly 82 residents in the Garapan area reported losses. Emergency relief cost savings were based on $330 per unit (in 1980 dollars). Average annual cost was D-4 TABLE D-4. STAGE DAMAGE DATA Basin (B) Elev. Number Accum. Struc. Content Accum. & Reach (R) Msl. Buildings Buildings Damage Damage Damage B2 - Rl 7 8 8 0. 0. 0. 7.5 4 9912.0 11448.3 21360.3 8 1 9 19824. 22897. 42721. B2 - R2 7 10 10 0. 0. 0. 7.5 5 9040.0 10369.5 19409.5 8 0 10 18080. 20739. 38819. B2 - R3 7 30 30 0. 0. 0. 7.5 21 17972.0 22657.8 40629.8 8 12 42 35944. 45316. 81260. B2 - R4 7 38 38 0. 0. 0. 7.5 26 24248.0 32425.0 56673.0 8 15 53 48496. 64850. 113346. 8.5 53 101692.0 107688.7 209380.7 9 1 54 154888. 150528. 305416. B2 - R5 6 5 5 0. 0. 0. 6.5 14 1280.0 4236.8 5516.8 7 24 29 2560. 8474. 11034. 7.5 36 16280.0 35519.4 51799.4 8 14 43 30000. 62565. 92565. 8.5 47 61360.0 103607.6 1694967.6 9 9 52 92720. 144650. 237370. TABLE D-4. STAGE DAMAGE DATA (Contd) Basin (B) Elev. Number Accum. Struc. Content Accum. & Reach (R) Msl. Buildings Buildings Damage Damage Damage B2 - R6 7 1 1 0. 0. 0. 7.5 0 220.0 815.4 1035.4 8 0 1 440. 1631. 2071. 8.5 2 880.0 2387.8 3267.8 9 3 4 1320. 3145. 4465. 9.5 7 2410.0 6553.5 8963.5 10 6 10 3500. 9962. 13462. B3 Rl 5 55 55 0. 0. 0. 5.5 29 19280.0 51075.6 70355.6 0 6 4 59 38560. 102151. 140711. 1 154446.5 234066.5 Ol 6.5 64 79620.0 7 10 69 120680. 206742. 327422. B3 R2 5 4 4 0. 0. 0. 5.5 6 2000.0 4257.1 6257.1 6 9 13 4000. 8514. 12514. 6.5 22 12540.0 23426.9 35966.9 7 18 31 21080. 38339. 59419. 7.5 31 41140.0 70003.5 111143.5 8 1 32 61200. 101668. 162868. TABLE D-4. STAGE DAMAGE DATA (Contd) Basin (B) Elev. Number Accum. Struc. Content Accum. & Reach (R) Msl- Buildings Buildings Damage Damage Damage B3 - R3 5 2 2 0. 0. 0. 5.5 4 1000.0 2128.6 3128.6 6 7 9 2000. 4257. 6257. 6.5 12 7500. 13683.6 21183.6 7 6 15 13000. 23110. 36110. 7.5 19 25820. 39867.7 65687.7 8 8 23 38640. 56625. 95265. B3 R4 5 1 1 0. 0. 0. 5.5 6 720.0 1259.9 1979.9 6 12 13 1440. 2520. 3960. 6.5 14 9960.0 17421.1 27381.1 7 3 16 18480. 32322. 50802. 7.5 20 35880.0 50202.5 86082.5 8 8 24 53280. 68083. 121363. B3 R5 6 6 6 0. 0. 0. 6.5 5 4320.0 6749.3 11069.3 7 5 11 8640. 13499. 22139. 7.5 12 20880.0 27072.2 47952.2 8 2 13 33120. 40646. 73766. 8.5 13 48240.0 58089.2 106329.2 9 0 13 63360. 75533. 138893. TABLE D-5. BASIN STAGE - EXCEEDENCE PROBABILITY DATA (STAGES ARE IN FEET, MSL) BASIN 2 REACH I REACH 2 REACH 3 STAGE PROBABILITY STAGE PROBABILITY STAGE PROBABILITY 3.090 0.6667 4.520 0.6667 5.050 0.6667 4.790 0.5000 5.300 0.5000 6.000 0.5000 5.790 0.1000 6.490 0.1000 7.340 0.1000 6.120 0.0500 6.890 0.0500 7.400 0.0500 6.470 0.0333 6.910 0.0333 7.460 0.0333 6.620 0.0200 6.990 0.0200 7.520 0.0200 6.690 0.0100 7.170 0.0100 7.590 0.0100 6.720 0.0050 7.240 0.0050 7.680 0.0050 6.720 0.0020 7.380 0.0020 7.800 0.0020 REACH 4 REACH 5 REACH 6 STAGE PROBABILITY STAGE PROBABILITY STAGE PROBABILITY 5.510 0.6667 6.080 0.6667 6.800 0.6667 7.300 0.5000 7.400 0.5000 8.520 0.5000 7.710 0.1000 7.810 0.1000 8.670 0.1000 7.870 0.0500 7.980 0.0500 8.780 0.0500 7.950 0.0333 8.070 0.0333 8.810 0.0333 8.040 0.0200 8.170 0.0200 8.860 0.0200 8.180 0.0100 8.320 0.0100 8.900 0.0100 8.300 0.0050 8.470 0.0050 8.980 0.0050 8.480 0.0020 8.680 0.0020 9.070 0.0020 D-8 TABLE D-5. BASIN STAGE - EXCEEDENCE PROBABILITY DATA (Contd) (,STAGES ARE IN FEET, MSL) BASIN 3 REACH 1 REACH 2 REACH 3 STAGE PROBABILITY STAGE PROBABILITY STAGE PROBABILITY 4.710 0.6667 4.730 0.6667 5.940 0.6667 5.190 0.5000 5.290 0.5000 6.310 0.5000 5.640 0.1000 5.800 0.1000 6.650 0.1000 5.820 0.0500 5.990 0.0500 6.790 0.0500 5.910 0.0333 6.090 0.0333 6.870 0.0333 6.030 0.0200 6.210 0.0200 6.990 0.0200 6.200 0.0100 6.390 0.0100 7.160 0.0100 6.380 0.0050 6.580 0.0050 7.340 0.0050 6.580 0.0020 6.820 0.0020 7.600 0.0020 REACH 4 REACH 5 STAGE PROBABILITY STAGE PROBABILITY 6.170 0.6667 6.180 0.6667 6.690 0.5000 6.750 0.5000 7.080 0.1000 7.170 0.1000 7.230 0.0500 7.340 0.0500 7.320 0.0333 7.440 0.0333 7.450 0.0200 7.580 0.0200 7.630 0.0100 7.780 0.0100 7.820 0.0050 7.980 0.0050 8.120 0.0020 8.320 0.0020 computed using urban damage computer program and utilizing stage-probability data from table D-5 and number of buildings in table D-4 with at least 1 foot of flooding over first floor. Emergency relief cost data are shown in table 0-6. Average annual emergency relief cost benefit is shown in table D-7. D-9 TABLE D-6. EMERGENCY RELIEF COST DATA Basin- Stage Number Accum Damagel/ Reach (Ft, Msl) Residences Residences ($1,000) 2-1 7 6 6 0 8 1 7 2.3 2-2 7 6 6 0 8 0 6 2.0 2-3 7 28 28 0 8 15 43 9.2 2-4 7 30 30 0 8 10 40 9.9 9 1 41 13.2 2-5 6 5 5 0 7 21 26 1.6 8 6 32 8.6 9 9 41 10.6 2-6 7 1 1 0 8 0 1 .3 9 3 4 .3 10 6 10 1.3 I/ Computed as follows: Accumulated residences w/ 1 foot of flooding x $330/unit. D-10 TABLE D-6. EMERGENCY RELIEF COST DATA (Contd) Basin- Stage Number Accum Damagel/ Reach (Ft, Msl) Residences Residences ($1,000) 3-1 5 53 53 0 6 4 57 17.5 7 9 66 18.8 3-2 5 4 4 0 6 5 9 1.3 7 4 13 3.0 8 0 13 4.3 3-3 5 2 2 0 6 5 7 .7 7 8 15 2.3 8 8 23 5.0 3-4 5 1 1 0 6 11 12 .3 7 3 15 4.0 8 4 19 5.0 3-5 6 4 4 0 7 0 4 1.3 8 0 4 1.3 9 0 4 1.3 l/ Computed as follows: Accumulated residences w/ 1 foot of flooding x $330/unit. D-11 TABLE D-7. AVERAGE ANNUAL DAMAGES Basin Residential Commercial Emergency R & Public Damage Relief Cost & Reach B2 - RI 0 0 B2 - R2 438 22 B2 - R3 9,496 843 B2 - R4 39,299 2,797 B2 - R5 42,032 3,026 B2 - R6 2,231 186 B3 - RI 50,622 4,860 83 - R2 5,921 416 B3 - R3 18,028 1,073 B3 - R4 43,839 2,413 B3 - R5 24,372 773 TOTAL $236,278 $16,405 Average Annual Flood Reduction Benefits (Existing Development) Average annual damages computed under improved conditions for the several alternatives are: Alternative #1 $7,000 Alternative #2 $7,000 Alternative #3 $7,000 The difference in average annual damage without improvement and with improvements for the several alternatives is the benefits from damage prevention and summarized in table D-8. D-12 TABLE D-8. AVERAGE ANNUAL FLOOD REDUCTION BENEFITS BY ALTERNATIVE Category Alternative 1 Alternative 2 Alternative 3 Damage without Improvement Residential, Commercial, Public $236,000 $236,000 $236,000 With Improvement 7,000 7,000 7,000 Net Average Annual Benefits $229,000 $229,000 $229,000 Business and Financial Losses. Benefits from prevention of business and financial losses are not expected to accrue from the project. Increased business activity outside the floodplain limits would offset any losses that may occur to flooded commercial enterprises. Affluence Factor. In computing flood damages to existing development, the future increase in damageable property must be considered to reflect fair treatment of what damages would occur. This was done by increasing the estimated value of the contents of the residential structures at a rate that per capita income is expected to grow. There is no per capita income projection series for Saipan. However, the lowest estimated per capita income series developed for Guam by POD is believed applicable in terms of rate of growth. This series is shown in table D-9. At this rate of growth, the value of contents for the average Garapan residence would grow to 75 percent of structure value (the maximum growth for which benefits are allowed) by 2024 is also shown in table D-9. Total average annual damages prevented resulting from the application of the affluence factor methodology to existing residential development is $10,000. TABLE D-9. PROJECTED PER CAPITA INCOME AND CONTENTS VALUE Per Capita Content Year Income l/ Value 1980 $3,000 1982 3,300* $4,812 1990 4,600 2000 6,100 2010 7,700 2020 9,900 2024 11,000* 16,000 2030 13,200 2032 13,900* * Interpolated or extrapolated 1/ In 1967 dollars NED Employment Benefits (EDA). The 1973 Census indicated Saipan had a 9.2 percent overall unemployment rate. No later data are available. However, due to the continuing migration into the District Centers, generally, in the islands of the Trust Territory and former Trust Territory, it is likely that D-13 the rate has increased since 1973. Employment during construction benefits (EDA Benefits) are claimed for this project. Employment benefits were computed in accordance with Part IX of the U.S. Water Resources Council final rule dated 14 December 1979. The construction labor cost is split between skilled and unskilled labor. Thirty percent of the skilled and 47 percent of the unskilled costs are claimed as benefits. The average annual EDA benefits discounted on the basis of a 50-year period of analysis at 7-1/8 percent is $5,000 for Alternatives 1, 2 and 3. Intangible Benefits. Intangible benefits accrued from the proposed project are reduction of health hazards associated with floods, and the improved morale of residents of the floodplain as a result of the reduction of flood damages and threat of life and limb. Summary of Benefits. The average annual benefits from alternative improvements presented are summarized in table D-10. The two key economic measures utilized for project justification are the net benefits and the benefit-to-cost ratio (BCR). The net benefit is the difference between the average annual flood control benefits (potential losses in absence of the project) and the average annual costs. The difference between the two values must be positive for economic feasibility. In addition, the plan with the highest value is designated as the alternative which contributes most to the NED objective. Another measure utilized in comparing plans is the BCR, which is the ratio between the average annual benefits to the average annual costs. The NED plan may not necessarily be the plan with the highest BCR. TABLE D-10. SUMMARY OF BENEFIT Average Annual Category Alternative 1 Alternative 2 Alternative 3 Flood Reduction Benefit Residential, Commercial, Public $229,000 $229,000 $229,000 Affluence Factor 10,000 10,000 10,000 Emergency Relief Savings 16,000 16,000 16,000 NED Employment Benefits 5,000 5,000 5,000 Total Average Annual Benefit $260,000 $260,000 $260,000 Total Average Annual Cost 241,000 255,000 277,000 Net Benefits 19,000 5,000 17,000 Benefit/Cost Ratio 1.08 1.02 0.94 D-14 0 GARAPAN FLOOD CONTROL SAIPAN, CNMI SOCIAL AND CULTURAL RESOURCES APPENDix E 0 APPENDIX E SOCIAL AND CULTURAL RESOURCES Table of Contents Page SOCIAL WELL-BEING E-1 CULTURE AND HISTORY E-1 DEMOGRAPHY E-1 COMMUNITY COHESION E-2 EMPLOYMENT, EARNINGS, AND EXPENDITURES E-2 LAND USE AND DEVELOPMENTAL PATTERNS E-3 LAND OWNERSHIP E-4 POWER E-4 WATER SUPPLY E-5 SANITARY SEWERAGE E-6 SOLID WASTES E-6 HIGHWAY TRANSPORTATION E-6 MEDICAL CARE E-7 POLICE PROTECTION E-7 FIRE PROTECTION E-7 TROPICAL STORMS/TYPHOONS E-7 CULTURAL RESOURCES E-10 PREHISTORIC PERIOD E-10 HISTORIC PERIOD E-10 List of Tables E-1 DEMOGRAPHY OF THE NORTHERN MARIANAS E-2 E-2 TYPHOONS SIGNIFICANTLY AFFECTING THE MARIANA ISLANDS, 1948-1976 E-8 APPENDIX E SOCIAL AND CULTURAL RESOURCES SOCIAL WELL-BEING CULTURE AND HISTORY. ]. Saipan was ori inally inhabited by Chamorros. They were relocated to Guam by the Spanish in 7660. Under Spanish rule, the Chamorro population and culture were nearly obliterated. The decline of the Chamorro population was further influenced by intermarriage with the Spanish, Mexican and Filipino, who were present in the islands. Surviving Chamorros resettled on Saipan in the 1800's. However, the native population was a mixed race with a culture and tradition reflecting Spanish colonial influence. They were Catholic, trained in agriculture and their matrilineal system replaced with a patrilineal one, although their extended family ties persisted. Being poor and having no mineral wealth, Saipan and its people attracted little attention from the out- side world. The native population consisted of subsistence farmers living in village establishments supplementing their farming with inshore fishing. In the 1800's, several hundred Carolinians established separate villages on Saipan. Their culture was not unlike the old Chamorro culture, but their language and culture set them apart from the native population. 