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ip i6 Beach Changes on Oahu as Revealed by Aerial Photographs Dennis Hwang A COASTAL ZOI\';E x INFORMATION CENTER 16. fA DE %W 500 H93 1981 I Beach Changes on Oahu as Revealed by Aerial Photographs Dennis Hwang July 1981 This document was prepared for the State of Hawaii Department of Planning and Economic Development by the Urban and Regional Planning Program andthe Hawaii Institute of Geophysics, University of Hawaii Technical Supplement Number 22, Coastal Zone Management Project, Urban and Regional Planning Program Technical Report HIG-81-3, Hawaii Institute of Geophysics Cooperative Report UNIHI-SEAGRANT-CR-81-07, UH Sea Grant College Program This report has been cataloged as follows: Hwang, Dennis. 1. Aerial photography in geomorphology. 2. Beach erosion-Hawaii. Beach changes on Oahu as revealed by aerial photographs. Prepared 3. Beaches. 1. University of Hawaii (Honolulu). Urban Regional Plan- by the Urban Regional Planning Program, Hawaii Institute of Geophys- ning Program. 11. University of Hawaii (Honolulu). Hawaii Institute of ics, and Sea Grant Program, Univ. of Hawaii for the Dept. of Planning Geophysics. 111. University of Hawaii (Honolulu). Sea Grant Program. and Economic Development, State of Hawaii. Honolulu; Hawaii Coas- IV. Hawaii. Department of Planning and Economic Development. V. tal Zone Management Program, DPED, State of Hawaii, 198 1. Hawaii Coastal Zone Management Program; I -Sup. 22. VI. Title. HT392.H321.No. I-Sup. 22 (x fr. Hawaii Coastal Zone Management (Technical supplement 22 - Hawaii Coastal Zone Management Pro- Program) gram; 1; HIG-81-3; UNIHI-SEAGRANT-CR-81-07) ABSTRACT An aerial photographic analysis of the beaches of Oahu was conduct- The sandy shoreline on Oahu has been placed into the following ed for a period of up to 50 years. The results indicate that the most management categories: unstable beaches are on sand bodies projecting from the coastline, such as Kualoa Point, Iroquois Point, and Paiko Peninsula. (1) Hazard Areas are subject to inundation by large winter waves. Beach changes on Oahu can be characterized by the coastline. On the north shore, intermittent erosion occurs when the beach is overwashed (2) Chronic Erosion Areas have a long-term history by waves of unusual height and force. Aerial photographs record the ef- which indicates erosion will continue in the future. fects of the December 1-4, 1969 storm, 1946 tsunami and possibly the 1 1957 tsunami. (3) Unstable Beaches have an alternating'history of ero- sion and accretion. These changes are unpredictable. Beaches facing the northeast trade wind direction are especially dynamic systems. The large long-term changes at Kualoa Beach, Kailua (4) Stable Beaches have had a small net change and range Beach and Lanikai Beach are partly caused by variations in sand trans- in the position of the vegetation line. port along the shoreline. Erosion problems- on the windward coast exist at north Kahuku Golf Course Beach, Kalanai Point, Laniloa Beach, (5) Accreting Beaches have grown continuously seaward. Hauula Beach Park, Swanzy Beach Park, Kaaawa Beach Park and Waimanalo Beach. The first three categories are of the greatest concern to coastal managers. Along much of the south shore, waves break at the seaward edge of a shallow fringing reef. As wave energy is reduced, many of the beaches are relatively stable. Erosion during the 1967 to 1971 interval, however, occurred at Hanauma Bay, east Kahala Beach and Paiko Peninsula. Sandy Beach, which is not protected by a fringing reef, also eroded during that period. Ewa Beach experienced erosion between 1958 and 1967. West Iroquois Point has been chronically eroding. On the leeward coast, the south end of Kahe Beach and the ends of Maili Beach have a history of persistent erosion. Most other beaches had no apparent long-term change. Nevertheless, periodic damage to the backshore area may occur from large Kona Storm waves or refracted North Pacific swell. ACKNOWLEDGMENTS This report was prepared for the State of Hawaii Department of Plan- This study was reviewed in whole or part by Earl Matsukawa (Urban ning and Economic Development by the Coastal Zone Management and Regional Planning Program, URPP), Cindy Bower (CZM), Dr. Project, Urban and Regional Planning Program (URPP), and the James E. Maragos, Karl Keller and Elaine Tamaye (U.S. Army Corps Hawaii Institute of Geophysics (HIG), University of Hawaii. of Engineers), Lori Chee (City and County of Honolulu, Land Utiliza- tion), Don Griffin (City and County of Honolulu, Department of Parks Research funding was provided through the Hawaii Coastal Zone and Recreation), Dave Parsons (Department of Transportation), Scott Management Program administered by the DPED. Publication funds Sullivan (Sea Engineering Services) and Paul Bartram (AECOS). were provided by the Hawaii Institute of Geophysics, and the Universi- ty of Hawaii Sea Grant College Program under Institutional Grant No. Field assistance was provided by Annabelle Lee (East-West Center) NA79AA-D-00085 from NOAA, Office of Sea Grant, U. S. Depart- and Carol Leong. The photomaps were designed and developed by ment of Commerce. Nancy Brown with the help of Karen Fukushima and Donald Houston. Sections of this paper were submitted to the Graduate Division of Numerous drafts of this document were typed by the URPP staff of the University of Hawaii as partial fulfillment for the degree of Master Paulette Dahlen, Pam Hunt and Barbara Awa. Rita Pujalet (HIG) of Science in Geology and Geophysics. edited the final report. Wendy Nakano of Sea Grant spent much time with the graphics and layout of the photomaps and text. Wendy Aerial photographs were obtained from the R. M. Towill Company, Yokota, URPP, set the type for this report. Air Survey Hawaii, U. S. Geological Survey and the U. S. Army Corps of Engineers. Mahalo to all those who contributed. During the various stages of research, Tom Dinell (Director, URPP), Norman Okamura (URPP) and J. Frisbee Campbell ( IG) 1. must also acknowledge my parents, John and Betty Hwang, who worked together to provide guidance to this study. I am grateful for supported my academic endeavors and whom provided much of the their individual and collective efforts. I thank my thesis chairman, Dr. moral support to complete my studies. Many thanks. Ralph Moberly (HIG), for his critical review of the report. The other members of my committee who provided valuable input were Dr. Doak Cox (Environmental Center) and Dr. Frank Peterson (Geology Department). H V TABLE OF CONTENTS INTRODUCTION I SECTION III - SOUTH SHORE 83 STUDY LIMITATIONS 3 Sandy Beach Park 84 Hanaurna Bay Beach Park .86 SECTION I - NORTH SHORE 5 Paiko Peninsula 88 Niu Beach to Wailupe Peninsula 91 Mokuleia Beach 6 Wailupe Beach Park and Residential Area 93 Kaiaka Bay Beach 12 Kahala Beach 95 Haleiwa Residential Area to Alii Beach Park 14 Kaalawai Beach and Kuilei Cliffs Beach Park 97 Haleiwa Beach Park 16 Iroquois Point 99 Kawailoa Beach 18 Ewa Beach 102 Waimea Bay Beach Park 21 Oneula Beach 104 Pupukea Beach 24 Nimitz Officers Beach 106 Sunset Beach 24 Nimitz Beach 108 Sunset Point to West Kawela 27 Barbers Point 110 Kawela Bay 29 Turtle Bay 31 SECTION IV - LEEWARD COAST 113 Kaihalulu Beach 33 Hanakailio Beach 35 Lanikuhonua Beach 114 Kahe Beach 114 SECTION 11 - WINDWARD COAST 37 Nanakuli Beach Park 116 Ulehawa Beach Park 118 Kahuku Golf Course Beach 38 Maili Beach 119 Malaekahana Beach 40 PokaiBay 121 Laie Beach 42 Mauna Lahilahi Beach Park 122 Laie Point to Pali Kilo Ia 44 Papaoneone Beach (Turtle Beach) 124 Kokololio Beach 46 Makaha Beach 126 Hauula Beach to Makao Beach 48 Keaau Beach 128 Kalaipaloa Point to Waiono Stream 50 Makua Beach 130 Punaluu Beach Park and Residential Area 52 Yokohama Beach (Keawaula) 132 Kahana Bay Beach Park 55 Mahie Point to Swanzy Beach Park 57 MANAGEMENT PROBLEMS ON OAHU 135 Kaaawa Residential Area to Kalaeokaoio Point 59 Kualoa Beach 60 MANAGEMENT STRATEGY 137 Kailua Beach 67 Lanikai Beach 71 SUMMARY 143 Waimanalo Beach 76 Makapuu Beach Park 80 BIBLIOGRAPHY 145 Vil LIST OF FIGURES FIGURE 1 Map of Oahu 2 2 Photomap Arrangements - North Shore 5 3 Waimea Beach Erosion 23 4 Photomap Arrangements - Windward Coast 37 5 Kualoa Beach Erosion 64 6 Photomap Arra 'ngements - South Shore 83 7 Photomap Arrangements - Leeward Coast 113 LIST OF PLATES PLATE I Mokuleia Beach (West End) 8 2 Sunset Beach (West End) 26 3 Kahuku Airfield 35 4 Laniloa. Beach 46 5 Kaluanui Beach so 6 Punaluu 54 7 Kualoa 62 8 Kualoa Beach Park 62 9 Kualoa Point 66 10 Kailua Beach Park 70 11 Lanikai Beach 74 12 Paiko Peninsula 90 13 Iroquois Point 101 14 Yokohama Beach (Keawaula) 134 viii INTRODUCTION Beach erosion and accretion are continuous natural processes to be The seasonal changes on Hawaii's beaches were first determined by expected on any sandy shoreline. So often in the past, however, devel- comprehensive field surveys during the 1962 to 1963 period (Moberly opment has progressed with the misconception that the beach is stable. and Chamberlain, 1964). In 1971, resurveys on selected beaches were This lack of appreciation' for the dynamic nature of the beach has led to conducted to determine the long-term trend over a period of approxi- the following problems. mately ten years (Campbell, 1972). While most study sites showed in- signifi,cant changes in the volume of beach sand, a few areas did display (1) in an attempt to protect endangered buildings from net accretion or erosion. erosion, seawalls, stone revetinents and boulder piles have been placed along much of Oahu's coast. Some of The objective of this study was to determine the patterns of long- these structures may have adverse impacts on the term beach change on Oahu by the use of sequential aerial photography. beach. For example, seawalls may reflect wave energy Since aerial photography extends further back in time than comprehen- resulting in the transport of sand offshore. This may sive beach surveys, a systematic analysis of old air photos would pro- cause the beach to narrow so much that access along vide for many beaches, the first indication of the long-term trend over the shore is blocked and the utility of the beach elim- a period of up to 50 years. This is a time scale that coastal planners may inated. In this manneri the total length of recreational find particularly useful. beaches on Oahu has steadily declined over the last 30 years. . The use of aerial photographs to monitor past shoreline movements on Oahu was applied for a study of Kailua Beach Park (Noda, 1977), (2) During development near the beach, many buildings Kualoa Beach Park (U.S. Army Engineers, 1977) and Kailua Beach have been placed in areas that are extremely vulnera- (Hwang, 1980). The methodology used in this report was described in ble to inundation by the large waveb associated with detail and tested for the study of Kailua Beach. Briefly, the method in- hurricanes, tsunamis and winter storms. Erosion com- volves the following steps. Sequential aerial photography of a given pounds this problem by reducing the natural buffer beach is obtained. The photos are scaled using field measurements, or- zone that protects beachfront structures from the sea. thophoto maps or extended control ftom tilt-ftee photographs. Points on the photo which have a stable position over the beach monitoring Although beach erosion in Hawaii will continue, the problems asso- period are then selected. Measurements from these stable reference ciated with this process can be alleviated and in some cases prevented. points to the vegetation line and water line on photographs of different The most effective strategy against erosion is to plan for the seasonal years will reveal how the beach has changed through time. and long-term changes of the beach prior to shoreline development. Implementing such a strategy would require a thorough understanding of the idiosyncrasies for each beach. It must be known, for example, whether a particular beach is likely to prograde or recede. If erosion is in process, what is the rate of retreat? Does the beach experience cycles of erosion and accretion and if so what is the range in the cycle? What is the magnitude of the seasonal change on the beach, or how susceptible is the backshore area to high wave inundation? This information must be obtained before the natural changes of the beach can be planned for. Beaches on Oahu have been divided into four sections. Beginning For each studied beach there is a textual description of the patterns with the -North Shore, Section 1; and moving clockwise around the of long-term shoreline change. For most of the beaches, except the island, the next 3 sections are on the Windward Coast, Section,11; small pocket cells, there is a table with the historic data and an air photo South Shore, Section 111; and Leeward Coast, Section IV (Figure 1). map showing the location of established transects. After presentation of the results for Oahu, a section on management problems which On the windward coast, a gap in the coverage exists for the stretch be- became,apparent during the course of research follows. The final sec- tween Kualoa Beach Park and Kailua Beach. Generally, the few tion of this paper is on beach management strategy based on the data beaches in Kaneohe Bay are composed of silt and mud. The beaches of from this report. Waikiki were also excluded from this study because of the artificial al- terations along the shoreline. Kauai Oahu Niihau Molokai Maui Section I - North Shore @'@--7N- Lanai Section 11 - Windward Coast @[email protected]'11X K71' Kahoolawe 16(f 21f N @Q a 'Ni Section IV - Hawaii Leeward Coa Section III - South Shore Figure 1. Map of Oahu. 2 STUDY LIMITATIONS Before using this report, the reader should be aware of the limitations All effort was made to determine the long-term beach sunimarized below. change no matter how unfavorable the study conditions. Not to do so would leave many problem areas on the coast Accuracy - The accuracy of the measurements for each unidentified. As some of the reference points are far from beach varies according to the height of the stable reference the beach, it is conceivable that an error greater than 10 feet points, their distance from the beach, and the quality of the could occur. If the reader is aware of such a case, disclosure aerial photographs. A theoretical estimate of the likely error of this information would be welcome. computed at a 95% confidence interval was determined as 12 feet for Kailua Beach (Hwang, 1980). Subsequent field Transect Spacing - Transects along the beach were estab- surveys and ground checks indicate that this figure may be lished at intervals of approximately 1,000 feet. For beaches conservative. that erode intermittently during large storm events this sample spacing could lead to the following problem. Calculating the likely error for each beach is time consum- ing, requires that many assumptions are made and often The degree of erosion caused by storm waves can vary sig- leads to an estimate that is misinterpreted. For this reason, nificantly from place to place. For example,-one beach sec- the uncertainty in the error for the individual beaches was tion may erode severely, whereas one hundred feet to the not determined. side no storm damage may be evident. These variations may be caused by the location of offshore reefs and channels, the Generally, changes in the vegetation line greater than 10 exposure of beachrock, the, orientation of the beach, and feet can be seen on the aerial photographs. This figure gives numerous other factors. a rough approximation of the accuracy in the data. On some beaches, the accuracy of the measurements may be greater When using the data in the report, it should be remem- because of the low reference points and their proximity to bered that uncertainties are introduced when a beach the beach. This is the case at Hauula Beach Park and Sandy change is extrapolated between the transects. This is espe- Beach, to name two examples. cially so for beaches on the north shore where the major long-term changes are caused by high wave iriundation. Any problems that were encountered in collecting data are mentioned in the sections for the individual beaches. If the exact long-term change is required for a particular For some areas, the stable reference points were in unfa- location far from the transects reported in this study, the in- vorable locations. In such cases, a connecting line was formation can be obtained on the aerial ph 'otographs filed drawn between the reference points. Measurements to the with the Urban and Regional Planning Department, Uni- beach were then made from a point on the stable line. While versity of Hawaii. this procedure introduces errors, it was the only way to obtain data for the Yokohama and Makapuu beach systems. Therefore, the data for these beaches should be regarded as first approximations subject to later revision. 3 Aerial Photographic Coverage - On some beaches, the most recent aerial photographs were taken in 1975 for the Army Corps of Engineers. Although more current photogra- phy is desirable, it is not essential in order to determine the characteristic change for each beach. For some of the shore- line in this study, the data exist over the 26-year period from 1949 to 1975. In most cases the data are more current. It was originally hoped to monitor the beaches with aerial photographs taken every five years. For beaches where the coverage is sparse, large gaps in the data may exist. On such beaches it is difficult or impossible to determine the timing of erosion events. In such a case, all that can be mentioned is that the beach had a specific net change over a certain time interval. 4 13 SECTION I - NORTH SHORE 12 11 L The north shore, extends from Kaena Point on the west to Kahuku 10 "-M' on the east (Figure 2). The major long-term changes on this coast are M caused by winter North Pacific swell. During the summer, the beaches are wide and have a gentle slope. When the winter surf arrives, the 9 beaches narrow and the foreshore slope steepens. Generally, no perma- nent damage to the backshore area occurs unless large waves overwash the beach-buffer zone. This may occur during a strong winter storm or tsunami. ffa 7 During the December 1-4, 1969 storm, almost all sections of the north s M hore suffered erosion. For many beaches, this storm caused the 6 major retreat in the vegetation line over a period of several decades, At 45 3 Waimea Beach, approximately half of the loss in the vegetation line be- 2 tween 1928 and 1975 occurred during this brief event. Fo beaches that are relatively narrow and have an irregular reef off- shore, winter surf damage may occur more frequently. This may be the for certain sections of Mokuleia Beach. case Historical data indicate that the north shore of Oahu is particularly 9% susceptible to tsunami runup. The 1949 aerial photograph of Kahuku V, Point shows that inundation from the 1946 tsunami was about 1,200 feet inland. On the 1958 photograph for Kealia Beach, the possible ef fects of the 1957 tsunami are seen opposite the middle of Dillingham Air Field. Because runup data for this beach section are unavailable, it cannnot be determined whether the killing of the vegetation was caused by tsunami inundation or artificial sand removal. Figure 2. Photomap Arrangements - North Shore. 5 Mokuleia Beach Table I - Mokuleia Beach (West End). Changes in the Mokuleia Beach is located at the west end of the north shore. In Vegetation Line in Feet. order to facilitate data presentation, this 6-mile-long stretch has been divided into a western, a middle and an eastern section. Transect Number Mokuleia Beach (West End) The west end of Mokuleia Beach is relatively undeveloped. Except Observation Period 1 2 3 4 5 6 7 for the cabins at Camp Erdman, the bathhouse at the Army Beach and Sep 28, 1949 - Nov 01, 1958 -79 +7 +1 -9 -85 the houses near transect 7, the land is otherwise bare (Photomap 1). West Mokuleia Beach experienced severe erosion during the Decem- Nov 01, 1958 - Aug 22, 1962 -21 +61 +95 +8 +16 +26 +62 ber 1-4, 1969 storm. At Camp Erdman, the vegetation line during the Aug 22, 1962 - Apr 22, 1967 +112 +142 '+6 + 1 +9 -8 +80 1967 to 1971 interval was cut back 38 feet (Table 1). One cabin, situat- ed near the vegetation line in 1967, was removed because of high Apr 22, 1967 - Mar 17, 1971 -182 -382 -22 -66 +2 -3 -19 waves. Other than the heavy damage from the 1969 storm, the beach at Camp Erdman appeared stable over the 26 years of observation. Mar 17, 1971 - Apr 11, 1975 -6 +3 -67 +12 +1 -2 +4 At the west end of Dillingham Air Field, near Mokuleia Army Apr 11, 1975 - Aug 06, 1979 0 -19 +6 +3 -79 Beach, two transects were established. The large fluctuations in the po- Net Change - Vegetation Line -15 -15 -67 -57 +17 +7 -37 sition of the vegetation line for transect 3 are partly due to the effects of Range - Vegetation Line 24 38 101 73 17 26 142 drainage from a nearby sand mining operation. At transect 4, the vege- Net Change - Water Line -6 -32 -2 +21 -2 +26 -8 tation line receded 66 feet during the 1967 to 1971 interval. This loss Is Range - Water Line 26 42 45 56 23, 33 31 attributed to the recession of sparse vegetation-from inundation by the December 1969 storm. - *No data 1 Change from Sept. 1949 - Aug. 1962 Along Kealia Beach, transects 5 and- 6 showed a net increase in the 2 The 1967photographs were taken on May 29 vegetation line over a 30-year period. Although this section of Moku- Net change is the total change in the position of a beach index line between the leia appears safe, the aerial photographs show the possible effects from earliest and most recent observation year tsunami inundation. Range is the difference between the observed extremes in the position of a beach index line. On the 1958 photograph for Kealia Beach, the vegetation has a light tone and is less extensive than in 1949 (Plate 1). On certain sections of this beach the stripping of the vegetation due to a sand mining opera- tion is clearly evident. On other beach sections, however, it appears that the vegetation may have been killed by the inundation of seawater, sand and debris from the 1957 tsunami. Although runup data for this beach are unavailable, about I mile to the west, estimated wave heights of 24 feet were recorded (Loomis, 1976). This estimate is the height of the maximum intrusion of the water onto the land. If the 1958 photo- graph records tsunami inundation, then wave runup was about 500 feet inland. 6 Kea J, 0 `4` 3 Diffin halwAir Aetd k A A,@ [email protected] NEW.", Transect 2 Transect 4 Photomap 1. Mokuleia Beach (West End) +20 1967 1967 Photographs by Air Survey Hawaii: March 1971 +10 1962 1962 - 1958 0 1949 - 1949 -10 1975 -20 1971 x -30 1975 -40 - 1971 -60 1979 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 7 MMMMW [email protected] 1957 tsunami at Mokuleia Beach (opposite the middle of Dillingham t JV Plate 1. Mokuleia Beach (West End). Possible inundation from the A irfield). The light streaks on the right side of the 1958 photograph are attributed to sand mining. It's At transect 7, the vegetation line has undergone large changes. The retreat of the vegetation line by 85 feet during the 1949 to 1958 period is attributed to human alterations. From 1958 to 1967, the vegetation line advanced seaward 142 feet. Over the 1967 to 1971 interval, the vegetation line receded 19 feet. This change is partly due to the Decem- -4, 1969 storm. Since 1971, the changes in the vegetation line ber I have been partially influenced by man. Over a 30-year period, there ap- pears to be no significant net change in the position of the water line. ...... .... Transect 7 faces a large offshore channel. This bottom configuration Z' would allow storm waves to break closer to shore. 