2. Following the Spanish-American War, Germany administered the island, establishing public schools, extending the road network, and organizing an agricultural economy based on copra. However, the Japanese dominated trade in the region and after World War I obtained control of the island. By 1930, the total population on Saipan was about 45,000 of which less than 10 percent were native (Chamorro and Carolinian). Koreans and Okinawans were imported to supplement Japanese labor. Japanese school was mandatory for all on the island. Garapan became the center of population and economy under Japanese administration. Following World War II, all the surviving Japanese on Saipan were expatriated to Japan. The native population previously confined to Chalan Kanoa were allowed to circulate freely and by 1947 subsistence agriculture replaced the previously thriving sugar economy. The native population had to adapt to a new language, a new form of government and new cultural values. Saipan remained under US Navy administration until 1962 when it became part of the Marianas District, Trust Territory of the Pacific Islands, a trusteeship of the United Nations administered by the United States. Saipan became the headquarters for the Trust Territory of the Pacific Islands, a factor enhancing the presence of other Micronesian cultures on Saipan. In 1978, Saipan and 15 other islands in the Marianas District entered into a convenant with the United States forming the Commonwealth of the Northern Mariana Islands, a status separate from the Trust Territory of the Pacific Islands with closer association with the United States. DEMOGRAPHY. 3. Of the three major islands in the Commonwealth, Saipan is the center of population, commerce, and government. The 1978 Commonwealth population was estimated at 14,850 (see Table E-1). The birth rate and death rate have remained relatively constant between 1972 and 1977. On the whole, the population is rather young and the ratio of males to females is relatively even. E-1 TABLE E-1 DEMOGRAPHY OF THE NORTHERN MARIANAS I. Geographical Featuresi/ Population 1973 Density per Islands Area_(sq mi) Population Sq Mi Saipan 47 12,366 265 Rota 33 1,104 35 Tinian 39 714 20 2. Population by age group and sex (mid-year estimate, 1978).@/ Age Group Population Male Female 0-14 6,810 3,490 3,320 15-64 7,580 3,790 3,790 65+ 460 220 240 Total 14,850 7,500 7,350 l/ Bulletin of Statistics, Trust Territory of the Pacific Islands, Office of Planning and Statistics, December 1978, Vol I,(3):p.11. 21 Socioeconomic Development Plan for the Northern Mariana Islands, 1978-1995, Office of Transition Studies and Planning, by Robert Nathan Associates, Inc., October 1977, p.54. COMMUNITY COHESION. 4. The estimated population of Saipan is about 12,400 (Office of Planning and Statistics, 1978). Chamorro, Carolinian, and Micronesian cultures constitute about 84 percent of the total population on Saipan. Tourism averages 700 persons per day and accounts for some of the island population. The proportion of natives in the total population declined from 92 percent in 1967 to 87 per- cent in 1973. Projections suggest that the native population may comprise 78 percent of the total population by 1985 (Physical Development Master Plan, 1978). The number of tourists visiting Saipan may increase to about 1,800 visitors per day by 1985. The majority of tourists visiting Saipan are from Japan while the second largest number comes from the United States. The distinctions between the Chamorro and early Carolinian cultures have faded, and the resident population has a strong identification by family groups and island community. Present cultural and ethnic views between residents and alien laborers, Americans, Japanese, and Micronesians are unknown. EMPLOYMENT, EARNINGS, AND EXPENDITURES. 5. The total resident work force in the Commonwealth in 1976 was about 6,500 persons (Office of Planning and Statistics, 1978). About 43 percent of the work force were employed in the money economy (jobs in the western sense) and about 4 percent were employed in the village economy (subsistence economy) (Robert R. Nathan Associates, Inc., 1977). However, the total number of persons employed in the Commonwealth was about 7,000 of which 27 percent were E-2 considered expatriates and 5,300 listed as Micronesian (Office of Planning and Statistics, 1978), which included the Trust Territory Headquarters employees. The data were insufficient to determine the ethnicity of the Micronesian group. Of the remaining resident work force, 19 percent were in school and about 34 percent were not in the labor market. More Micronesians hold lower paying jobs ($10,000 or less per year) than expatriates and more expatriates hold high paying jobs ($15,000 or more per year) than Micronesians. About 56 percent of those employed earned less than $10,000 per year. Government employed about 50 percent of the working force. Tourism (services) and wholesaling accounted for 68 percent of the employment and wages in private industry. Tourism is expected to be a significant economic force in the near future, but the govern- ment hopes to diversify economic growth. Manufacturing and handicrafts accounted for about 3 percent of the employment and wages earned in the Common- wealth in 1976 (Robert R. Nathan Associates, Inc., 1977). Essentially all materials and consumer items in the Commonwealth were imported. Excluding oil products, total reported imports in FY 1976 were $12.5 million, equivalent to $750 per capita. Food imports were equivalent to $280 per capita. The total number of taxpayers in the Commonwealth in Fiscal Year 1976 was 6,200 persons and the number is expected to decrease with the application of US Tax Laws. Under US tax rules, approximately 70 percent of the taxable wage earners would not have to file a tax return and another 20 percent would be entitled to a refund (Robert Nathan and Associates, Inc., 1977). LAND USE AND DEVELOPMENTAL PATTERNS. 6. Prior to World War II, Saipan was essentially an agricultural colony of Japan where 30,000 acres were cultivated with over 18,000 acres cultivated in sugarcane. The population was centered around Garapan, which became a boom town. During World War II, Japanese agricultural fields and sugar mills were destroyed and replaced by a huge military complex of warehouses, airfields, military encampments, and munition storage areas. The local population were relocated from Garapan to Chalan Kanoa, which remains the most populous area in the Northern Mariana Islands and can be considered the government and economic center of the Commonwealth. Today, most of Saipan's 46 square miles of land area is relatively unused. A few hundred acres are cultivated, but the most productive area of marketable products is the 50-60 acre plot at the Kagman A i ltural Experiment Station (Pacific Planning @nd Design Consul- qricu tants, 78). Approximately 1,150 acres is used for grazing Primary agricul tural lands are located in the Kagman and Kobler Airfield areas at Saipan. Pasturelands for grazing and subsistence farming are located in the hills of Saipan. 7. An 11-mile area along the western coast of Saipan from Susupe to San Roque contains the bulk of the population on Saipan. The Chalan Kanoa, Susupe, San Jose and San Antonio villages in the southern area of Saipan contains 45 per- cent of the native population on Saipan. The central part of the coast includes the village of Garapan. The island's only port facilities and concen- tration of industrial development are located at Garapan in the Tanapag Harbor area. The Garapan area contains about 24 percent of the island population. The villages of Tanapag, San Roque, Capital Hill and Navy Hill rely upon Garapan for needed services; these areas contain about 16 percent of the island population. 8. The Garapan area is experiencing more rapid residential and population growth than any other village on Saipan. The Garapan Estates and two Sugar E-3 Kin qevelopments are expected to more than double the area's population. Two of ?a1pan's most modern hotels and the best beaches are located in Garapan. Tanapag Harbor is located north of* the residential area and is the primary port and industrial area on Saipan. The Physical Development Master Plan for Saipan (Pacific Planning and Design Consultants, 1978) assumes that Garapan will remain a desireable location for new residential growth because of the availability of easily developable land. The community master plan provides for a resort-tourist industry, memorial park, historical park, port and industrial facilities, a fishing village, new junior high and elementary schools, and a new hospital. The plans call for residential growth around the junior high school and east of the school site. LAND OWNERSHIP. 9. In the Commonwealth society, landownership is closely tied with family solidarity and a sense of group responsibility and participation. Among some people, especially those of Carolinian descent, it is considered a solemn duty to retain land within the family. Thus, people are reluctant to sell land and the desire to own land is said to have resulted in a relatively high market valuation of land (Physical Development Master Plan, 1978). On the other hand, some segments of the population especially some of Chamorro descent, view land as an economic commodity to be bought or sold in the market place for monetary gain. Historical changes in land law systems (Spanish, German, Japanese and American) have created extremely complex and often contradictory sets of land records. Many conflicts and much confusion regarding property ownership exist, and many titles to private parcels are in dispute. Under German and Japanese rule, the government took over all land not enclosed or cultivated, a practice which prevented the accumulation of large private estates. Approximately 40 to 50 percent of the land on Saipan is privately owned and-the remainder is publicly owned. POWER. 10. Historically, only the government has been in a position to produce and distribute electrical power in the Northern Mariana Islands. The power system suffers from poor maintenance, deteriorating hardware and equipment, and frequent and pro1onged outages of the primary power source. The system is dependent upon oil and costs are expected to increase with rising world oil costs. Energy conservation practices are not in effect and the growth of electrical demand is expected to be significant. 11. The primary source of power production on Saipan is the power barge "Impedance," commissioned in 1943, on loan from the US Army Corps of Engineers at no cost to the Commonwealth. The Impedance has the capability of generating 30 megawatts (MW) of power, but suffers from frequent and prolonged outages due to poor maintenance and deterioration. A standby power plant consisting of four diesel generators has the capability of supplying 7.4 MW and can be expanded with the addition of two small generators to 10 MW capacity. Emergency power generating equipment include seven small generators with a combined capability of 4.4 MW. Present power usage is about 11.2 MW. Power distribution is dependent upon 72 miles of primary lines (13.8 KVA) and 96 miles of secondary line. Two primary lines pass through the Garapan and serve the area south of the power barge. The lines carry 80 percent of the system load to the southern area of Saipan. The Physical Development Master Plan for Saipan estimated that power demands will increase to 23 MW by 1985 resulting E-4 from the commercial, residential and industrial growth of Saipan envisioned in the plan. The master plan proposed construction of a new power plant consist- ing of several 7.5 or 10 MW diesel generators which would be capable of produc- ing 20 MW of electrical power by 1985. A new power plant, which will replace the power barge "Impedance", is presently being constructed near the seaplane ramps in Tanapag Harbor. WATER SUPPLY. 12. The water supply system suffers from deterioration, inadequate supply and conservation, poor water quality, and inadequate water pressure. The problems have resulted in poor fire protection, construction of private rainwater collection systems and periodic closing of water supply system to replenish water reservoir storage. 13. Major sources of groundwater on Saipan are basal well fields, high level aquifers lying above sea level and water reservoirs. The principal basal water areas include the Isley-Kobler field area and the Rapugau District. The most important high level groundwater resources are found at Agag and include Donni and Tanapag Springs. New well exploration has been concentrated in the Tanapag, Rapugau, Agag and Chacha areas on Saipan. The groundwater has high chlorides, hardness and total solids content requiring water softening treat- ment. Two treatment plants are located at Isley and Maui IV. However, these plants are not functioning properly due to the low capacity of the filters. The Physical Development Master Plan indicated that the filters must be backwashed every two days to be effective. Water salinity is controlled by reducing pumping of existing wells and dilution with water from the reservoirs. Most households have resorted to using cisterns to privately collect rainwater for drinking and cooking. In order to replenish water storage reservoirs, water supply valves are periodically closed, which introduces air into the water lines increasing rusting in the lines. 