1949 INN 1958 8 Many of the homes from the Episcopal Church to the Polo Field and Mokuleia Beach (Middle Section) along Crozier Drive are less than 20 feet from the edge of the vegeta- tion line or a seawall. Because of this development close to the shore, The middle section of Mokuleia Beach has experienced small long- any loss to the beach or vegetation is of great concern to the residents. term changes. Transects 10 to 13 had a net loss in the vegetation line of For many of these homes, erosion of only 10 feet would reduce the 8 to 12 feet (Photomap 2, Table 2). Generally, the major erosion oc- natural buffer zone significantly. curred during the 1967 to 1971 period, At transect 15 the vegetation line receded 15 feet during the 1949 to 1958 period. Since the 1946 and 1957 tsunamis, much of the land behind this beach has been developed. When a large storm or tsunami reoccurs, the property damage for these residential areas could be extensive. -A ft% t 1911, 300 Irv 0 %A Transect 11 Photomap 2. Mokuleia Beach (Middle Section) 1958 Photographs by Air Survey Hawaii: March 1971 1967 1962 1! 0 1949 C 1971 10 1975 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 9 Table..2., Moku.1eia teach, (Middle Section). Changes in the Vege- tation Line in Feet. Transect Number Observation Period 8 9 10 11 12 13 14 15 16 Sep 28, 1949 - Nov 01, 1958 -6 +4 +6 -4 +12 -152 -42 Nov 0 1, 1958 -Aug 22, 1962 -1 -5 -4 @3 -63 +7 +28 +20 Aug 22, 1962 - Apr 22, 1967 +8 +7 +3 -3 -7 -2 -8 -9 Apr 22, 1967 - Mar 17, 1971 -2 -3 -8 -12 -5 -2 +7 -1 Mar 17,1971 - Apr 11, 1975 -1 .2 -8 -11 -7 +2 -3 +5 +24 Apr 11, 1975 - Aug 06, 1979 +12 +9 -1 * +8 + 1 -4 -8 + I Net Change - Vegetation Line +9 +5 -11 -8 -8 -12 +6 + 1 +10 Range - Vegetation Line 12 12 17 14 16 15 13 28 20 Net Change - Water Line -18 -8 +22 +6 -7 0 -5 +17 0 Range - Water Line 18 49 50 25 31 25 43 89 43 *No data I To seawall 2 The 1949photographs were taken on May 7 3 Change from 1949 to 1962 4 Change from 1967 to 19 75 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range 45 the difference between the observed extremes in the position of a beach index line. Mokuleia Beach (East End) the vegetation line for transects 18 and 21 receded over 15 feet. This change is attributed to the severe damage from the December 1969 Between 1949 and 1979, the vegetation line along most of East storm. Mokuleia grew seaward. Although this stretch appears to have a long- term history of accretion, there are periods when erosion occurs. The most recent aerial photograph for East Mokuleia was taken on During the 1949 to 1958 period, the vegetation line at transect 20 August 1979. Since then, several sections of the beach were damaged receded 21 feet (Photomap 3, Table 3). Over the 1967 to 1971 interval, 10 NI, o '3 77i, 01i V 'tI Z [email protected] Transect 18 Transect2l Photomap 3. Mokuleia Beach (East End) Photographs by Air Survey Hawaii: March1971 +30 - +20 - 1962 1967 1967 +10 - 1962 1975 19 5 -5 0 - 1958 -6 1971 19.'8 -10 - 1949 1971 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. by the large waves during the winter of 1980. Near transect 21, a six- foot-high escarpment was cut within a few feet of one house. Kaiaka Bay Beach East Mokuleia Beach has the same problems as many sections of the The aerial photographic data for Kaiaka Bay Beach exist from 1958 to north shore. The development close to the beac 'h makes homes ex- 1975. Over this 17-year interval, the vegetation line and water line at tremely susceptible to inundation from winter waves and tsunamis. mid-beach advanced seaward 45 to 50 feet (Photomap 4, Table 4). The major accretion of the vegetation occurred during the 1958 to 1962 and 1971 to 1975 intervals. Table 3 Mokuleia Beach (East End). Changes in the The dark sand at Kaiaka Beach consists primarily of sediments de- rived from erosion of the hinterland. There appears to be little source Vegetation Line in Feet. of carbonate sand, for the beach is a closed littoral cell with no offshore reef. The small amount of calcareous sand present may be derived from coastal erosion of a fossil reef. Transect Number ,Observation Period 17 18' 19 20 21 22 23 Table 4 - Kaiaka Bay Beach. Changes in the Vegetation May 07, 1949 - Nov 01, 1958 -1 +3 * -21 Line and Water Line in Feet. Nov 01, 1958 - Aug 22, 1962 01 +20 * +11 +11 +20 +19 Observation Period Vegetation Water Aug 22, 1962 - May 29, 1967 +21 -6 +7 +5 +8 -2 May 29, 1967 - Mar 17, 1971 +3 -16 +7 -2 -17 - 1 -1 Nov 01, 1958 - Aug 22, 1962 +21 -16 Mar 17, 1971 - Apr 11, 1975 -1 +3 -3 -3 +5 -5 +8 Aug 22, 1962 - May 29, 1967 + 1 +22 Apr 11, 1975 - Aug 06, 1979 +11 * +3 May 29, 1967 - Mar 17, 1971 +4 +44 Net Change - Vegetation Line +33 +4 +7 -8 +4 +22 +24 Mar 17, 1971 - Apr 11, 1975 +23 -4 Range - Vegetation Line 34 23 7 21 17 28 24 Net Change - Water Line +10 -162 + 1 -17 +14 +37 +13 Net Change +49 +46 Range - Water Line 25 182 26 33 14 37 24 Range 49 66 No data Net change is the total change in the position of a beach index line between the Built wall earliest and most recent observation year i 2 From 1949- 19 79 Range is the difference between the observed extremes in the position of a Net change is the total change in the position of a beach index line between the beach index fine. earliest and most recent observation year Range Is the difference between the observed extremes In the positlon of a beach index line. 12 Yw, ,kN k. A L w Feet 4 Photomap 4. Kaiaka Bay Beach Photographs by Air Survey [email protected] March 1971 13 Measurements on the vegetation line, however, suggest a large ero- Haleiwa Residential Area to AM Beach Park sion event during the 1971 to 1975 period. This change could be at- tributed to the deposition of sand inland by strong winds or waves. The beach from the Haleiwa residential area to Alii Beach Park is There appears to be no long-term erosion, as many palm trees are locat- about 4,000 feet long. Over this stretch six transects were established ed seaward of the line of lower vegetation. (Photomap 5). When Alii Beach Park was built, the change from salt-tolerant coastal Along the residential section, seawalls are present along much of the plants to the grass at the park may have caused the vegetation line to beach. Therefore, the set of data on the vegetation line is limited. In recede. front of one undeveloped lot at transect 1, the vegetation line grew sea- ward 35 feet over the 1962 to 1971 period (Table 5). The water line data for transects 1 and 2 also show an accretion of 28 to 50 feet. This accretion was recorded during all four observation inter- Table 5 - Haleiwa Residential Area to AM Beach Park. vals. From May 1949 to April 1975 several outcrops of rock have Changes in the Vegetation Line in Feet. become surrounded or covered by sand. The Haleiwa residential area appears to have a long-term history of accretion. Unfortunately, when the beach was developed, no allowance Transect Number was made for the large seasonal changes or short-term erosion events that are inevitable on the north shore. As a result, protective structures Observation Period 1 2 3 4 5 6 were required at this beach. Several of the houses at Haleiwa are less than 20 feet inland of the May 08, 1949 - Aug 24, 1962 +41 +7 +7 +18 +9 seawalls. Although the offshore reef may absorb some wave energy, Aug 24, 1962 - Apr 22, 1967 +13 * +2 -2 -5 -14 the potential for damage from winter waves and tsunamis is always present. Apr 22, 1967 - Jan 23, 1971 +22 * +4 +20 -3 0 At Alii Beach Park, the littoral cell is divided by an outcrop of rock. Jan 23, 1971 - Apr 11, 1975 -9 * +1 -16 -73 -56 To the west of the rock, the beach has grown, over a 26-year period. Net Change - Vegetation Line +26 +4 +14 +9 -63 -61 From 1949 to 1975 the vegetation line for trarisects 3 and 4 grew sea- Range - Vegetation Line 35 4 14 25 81 70 ward 14 feet and 9 feet, respectively. Over the same interval, accretion Net Change - Water Line +28 +502 +52 +29 +36 +42 of the water line was up to 52 feet. Range - Water Line 28 502 52 46 38 46 East of the rock, the water line and vegetation line changes indicate a No data different beach history. From 1949 to 1975, the water line near the park To seawall bathhouse extended seaward 42 feet. On the aerial photograph this 2 From 1949-1975 change is shown by the coverage of beachrock by sand. Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the. difference between the observed extremes in the position of a beach index line. 14 4 Transectl Transect 5 +40 - 1971 4-30 1975 t20 - 1962 1967 - 1967 +10 1971 0 1962 1949 -20 -30 - [email protected] -40 - @ai -50 -60 1975 W], NO -4 74 -70 -Wl 27" @-T, --V Photomap 5. Haleiwa Residential Area to AM Beach Park Photographs by Air Survey Hawaii: April 1975 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 15 Haleiwa Beach Park Table 6 - Haleiwa Beach Park. Changes in the Water The history of erosion at Haleiwa Beach Park prior to 1965 is de- Line in Feet. scribed in the National Shoreline Study (U.S. Army Engineers, 1971). Since 1965, the configuration of the beach has been altered by a groin, an offshore breakwater and several beach repair projects. Transect Number In this study, the data for Haleiwa Beach Park were obtained from Observation Period 1 2 3 4 5 measurements to the water line over the eight-year period from 1967 to 1975. During this interval the beach changes were partly artificial. In 1970, the Army Corps of Engineers spread 7,000 cubic yards of sand Apr 22, 1967 - Jan 23, 1971 +49 +11 +15 +12 -1 along the shoreline to repair the beach from the December 1969 storm Jan 23, 1971 - Apr 11, 1975 +64 +22 -30 -22 -30 (U.S. Army Engineers, 1971). The high waves during this storm washed beach sand onto the parking lot, baseball field and highway. Sand was Net Change - Water Line +113 +33 -15 -10 -31 also carried over the boulder groin into the boat channel. In 1974, an es- Range - Water Line 113 33 30 22 31 timated 4,000 cubic yards of sand from the Haleiwa boat channel were placed on the beach. Net change is the total change in the position of a beach index line between the earliest and most recent observation year The photographic data between 1971 and 1975 show that the water Range is the difference between the observed extremes in the position of a line at the south end of Haleiwa Beach grew seaward 64 feet while at the beach index line. north end it eroded 30 feet (Photomap 6, Table 6). Erosion was also recorded for the sections immediately to the north and south of the off- shore breakwater. Although Haleiwa Beach was modified artificially during this period, the data indicate the possibility of a slight long-term littoral drift to the south. Observations during October and December of 1972 indicate a pre- dominant north-south current with strong rip currents to either side of the breakwater (Gerritsen, 1978a). This circulation pattern coincides strongly with the beach changes observed during the 1971 to 1975 period. Generally, longshore currents carry sand along the beach in a southerly direction. The sand is carried seaward by strong rip currents to either side of the breakwater. These currents have formed a tombolo near the breakwater. Weaker rip currents in the vicinity of the groin have the potential to carry sand offshore. To reduce the possibility of sand loss from the beach, "T" groins can be constructed to divide the system into three subcells (Gerritsen, 1978a). A cheaper and more esthetically pleasing alternative might be a combination of structural measures and periodic sand relocation from the south end of the beach to the north. 