14. Total water production on Saipan varies from 2 to 2.4 million gallons per day (mgd). Based on a population of 14,000 and a daily production rate of 2.4 mgd, total water consumption per capita is 171 gallons per day. Metered homes consumed an average of 480 gallons per day. However, many homes are not metered and significant leakages and losses in the system most likely occur. 15. For an average family of five, the average rate of water consumption is 95 gallons per person per day. The Physical Development Master Plan estimated that by 1985 water requirements will average about 3 mgd including urban and industrial uses. Water demands in the Garapan area by 1985 are estimated at 2 mgd. To meet future water demands the existing water supply system servicing the Garapan area will supplemented by the addition of a 0.5 million gallon reservoir at San Roque. 16. The Garapan area is serviced by the Central Coastal and Navy Hill water system. The system includes five basal wells in the Rapugau District, four reservoirs and two springs. The reservoir system has a total capacity of 1.7 million gallons. The wells have a total pump capacity of 240 gallons per minute, and the springs have a capacity of about 250 gallons per minute. Two emergency reservoirs having a capacity of 12 million gallons are located at Tanapag. The Garapan area is serviced by a 6-inch line. Major improvements to the distribution system servicing north and south Garapan were proposed in the Physical Development Master Plan. E-5 SANITARY SEWERAGE. 17. Parts of the Saipan sewerage system were constructd by the United States during World War II. Many areas are still using cesspools and septic tanks which are showing some indications of failure. The Garapan area is serviced by the Central Highland and Coastal Sewer System which includes North Garapan, Tanapag, the Navy and Capitol Hill, the hotels and Garapan Elementary School. The South Garapan area still uses private cesspools and septic tanks. The central sewer system collects and conveys wastewater to a primary treatment plant in the Rapugau District where the treated effluent is discharged into Tanapag Harbor. The treatment plant has a design capacity of 0.3 mgd with pro- visions to expand to 0.6 mgd and employs a Door Clarigester. The treatment includes primary sedimentation, digestion of settled solids, and chlorination. [email protected] wastewater flows by 1985 in the Central Highland and Coastal area is estimated at 2.0 mgd of which 50 percent will be attributable to a 250-acre industrial area in Tanapag. The Physical Master Development Plan proposed the construction of a new treatment plant in Northern Tanapag or in the South San Roque area. SOLID WASTES. 18. The present solid waste collection and disposal system on Saipan was judged inadequate in the Physical Development Master Plan. There is no organized refuse collection service for the majority of the residences on Saipan. Wastes are hauled to a dump at Puerto Rico in Garapan or to many numerous unauthorized areas. The Puerto Rico dump is a shoreline fill '1 operation. Hazardous wastes are not handled with any standard procedure. Burning at private residences is not uncommon. Regular solid waste collection is provided at government housing areas, and publ*.ic institutions,.such as schools, hospitals and government offices. The Rhysical Development Master Plan estimates that there was.about 12,190 tons of refuse (146,280 cubic yards) in 1978. The estimate was based on about 4 pounds of refuse generated per day per capita with an increase of 0.5 pounds per day per capita per year. By 1985, estimated refuse generated on Saipan could be 18,843 tons (225,116 cubic yards). The Physical Development Plan recommended that the existing dump in Garapan at Puerto Rico be closed and investigations be initiated in operating sanitary landfills at the Isley Kagman and San Roque areas. HIGHWAY TRANSPORTATION. 19. The existing road system on Saipan originates from two sources: (1) the network of roads constructed by the Japanese prior to World War II and (2) the network of roads constructed by American Armed Forces shortly after 1944. Thus, most of the paved roads are over 30 years old and have deteriorated due to the absence of a regular maintenance program. In 1976, there were about 4,200 vehicles on the island. The number of private vehicles in 1976 was about 3,775, doubling the number registered in 1974. While traffic moves rather freely on the road system, significant traffic congestion occurs along the Beach Road in Chalan Kanoa. The Beach Road is the only road which provides continuous access to Tanapag Harbor, the Garapan area and the government hous- ing areas from the population and government center at Susupe-Chalan Kanoa. The West Coast Highway provides the fastest and most direct route from southern Saipan to Tanapag. E-6 MEDICAL CARE. 20. Health services in the Commonwealth are provided by the government and are organized into essentially four divisions: hospitals and dispensaries, public health, dental services, and environmental health and sanitation services. Major health service facilities are located on Saipan. Rota and Tinian have primary and emergency care facilities. The outer islands are provided health services through outpatient care, monthly visitations by a medical team and village nurse concept. The adequacy of the facilities in comparison to the U.S. is poor and the ratio of medical staff to population is low (0.56 physician to 1,000 population, 0.13 registered nurses to 1,000 population). Commonwealth residents are charged lower rates than non-residents, but costs are very low for all patients. Heart disease and malignant neoplasm are lead- ing causes of death with accidents, diabetes, cerebral vascular accidents and pneumonia following in frequency. POLICE PROTECTION. 21. Crime is on the increase in the Commonwealth and is expected to continue to grow as a problem in relationship to the growth of the tourist industry. The police force, criminal retention, and justice system was judged to be inadequate. Felonies increased 13 percent and misdemeanors increased by 8 percent between 1974 and 1976. The police force consists of 47 officers on Saipan, 5 officers on Tinian and 7 officers on Rota. Criminal retention facilities are located in the police station at the Saipan Civic Center. Escape from the retention facility is not uncommon. There are no criminal counseling or vocational programs for rehabilitation. On an average there are usually 12-15 adults and 5-7 juvenile adults in the retention facilities. FIRE PROTECTION. 22. Fires in the Commonwealth are on the increase and the fire protection system was also judged to be inadequate. The Fire Department is located at the Civic Center in Susupe. In Fiscal Year 1976 the Fire Department responded to 227 calls, an increase from 157 in Fiscal Year 1975. Response time within the Susupe-Chalan Kanoa area is 5-8 minutes. Although there are 108 fire hydrants on Saipan, the hydrants are useless at night because the water system is shut down at night to conserve water. The staff of the Fire Department consists of 15 firemen on Saipan and I on Rota. The police on Rota and Tinian double as firefighters. The firefighters at the Civic Center also provide fire protec- tion at the airport when flights are scheduled. The fire equipment at the Civic Center include one pumper and one nurse truck. Another pumper was to be purchased in Fiscal Year 1978. TROPICAL STORMS/TYPHOONS. 23. The Commonwealth did not have a disaster preparedness plan as of October 1977. Typhoons are a constant threat to life and property as a result of high winds and flooding due to heavy rainfall and high seas. The Mariana Islands lie within an area where tropical storms develop into typhoons. At least 19 typhoons occur annually across the western North Pacific and South China Sea. Several of these typhoons in various stages of development threaten the Mariana Islands annually. During a 28-year period (1948-1975) 70 tropical storms and typhoons were tracked within 180 nautical miles of Guam (120 miles south of Saipan). Twenty-six (26) of these were full strength typhoons. Based on the E-7 period of record, there is greater likelihood of a developing typhoon threaten- ing the Mariana Islands during all months of the year. The majority of typhoons occur during the rainy season from August through November with the peak activity occurring in October and November. A secondary peak of activity also occurs in April and May. One typhoon a year affects the Mariana Islands. However, the character of typhoon frequency is irregular. No typhoons occurred in 11 years of the 28-year period, although tropical storms occurred. Of the typhoons that affected the Mariana Islands, all originated in the Truk- Kwajalein area of the Trust Territories. These storms travel westward from the Yruk-Kwajalein area toward the Mariana Islands, where they generally approach the Mariana Islands from the south and southeast quadrant. Nine typhoons significantly affecting the Mariana Islands are listed on Table E-2. Record of damages from the Commonwealth are incomplete. TABLE E-2 TYPHOONS SIGNIFICANTLY AFFECTING THE MARIANA ISLANDS, 1948-1976 Date Name Remarks November 1949 Typhoon Allyn Eye passed 60 nautical miles south of Guam. Wind gusts over 100 knots. Several injuries, no deaths. No damage reports from Commonwealth area avail- able. November 1957 Typhoon Lola Eye passed 40 nautical, mil-es south of Agana. Wind gusts over ''100 knots. No damage reports from Con wionw'ealth area available. November 1962 Typhoon Karen Eye passes,ov& Guam. Wind gusts 150-160 knots. No damage reports from Commonwealth area available. April 1963 Typhoon Olive Eye passed 35 nautical miles south of Agana. Wind gusts 85-90 knots. Damages on Saipan: $4.4 million, 95% of all homes destroyed and all utilities inoperative. December 1963 Typhoon Susan Eye passed 70 nautical miles north of Agana. Wind gusts of 70 knots. Damages in Commonwealth: 25%-90% of homes on Rota, Tinian and Saipan damaged. November 1967 Typhoon Gilda Eye passed over Rota. Wind gusts 60 knots. Damages on Rota: 100 buildings destroyed, 500 homeless, 8 injuries, no deaths. is E-8 April 1968 Typhoon Jean Eye passed 95 nautical miles north of Agana. Wind gusts on Saipan 140-150 knots. Damages on Saipan: $16 million, thousands homeless, 90% of homes destroyed, no injury and no deaths. November 1975 Typhoon June Eye passed 215 nautical miles west- southwest of Guam. Wind gusts 70 knots. No damage reports from Commonwealth available. May 1976 Typhoon Pamela Eye passed over Guam. Wind gusts over 100 knots for 18 hours. No damage report from Commonwealth area. E-9 CULTURAL RESOURCES PREHISTORIC PERIOD. 24. Based on comparative dates and settlements on nearby Guam, Saipan was probably occupied as early as 1500 B.C., although no firm dates yet exist for Saipan. Most evidence of prehistoric settlement exists today at inland loca- tions, many of which it has been hypothesized were once prehistoric coastal environments. The places along historic shorelines have undergone severe modification by the Japanese and Americans between 1930 and 1945. The shore- line consists of fill material and/or concrete. Thus, the likelihood of find- ing any prehistoric (archaeological) sites in flat coastal areas is negligible. No prehistoric archaeological sites on Saipan Island are currently eligible for or listed on the National Register of Historic Places. HISTORIC PERIOD. 25. The Mariana Islands were discovered by Magellan in 1521, but no detailed information became available until after 1668, when the first Spanish mission began on the Island of Guam. In the later 18th century, all natives were reportedly removed from the Northern Marianas in order to assure the primacy of Guam as a rest and refitting station for the Manila Galleon trade route. Permanent resettlement of the Island of Saipan did not occur until 1842 with the arrival of Carolinians and subsequently, Chamorro colonists. For 15 years between 1899 and 1914, Saipan was under German control, but the initial modernization of the island came under the Japanese from 1914 to 1944. Garapan and Chalan Kanoa became the island's major population centers, the island was intensively cultivated, primarily in sugarcane, and tens of thousands of Japanese permanently colonized the islands. Among the surviving Japanese structures, two are listed on the National Register of Historic Places; the Japanese Hospital and the Japanese Lighthouse, both in the vicinity of Garapan. Two memorials to the Japanese defense of the island also are listed: Banzai Cliff and Suicide Cliff,, both in northern part of the island. The Sugar King Historic Park is planned to include the Japanese Hospital, jail, sugar train and the Sugar King Monument. 26. Two cultural resource reconnaissance studies, one conducted by the Corps of Engineers and one by the National Park Service, identified historic features in the American Memorial Park and a prehistoric midden site along the,. West Coast Highway. Both surveys utilized the services of the Pacific Studies Institute. The National Park Service survey identified eight historic sites in the park as eligible for inclusion to the National Register of Historic Places. The sites consist of Japanese fortifications storage tanks and barracks and bathhouse. A Japanese pillbox and bunker are located in the outlet channel area,.but not within the channel easement. The Corps of Engineers survey identified a prehistoric midden site in the diversion channel alignment. The site may be eligible for listing on the National Register of Historic Places as it may contain scientific data that could be used in developing an understanding of prehistoric settlement and use of coastal resources on the west coast of Saipan. The midden recovered from the site consisted of pottery sherds and shells unearthed by sewer construction along the highway alignment. The construction of the sewerline may have destroyed a portion or all of the site, and the construction of a proposed waterline through the same area may destroy the remaining portion of the site, if any. E-10 No archaeological sites were found in the Hafa Adai Hotel outlet channel alignment. No surveys were conducted of the Garapan Elementary School outlet channel alignment. However, based on the results of the Hafa Adai Hotel channel alignment, no historic and archaeological sites are anticipated due to the highly modified nature of the area. Much of the area was destroyed and modified during World War II and the post-war era. E-11 GARAPAN FLOOD CONTROL SAIPAN, CNMI PUBLIC INVOLVEMENT 11 APPENDix F I APPENDIX F PUBLIC INVOLVEMENT APPENDIX Page Public Involvement Program F-1 Summary of Public Workshop F-2 Draft Report and Environmental Statement Review F-4 LIST OF TABLES Table Page F-I Attendance at Public Workshop, 21 March 1979 F-3 PUBLIC INVOLVEMENT APPENDIX PUBLIC INVOLVEMENT PROGRAM 1. The public, as broadly interpreted by the US Army Corps of Engineers, is any affected or interested non-Corps of Engineers entity which includes other federal and local government agencies, public and private organizations, and individuals. The public participation program is directed to maintaining the information flow, achieving a mutual understanding and acceptance of the problems and needs, and attaining the interest level necessary for proper decisionmaking. 2. The objectives of the public participation program for this study are: a. To inform the public of the current Corps of Engineers planning process. b. To surface key planning issues and concerns so that they are given full consideration. C. To help formulate and assess potential plans of improvement. d. To offer technical, historical, and localized information pertinent to the study. 3. The US Army Corps of Engineers, Honolulu District, has the responsibility for conducting the study. The study is being coordinated with the Coastal Resources Management Office, CNMI, who is serving as the local coordinating agency. 4. The public involvement program has consisted of study notification and coordination meetings with key governmental agencies and officials, and a public workshop to obtain public input on identifying problems, needs and possible solutions to the flooding problem in Garapan. After this draft report is circulated to federal and local agencies and interested indivi- duals, a public meeting will be held to obtain the public's views on the alternative plans of improvement. Public views and concerns expressed at this meeting and during the report review period will be incorporated into the final report, and a second public meeting will be held to present the final selected plan. SUMMARY OF PUBLIC WORKSHOP 5. Government of Northern Marianas agencies and officials were notified in January 1979 of the initiation of detailed studies for the flood problem at Garapan. An informal workshop was conducted on 21 March 1979 at Marianas High School. It was attended by interested citizens and goverment representatives (Table F-1). Local TV coverage was also provided. The following concerns were expressed at the meeting: a. Flooding due to Tropical Storm Carmen in August 1978 was the worst flooding in the memory of many Garapan citizens. b. Flooding in Garapan can be attributed to: (1) General gradient of the basin slopes toward the MIHA developments of Annex I, Annex 11, and Puntan Muchot (Figure 5 of the Main Report). (2) The present flood control measures in Garapan consist of ponding basins. These basins, which are designed to control interior discharge only, are flooded by basin runoff and often overflow, causing inundation of nearby homes. (3) The Garapan area, below West Coast Highway, is very flat which results in a limited conveyance of runoff to the ocean. This condition, along with the lack of drainage channels, causes serious ponding problems in lowlying areas. According to longtime residents, drainage channels once existed in Garapan. However, these channels were obliterated by development. C. According to MIHA authorities, flooding is an annual occurrence in Garapan. d. Siltation of offshore areas should be minimized or controlled as much as possible. F- 2 TABLE F-1 Attendance at Public Workshop 21 March 197T Federal, Corps of Engineers Mr. Russell Takara, Project Engineer Mr. Mitsuo Waki, Hydraulic Engineer Mr. David Dang, Economist Mr. Edward Yoshimura, Hydraulic Engineer Mr. Ronald Pang, Estimator Federal, Others Mr. Otto Van Der Brug, US Geological Survey, Guam Mr. Dan A. Davis, US Geological Survey, Honolulu Government of Northern Mariana Islands Mr. M. Obradovitch, Department of Public Works, CNMI Mr. Alfred Pangelinan, Department of Public Works, CNMI Mr. Pete A. Tenorio, Executive Director, Marianas Public Land Corp. Mr. Lorenzo L.G. Cabrera, Executive Director, Mariana Islands Housing Authority Ms. Martha McCart, Coastal Zone Manager, CNMI Mr. George Chan, Environmental Protection Agency, CNMI Government of the Trust Territory of the Pacific Islands Mr. Mike Gawel, Planning Office, TTPI Individuals Ms. Margarit Reyes Mr. Frank T. Rogones Mr. Pedro Sasamoto Mr. Malcolm F. Stiles Mr. Ben Taguchi Mr. James Tamura Mr. Joaquin A. Tenorio F-3 DRAFT REPORT AND ENVIRONMENTAL STATEMENT REVIEW 6. The draft document was sent to the following agencies for review: a. U.S. Government Agencies Advisory Council on Historic Preservation, Washington and Denver Offices Department of Commerce Deputy Assistant Secretary for Environmental Affairs Regional Representative Coastal Zone Management, Pacific Region National Marine Fisheries Service .National Oceanic & Atmospheric Administration, SW Region Environmental Protection Agency Regional IX, EIS Coordinator Officer of Field Activities Department of Health, Education and Welfare Regional Administrator Department of Housing and Urban Development Assistant Secretary for Community Planning and Management Regional Administrator Honolulu Area Office Department of the Interior Office of Environmental Project Review Interagency Archaeological Services Fish and Wildlife Service, Portland and Honolulu Offices National Park Service, San Francisco and Honolulu Offices Geological Survey Department of Transportation Commander, 14th Coast Guard District Federal Highway Adminitration F-4 b. Commonwealth Office of the Governor Department of Public Works Mariana Islands Housing Authority (MIHA) Commonwealth Historic Preservation Office, Department of Natural Resources Officer of Planning and Budget Mayor of Saipan Division of Marine Resources Development Division of Environmental Quality Office of Coastal Resources Management Marianas Public Land Corporation Department of Public Health F-5 0 GARAPAN FLOOD CONTROL SAIPAN, CNMI RECREATION AND NATURAL RESOURCES APPENDix G 0 APPENDIX G RECREATION AND NATURAL RESOURCES TABLE OF CONTENTS Page RECREATION G-1 NATURAL RESOURCES G-2 GEOLOGY G-2 VEGETATION G-2 WETLANDS G-2 WILDLIFE G-6 MARINE RESOURCES G-6 ENDANGERED SPECIES G-8 MIGRATORY BIRDS, WILDLIFE REFUGES, AND MARINE SANCTUARIES G-8 GROUNDWATER AND COASTAL WATER QUALITY G-10 LIST OF TABLES Table No. Page G-1 DOMINANT PLANTS IN THE GARAPAN DRAINAGE G-3 G-2 A CHECKLIST OF WETLAND VEGETATION IN THE GARAPAN AREA G-4 G-3 LIST OF AVIFAUNA OBSERVED IN THE GARAPAN AREA G-7 G-4 LIST OF GUAMANIAN BIRDS AND MAMMALS BEING REVIEWED FOR POSSIBLE LISTING ON THE FEDERAL LIST OF ENDANGERED AND THREATENED SPECIES G-9 G-5 WATER QUALITY MEASUREMENTS G-11 LIST OF FIGURES Follows Page G-1 RECREATION RESOURCES G-2 G-2 NATURAL RESOURCES G-2 APPENDIX G RECREATION AND NATURAL RESOURCES RECREATION 1. Recreation problems and needs have been previously reported in the Northern Mariana Islands Park and Outdoor Recreation Resource Study (April 1977) and the Physical Development Master Plan for the Commonwealth of the Northern Mariana Islands, Volume II, Saipan (January 1978). The studies indicate that a multitude of recreational facilities already exist on Saipan and that there is a need to improve or renovate the facilities. These facili- ties include 13 basketball courts, two public tennis courts, five public little league baseball fields and quasi-public facilities associated with hotels and government housing areas. In the Garapan area, picnic facilities are located at Puntan Muchot, basketball courts are located at the International Hotel, a multipurpose field is located at the Garapan Elementary School, a boat ramp is located at the Garapan Dock and a historic park is located at the Sugar King Monument. The studies recommended development of recreational facilities for children of pre-school age, mini-parks, neighborhood playgrounds, and community playgrounds. The needs will be met by combining the recreational facilities with school and area center facilities. Plans for recreation development in the Garapan area include the development of a junior high school, the American Memorial Park which will serve as a regional park on Saipan, and expansion of the historic park centered around the Sugar King Monument, Japanese sugar train, hospital and jail (see Figure G-1). The development of a small boat harbor at Garapan Dock would serve commercial and recreational boating and fishing needs. Recreation facilities and resources are summarized below: a. Scenic and Wild Rivers. None are present in the Garapan area. b. National Trails. None are present in the Garapan area. c. Natural Landmarks. None are present in the Garapan area. d. National Shoreline, Parks or Beaches. The site of the proposed American Memorial Park is located just-5-orTF of the Garapan. The park lands were set aside by the United States Government (133 acres) for public use as a memorial to the American and Marianas people who were killed or wounded in the Marianas campaign during World War II. e. Water Contact Recreation. Pole and cast net fishing activities occur along the Garapan shoreline. e recreational boats and skin diving tour boats operate out of the American Memorial Park area. A boat launching ramp is also located at the Garapan dock area. Micro Beach and Beach Drive Park provide passive recreation areas for swimming and bathing. The US Fish and Wildlife Service (1979) indicated that a surfing site is located outside the lagoon barrier reef at the Garapan entrance channel mouth, but a reference for the source of information is not available. G-1 NATURAL RESOURCES GEOLOGY. 2. The Garapan area is located on the west coastal plain of Saipan. The plain is composed of beach sand, coralline sand-rubble fill and clay overlying lime- stone. Puntan Muchot is a sandy point. The Garapan and American Memorial Park areas consist of filled land. Saipan Lagoon is a high-island with barrier reef lagoon. The barrier reef lies approximately 3,000 feet offshore from the Garapan area. VEGETATION. 