16 Haleiwa Boat Harbor M 4, 2 'v. Qw- -"0*9001 Photomap 6. Haleiwa Beach Park Photographs by Air Survey Hawaii: April 1975 17 From transects 6 to 11, the vegetation line has had a tendency to Kawailoa Beach grow seaward. This accretionary trend was offset by the large losses of up to 42 feet during the 1967 to 1971 interval (Photomap 7 cont.). The The western section of Kawailoa Beach covered by transects 1 high waves during the December 1-4, 1969 storm caused erosion of the through 5 is characterized by small long-term changes (Photomap 7). vegetation and much structural damage on Kawailoa Beach. All five transects show the range and net change in the position of the vegetation line to be under 10 feet (Table 7). At transect 4, however, the water line receded 57 feet over the 1962 to 1975 period. This change has gradually exposed rock along the shoreline'. If the protective beach continues to diminish in size, several homes may become more susceptible to winter wave inundation. Table 7 - Kawailoa Beach. Changes in the Vegetation Line in Feet. Transect Number Observation Period 1 2 3 4 5 6 7 8 9 10 11 May 08, 1949 - Aug 24, 1962 +4 +6 +7 +5 +11 -3 +23 Aug 24, 1962 - Apr 22, 1967 0 + I + 1 -2 0 +5 +3 +3 +5 +7 +13 Apr 22, 1967 - Jan 23, 1971 -2 -1 -4 -3 -7 -12 -13 -7 -12 -2 -42 Jan 23, 1971 - Apr 11, 1975 -4 -4 -1 -4 +2 +3 +10 +2 0 +3 +10 Net Change - Vegetation Line -6 0 +2 -9 +2 +1 0 +9 -7 +5 +4 Range - Vegetation Line 6 5 7 9 7 12 13 14 12 8 42 Net Change - Water Line * +2 +4 -57 +46 +41 -30 -1 +6 +4 +4 Range - Water Line * 68 39 57 46 104 30 29 17 45 20 No data Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 18 'T - V -7- Transect 6 Photomap 7. Kawailoa Beach +40 - Photographs by Air Survey Hawaii: April 1975 +30 - +20 - +10 - - 1967 - 1962 0 - 1975 1949 -10 - 1971 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 19 4L 4, [email protected] 9W Photomap 7. Kawailoa Beach (continued) Transect 11 +40 - Photographs by Air Survey Hawaii: April 1975 1967 2 +30 - +20 1962 +10 .2 1975 0 1949 1971 Absolute change is the change in the position of the vegetation line compared to the earliest or -10 base year. 20 From August 24, 1962 to April 22, 1967, the water line grew seaward Waimea Bay Beach Park 75 feet. During the next observation period, to January 1971, the beach receded about 60 feet. A possible cause for this change is dis- Waimea Beach is a closed littoral cell bounded by two rocky pro- cussed below. montories and deep offshore waters. Therefore, there is little supply of sand from adjacent sections of the coast. There also appears to be little The changes of the vegetation line at Waimea Beach show a consider- contribution from Waimea Stream as most of the sand is of marine ably different trend than the water line. From 1928 to 1949, the vegeta- origin (Moberly and Chamberlain, 1964). Finally, the offshore reef at tion line at mid-beach receded about 63 feet. Due to a lack of aerial pho- Waimea is limited in extent and confined to the narrow shelf at the tographic coverage, it is not known whether the loss occurred at a northeast side of the bay. For this reason, biological contributions of steady 3 feet per year or suddenly during a large storm event. Perhaps sand to the beach may be exceedingly slow. some of the erosion was caused by the 1946 tsunami, which did tremen-, dous damage to the Hawaiian Islands. With no active sand supply to balance the losses from sand mining and winter storms, Waimea Beach must be eroding. Evidence from an 1884 survey map and old air photos support this conclusion. The 1884 survey map of Waimea Bay reveals that the water line was Table 8 - Waimea Bay Beach Park. Changes in the Vege- once seaward of Table Rock (Photomap 8). The 1928 aerial photograph tation Line in Feet. also shows this rock surrounded by sand. Today, Table Rock is used as a diving platform and a race marker for swimmers. It is apparent that Waimea Beach has receded considerably. Transect Number Table 8 shows the historic changes in the position of the vegetation Observation Period 1 2 3 Average line for the three transects established at Waimea. Because of the exten- - sive alterations inland, no single transect records the beach change 1928 - May 08, 1949 -63 -63 over the entire 47-year period. In order to maintain continuity, the average of the measured changes for each observation interval has May 08, 1949 - Aug 24,1962 -28 -28 been computed. This figure appears in the right-hand column of Table 8. A similar calculation was performed for the data on the water line. Aug 24, 1962 - Apr 22, 1967 0 -6 -3 On Figure 3, the historic position of the vegetation line and water Apr 22, 1967 - Jan 23, 1971 -65 -46 -56 line is drawn against time. Over a 47-year period, the net loss in the water line was 194 feet. The major erosion occurred during the 1928 to Jan 23, 1971 - Apr 11, 1975 +11 -5 +3 1962 period when the beach receded 215 feet. It is not known how much of this change is seasonal as opposed to long-term. The 1962 Net Change - Vegetation Line -147 photograph, however, was taken at the end of the summer when the Range - Vegetation Line 150 beach should. have been in a high accretion state.'Therefore, the 215 Net Change - Water Line -194 feet of erosion may be an underestimate of the real long-term change. Range - Water Line 215 The water line retreat during this interval was partly caused by the sand * No data mining operation at Waimea, although the full impact of the industry Net change is the total change in the position of a beach index line between the on the beach is unknown. earliest and most recent observation year Range Is the difference between the observed extremes in the position of a beach index line. 21 Z Z Table R T X - -ON 3 LV, -- ---- A 4- - ICU Represents pooled data from three transects +20 - St @ [email protected] 750 0-- 1928 W, MI -20 - -40 - -60 1949 Photomap 8. Waimea Bay Beach Park -80 - 1962 Photographs by Air Survey Hawaii: April 1975 -106 1967 -120 -140 1975 1971 -160 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 22 From 1949 to 1967, the vegetation line receded at a Tate of about 1-2 feet per year. This loss is concurrent with the sand mining operation at Waimea. -50 - The highest rates of erosion for both the water line and vegetation 5 ft./yr. line occurred during the 1967 to 1971 period (Figure 3). The rates of re- treat were about 14 to 15 feet per year when averaged over a four-year -100 - period. This loss was not steady, how ever, but occurred during the large storm of December 1-4, 1969. During this storm, tremendous waves filled Waimea Bay with turbulent water. Ground photographs show storm waves running up onto the beach and cutting a scarp in the -150 91t./yr. 15 ft./yr. vegetation. Inundation was more than 750 feet inland and several sec- tions of the highway and parking lot were covered with rocks and sand (State of Hawaii, DLNR, 1970). ft. yr. E -200 It appears that sand put into suspension by storm waves was carried outside the breaker zone by rip currents and deposited at depths where 2 ft./yr. ...... summer waves cannot move sediment shoreward. Thus, the sand was _250 I ft,/ylr. permanently removed from the beach system, sand mining 14 ft./yr. If the vegetation line records the real long-term trend, then the data ? -a- 190 1965 show that Waimea has eroded continuously. Although the sand mining -300 L operation was undoubtedly part of the cause, the measurements indi- -A cate that Waimea Beach can be permanently damaged by periodic 1930 1940 1950 1960 1970 1980 storm events. Figure 3. Waimea Beach Erosion. The changes in the water line and Since the water line has a large seasonal change superimposed on the vegetation line represent the average of three transects established at long-term trend, it is difficult to determine the full impact of the sand mining operation on Waimea Beach. In this case, the seasonal change is the beach. noise in the data and complicates the interpretation on changes in the water line. Over nearly half a century, Waimea Beach, which acts as a buffer zone to protect the vegetation and inland structures from wave attack, has been reduced in size. Another storm, such as the one that occurred in December 1969, could damage the facilities at the beach park. If this occurs, the state may be inclined to save the park by structural means or sand replenishment. Either of these measures would be a costly and perhaps temporary solution, 23 grow seaward. This trend was offset during the 1967 to 1971 period by Pupukea Beach losses of up to 21 feet caused by the storm of December 1-4, 1969 (Pho- tomap 9, Table 9). The small 300-foot-long pocket beach east of Waimea had a net change of + 12 feet between 1949 and 1975. Over the same period, the The severe damage at Sunset caused by the 1969 storm is explained vegetation line receded 25 feet. The major loss occurred during the in a post-flood report (State of Hawaii, DLNR, 1970). One of the worst- 1967 to 1971 interval when the vegetation line receded 42 feet. This stricken areas was at the west end of Sunset Beach, in front of Ke Iki change is attributed to the December 1969 storm. Road. An examination of the 1967 and 1971 photographs shows that at least two houses were swept off their foundations by the large waves Sunset Beach (Plate 2). In all, 14 houses were demolished along this stretch. Sunset Beach is characterized by large seasonal changes in the water Retreat of the vegetation line was recorded for transect 8 during the line and relatively small long-term changes in the vegetation line. Over 1971 to 1975 observation period. This change appears localized. All a 30-year period, there has been a slight tendency for the vegetation to transects, except for 8, show little net change or small gains in the vege- tation line over a 30-year period. Table 9 - Sunset Beach. Changes in the Vegetation Line in Feet. Transect Number Observation Period 1 2 3 4 5 6 7 8 9 10 11 May 08, 1949 - Aug 24, 1962 -4 +4 +12 +15 -3 +5 +2 -5 +6 -2 Aug 24, 1962 - Apr 22, 1967 0 +13 +12 -1 +5 -2 +7 0 +23 +4 +9 Apr 22, 1967 - Jan 23, 1971 -2 -18 -11 + 1 -15 -2 -14 -10 -21 +7 -11 Jan 23, 1971 - Apr 11, 1975 +4 -1 -4 -4 +5 +9 -3 -10 +7 +4 +12 Apr 11, 1975 - Apr 03, 1979 -6 -5 -2 +5 +3 + I + 1 -1 -7 +2 Net Change - Vegetation Line -8 -7 +7 +16 -8 +13 -7 -19 +3 +14 +10 Range - Vegetation Line 8 24 24 16 15 13 17 20 23 21 14 Net Change - Water Line -22 -15 [email protected] -48 -99 +2 -17 -16 +59 -26 -6 Range - Water Line 140 64 92 158 199 133 118 53 77 33 33 *No data Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 24 Sunset Vt, 7Z A @Zt7 -N i 0 111 Transect 2 Transect 5 Transect 9 Photomap 9. Sunset Beach +20 - Photographs by Air Survey Hawaii: Apri11975 1967 1967 +10 - 1967 1975 00 1962 -Z, 1949 1,-' 1979 0 1949 1949 Oqz-, 1971 1962 1971 1975 -10 1975 1971 1962 6 1979 M Absolute change is the change in the position of the vegetation line compared to the earliest or base year. -20 25 Plate 2. Sunset Beach (West End). Damage from the December 1-4, 4 1969 storm at west Sunset Beach. Note the recession of the vegetation and the houses missing on the 1971 photograph. 44, 1967 sk @@, WE S, ',@4 -z"T ItT., F1, ""S S 0,104SIAZ Z%tZ 1971 26 At .west Ka un Iala Beach, the vegetation line for transects I and 2 has Sunset Point to West Kawela.. ,.receded over: a 29-year period (Table 10). The stable reference point for transect I is located far fro.m,the"vegetation line so the accuracy may The beach from Sunset Point to West Kawela is about 2 miles long. be poor. Although'th'e 9tab16 reference point for transect 2 is in the Along this stretch of coast are found Ahe following beach sections: water, it. is closer. to the beach and probably has an accuracy of under Kaunala Beach, Waialee Beach Park, and Pahipahialua Beach (Pho- ten feet. Over the 1949 to 1978 interval, the vegetation line at transect tomap 10). 2 receded 35 feet. This erosion was recorded in three of the four obser- vation periods. The loss was especially high during the 1967 to 1971 in- terval and may, be attributed to erosion by the December 1-4, 1969 storm. Transect 2 Transect 4 Transect,8 Photomap 10. Sunset Point to West Kawela Photographs b .y Air Survey Hawaii: June 1975 +20 - 1963 1; +10 - - 196.7 2 1963 C 0 1949 - 1949 1949 1967 - 1975 1967 -10 1971 -20 - 1971 1975 -30 - 1971 1978 1975 -40 - Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 27 Table 10 - Sunset Point to -West Kawela. Changes, in the Vegeta- tion Line in Feet. Transect Number Observation Period -1 2 3 4 5 6 7 8 9 May 08, 1949 - Nov 0 1, 1963 -7 +62 +16 +3 0 +25 +3 -2 Nov 01, 1963 - Apr 22, 1967 -10 -71 -18 -3 +14 +7 0 -12 +13 Apr 22, 1967 - Jan 23, 1971 -3 -23 -16 -24 -13 +7 +3 -12 -15 Jan 23, 1971 - Jun 03, 1975 -3 +3 +9 +4 -4 -4 +9 -14 +2 Jun 03, 1975 - Jun 02, 1978 +3 -8 -10 * +5 -8 -2 Net Change - Vegetation Line -20 -35 +27 -7 +5 +2 +37 -35 -4 Range - Vegetation Line 23 35 62 27 17 14 37 38 15 Net Change - Water Line +11 +7 -1 -39 +11 +8 -27 -2 Range - Water Line 59 42 24 54 25 14 27 23 No data Change from 1949- 196 7 Net chdnge is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. At transect 3, the large changes in the vegetation line reflect the At Waialee Beach Park, the vegetation line at transect 8 receded 38 strong influence of a stream flowing 35 feet to the east. These changes feet over the 1963 to 1975 period. The erosion at this section has under- are not representative of adjacent beach sections. Over a 29-year mined an old bridge. period, there has been little net change in the position of the water line. Transect 9 was established at Pahipahialua Beach. Over a 29-year ,Tra,nsects 4 and 5 are located at east Kaunala Beach. Generally, the period there has been a small net change in the vegetation line and vegetation line for this stretch had an increasing trend except for the water line. Thirteen feet of sparse vegetation grew seaward from 1963 large losses during the 1967 to 1971 interval. Erosion of up to 24 feet to 1967 but was cut back during the next observation period. was probably caused by the December 1-4, 1969 storm. The stretch of beach covered by transects 6 and 7 has been stable or shows a slight increasing trend. 28 Kawela Bay Table 11 - Kawela Bay. Changes in the Vegetation Line All five transects at Kawela Beach show that the vegetation line was in Feet. either stable or grew seaward between 1949 and 1978. Over this period, the vegetation at the west end of the beach had no net change while at the east end there was accretion of 37 feet (Photomap 11, Table 11). Transect Number The changes in the vegetation at mid-beach fell between these extremes. Observation Period 1 2 3 4 5 The water line data for Kawela Bay show beach accretion of I @ to 27 feet over a 29-year period. Although these changes may be seasonal, May 08, 1949 -Nov 01, 1963 +6 +18 -2 +7 +31 the gradual growth of the beach during four of the five observation peri- Nov 01, 1963 - Apr 22, 1967 +9 +2 +4 -1 +3 ods suggests a long-term accretionary trend. Kawela Bay is a natural sediment sink. Sand produced on the exten- Apr 22, 1967 - Jan 23, 1971 -2 +7 +11 sive reef is washed ashore by wave action. Once on the beach, the sand Jan 23, 1971 - Jun 03, 1975 -111 -7 -8 +5 +21 is confined by the rocky promontories to either side of the bay. Some loss may occur through the small reef channels but not enough to cause Jun 03, 1975 - Jun 02, 1978 -4 +2 +17 -9 + I beach retreat. Net Change - Vegetation Line 0 +13 +18 +13 +37 Even though the beach at Kawela Bay has a history of accretion Range - Vegetation Line 15 20 20 22 37 storm and tsunami events have inflicted severe damage to the residen) Net Change - Water Line +18 +26 +19 +27 +19 tial areas. During the 1946 tsunami, one house at Kawela was lifted off Range - Water Line 25 26 26 29 25 its foundation and carried across the road into the sugar field (Shepard et al., 1950). On December 1-4, 1969 large storm waves demolished *N6 da ta two homes and damaged at least ten others (State of Hawaii, DLNR, 1 Change from 1967-1975 1970). The property damage inflicted at Kawela by these separate Net change is the total change in the position of a beach Index line between the events demonstrates the potential danger in developing the north earliest and most recent observation year shore. Range is the difference between the observed extremes in the position of a beach index line. 29 2 N, 4 [email protected] [email protected] 500 7W 1000 Fet Photomap 11. Kawela Bay Photographs by Air Survey Hawaii: June 1975 30 Turtle Bay Table 12 - Turtle Bay. Changes in the Vegetation Line in The shoreline at Turtle Bay has two beaches that are separated by a Feet. 400-foot stretch of rock and raised reef. To the west of the rock lies a 1,000-foot-long beach and residential area (Photomap 12). Over a 29-year period the vegetation for this beach grew seaward. At transects Transect Number I and 2, the net gains were 19 and 6 feet, respectively (Table 12). During the same period, the water line for both transects receded 15 Observation Period 1 2 3 4 5 feet. This change may be seasonal. Although the vegetation line for this beach section grew from 1949 May 08, 1949 -Nov 0 1, 1963 +7 -3 to 1978, there is an indication that erosion had occurred previously. 0 1n Nov 01, 1963 - Apr 22, 1967 +7 +11 the 1949 photograph, several houses are almost at the vegetations edge. It is unlikely that these structures were built so close to the beach. Apr 22, 1967 - Jan 23, 1971 +8 + I To the east of the beachrock, lies a concave beach fronting the Hyatt Jan 23, 1971 - Jun 03, 1975 -3 +2 Kuilima Golf Course. Because of the extensive modifications inland, the data for this beach are not continuous. Jun 03, 1975 - Jun 02, 1978 0 -5 -11 -5 -12 Between 1949 and 1967, the vegetation line for the beach was stable Net Change - Vegetation Line +19 +6 -11 -5 -12 or grew slightly. In 1971, the construction of the golf course was in Range - Vegetation Line 22 14 11 5 12 progress. From 1975 to 1978, erosion of the vegetation line of I I to 12 Net Change - Water Line -15 -15 +4 -4 -18 feet occurred. At the east end of this beach the water line receded 18 Range - Water Line 22 16 4 4 18 feet. Some of the condominiums at east Turtle Bay are about 35 feet from the vegetation line. Any erosion along this stretch would make No data these structures more susceptible to wave inundation. Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a As the data from the aerial photographs for this portion of the beach beach index line. are scattered, it is not possible to predict future trends. It appears, how- ever, that the position of the vegetation line was stable for most of the 29 years covered by the aerial photographs. 31 0 250 500 750 1000 feet as 'mom M, 'W A [email protected] i1% Photomap 12. Turtle Bay Photographs by Air Survey Hawaii: june1975 32 Kaihalulu Beach Table 13 - Kaihalulu Beach. Changes in the Vegetation Kaihululu Beach is situated between Kalaeokamanu Point and Line in Feet. Kahuku Point (Photomap 13). Over a 29-year period, the vegetation line for this beach had a small net change. Nevertheless, the vegetation line at transect I receded 18 feet during the 1967 to 1975 period (Table Transect Number 13). This loss was probably caused by the December 1-4, 1969 storm. The data from the water line indicate that this beach has diminished Observation Period 1 2 3 in size. In 1949, beachrock extended from Kahuku Point to the west end of Kahuku Airfield. The 2,700-foot stretch to the west was primari- May 08, 1949 - Nov 0 1, 1963 +4 0 +6 ly sandy beach. By 1963, the beach at transects 1 and 2 receded 57 and Nov 01, 1963 - Apr 22, 1967 +7 -4 +7 69 feet. This loss exposed 2,400 feet of beachrock along the shore. As of June 1978, only a 300-foot-wide beach was in direct contact with the Apr 22, 1967 - Feb 06, 1971 -5 sea. Since 1963 west Kaihalulu Beach has had small fluctuations in its Feb 06, 1971 - Jun 03, 1975 -181 0 width. From a qualitative analysis of the aerial photographs, this beach Jun 03, 1975 - Jun 02, 1978 +5 0 has grown slightly from 1963 to 1978. Net Change - Vegetation Line -2 -4 +8 The middle portion of Kaihalulu Beach near west Kahuku Air Field Range - Vegetation Line 18 4 13 was inundated by the 1946 tsunami. On the 1949 aerial photograph, it Net Change - Water Line -54 -77 is seen that sand and debris were scattered up to 900 feet inland along Range - Water Line 57 77 several sections of the Kahuku runway. These deposits do not appear to be windblown for the same reasons as discussed in the next section for No data Hanakailio Beach. ; Change from 196 7 to 19 75 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the -difference between the observed extremes in the position of a beach index line. 33 Kahuku 00'int v" Mir Beach Cf" Feef Photomap 13. Kaihalulu Beach and Hanakailio Beach Photographs by Air Survey Hawaii: June 1975 34 It may be argued that the sand deposits located on the airfield in 1949 Hanakailio Beach are windblown. This appears unlikely for the following reasons: Hanakailio Beach is bounded by Kahuku Point on the west and Kalaeuila Rock on the east (Photomap 13). This beach is fronted by a (1) The sand deposits do not have a shape characteristic of nearly continuous stretch of beachrock that protects the vegetation dunes. from normal winter waves. Occasionally, the protective barrier is over- come by waves of unusual height and force..This occurred during the (2) The long axis of the sand body does not have a pre- 1946 tsunami, when large waves drove inland across the beachrock and ferred orientation. This would be expected of dunes dunes. Inundation onto the Kahuku airstrip was more than 1,200 feet formed by strong prevailing northeast trade winds. In- inland (Plate 3). stead, the axis is approximately perpendicular to the shoreline. This would occur as the tsunami wave re- fracts to hit the shoreline head on. (3) The sand deposits are seen only on the 1949 aerial photograph but not on photographs before or after. If the sand bodies are wind derived, they should be form- ing continuously. On the 1928 photograph, some wind deposits with the characteristic shape and orientation are evident. These deposits are located south of Kalaeuila Rock. g,e (4) Stereoscopic examination of the 1949 photographs show that debris and rubble are concentrated where 'ZN the wave crossed the vegetation. (5) On a field check du4ing the end of summer 1980, several blocks of beachrock were located on and near the airfield. These rocks could not be moved by the wind. The tsunami inundation at Kahuku Airfield was aided by the smooth surface of the runway. Waves lost little energy in crossing this feature. As a result, structures more than 1,200 feet inland were threatened by 1949 runup. For more information on the damage caused by the 1946 tsu- I nami, the reader is referred to Shepard et al., 1950. Plate 3. Kahuku Airfield. Sand washed ashore by the 1946 tsunami is shown on the 1949 photograph of Kahuku Airfield. 35 14 SECTION 11 - WINDWARD COAST 15 16 The windward coast extends from Kahuku on the north to Makapuu Point on the south (Figure 4). Generally, beaches on this shore are 17 dynamic features that change under trade wind conditions and refracted _2 OV 18 North Pacific swell. The major findings for this section are summarized 19 below. 20 The most unstable beach on the windward coast is at Kualoa Point where chronic erosion of 350 to 400 feet occurred during the 1928 to 21 1980 period. 