3. Four generalized vegetation communities were briefly described by the US Fish and Wildlife Service (1979); a coastal strand, urban area, tangan-tangan community and forest community. The coastal strand community included beach morning glory, hibiscus, coconut, ironwood and various grasses and shrubs. The urban community included a mixture of plants from all other vegetation communities including a variety of garden vegetables and decorative shrubs. The tangan-tangan community consisted of pure stands of tangan-tangan and stands mixed with grasses and sword plants. Hibiscus, upland taro and pandanus were components of the tangan-tangan community in damper areas with deep soils. The forest community was dominated by a mixture of tall (20-75 feet) introduced food or ornamental trees together with pandanus bamboo, hau and ironwood. A list of 31 plant species was provided (Table G-1). WETLANDS. 4. Two wetlands were located in the Garapan area. The smaller one (see Figure G-2) was about 250 meters in diameter bordered on three sides by roads and several ill-defined roads through it. Grasses dominated the vegetation and the presence of duckweek (Lemna minor) suggested that the wetland was permanently wet (Moore, et species were found to be common in the wetland, and elephant grass (Pennisetum purpureum), California grass (Brachiara mutica) and guinea grass (Panicum maximum) were abundant in the wetland (TaM_G-2). Juan C. Tenorio--an-T _Ass@ociates, Inc. put the location of the wetland closer to the Navy Hill Road and the Coastal Highway, which divides the wetland into two parts. The second wetland is located in the American Memorial Park area and is about 200 meters in diameter. The area was once part of an airfield and is crossed by eroded, overgrown asphalt roads. The area was and is probably still being used as a dump by the local popula- tion. The area is poorly drained and marshy, and the fill and asphalt from the air strip probably made the area a convenient catchment basin. Grasses dominated the vegetation in the wetland. Fifteen plant species were listed as common (Table G-2), and the elephant, California and Guinea grasses were again dominant. Hibiscus (Hibiscus tiliaceus) and tangan-tangan were also common around the wetland. The ironwood tree (Casuarina equisetifilia) dominates the overstory. Both wetlands have freshwater, probably as a res of ponding stormwater, and are probably present due to alterations in the surrounding areas. The National Park Service indicated that the Unai Sadog Tase shoreline in the American Memorial Park is dominated by mangrove. Thus, the area could also be classified as a wetland. G-2 PA CIFIC 0 C E A N PUNTAN MUCHOT BOAT A MICRO BEACH ANCHORAGE CONTINENTAL (4 AMERICAN N HOTEL MEMORIAL PARK INTER- CONTINENTAL HOTEL G04RAPAN qo,JLEMENTARY 0 SCHOOL HISTORIC FUTURE JAPANESE HAFA ADAI HOTEL JUNIOR H LIGHTHOUSE SCHOOL < 0 cr BOAT RAMP SUG A R K I rG- HISTORIC PARK w co L SOURCE OF INFORMATION 1. PHYSICAL DEVELOPMENT MASTER PLAN FOR 0 THE COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS, VOL. 11, SAIPAN 1978. BEACH DRIVE 2. DRAFT, NATURAL RESOURCE STUDY, 1979. BEACH PARK w GARAPAN FLOOD CONTROL SAIPAN, CNMI 0 0.1 0.2 0.3 0.4 0.5 F= --i RECREATION RESOURCES SCALE IN MILES U.S. ARMY ENGINEER, DISTRICT, HONOLULU FIGURE G -I P A C / F C 0 C E A N // N\ CORAL DREDGED RUBBLE AREA PUNTAN MUCHOT % SAND AND SAND AND A MICRO BEACH SEAGR ASS SEAGRASS \X CONTINENTAL AMERIAN N HOTEL MEMORIAL PARK INTER- CONTINENTAL WETLAND HOTEL GARAPAN oo ELEMEN RY 4b440SCHO L POSSIBLE WETLAND 040 HAFA ADAI HOTEL WETLAND 110 SAND AND EXISTING DRAINAGE DITCH SEAGRASS DREDGED 0 AREA cr SOURCES: cn w < 1. MOORE, ET ALI 1977, INVENTORY AND MAPPING OF ao 0 WETLAND VEGETATION IN GUAM, TINIAN AND SAIPAN, MARIANA ISLANDS. 2. MaE PACIFIC,INC., 1979, FACILITIES PLAN FOR THE ISLAND OF SAIPAN, MARIANA ISLANDS. (SAND AND 3. AMESBURY, S., ET AL, A SURVEY OF FISH SEAGRASS RESOURCES OF SAIPAN LAGOON, MARCH 1979 w DRAFT 'n 3c 4. JUAN TENORIO AND ASSOCIATES, INC., ORNITHOLOGICAL SURVEY OF WETLANDS IN GUAM, SAIPAN, TINIAN AND PAGAN, 1979. GARAPAN FLOOD CONTROL SAIPAN, CNMI 0 0.1 0.2 0.3 0.4 0.5 --------q I I I NATURAL RESOURCES SCALE IN MILES U.S. ARMY ENGINEER, DISTRICT, HONOLULU __j FIGURE G - 2 TABLE G-1. DOMINANT PLANTS IN THE GARAPAN DRAINAGE Reported by US Fish and Wildlife Service Biologist, 1979 COMMON NAME SCIENTIFIC NAME TREES Kapok Tree Ceiba pentandra African Tulip Tree Spathodea campanulata Ironwood Casuar -eg-u-is-eTifolia Tangan Tangan LeucaeRa-leucocophala Papaya Tarica papaXa . Breadfruit Artocarpus incisus or mariannensis Mango Manqifera indica Bamboo Bambusa vul2arls Banana Musa sp. Coconut Cocos nucifera Betel Nut Wr-eca cathecu Acacia Tc-a E ir a- co-n-f u-s a Flame Tree Delonix regia Screw Pine 13-a-5d7afias-f-e-c-forius Nilo Thespes'l a Hau Hibiscus tiliaceus F I ucheY-i nd I ca UNDERGROWTH Rat-tail Dropseed Sporobolus elon2tus Lovegrass Eragrostis tenella Guinea Grass Panicum maximum Sword Grass Miscanthus floridulus Crowfoot Grass uactyloctenium ae-g-y-pTium Lagundi Vitex trifolia Sword Plant sansevieria trifasciata Passion Fruit Passi'flora foeti3a var. hispida Sed e Cyperus odoratus Canglebrush Cassla alata Coffee-Senna C. occidentalis Upland Taro Alocasia Fa-crorrhiza False Verbena Stachytarpheta 5_dica Beach Morning Glory 1pomoea pes-caprae Nigas Pemphis acidula SOURCE: US Fish and Wildlife Service, Planning Aid Letter, 27 September 1979. G-3 TABLE 0-2. A CHECKLIST OF WETLAND VEGETATION IN THE GARAPAN AREA A = abundant C = common S = seldom R = rare Scientific Name Common Name Small Wetla' MONOCOTYLEDONAE CYPERACEAE Cyperus brevifolius (Rottb.) Hasskarl S C. compressus L. C C. cyperinus (Retz.) Suringar S/R C. ligularis L. C C. odoratus L. C Fimbristylis cymosa R. Br. C GRAMINEAE Eleusine indica (L-) Gaertn. Goose grass; Chaguan Kabayo C Panicum maximum Pennisetum. polystachion (L.) Schultes P. purpureum Schumacher Elephant grass A Phragmites karka (Retz) Trin. ex Steud. Karriso S Brachiara (Forsk.) Stapf A LEMNACEAE Lemna CF. minor L. Duckweed S DICTYLEDONAE CASUARINACEAE Casuarina equisetifolia L. Ironwood; Gago C COMPOSITAE Pulchea indica (L-) Less. CUCURBITACEAE Momordica charantia L. Bitter melon; Admagoso C LEGUMINOSAE Albizia lebbeck (L.) Bentham Siris tree; Mamis S Cassia alata L. Candlebush; Andadose; Akapulko C C. occi-dentalis L. Mumutun-sable; Coffee-senna C *Text (Moore, 1977) indicates Panicum, maximum was included in the dominant grasses. TABLE G-2. A CHECKLIST OF WETLAND VEGETATION IN THE GARAPAN AREA A = abundant C = common S = seldom R = rare Abunda Scientific Name Common Name Small Wetland Desmanthus virgatus (I.) Willd. C Leucaena lecocephala (Lam.) deWit Tangan-tatigan C Mimosa pudica L. Sleeping grass Pithecellobium dulce (Roxb.) Bentham Kamachile Sesbania cannibina (Retz.) Persoon S ONAGRACEAE Ludwigia octivalvis (Jacq.) Raven Titimo MALVACEAE Hibiscus tiliaceus L. Pago Sida acuta Burm. Escobilla Papago S S. rhombifolia L. Escobilla Dalalai S PASSIFLORACEAE Passiflora foetida var. hispida Love-in-a-mist; Kinahulo Adao C (Triana & Planch.) Gleason P. suberosa L. RUBIACEAE Morinda citrifolia L. Lada; Indian Mulberry SOURCE: Inventory and Mapping of Wetland Vegetation in Guam, Tinian and Saipan, Mariana Moore, P., et al, June 1977. WILDLIFE. 5. Ten species of birds were observed in the urban and beach area of Garapan by the US Fish and Wildlife Service (1979), and ten species of birds were observed in the upper watershed (Table G-3). The avifauna was more diverse in the upper watershed than in the urban and beach areas. About 126 birds were seen in the upper watershed as compared to 107 birds observed in the urban and beach area. The eurasian tree sparrows were the most abundant species observed. Within the upper watershed, cardinal honeyeaters and eurasian tree sparrows were the most abundant birds observed. In the urban and beach area t e cardinal honeyeater, eurasian tree sparrow, Philippine turtle dove and the bridled white-eye were the most abundant birds observed. Two US Fish and Wildlife Service biolo ists reported observing a Marianas crow in the upper watershed. This was t9e first report of the presence of the Marianas crow on Saipan, however, the sighting has not been confirmed. 6. Avifauna in two wetland areas were surveyed in 1979 (Juan Tenorio and Associates, Inc., 1979). Seventeen species of birds were observed. Six species were found in the smaller wetland and 12 species were found in the larger wetland. Only the Chinese least bittern was common to both wetlands. The ruddy turnstone and the Chinese least bittern were the most abundant birds in the smaller wetland. The Philippine turtle dove, gallinule, white tern, cardinal honeyeater and the bridled white-eye were the most frequently seen birds in the larger wetland. MARINE RESOURCES. 7. A survey of fish resources in Saipan Lagoon was completed by Amesbury, et al (draft, 1979). The survey identified 24 fish habitats and 249 fish species in the lagoon. Twenty-two species of fish were identified as econom- ically valuable fish, and their abundance and distribution in the lagoon were estimated. Equilibrium yields of exploitable fish were also estimated. The distribution of fish larvae and eggs was studied by analysis of plankton net tows. The marine flora and fauna and oceanographic and water quality characteristics of Tanapag Harbor were studied by Doty and Marsh (1977) for one year. The US Fish and Wildlife Service (1979) provided qualitative data on marine resources at the Garapan dock, American Memorial Park boat mooring area, North Tanapag Harbor and Chalan Kanoa sugar dock. 8. In the Garapan area, Amesbury identified two fish habitats at the outlet of the existing drainage ditch adjacent to the Hafa Adai Hotel. The inshore habitat (Amesbury: Habitat 2) consisted of a substrate of fine sand dominated by stands of seagrass, Enhalus acroides, sometimes mixed with other seagrasses and algae. Rabbitfish the most abundant fish in the habitat and goatfish and snappers were relatively abundant. Thirty-eight species of fish were associated with the habitat. The mid-lagoon habitat (Amesbury: Habitat 7) consisted of a sand and rubble substrate dominated by a mixture of algae which included Padina, Caulerpa and Dictyota. A moderate diversity of fishes occur in the habitat, but economici-llyimportant fishes did not occur in high abundance. Fifty species oil fish were associated with the habitat type. Plankton net tows at the Garapan Dock found a fish egg density of 10.5 individuals per cubic meter and a fish larvae density of less than one individual per cubic meter. G-6 TABLE G-3. LIST OF AVIFAUNA OBSERVED IN GARAPAN AREA Observe Scientific Name Common Name Upper Watershed.!/ Urban-Beach Are-all Myzomela cardinalis Cardinal Honeyeater 50 17 Cleptornis marchei Golden honeyeater 10 1 Paser montanus Eurasian tree sparrow 30 51 Corvus kubaryi Marianas Crow 1 - Gygis alba White tern 12 2 Gallicolumba xanthonura. White throated dove I - Ptilinopus roseicapilla Marianas fruit-dove 2 - Streptopelia bitorquata Philippine turtle dove 8 17 Halcyon chloris Collared Kingfisher 4 - Zosterops conspicillata Bridled white-eye 8 13 Rhipidura rufifrons Rufous-fronted fantail - I 2 Pluvialis dominica Lesser Golden Plover Numerius phaeopus Whimbrel - 2 Heteroscelus incanum Wandering Tattler - 1 Ixobrychus Sinensis Aittern (Yellow, Chinese Least) - - Acrocephalus luscinia luscinia Nightingale Reed Warbler - - Reef Heron - - Ruddy Turnstone - - Micronesian starling - - Ground Dove - - Gallinule chloropus Marianas Gallinule - - Pacific Golden Plover - - TOTAL INDIVIDUALS 126 107 TOTAL SPECIES 10 10 I/ US Fish and Wildlife Service, 1979. j/ Birds per 100 minutes of field contact, Juan Tenerio and Associates, Inc., 1979. 9. The US Fish and Wildlife Service (1979) provided a qualitative description o-F the marine ecosystem at the Garapan Dock. Their report identified three habitat types at the dock; a shoreline and rubble habitat, a dredged area habitat and a habitat similar to Amesbury's Habitat 2. The rubble along the edges of the dredged area were reported to be visited by schools of cardinal ftsh, juvenile squirrel fish, sweepers, damselfish, adult surgeonfish, rabbit- fish, snappers, goat fish, an occasional eel and a variety of gobies and blennies. Live coral coverage was estimated visually to be 5%. The bottom of the dredged dock basin was sandy and a variety of algae and sea grasses was estimated to cover 90% of the substrate. Fewer fish were seen and those present principally included a few snappers and schools of goat fish. The jellyfish, Cassiopea sp. was considered the predominant invertebrate. A unique habi at-area was provided b'y the numerous wrecks in the area which provided habitat for a variety of fish and invertebrates. 10. In the American Memorial Park area facing Tanapag Harbor, Amesbury described three habitat types. These habitats included the inshore habitat previously described (Habitat 2), a dredged area habitat (Habitat 9) and coral rubble habitat (Habitat 4). The dredged area habitat was described as a silty rubble substrate littered with wreckage and some coral growth. The water was judged to be rather turbid, but the greatest number of high-bodied jacks were observed.in this habitat. The jacks were small subadults swimming in schools. The coral rubble habitat was described as a habitat dominated by patches of Halodule and a diverse assemblage of Caulpera. The highest counts of silver- sides occurred in this habitat although their abundance was low. The US Fish and Wildlife Service described the environment inside the Memorial Park harbor which is not applicable to the impact area, although the species observed in the harbor may be present at the impact area. 11. Amesbury's studies were the most definitive for the project area. In comparison to the other habitats described, the habitats at the project sites were not found to have a high diversity of fish or high abundance of fish egg and larvae. However, the high densities of juvenile, economically important fish prompted him to recommend conservation of the habitats described. ENDANGERED SPECIES. 12. No endangered or threatened species list for the Northern Mariana Islands has been developed. The Endangered Species Coordinator, US Fish and Wildlife Service indicated that the threatened green sea turtle has been seen in Saipan Lagoon. The status of ten birds and two mammals on Guam is being reviewed for possible nomination for inclusion to the Federal List of Endangered and Threatened Species. The status review on Guam does not necessarily reflect the status of the birds or mammals in the Northern Mariana Islands region. For reference, a list of birds and mammals being reviewed on Guam is provided in Table G-4. The nightingale reed warbler is listed as endangered on the Federal List of Endangered and Threatened Species in its range within the Trust Terri- tory of the Pacific Islands. MIGRATORY BIRDS, WILDLIFE REFUGES, AND MARINE SANCTUARIES. 13. Migratory shorebirds were observed by the US Fish and Wildlife Service (1979) in the beach-urban area of Garapan. No breeding or nesting areas were identified. No wildlife refuges or marine sanctuaries have been designated in 0 the Garapan area. G-8 TABLE G-4. LIST OF GUAMANIAN BIRDS AND MAMMALS BEING REVIEWED FOR POSSIBLE LISTING ON THE FEDERAL LIST OF ENDANGERED AND THREATENED SPECIES Common Name Scientific Name Marianas Fruit Bat Pteropus mariannus mariannus Little Marianas Fruit Bat Pteropus tokudae Marianas Fruit Dove Ptilinopus roseicapillus Marianas Gallinule Gallinula chloropus quami Guam Rail Rallus owstoni Edible Nest Swiftlet Collocalia inexpectata bartschi Micronesian Kingfisher Halcyon cinnamomina cinnamomina Micronesian Broadbill Myiagra oceanica freycineti White-throated Ground Dove Gallicolumba xanthonura xanthonura Cardinal Honey-eater Myzomela cardinalis saffordi Marianas Crow Corvus kubaryi Bridled White Eye Zosterops conspicillata conspicillata SOURCE: Federal Register, 44(98): 29128-29130 (May 18, 1979). C3 - 9 GROUNDWATER AND COASTAL WATER QUALITY. No water quality standards have been established for Saipan. Two water studies provide information on coastal water quality: (1) "Marine Survey of .1 :anapag, Saipan: The Power Barge "Impedance," Doty and Marsh, March ITTT.-and (2) Facilities Plan for the Island of Saipan, Mariana Islands, M&E Pacific, Inc., for the Department of Publi-c Works, Government of--tFe-Northern Mariana Islands. The data are applicable to the Unai Sadog Tase and the Saipan Harbor channel and are presented in Table G-5. The Garapan wastewater treatment plant which serves the northern coast and central highlands of Saipan including the villages of Tanapag, Garapan, Puntan Mutchot and the Capital Hill and Navy Hill government housing areas discharges about 0.43 mgd of primary treated effluent into Tanapag Harbor. Infiltration is believed to account for 70-75% of the average daily flow into Tanapag Harbor. The power barge "Impedance" discharges about 29 mgd of thermal effluent into Tanapag Harbor at Baker Dock. The major non-point sources in the Garapan area are surface runoff from upland and urban areas, and possibly subsurface and surface discharges from cesspools and privies. Surface discharges from cesspools and privies occur during periods of intense rainfall, especially in the lower Garapan area. Floodwaters have caused cesspools and privies to overflow and carry the wastewaters into the lagoon. An intermittent drainage ditch in the Garapan area enters Saipan Lagoon near the Hafa Adai Hotel. There are no potable groundwater sources in the Garapan area. G-10 TABLE G-5. WATER QUALITY MEASUREMENTS Lagoon (Source: M&E Pacific, Inc., 1979) Total Salinity Turbidity D.O. TKN N03-N Total P Coliform Station. pH Temp(00 (0/00) (NTU) (mg/1) (ug/1-N) (ug/1) (ui/1) (#/looml) 4 Top (T) 8.3 28.9 33.7 0.86 5.9 250 0.8 10 1 4 Bottom (B) 8.3 28.5 33.6 0.45 6.1 325 0.3 13 1 5T 8.2 28.8 33.7 0.65 6.2 378 0.5 36 1 5B 8.2 28.6 33.8 0.44 6.0 235 0.3 18 1 6T 8.2 28.7 33.4 0.67 6.1 304 0.6 24 20,000 6B 8.25 28.5 33.7 1.20 5.9 341 0.3 17 13 NO2 NO3 PO4 Unai Sadog Tase (Source: Doty and Marsh, 1977) ug-at./l 6 26.8 33.3 7.46 0.07 0.17 0.11 8. 27.6 24.4 8.17 0.02 0.03 0.16 9 GARAPAN FLOOD CONTROL SAIPANj CNMI COMPLIANCE DOCUMENTS APPENDIX H 0 APPENDIX H COMPLIANCE DOCUMENTS Title Item No. Section 404 Evaluation Report I U.S. Fish and Wildlife Service Planning Aid Letter GARAPAN FLOOD CONTROL STUDY EVALUATION OF THE EFFECTS OF THE DISCHARGE OF DREDGED OR FILL MATERIAL INTO WATERS OF THE UNITED STATES USING U.S. ENVIRONMENTAL PROTECTION SECTION 404(b) GUIDELINES 1. Troject DescriRtion. a. Description of the proposed discharge of dredged or fill material: (1) General Characteristics of the Material. The material used to line the flood control channel will consist of 20-250-pound limestone rocks (riprap) and 3-inch or less limestone aggregate (bedding layer) which will also be used to construct a temporary dredge causeway. Con- crete will be used to construct the culverts under the coastal highway and beach roads. (2) Quantity of material.proposed for discharge. Plan 1 Plan 2 Plan 3 Riprap 3,500 CY 3,800 CY 5,000 CY Bedding Material 1,800 CY 2,500 CY 3,000 CY Concrete 100 CY 250 CY 500 CY A temporary dredge causeway needed for dredging the channel outlet in Saipan Lagoon will utilize approximately 1,600 CY of bedding material. (3) Source of Material. The material will be quarried from Black Micro Quarry on Saipan. b. Description of the proposed discharge site for the dredged or fill material: (1) Location of the Discharge Site. Garapan, Saipan (see attached figure). (2) Type of Discharge Site Involved. The fill material will be used to protect the outlet channel for the Garapan Flood Control project from erosion. (3) Method of Discharge. The material will be placed in the channel banks by crane. The temporary fill will be placed by bulldozer and removed by crane and bucket. (4) Date and Length of Time When Discharge Will Occur. The discharge will occur within 5 years of project approval, and it will take about 7 months to complete the outlet channel construction. (5) Project Life of the Discharge Site. The flood control channel will have an estimated economic life of 50 years. (6) Trovide Bathymetry (if open water site): Not applicable. I 2. Physical Effects . Potential Destruction of Wetlands - The discharge of the fill material would not involve the destruction of any wetland areas. Channel alignments associated with Plans 1 and 3 do not physically affect any wetlands in the Garapan areas. Plan 2 passes in close proximity to a wetland in the American Memorial Park and will require special construction methods to prevent the wetland from draining into the flood control channel. The diversion channel, a feature common to the three plans may involve work in a wetland area, which has not: been clearly identified or located. 3. Chemical-Biological Interactive Effects. a. The material proposed for discharge meets the criteria for exclusion from elutriate and bioassay testing. The fill material will consist predominantly of gravel or other naturally occurring material with particle sizes larger than silt. b. Impacts on the Water Column: (1) Reduction in Light Transmission.. The placement of the bedding material and the temporary causeway will temporarily increase water turbidity since the material will contain some fine, limestone dust. Concrete and riprap placement will not increase water turbidity. (2) Degradation of Water Aesthetics. The increase in water turbidity will temporarily degrade water aesthetics. (3) Direct Destructive Effects on Nektonic and Planktonic Populations. No effect is anticipated because the fill is not expected to contain toxic substances. (4) Presence of Contaminants in the Fill Material. The fill is not expected to contain any contaminants since it will be obtained from a quarry source. (5) Concentration of Contaminants. Not applicable. The material meets criteria for exclusion from elutriate testing. (6) Comparison of Constituent Concentrations with Applicable Water quality Standards. Not applicable. (7) Size of the Mixing Zone. Not applicable. Except for the temporary dredge causeway, all fill material will be confined to the discharge site. C. Site Comparisons: Not applicable. All the alternative discharge sites consist of dredged channels extending from Saipan Lagoon to the Coast Highway. Contaminant content of the material proposed for discharge is not deemed critical to warrant selection of another discharge site. 2 4. Impacts of the Discharge at the Discharge $ite. a. Need for the proposed activity; The discharge is related to the construction of a flood control channel which is needed to reduce flood damages and losses in the Garapan area. b. Availability of alternate discharge sites and methods of discharge: The alternative outlet channel alignments through the Garapan area are being considered. The construction of the channels using riprap material is similar for three alternative outlet channel alignments. c. Description of the impacts on the following items: (1) Chemical,PhysicalI and Biological Integrity of the Aquatic Ecosystem. No effect. The aquatic ecosystem will be man-made with the discharge created by excavating a channel on land. The fill material is inert and will not introduce any new pollutant discharges into the new aquatic ecosystem. (2) Food Chain and Trophic Level* No effect. (3) Diversity_of Plant And Animal Species. The rocky habitat formed by the placement of the riprap will be colonized by organisms preferring solid substrates. (4) Movement into and but of Feeding, Spawning, Breeding, and Nursery Areas . No effect. (5) Wetlands that have Significant Functions on Water Quality Maintenance. No effect. (6) Areas that Serve to Retain Ndtutdl_High Waters or Flood Waters. The fill will not effect water storage capacity of the floodplain. (7) Degradation of Water Quality. No long-term degradation anticipated as a result of the placement of the fill material. d. Description of methods to minimize water turbidity: (1) The channel will be constructed without connection to the ocean for the majority of its length. All the fill will be placed in a man-made channel and no turbid waters will be discharged into the lagoon during the majority of the construction period. This action will also allow any fine material, suspended in the water column, to settle out in the channel. (2) The majority of the material to be placed in the water will consist of material larger than silt size and will not be easily eroded. In particular, the temporary dredge causeway will be constructed using bedding material and not fine sand. (3) Any dewatering effluent will be discharged into a stilling basin to remove sediments prior to discharge into the lagoon. 