22 23 The accretion-erosion cycle at Kailua Beach Park coincides in timing 24 and magnitude with the one for south Lanikai Beach. This suggests that similar nearshore processes are in operation at both beach systems. Some important differences exist that are discussed for the individual 25 beaches. At Waimanato Beach, the north end (Bellows Air Field Beach) and the south end have a history of erosion. Some sections at middle Wai- manalo grew while others receded. No clear pattern is seen. Chronic erosion areas on the windward coast include north Kahuku Golf Course Beach, middle and south Laniloa Beach, Hauula Beach Park, Kualoa Beach Park and Bellows Air Field Beach. Erosion prob- 'V! lems exist at Kalanai Point, Swanzy Beach Park, Kaaawa Beach Park, t"11,11>1 WIZOW-g.111111", Kailua Beach, Lanikai Beach, south Waimanalo Beach and many sec- 26 tions of the coast along the Karnehameha Highway. MR- OM Accretion was found at Kahana Bay, Punaluu Beach Park and Kalua 27 nui Beach. 28 0, M M, 29 ROE 5 M M, 1 I'= I'M, I Q 30 M=M Figure 4. Photomap Arrangements - Windward Coast. 37 Kahuku Golf Course Beach Table 14 - Kahuku Golf C .ourse Beach. Changes in the The adverse effects of a sand mining operation on Kahuku Golf Vegetation Line in Feet. Course Beach are shown on the aerial photographs. During the 1949 to 1967 period, water line retreat of 114 feet exposed beachrock along the shoreline. Over the same interval, the vegetation line at transect 4 grew Transect Number sea'ward 283 feet (Photomap 14, Table 14). This change reflects the recovery of the vegetation line from its stripped position in 1949. On Observation Period 1 2 3 4 some sections of Kahuku, where the beachrock is wide and offers ade- quate protection, the vegetation has grown within a few feet of the ex- posed rock. Sep 28, 1949 - Apr 23, 1967 -43 +49 +75 +283 Since termination of the sand mining operation, most sections of Apr 23, 1967 - May 26, 19712 -3 -5 +18 +7 Kahuku Golf Course Beach have been stable or grew. One exception is May 26, 1972 - Jun 03, 1975 -7 +9 +15 -9 the northwest end of the beach where erosion of 53 feet was recorded during the 1949 to 1975 period. On the aerial photographs, this change Net Change - Vegetation Line -53 +53 +108 +281 is shown by undermining of. the cemetery fence. This section of the Range - Vegetation Line 53 53 108 290 beach has a 15-foot-high erosional, scarp cut into the vegetated dune Net Change - Water line -34 -88 -65 -58 field. Range - Water line 68 104 114 58 Net change is the total change in the position of a beach index line between the earliest and most recent observation year I Range is the difference between the observed extremes in the position of a beach index line. 38 et -2 IV 4 AU, Transectl +10 0 1949 Photomap 14. Kahuku Golf Course Beach -10 Photographs by Air Survey Hawaii: May 1972 -20- -30- -40- 1967 - 1972 -50- - 1975 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. -60 39 Malaekahana Beach Table 15 - Malaekahana Beach. Changes in the Vegeta- Malaekahana Beach is situated between Makahoa Point and Kalanai tion Line in Feet. Point. The most unstable section ofthis beach is at the south end, near Kalanai Point (Photomap 15). Over a 26-year period, the vegetation line and water line receded 26 feet and 64 feet, respectively (Table 15). Transect Number The major loss occurred during the 1967 to 1975 period when the vege- tation line retreated at a rate of about 5 feet per year. Observation Period 1 2 3 4 5 6 The wave pattern at Kalanai Point is complicated by refraction around Mokuauia (Goat) Island. Wave sets hit the point from the Sep 28, 1949 - Dec 29, 1959 +11 +10 +11 +11 +29 +3 north, south and east. The erosion at kalanai is caused by the con- Dec 29, 1959 - May 12, 1964 +7 +15 +4 -7' 0 +5 centrated wave energy at the point. The lost sand may be transported north, toward Makahoa Point, or to the south near Laie Point. These May 12, 1964 - Apr 23, 1967 -13 -18 -17 + 1 -11 +9 two beach sections have a 26-year history of accretion (see Laie Beach). Most of Malaekahana Beach has been stable or grew when averaged Apr 23, 1967 - May 26, 1972 +12 -2 +8 * +11 -20 over a 26-year period. Nevertheless, short erosion events can occur. May 26, 1972 - Apr 13, 1975 +21 +11 + 1 * -12 -23 During the 1964 to 1967 period, the vegetation line receded for much - of the beach. It has been estimated, though, that about half of the Net Change - Vegetation Line +19 +16 +7 +5 +17 -26 recorded loss for transects I to 3 is due to relief displacement on the Range - Vegetation Line 19 25 17 11 29 43 1967 aerial photographs. Net Change - Water Line +40 +36 -11 -3 -6 -64 Range - Water Line 94 99 72 24 77 96 *NoData 1 The 19 75 photographs were taken on June 3 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range Is the difference between the observed extremes in the position of a beach index line. 40 TP N- 5 VN '0 2 j Jet K Ka a Transectl Transect 6 +30 - 1975 1964 +20 - 1972 1967 Photomap 15. Malaekahana Beach +10 1959 1964 1967 Photographs by Air Survey Hawaii: May 1972 1959 0 - 1949 1949 -10 1972 -20 1975 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. -30 41 Laie Beach Table 16 - Laie Beach. Changes in the Vegetation Line in Laie Beach is bounded by Kalanai Point to the north and Laie Point Feet. to the south. The erosion at Kalanai Point was discussed previously in the section for Malaekahana Beach. The data for this portion of the beach appear as transect I on Photomap 16 and Table 16. Transect Number Except for the erosion at Kalanai Point, most sections of Laie Beach Observation Period 1 2 3 4 5 6 7 have been stable or grew when data were averaged over a 30-year period. The maximum accretion occurred at the south end of the beach, where the vegetation line advanced seaward 28 feet over the Sep 28, 1949 - Dec 29, 1959 +3 -13 +10 -7 -2 -12 +8 1949 to 1979 period. Although the net changes of the vegetation line in- dicate beach stability or growth, minor erosion events were recorded Dec 29, 1959 - May .12, 1964 +5 0 +2 -1 +8 +7 +10 for transects 2 and 6. May 12, 1964 - Apr 23, 1967 +9 +20 0 -3 -2 -12 +4 The changes in the vegetation line for Laie show a strong relationship Apr 23, 1967 - May 26, 1972 -20 -1 +9 +9 +10 +12 -2 with adjacent beach sections. Over a period of observation between 26 and 30 years, the vegetation line at the northwest end of the beach May 26, 1972 - Apr 13, 1975 -23 -8 -9 -2 -3 +8 +9 eroded 26 feet while at the opposite end, it grew seaward 28 feet. The net changes in the vegetation line for the middle of Laie fell between Apr 13, 1975 - Apr 12, 1979 -1 +5 +3 -1 these extremes. The range in the position of the vegetation line is great- est for the two ends and smallest in the middle. The overall pattern sug- Net Change - Vegetation Line -26 -2 +12 +16 +6 +28 gests that the long'-term changes at Laie are caused by sand transport Range - Vegetation Line 43 20 21 11 18 23 29 along the shoreline from northwest to southeast. This hypothesis can Net Change - Water Line -64 +46 +20 +76 +34 +50 +64 be tested by conducting sand tracer experiments at Laie. Range - Water Line 96 46 32 76 45 50 64 That sand accumulates north of Laie Point is to be expected. This *No Data Net change is the total change in the position of a beach index line between the protrusion, which consists of eolianite, protects sections of the beach earliest and most recent observation year from southerly waves but allows waves from the no.rth to transport Range is the difference between the observed extremes in the position of a sand. beach index line. Laie Beach goes through an annual variation in width of about 30 feet (Moberly and Chamberlain, 1964). These annual changes are primarily due to onshore-offshore exchange between the beach and reef reser- voirs. It appears that both onshore-offshore and alongshore transport of sand are processes occurring at the beach. 42 wow", [email protected],anai Point, AW V @J Na, 7, 11 -WWI p, '64 if 71 4. /f Transect 1 Photomap 16. Laie Beach +20 1967 +10 1964 Photographs by Air Survey Hawaii: May 1972 1959 0 1949 -10 1972 -20 1975 -30 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 43 Laie Point to Pali Kilo Ia Table 17 - Laie Point to Pali Kilo Ia. Changes in the The 1.25-mile stretch of beach between Laie Point and Pali Kilo Ia Vegetation Line in Feet. curves around Kehukuuna Point (Photomap 17). To the north of the point is the 1-mile-long Laniloa Beach. South of the point is Pounders Beach. Transect Number The vegetation line at the north end of Laniloa Beach (transects Observation Period 1 2 3 4 5 6 7 8 1-3), has had small changes of erosion and accretion (Table 17). No clear pattern is seen from the data. Over a 26-year period, this section of beach has been stable or grew. Sep 28, 1949 - Jul 23, 1959 -8 +8 +2 -35 -44 -22 -4 +5 The middle and south sections of Laniloa Beach (transects 4-7) have Jul 23, 1959 - May 12, 1964 +11 +1 -9 +4 -6 -51 a history of severe 6rosion. The worst problem is located on a 500-foot May 12, 1964 - Apr 23, 1967 -8 + 1 -1 +2. -2 * -282 -112 section of the beach near transect 5. An examination of the 1949 aerial photograph shows fallen trees on the beach, an indication that erosion Apr 23, 1967 - May 26, 1972 +3 -3 +11 -2 -14 * +8 -16 had occurred previously. Sinc61949, the beach at transect 5 has receded for all five observation periods. Between 1949 and 1975, the vegetation May 26, 1972 - Apr 13, 1975 + 1 +8 -6 -3 -4 -6 +15 line eroded 70 feet (Plate 4). 1 Net Change - Vegetation Line -1 +15 -34 -70 -27 -30 -7 During a field check in August 1980, the northeast trade waves Range - Vegetation Line 11 15 11 35 70 27 32 27 broke against the base of a 15-foot-high escarpment in the vegetated Net Change - Water Line +12 +22 -8 -23 -54 -173 +20 -20 dune field. Forty-foot trees were being undermined and several were Range - Water Line 20 36 23 38 60 273 44 68 on the beach. Stone walls and piles of boulders, which were built to pro- No Da ta tect houses, completely blocked access along the shoreline. Toboulder waH 2 Change from 1959- 196 7 Between 1972 and 1975, one house was removed because of erosion. 