3 e. Description of methods to minimize degradation of aesthetics, recreation, and economic values: (1) The outlet channel is expected to increase recreational diversity and reduce flood damages and losses resulting in economic benefits to the floodplain residents. (2) A foot bridge will be placed over the channel near the mouth of the channel to permit free pedestrian movement along the shoreline. f. Other methods investigated to minimize possible harmful effects: (1) Appropriate scientific literature developed by EPA. (2) Consideration of alternatives to open water discharge, such as confined discharges. (3) Use of disposal sites where physical environmental characteristics were amenable to the type of dispersion desired. (4) Discharge beyond the baseline of the territorial seas. (5) Covering any contaminated material with cleaner material. (6) Conditions to minimize runoff from confined areas. g. Impacts on the following items of water use: (1) Municipal Water Supply Intakes. No effect. (2) Shellfish. No adverse effect. The discharge increases habitat for potential use by shellfish.. (3) Fisheries. No effect. The channel may increase fish nursery, spawning and rearing habitat. (4) Wildlife. No effect. (5) Recreational Activities. No effect. (6) Benthic Life. The fill creates new aquatic habitat for benthic life. (7) Wetlands. No effect. (8) Submersed Vegetation. No effect. (9) Size of the Disposal Site. No effect. (10) Coastal Zone Management Programs. No effect. 4 5. Determinations. a. An ecological evaluation was made following the guidance in 40 CFR 230.4, in conjunction with the evaluation consideration of 40 CFR 230.5. b. Appropriate measures were identified and incorporated in the proposed plan to minimize adverse effects on the aquatic environment as a result of the discharge. c. Consideration was given to the need for the proposed activity, the availability of alternative sites and methods of discharge that are less damaging to the environment, and such water quality standards as appropriate and applicable by law. d. Wetlands: In Plans 1 and 3, the proposed fill and the activity associated with it will not cause permanent unacceptable disruption of the beneficial water quality uses of the wetland ecosystem. Plan 2 requires that impermeable membranes or other methods be employed to prevent possible movement of water from a wetland in the American Memorial Park into the flood control channel. 6. Findings. The alternative discharge sites for the Garapan Flood Control study outlet channel is specified through the application of the Section 404 (b)(1) guidelines. 5 PA CIFIC 0 C F A N PUNTAN MUCHOT MICRO BEACH PLAN 2 V.A CONTINENTAL AMERICAN HOTEL MEMORIAL PARK INTER- CONTINENTAL HOTEL PLAN 3 GARAPAN Q* ELEMENTARY OSCHOOL HAFA ADAI HOTEL PLAN I 0 cr cn w < co 0 cc GARAPAN FLOOD CONTROL SAIPAN, CNMI 0 0.1 0.2 0.3 0.4 0.5 ALTERNATIVE PLANS SCALE IN MILES U.S. ARMY ENGINEER, DISTRICT, HONOLULU United States Department ofthe Interior FISH AND WILDLIFE SERVICE FJ& I P LY 11 [email protected] 300 ALA MOANA BOULEVARD Room 6307 3. ISO P 0 BOX 50167 HONOLULU, HAVIA11 96850 September 27, 1979 Lt. Col. B. R. Schlapak U.S. Army Engineer District Honolulu Building 230 Fort Shafter, Hawaii 96858 Re: Garapan Area Flood Control, Saipan, CNMI Dear Sir: This is the U.S. Fish and Wildlife Service's planning aid letter on the proposed U.S. Army Corps of Engineers' Garapan Area Flood Control Project, Saipan, Commonwealth of the Northern Mariana Islands. It has been prepared under the authority of and in accordance with provisions of the Fish and Wildlife Coordination Act (48 Stat. 401, as amended; 16 U.S.C. 661 et seq.), however, it does not fulfill Section 2(b) of the Act. When final plans with alternatives have been received from the Corps, the Service will prepare a detailed report with recommendations for the protection, conservation, development, mitigation and/or compen- sation for project caused fish and wildlife resource losses. The project is being planned under Section 205 of the 1948 Flood Control Act, as amended. This report is based on data gathered from existing published and unpublished documents, on Service field investigations on May 3-4, 1979 and files. Project engineering features were taken from the Corps Reconnaisance Report dated 24 November 1978. Project Description The Corp of Engineers Reconnaissance Report (Nov. 1978) indicates a tentative plan to build a 1,300-foot long by 20-feet wide, rectangular, concrete channel, a 5,000-foot long by 7-feet high earth levee and two, 20-foot clear span bridges at Garapan, Saipan (Fig. 1, 2). The levees will direct sheet flow into the channel which will convey it to the sea just south of the Garapan Dock area (Fig.2, Ref. 1). No estimate of channel depth is given. CONSERVE AMERICA'S Ak ENERGY Save Energy and You Serve America! 2 roject Description Without The Project The Commonwealth of the Northern Marianas is a group of fourteen islands located approximately 3,800 miles west of Hawaii. The island group runs north-south for a distance of about 440 miles and has a total land area of approximately 184 square miles. The island of Saipan is the largest in the group (Fig. 1). It is also the capital and center of population and commerce for the Commonwealth. Saipan is approximately 13 miles long, four miles wide, with a total land area of 46.7 square miles. Garepan Village is located on Saipan's west-central coast. Prior to its nearly complete distruction during World War II, it was the principle population center on Saipan. Extensive rebuilding was done after the U.S. invasion to facilitate administrative services and storage of war-related materials. Since the late 19401s, most of the U.S. military buildings have deteriorated or have been replaced by residential or light commercial buildings. Garapan is also the site of three major hotels. These are located along the white sand Micro Beach that borders a wide, shallow lagoon. Aerial photographs (February 23, 1944, on file at U.S.G.S. Honolulu Office) indicate that most of the Japanese village was concentrated on a .8-mile wide coastal plain. This area has a lime-sand or artifical fill substrate. It may have been quite marshy at one time as evidenced by the small marsh that is present in an unfilled area along the northern edge of the village (Ref. 4). Inland from the village the land rapidly rises in a series of terraces that form Saipan's central limestone hill range. Mt. Tagpachau (1,555 feet), Saipan's highest elevation is about 2.5 miles southeast of the village. The slopes of this geologically complex, but principally Tagpachau limestone ridge, are dissected by steep ravines and occasional nearly vertical fault cliffs. The narrow ravines and areas along the cliffs appear to have been shrub or forest vegetation in 1944, while much of the remaining terraces were cleared and cultivated in what appears to be sugarcane. Aerial photographs from 1978 show little little evidence of farming along the slopes above Garapan. There are no perennial streams within the project area. The deep, valleys on the hillsides contain intermittant stream channels but there are no defined channels crossing the coastal plain. The watershed within the project area covers 1.9 square miles (Ref. 1). Post World War II construction obliterated Japanese drainage ditches in Garapan and provided no replacements. Runoff as sheet flow, after heavy rains now moves overland toward the low lying urban areas and causes serious flood damage. A major flood that occurred in August 1978 resulted in Garapan and other areas in Saipan being declared a major disaster area (Ref.1). Flood problems in parts of Garapan are compounded by roads being elevated above the house lot levels and an inadequate urban drainage system. 3 Service field investigations involved a visual survey of the northern end of the drainage system. Lack of defined trails and a high density of wasps precluded extensive exploration of the upper watershed. An additional ground survey was done along the beach from Muchot Point to the Garapan Sugar Dock area. Extrapolation of ground survey information to 1978 aerial photographs indicates that previously cleared areas in the watershed have revegetated with nearly pure stands of tangan-tangan (Leucaena leucocephala). The closed tangan-tangan canopy is 15-20 feet high and dense enough to inhibit extensive undergrowth in the more xeric hillside habitats. Ravines, however, have deeper soil that retains water better than the slopes. In these areas undergrowth is often highly developed with dense areas of grasses and sword plants. Hau, upland taro and pandanus are also important constituents of the damper tangan-tangan areas (Table 1) . The remaining forest vegetation is generally dominated by a 20-75 feet-high mixture of introduced food or ornamental trees along with pandanus, bamboo, hau and ironwood (Table 1). The beach has typical strand vegetation including beach morning glory, hau, coconut, ironwood and various grasses and shrubs (Table 1). Urban vegetation includes many of the above species, especially flame trees, and a variety of garden vegetables and decorative shrubs. Few terrestrial animals other than birds, introduced land snails and domesticated farm species were observed within the watershed (Table 2). The upper watershed harbors a high (subjective judgment) population of birds (Table 3). Except for the Eurasian tree sparrow and the Philippine turtle dove, the avifauna is dominated by indigenous or endemic (to the Mariana Islands) species. Golden honeyeaters, endemic to Saipan, are common. Four species, Marianas crow, white-throated dove, Marianas fruit-dove and cardinal honeyeaters have been proposed for federal listing as Endangered Species in Guam, the most southern Mariana Island. The Marianas fruit bat which has also been proposed for Endangered status, may be present in this area but it was not observed (Ref. 5). The environmentally disturbed urban areas of Garapan have a higher exotic component in the avifauna (Table 3). Philippine turtle-doves and Eurasian tree sparrows are much more common here than in the upper watershed. The proposed endangered bridled white-eye was the only resident native bird that increased in abundance within the urbanized areas. Three native migrant wading birds were seen along the beach and one additional native terrestrial bird, the rufous-fronted fantail. was 4 in a small grove of trees. Based upon the Shannon-Wiener Diversity Index and equitability quotient (Table 3), the upper watershed has a more diverse avifauna than the urban area. Greater vegetation stratification, higher topographical relief, decreased human disturbance and greater abundance of mature fruit trees on the slopes perhaps accounts for the difference in equitability and in the greater presence of native bird species. A nearby swamp that was not closely surveyed because it was not within the proposed project boundaries should be mentioned here because of its proximity to the project. It lies just north of the project and east of the Japanese Small Boat Harbor. This area was an open water Phragmites - Scirpus dominated marsh before the U. S. invasion. Since the invasion, the marsh has been partially filled and has changed to a hibiscus - hau - tangan-tangan swamp with standing but not open water. Service biologists heard nightingale reed warblers and saw the Marianas gallinule in the marsh in May 1979. The reed warbler is classified as an endangered species and the gallinule is being proposed for endangered status (Ref. 5). The nearshore marine environment is principally a sandy algae-seagrass habitat (Table 4) that is inhabitated by at least 32 species of fish and an unknown variety of invertebrates (Table 2, Ref. 6). There is little solid substrate near shore except for cement and coral rubble within the Garapan Dock area. As a result, few corals are present. The most obvious invertebrates were a coral, Pocillipora damicornis, along the dock, sea cucumbers, mainly Holothuria atra and the jellyfish, Cassiopea sp. Environmental Setting With The Project The preliminary project description indicates that all structures would be located within the present or former urbanized areas of Garapan (Fig. 2). Most of the project area is now covered with nearly pure stands of tangan-tangan although there are a few patches of taller vegetation, e.g., at the Sugar-King Memorial Site, that existed even before the U. S. invasion. Construction of the levee would destroy the vegetation and thus habitat for a number of bird species. This environ- mental degradation should be temporary and levee construction may allow bird habitat enhancement if a variety of plant species are used to revegetate the levee. Increased plant species and statigraphic diversity should eventually be reflected in increased faunal diversity. The channel would also have a minimally adverse effect on the terrestrial biotic environment. If the channel bottom is below sea level, it would retain water and sediments and perhaps provide some additional feeding habitat for wading birds. The concrete sides and shallow areas within the channel may provide habitat for brackish water flora and fauna including mudskippers, juvenile mullet and flagfish (Kulia sp.). 5 The tentative seaward opening of the channel will very likely be a site for silt deposition. This problem will probably accelerate as land is cleared and the Garapan area is more intensively urbanized. Prolonged siltation at the mouth may be detrimental to the present nearshore biotic community although little is known about the ability of shallow water sea grasses and algae to maintain themselves while being subjected to various levels of siltation. There are tentative plans to construct a small boat harbor at Garapan Dock. If the harbor is constructed, it would probably trap silt released from the channel. Patterns on aerial photographs of the Garapan Dock area suggest that strong currents flow north. Filling of former trans-reef channels along Garapan indicates that substantial sediment transport takes place. Frequent input of fine sediments into the proposed harbor may result in constant high turbidity and consequently prevent the recovery of the sea grass community following harbor construction. The small swampy area just north of Garapan may experience either beneficial or adverse effects if runoff water is directed into it. Siltation would eventually raise the floor of the marsh enough to allow the invasion of mesic vegetation and depletion of Phragmites and other wetland plants. However, if silt is removed from the runoff prior to its entry into the marsh, the increased water input may allow expansion of marsh vegetation. This swamp is inhabited by the endangered nightingale reed warbler and the proposed endangered Marianas gallinule. Both of these species are dependent upon marsh habitat. Discussion/ Recommendations Although the Garapan area was devastated during World War II and highly altered by post-invasion construction, much of the area has substantial native faunal populations. With the possible exception of the Marianas megapod, which may have been present before World War II, there has probably been an increase in bird populations within the project area. This resulted from the succession of previously cultivated fields into a shrub community and in the revegetation of much of the urban Garapan area after post-World War buildings were abandoned and deteriorated. The upper watershed has a high proportion of indigenous and endemic birds while the urbanized Garapan Plain hosts a greater exotic element. There are four birds that are proposed for endangered status present in the upper drainage, an area that is also suitable Marianas megapod habitat. This latter species, considered extinct on Saipan in 1949 (Ref. 8), is becoming re-established on Saipan. Service biologists heard four individuals at Marpi Point behind the "last Japanese command post" monument on May 5, 1979. Much of the previously cleared land has been revegetated with tangan-tangan. The nearly monotypic stands of this shrub are so dense that expansion 6 of more diverse surrounding forest communities is probably inhibited. Low strategraphic complexity within the tangan-tangan communities probably relates to the low variety of birds and probably other fauna in this habitat type. In order to minimize adverse effects to fish and wildlife resources within the Garapan region, we believe the following recommendations should be followed during development and construction of this project. 1. Contruction should be limited to the former urbanized area of Garapan. 2. Vegetation in the watershed above Garapan should not be disturbed. 3. The location of the channel outlet should not be up current from the proposed small boat harbor at Garapan. 4. The heavy use of Micro Beach by tourists that observe fish and wildlife habitat while snorkeling indicates that that area should not be used as an outlet location. 5. The former dredged channel just south of the Intercontinental Hotel appears to be the site that would be least damaging to the marine environment. Aerial photographic evidence suggests that longshore currents are moving in a more seaward direction at this point than at other points within the project boundaries. We recommend that the outlet channel be located at this site. Onsite current analysis should be conducted in order to confirm our photographic analysis. A prediction of sediment transport and deposition should be included as part of future project plans. 6. If the swamp north of Garapan is considered as an outlet, the amount of siltation or water retention should be predicted as part of the project plans. 7. All proposed alternatives should include a means of trapping silt, such as silt basins, sod waterways, etc. before it enters the lagoon. 8. The channel should be lined with sod instead of cement. 9. Because of the high number of endangered and proposed endangered animals present within this watershed, particular care should be taken to avoid destruction of vegetation during construction. 10. The Office of Endangered Species, U.S. Fish and Wildlife Service, should be contacted in regard to the proposed and possible existing endangered species within the project area. 7 We appreciate this opportunity to comment. Sincerely yours, J; Maurice H. Taylor Field Supervisor Division of Ecological Services cc: PIA NMFS CNMI- DNR EPA, San Francisco ES, Wash D. C. Region I Area Offices 8 REFERENCES 1. U. S. Army Corps of Engineers. 1978. Garapan Area Flood Control, Saipan, Northern Mariana Islands Reconnaissance Report. 2. Cloud Jr., P. E., R. G. Schmidt, H. W. Burke. 1956. Geology of Saipan Mariana Islands. U.S. Department of Interior, Geological Survey. Prof. Pap. 280. 445p. 3. Davis, D. 1970. Draft Topographical Map of Saipan. U.S. Department of Interior, Geological Survey, Honolulu Office. 4. U.S. Army Map Service Far East. 1953. North Chalan Kanoa Map. Sheet 3367 1 SW Series W843. 5. U.S. Fish and Wildlife Service. 1979. A dozen animals from Guam are to be reviewed as possible Endangered Species Candidates. Region One News Release 75-35. 6. Amesbury, S. S., D. R. Lassuy, R.F. Myers and V. Tyndzik. 1979. A survey of the fish resources of Saipan Lagoon. Commonwealth of Northern Mariana Islands CZM. Draft Report for Contract S79-02. 7. FitzGerald Jr., W. J. and W. J. Tobias. 1974. Marine Survey of Saipan Lagoon. A preliminary survey of the marine plants of Saipan Lagoon. University of Guam Marine Laboratory. Environmental Survey Report. No. 17. 8. Marshal, J. T. 1978. The Endemic Avifauna of Saipan, Tinian, Guam and Palua. The Condor.. 51:200-222. Oda KYO um Iftisco a"NILA ROTA NOLULU T14E PACIFIC AREA MATUTE MILE,$; FARALLON TAM 46T.4 Of PAJARAS 41BA"t .&MAUQ SAIPAN '*ASUNCION AGRINAN SAN .0 PAGAN ROQUE - ALAIWAGAN To" GUGUAN SARICAN On ANATA14AN GARAPAN FARALLON iWealgi Of LLA if SAIPAN AGUUAN,0 TINIAN ,c:9 ROTA CHALA UAM KAwM PUNTAN KAGMAN Fig. PUNTAN Map of AGIN"" Project LOC(Ition P" Cw . -@a@z of Garapan Flood Control 8,qlo ,4,v PUMAII NA"AN Japanese\ Mu c hot P o i n t Small BoaV,,,@\ H a r b Fig. 2 GARAPAN Flood Conlro IPro iec t Ar ea (Ref, 1,2,3) cy 0Im i nch e q u aIs440 yard s q@y% Pr o p o s e dL e v e e K 0 CL 14 Iroposed Channel Limit of Project Area Scrub/ Forest 1951 Scrub/ Fore st 1978- Within Pr a!aCt, Ur b.a n, Areas Ata 1978 0 Mt. Tagpochau plants [email protected], in 'Llic, Garapan Drainage. ca-141W IJR%E SCIF_NTIFIC IWE TREES Kapok Tree Ceiba pentandra African Tulip Tree '9p-athodea cwManulata Irommood Casuarina equisetifolia Tangan Tangan. Leucaena leucocophala Papaya Carica papaya Breadfruit Artocarpus incisus or mariannensis Mango Mangifera indica B&rboo Bambusa vulgaris Banana Musa sp. Coconut Cocos nucifera Betel Nut Areca cathecu Acacia Acacia confusa Flame Tree Delonix regia Screw Pine Pandanas tectorius Nilo Thespesia populnea Hau Hibiscus tiliaceus Pluchea indica UNDERGRONM Rat-tail Dropseed @Mrobolus elongatus Loovegrass hragrostis tenelia Guinea Grass Panicun n-oximum Sword Grass MiscanthZ@tslo@ridulus Crowfoot Grass Dactyloctenium aegyptiun Lagundi Vitex trifolia Sword Plant Sansevieria trifasciata Passion Fruit Passiflora foetida var. hispida Sedge Cyperus odoratus Candlebrush Cassia alata Coffee-Senna C. occidentalis Upland Taro Tlocasia rmcrorrhiza False Verbena Stachytarpheta indica Beach Morning Glory Ipcrmea pes-caprae Nigas Perrphis acidula .LE 2. Vertebrates or belic-ved to b-- pi-i -sent in Gur@-Ap-m v.utershed and nearshore area. See Table 3 for birds. 031vaN, N-V.E SCIF1,UIFIC DWE. MWAALS cow Bos sp. Pig Sus scrofa Dog Canis farniliaris Cat Felis dcrresticus Marianas Fruit Bat Pteropus mariannus Norway Rat Rattus norvegicus Roof Rat R. rattus Polynesian Rat R. exulanis Nbuse Mas nusculus REPTILES -Bluetail Skink Bw i a cyanura Brown Skink Fzm i a sp. Green Skink E@-x@rolepis smragdina Green Anole Anolis sp. Indian hionitor Varanus indicus Geckos Gekkonidae Green Sea Turtle Chelonia nrjdas Pacific Hav&sbill Tkirtle Ereiii;-chelys imbricata AMIHIBIANS Marine Toad Bufo niarinus FISHES* Spotted Wray Gyrmothorax nebulosa Squirrelfish FImTmo sam-nara Squirrelfish Myr i pr i s t i s iiilrd j an Cardinalfish Apogon novenfasciatus Cardinalfish A. nubilis Cardinalfish Tar-arm* quinqu lineata Snapper W t j ix-Tu--, fu I vus Blueline Snapper L. kasmira Snapper iiit-]"anus sp. IIY-I@BIIII 2. (Cj-,-II inued) CMIM3N NV& SCIENTIFIC MhE FISHES* Rudderfish Gerres,arMeus Scorpionf i sh Scorpaenodes gumnensis Mireadfin Butterflyfish Chaetodon auriga Saddleback Butterflyfish, S.. ephippi Mireespot Damselfish Dascyllus trimaculatus Darnse 1 f i sh Eupoaacentrus albiTa-sciatus Damselfish Gyphidodont., s.leucopamus Damselfish Plectroglje@idodon leucozona Wasse Cheilinus trilobatus Wrasse Cheilinus sp. Wasse Cheilio inennis Wasse Ra-lich3eres trimaculatus Wasse Stetho.ulis strigiventer Wasse Stet sp. Parrotfish Scarus ghobban Parrotfish S. soFdicTu-s- Parrotfish &arus sp. Surgeonfish Acanthurus xanthopterus Rabbitfish Signaus argenteus Rabbitfish S. spinus Sabretooth Blennie PlegiostrFMI tapeinosoma Blermie ga-larias faii-ciatus Goby Amblygobius albinaculatus *Species listed for nearshore habitat at Garapa'n by Amesbury et al (1979). TAW@E 3. Birds observed in the Garapan Drainage, @&y 3, 1979. SPECIES Upper Northern Drainage Urban-Beach Area 0900 - 1100 hr 1200 - 1300 hr No. Cbserved % No. Cbserved % CUJACN NANE, SCIENrIFIC NAME Car(lioal Honeyeater* &Vzomela cardinalis 50 39.7 17 15.9 ""Iolde.,i Honeyeater Cleptornis marchei 10 7.9 1 .9 .;..ura:3ian Tree Sparrow Passer ffx)ntanus 30 23.8 51 47.7 Crow* Grvus kubaryi 1 .7 J T(:! rn Uygis @alba 12 9.5 2 1.9 lihi-L,- 'Eiroated Dove Gallicolurba xanthonura 1 .7 ,.;xiltzi:,@_; Fruit-Dove Ptilinopus roseicapilla 2 1.6 i :1 p') i ne 3.1ur t 1 e-Dove Str top-eli'a bitorquata 8 6.3 17 15.9 U I lialcyon chloris 4 3.2 I lo rt@ I Kingf i sher 0 V -lite A -eye* Zosterops conspicillata 8 6.3 13 12.1 i,@ufk)@Is-frontcd Fantail Rhipidura rufifrons 1 .9 Golden Plover Pluvialis dminica 2 1.9 e Nunerius phaeopus, 2 1.9 Tattler fieteroscelus incan= 1 .9 Total Individuals 126 100% 107 100% Total Species S 10 10 Shannon-Wiener Index of Diversity Pi"910pi .7499 .6811 H max = loglos 1.00 1.00 Equitability = E H/H frax .7499 .6811 *proposed endangered species (Ref. 5) 4 .7sla-rine Plants in sandy inshore habitat along Garapan. 40 Reported by FitzGerald and Tobias (1974). Location: 1400 yards north of Garapan Dock. 29.7% algal cover, 70.3% sand. Species in decreasing orderof abundance "I. Chondria repens 5. Necmeris vanbosseae 2. Ia`urenc1a-=o Ica 6. U=aci aria lichenoides 3. Acanthophora spicifera 7. Calothrix confervicola 4. Microcoleus lyngbyaceus 8. Schizothrix calciocola Locatiom, Garapan Dock. No percent cover or abundance indicated. Species observed Green Algae: Enteramrpha c@Messa Halimeda n-acroloba H. opunti Dicty@sphaeria versluyii Valonia fastigiata Red Algae: SprVidia filamentosa Tolplocladia g1cmerulate Seagrass: Enhalus acoroides Halodule ininervis Hajophila minor @j I Ili@luillillilliliffi@ i 3 6668 14101 6586