3From 1949-1975 On the 1975 photographs, several houses are within 30 feet of the vege- Net change is the total change in the position of a beach index line between the tation line. Along this 500-foot stretch of Laniloa Beach, erosion of earliest and most recent observation year about 3 feet per year has occurred. If the trend continues as it has in the Range Is the difference between the observed extremes in the position of a past, these houses would be undermined in a decade. beach index line. It is apparent that the 40-foot-setback line for this beach is of little value. Under the Coastal Zone Management Act of 1977, the county has the power to regulate new development within the 100-yard zone of the Special Management Area. To the south of Kehukuuna Point is the 1,500-foot-long Pounders Beach. Over a 26-year period, this beach has had a net change in the po- sition of the vegetation line of -7 feet. This beach was not necessarily stable, as the range in the position of the vegetation line was 27 feet. 44 Transect5 Transect7 Transect8 [email protected] A tt;[email protected] +10 - 1959 '7 0 1949 1949 1949 1959 1967 -to - 1975 -20 1972 1972 -30 - 1975 1967 ON, 1959 2 3 "N 19fi4 X 1967 -60 1972 -70 1975 .4, A N IF 7i", q Photomap17. Laie Point to Pali Kilo la Photographs by Air Survey Hawaii: May1972 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 45 A erosion at Plate 4. Laniloa Beach. Between 1949 and 1975, chronic Laniloa Beach resulted in a 70-foot retreat of the vegetation line. Note the trees on the beach on the 1949 photograph. Compare the position of the vegetation line with the highway on the 1949 and 1975 photographs. @A Kokololio Beach The stretch of shoreline between Pali Kito la and Kaipapau Point is 'av about 4,000 feet long (Photomap 18). Over a 26-year period, the north end of this beach grew slightly while the south end, at transect 3, was relatively stable (Table 18). Table 18 - Kokololio Beach. Changes in the Vegetation Line in Feet. 1949 Transect Number 41 lo Ow Observation Period 1 2 3 -P Sep 28, 1949 - Jul 23, 1959 +10 -6 -5 r Fl- Jul 23, 1959 - Apr 23, 1967 +6 +7 +4 Apr 23, 1967 - May 26, 1972 -1 +12 0 May 26, 1972 - Apr 13, 1975 + 1 -2 -7 Net Change - Vegetation Line +16 +11 -8 Range - Vegetation Line 16 19 8 Net Change - Water Line +10 +21 +2 Range - Water Line 47 35 62 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a 19751 beach index line. 46 j JJ [email protected] [email protected] & Photomap 18. Kokololio Beach Photographs by Air Survey Hawaii: May 1972 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 47 Hauula Beach to Makao Beach Table 19 - Hauula Beach to Makao Beach. Changes in Over a 30-year period, the residential beach at north Hauula (transect the Vegetation Line in Feet. 1) has been stable (Photomap 19). The range in the position of the vegetation line was about 10 feet and the net change was insignificant (Table 19). Transect Number The northern section of Hauula Beach Park has had a history of Observation Period 1 2 3 4 5 6 7 8 minor erosion. From 1949 to 1979, the vegetation line receded inland 10 feet. This trend appears to be continuous. For the middle section of Hauula Beach Park, erosion has been more severe. Retreat of the vege- Sep 28, 1949 - Dec 29, 1959 -8 -4 -16 +10 +18 +5 -6 tation line was recorded for all six observation periods. The major Dec 29, 1959 - Nov 14, 1964 +6 + 1 -3 -2 -6 -15 -2 +3 losses occurred during the 1949 to 1959 and 1975 to 1979 intervals. Over a 30-year period, the vegetation line has receded about 39 feet. A Nov 14, 1964 - Apr 23, 1967 -6 -1 -4 -3 +81 -5 0 -21 continuation of the trend would undermine more of the ironwood trees and threaten the pavilion that was constructed in 1947. For further Apr 23, 1967 - May 26, 1972 0 -2 -4 +11 +5 -1 details on the erosion at this park, the reader is referred to the National Shoreline Study (U.S. Army Engineers, 1971). The vegetation line at May 26, 1972 - Apr 13, 1975 -2 -3 -2 0 0 -7 the south section of the park (transect 4) has grown slightly over a Apr 13, 1975 - Apr 19, 1979 +9 -1 -10 -1 30-year period. Although the vegetation line at transects 5 and 6 has had a -small Net Change - Vegetation Line -1 -10 -39 +15 +2 +3 -5 -5 change in position, erosion problems exist because houses have been Range - Vegetation Line 10 10 39 16 8 20 10 6 Net Change - Water Line +17 +9 +3 +25 -82 -4 -43 -112 built close to the shore. Along much of the beach near transect 5, sea Range - Water Line 20 28 33 32 322 19 533 302 walls have been built to protect the property. At transect 6 the range in the position of the vegetation line over a 26-year period was 20 feet. No Data To seawall Along the highway at Makao Beach, the vegetation line for transect 3 2 From 1949_ 19 75 receded 10 feet during the 1959 to 1975 period. If this trend continues, 3 From 1949-1972 the construction of a stone wall would be required to protect the road. Net change is the total change in the position of a beach index line between the A boulder wall protects the highway in front of transect 8. earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 48 L 444 @M. W SMO A Transe ct 3 Transect 6 +20 - 1959 +10 - 1964 1972 0- 1949 1975 1949 Photomap 19. Hauula Beach to Makao Beach 1967 -10 - Photographs by Air Survey Hawaii: May 1972 1959 -20 - 1964 1967 -30 - 1972 1975 -40 - 1979 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. -50 49 Kalaipaloa Point to Waiono Stream The stretch of beach between Kalaipaloa Point and Waiono Stream is approximately 2. miles long. Both the residential sections and the high- way along this coast have been stabilized by seawalls and boulder piles. The residential section marked by transect I has had a history of ero- sion as indicated by the structures built along the shoreline. In 1967, seawalls and revetments spanned the entire 900-foot stretch of beach. Between 1967 and 1972, several of these structures had disappeared, perhaps because of damage from the winter storms of 1968 and 1969. The residential area at transect 2 is completely spanned by seawalls. At the south end of this stretch, a wall was constructed perpendicular to the shoreline to provide flood protection from Kaliuwaa Stream (Pho- tomap 20). This structure and the stream tend to trap sand transported from offshore or along the coast. Immediately to the south, at Kaluanui Beach, accretion in the vegetation line of approximately 75 feet has oc- curred over a 26-year period. A major residential area has been built on this accretion plain (Plate 5). 1949 The section of the shoreline covered by transects 3 to 5 has been rela-. tively stable over a 26-year observation period. The net changes in the vegetation line for the three transects were under 10 feet (Table 20). At transect 6, the vegetation line receded 26 feet over the 1949 to 4, @g" 1967 period. This erosion has threatened three houses. "MM y Transect 7 was established behind the Kamehameha Highway. B 1959 a stone wall was constructed to protect this roadway.' Over a 26-year period, the net change in the position of the vegeta- tion line for transect 8 was under 10 feet. The range in the position of the vegetation line was 19 feet. Plate 5. Kaluanui Beach. Accretion to the south of Kaliuwaa Stream. Note the houses built on the newly formed land. 1975 50 N, Vol -7 V, 2 -W 1A Rr @x V" "41 [email protected] 7 t aluanut V ir R IV M V Transect 6 Photomap 20. Kalaipaloa Point to Waiono Stream Z +to Photographs by Air Survey Hawaii: May1972 0 1949 -10 - 1959 1964 -20 - 1972 1967 -30 - Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 51 Table 20 - Kalaipaloa Point to Waiono Stream. Changes Punaluu Beach Park and Residential Area in the Vegetation Line in Feet. Prior to 1949, the north section of Punaluu Beach Park experienced erosion. Boulders were placed along the shoreline to protect the under- mined trees. Since then, the beach fronting the park and residential Transect Number area has grown considerably (Photomap 21). Observation Period 1 2 3 4 5 6 7 8 Over a 30-year period, the vegetation line at the beach park grew sea- ward about 59 feet (Table 21). A bathhouse was constructed on this newly formed land. Accretion at the park appeared continuous except Sep 28, 1949 - Dec 29, 1959 +31 +11 -8 +6 +2 -18 +51 0 for the 1964 to 1972 period when the vegetation line receded 16 feet. Dec 29, 1959 - Oct 14, 1964 * +5 -4 -5 -1 -5 This change is partly attributed to the large winter storms of 1968 and 1969 (U.S. Army Engineers, 197 1). Oct 14, 1964 - Apr 23, 1967 * +3 -8 -1 -7 * +19 At the residential section of Punaluu, field surveys indicate that the Apr 23, 1967 - May 26, 1972 * -10 +12 +4 +6 * -10 vegetation line advanced seaward 18 feet during the 1962-1972 period U. F. Campbell, unpub. data). From aerial photographic measure- May 26, 1972 - Apr 13, 1975 * +3 -4 -3 -2 ments, the vegetation line accreted 63 feet over a 30-year period (Plate 6). It appears that sand from the nearby reef is an important contributor Net Change - Vegetation Line +3 + 1 -7 +2 -3 -20 +2 to this beach. Range - Vegetation Line 3 1 10 12 6 26 19 Net Change - Water Line -202 +172 +42 -10 +8 -11 +172 +3 The portion of the shoreline marked by transect 3 appears relatively Range - Water Line 222 302 53 43 34 29 302 47 stable. Over a 26-year period the net change in the vegetation line was -8 feet and the range was 12 feet. *No Data I To stone or boulder wall Transect 4 was established along the north-trending section of the 2 From 1949- 19 75 Punaluu residential area, Nine groins and several seawalls were con- Net change is the total change in the position of a beach index line between the structed along this stretch. These structures may have temporarily earliest and most recent observation year Range is the difference between the observed extremes in the position of a stabilized the shoreline. Over a 26-year period, the beach within the beach index line. groin field has grown slightly. 52 t 7, 15 n, nt-, $,4 k", & ,it, 2 4 "PUniiuu'geach Park [email protected] ransec +70 - +60 1979 1975 Z +50 1972 C +40 1967 Photomap 21. Punaluu Beach Park and Residential Area +30 - 1959 1964 Photographs by Air Survey Hawaii: May 1972 +20 - +10 - 0 1949 -10 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 53 "T Table 21 Punaluu Beach Park and Residential Area. Changes in the Vegetation Line in Feet. "an W-W_" k N Iransect Number n V [email protected] V Observation Period 1 2 3 4 4111 bk. Oct 29, 1949 -Dec 29, 1959 +35 +29 -3 A'AL- Dec 29, 1959 - Oct 14, 1964 +3 0 +7 +151 U, Oct 14, t964 - Apr 23, 1967 -6 +6 -9 +6 Apr 23, 1967 - May 26, 1972 -10 +18 + 1 -7 t4l May 26, 1972 - Apr 13, 1975 +28 +3 -4 @6 & Apr 13, 1975 - Apr 17, 1979 +9 +7 1949 Net Change - Vegetation Line +59 +63 -9 +8 Range - Vegetation Line 59 63 12 21 Net Change - Water Line +18 +20 -47 +19 Range - Water Line 112 48 39 69 No Data 71 Change from 1949- 1964 UK Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 4A Plate 6. Punaluu. Over a 26-year period, the vegetation line for the N A beach at Punaluu grew seaward 56 feet. Compare the position of the vegetation line with the highway on the 1949 and 1975 photographs. 1975 54 Kahana Bay Beach Park Table 22 - Kahana Bay Beach Park. Changes in the Vege- The sedimentology of Kahana Bay has been described in a report by tation Line in Feet. Coulbourn (1971). According to this study, the barrier beach at Kahana receives sand from two main sources. Some terrigenous sedi- ment is supplied to the beach from Kahana Stream. Most of the sedi- Transect Number ment from the stream is finer than sand size and is eventually lost off- shore. The major.supply of beach sand is derived from the eastern reef Observation Period 1 2 3 4 flat near Huilua fishpond. On the aerial photographs, a sand bar is seen extending from the reef flat to the east central portion of the beach. 1928 - Oct 29, 1949 +16 +87 This sand plume may delineate the avenue of sand transport to the beach. Oct 29, 1949 - Oct 14, 1964 +7 +16 +13 +55 The field evidence for accretion at Kahana Beach is abundant. Two Oct 14, 1964 - Apr 23, 1967 +7 0 +2 -6 crescentic beach ridges marking former shoreline positions are located inland of the present-day beach (Coulbourn, 1971). Young ironwood Apr 23, 1967 - May 26, 1972 +7 +6 +7 +7 trees and sparse vegetation extend seaward, indicating recent accretion (J. F. Campbell, personal communication). Kahana Beach has a gentle May 26, 1972 - Jun 02, 1975 + 1 +29 -30 slope and a profile that is continuous in the absence of an erosional scarp. Net Change - Vegetation Line +21 +39 +51 +113 Range - Vegetation Line- 21 39 51 143 From aerial photographic measurements, the vegetation line at the Net Change - Water Line -4 +76 +54 +116 east section of the beach grew seaward 113 feet over a 47-year period Range - Water Line 38 76 69 134 (Photomap 22, Table 22). Over a similar period, accretion of the vege- * No Data tation line at the west end was 39 feet. Net change is the total change in the position of a beach index line between the earliest and most recent observation year Although Kahana Beach has a long-term history of accretion, there Range is the difference between the observed extremesin the position of a are periods when erosion occurs. In April 1963, a storm cut the beach beach index line. back 100 feet, but by mid-August of the same year, the beach grew back 50 feet (Moberly and Chamberlain, 1964). During the 1972 to 1975 period, the vegetation line receded 30 feet at the east end of Kahana Beach. 55 J,'[email protected] P11, WV 31- 5-, k, [email protected]`,`Wfijep M& @5 [email protected] V- 4 T- Y4 Transect4 @Z fZ= +150- h, 1972 A k 4 +140 1964 1967 +130 +120 - @,W 1975 +110 - +100 - +90 - 1949 +80 Ji, A +70 -5 +60 - +50 - +40 - Photomap 22. Kahana Bay Beach Park +30 - Photographs by Air Survey Hawaii: May1972 +20 - +10 - @3 0- 1928 Absolute change is the change in the position of the vegetation line compared to -10 - the earliest or base year. 56 Mahie Point to Swanzy Beach Park Table 23 - Mahie Point to Swanzy Beach Park. Changes The stretch between Mahie Point and Swanzy Beach Park is about in the Vegetation Line in Feet. 4,000 feet long. Seawalls protecting the highway and beach park from erosion are found along much of this coast. Transect Number Four transects were established for those sections of the beach that had vegetation fronting the seawalls (Photomap 23). It was hoped that Observation Period 1 2 3 4 the changes in the vegetation would provide clues on the timing and - extent of wave attack on this shore. Oct 29, 1949 -Apr 23, 1967 -9 -16 -181 For the stretch of beach along the highway there has been little net Apr 23,1967 - May 26, 1972 -22 -3 +6 change in the vegetation line and water line over a 26-year period (Table 23). From the historic data, there appears to be no immediate May 26, 1972 - Apr 13, 1975 +5 +12 +7 dangerto *the highway or to the seawall near the Crouching Lion Res- taurant. Nevertheless, a large storm or hurricane could cause structural Net Change - Vegetation Line +3 0 -3 -18 damage as many sections.of the road are within a few feet of the water. Range - Vegetation Line 5 12 16 18 Net Change - Water Line +3 -2 +15 -413 At Swanzy Beach Park, historic data indicate that the seawall is Range - Water Line 16 13 25 543 becoming increasingly vulnerable to wave attack and deterioration. The 1949 photograph shows this structure fronted by a continuous *No Data beach that varied in width from 23 to 70 feet. Over the next 26 years, 1 To seawall water-line retreat of up to 41 feet has exposed sections of the wall to 2 ange from 1949 to 19 72 wave attack. 3from 1949-1975 Net change is the totbl change in the position of a beach index line between the From 1949 to 1967, 18 feet of vegetation fronting the seawall was earliest and most recent observation year lost. During.the 1968 to 1969 period, winter storms damaged the beach Range is the difference between the observed extremes In the position of a ,and undermined the wall (U.S. Army Engineers, 1971). Problems such beach index line., as these will become more common if the small amount of sand that re- mains continues to disap6ear. At the present, boulders front the wall to provide additional protection from waves. 57 41, fW 77' AN 0, 7 ,V Ilk -Z 50 Transect 4 Photomap 23. Mahie Point to Swanzy Beach Park +10 - Photographs by Air Survey Hawaii: May1972 E & o -- 1949 C -10 .2 1967 -20 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 58 To the south of the residential area, boulders and a stone wall protect Kaaawa Residential Area to Kalaeokaoio Point the highway from wave attack. Measurements at transect 2 show a net loss in the vegetation line of 14 feet during the 1949 to 1967 period. The portion of the windward coast covered in this section is about 1.7 Over a 26-year period, the water line advanced seaward 24 feet. Under miles long and includes the Kaaawa residential area, Kaaawa Beach normal wave conditions, there appears to be little danger from erosion. Park, Kalaeoio Beach Park, Kanenelu Beach and several stretches of Nevertheless, a large storm or hurricane could undermine the seawall beach fronting the highway. The reader is referred to Photomap 24 for and damage the highway. the location of the transects. At Kaaawa Beach Park (transects 3 and 4), severe erosion has oc- The section of Kaaawa Beach at transect I has a history of change curred. Between 1949 and 1972, the vegetation line at transect 4 reced- similar to that of Swanzy Beach Park. On the 1949 photograph, a ed 34 feet. Over the same period, the vegetation to the side of the park narrow beach once fronted the residential area. By 1975, the beach was bathhouse was cut back 55 feet. Most of the erosion occurred prior to replaced by boulders, and 14 feet of vegetation was lost (Table 24). 1967. Part of the loss is attributed to the high winter waves of December fi [email protected] Fie _7 1000 feet t Transect I Transect 4 Photomap 24. Kaaawa Residential Area to Makahonu Point +10 - Photographs by Air Survey Hawaii: Apri11975 S u - 19.49 '1949 -10 - 972 1 ::[email protected] 1975 1975 -20 1967 1967 1972 -40 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 59 Transects 6 to 8 were established for the stretch of beach fronting the Table 24 Kaaawa Residential Area to Kalaeokaoio highway. The c 'hanges at Makahonu ,Point (transect 6) were relatively small, but immediately northwest of the point, a section of beach has Point. Changes in the Vegetation Line in Feet., disappeared and the highway is fronted by boulders. South of Maka- honu Point (transects 7-8), erosion was recorded over the 1949 to 1972 period. The maximum losses were 15 feet from the vegetation line and Transect Number 36 feet from the water line. This stretch of highway is susceptible to erosion. Observation Period 1 2 3 4 5 6 7 8 Oct 29, 1949 - Apr 23, 1967 -17 -141 -12 -26 +8 Kualoa Beach Apr 23,1967 - May 26, 1972 +4 +3 -8 -5 +152 -132 -152 Kualoa Beach is a cuspate foreland, or simply, a cusp-shaped sand body projecting from the coastline. In order for this feature to have May 26, 1972 - Apr 13, 1975 -1 -3 +18 -4 -7 formed, accretion must have predominated in the past. Now, however, analysis- of the most recent erosion indicates that this entire plain may Net Change - Vegetation Line -14 -14 -12 -16 - 1 +8 -13 -15 disappear (J. C. Kraft, Sea Grant Report, in prep.). Range - Vegetation Line 17 14 12 34 9 15 13 15 Net Change - Water Line -18 +243 -74 -75 -46 -4 -36 -32 A detailed report on erosion has been conducted -for Kualoa Beach Range - Water Line 35 273 74 81 46 21 36 32 Park (U.S. Army Engineers, 1977). The major findings of that study show erosion between 1949 and 1975 of 215 feet at the point, and 120 *No Data to 150 feet along the eastern section of the beach. At the south shore, 1 To Seawall there has been a long history of accretion. 2 Change from 1949- 19 72 3 Change from 1949-19 75 The U.S. Army Engineers study contains an 1882 survey map of Net change is the total change in the position of a beach in .dex line between the Kualoa Beach, showing Apua Fishpond at the water's edge, and Kualoa earliest and most recent observation year Range is the difference between the observed extremes in the position of a Point with a blunt shape. Sometime between 1882 and 1928 accretion beach index line. had built the point so that it protruded seaward. Since then, erosion has returned the point to a blunted shape. 1968 and January 1969, which undercut coconut trees and the park Although the history of erosion at Kualoa Beach has been document- bathhouse (U.S. Army Engineers, 1971). From 1972 to 1975, the vege- ed, afurther investigation was made using a slightly different approach. tation line grew seaward about 18 feet. Part of this change may be at- By this study, it was hoped some additional conclusions could be drawn tributed to a sand replenishment project (U.S. Army Engineers, 1974). that would help in the management of the beach. Some of the findings in the study are summarized below: Over a 26-year period, the water line at Kaaawa Beach Park receded 75 feet. This figure may be an overestimate as problems were encoun- (1) To the north of the beach park, the stretch of shoreline tered in locating the water line on the 1949 photograph. along the highway has been severely altered by a series of groins (Photomap 25). Immediately upcurrent of Measurements on the'vegetation line for Kalaeoio Beach Park (tran- each groin, the beach has been stable or grew. The net sect 5), indicate that the beach has been stable over a long-term. Al- changes in the vegetation line for transects I to 4 are though there was a net loss of 46 feet to the beach, the significance of less than 10 feet (Table 25). Downcurrent of each this change is unknown, since difficulty was encountered in locating groin, the beach has been starved (Plate 7). Along the water line. - several sections of the coast, only a seawall protects 60 0 Oldisland' aman's Hat) A -3, Kualoa 4 Transect 5 Transect 6 Transect 8 Transect 9 6-- +300 +250 - 1971 1975 +200 - 1967 1978 +150 - 1949 +100 - '6 +50 - 0 1000 Feet N" 0 1949 1949 1928 1928 C -50 1949 -2 1967 1967 Photomap 25. Kualoa Beach -100 - 1971 1971 1975 1975 Photographs by Air Survey Hawaii: April 1975 -150 - 1978 1978 -200 1967 -250 1971 1975 -300 1978 -350 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 61 . . ..... . .. 1928 1928 7., L.._ AL, 1978 1978 Plate 7. Kualoa. Between 1928 and 1978, erosion to the south (right) Plate 8. Kualoa Beach Park. A continuation of the erosion trend at of the groin has stripped the protective beach and vegetation fronting the north end of Kualoa Beach Park would undermine the Kamehame- the highway. ha Highway. Compare the position of the vegetation line with the high- way on the 1928 and 1978 photographs. 62 Table 25 - Kualoa Beach. Changes in the Vegetation Line in Feet. Transect Number Observation Period 1 2 3 4 5 6 7 8 9 10 11 1928 - Nov 29, 1949 .56 -53 +138 -159 +72 Nov 29, 1949 - Apr 22, 1967 0 -1 -81 -91 -134 -165 +38 +64 +85 -Apr 22, 1967 - Dec 16, 1971 -6 -14 -7 -19 -21 ; +82 -4 +31 Dec 16, 1971 - Apr 13, 1975 +81 01 +11 +4 -22 -15 -12 -30 -22+153 -3 Apr 13, 1975 - Oct 09, 1978 -1 +9 -1 0 -1 -9 -51 -58 -66. -7 -8 Net Change - Vegetation Line +7 +9 0 -3 -118 -122 -272 -327+170 +47+177 Range - Vegetation Line 8 9 1 7 118 122 272 327 258 213 188 Net Change - Water Line +6 -10 -20 -14 -134 -147 -M -367+122 +14+159 Range - Water Line 17 12 20 25 134 147 312 367 230 222 175 *No Data I Change from 1967-1975 Net change is the total change in the position of a beach index line between the earliest and most recent observationyea,r Range is the difference between the observed extremes in the position of a beach index line. the highway from wave attack. During a large storm or neers, 1977). Before these structures were installed, hurricane, extensive damage to the residential areas the shoreline was continuous. Sand flowed easily from and highway could occur. north to south building the point. With the installation of the groins came three major changes. First, accre- Unless remedial measures are taken, the erosion tion updrift and erosion downdrift of the structures oc- downcur'rent of the southernmost groin will under- curred. Second, .the groins may have reduced the mine the highway in the near future (Plate 8). From strength of the north-south longshore current. Finally, 1928 to 1978, the vegetation line receded about 135 the groins have deflected some sand offshore. These feet. As of 1978, there was 60 feet of vegetation front- three changes have combined to reduce or cut off the ing the highway. sand formerly feeding Kualoa Point. -It may be more thaWa coincidence that the emplace- (2) The eastern section of Kualoa Beach Park has receded ment of the groins and the onset of 'erosion at kua)oa about 120 feet over the 1949 to 1978 observation Point occurred sometime after 1882 (U.S. Army Engi- period (transects 5-6). When averaged over a 29-year 63 period, the rate of erosion is about 4 feet per year. This 0 rate has not been constant but varies from 2 to 5 feet per year. Over the study interval there appears to be no significant increase in the rate of retreat. This suggests that the reduction in sand from upcurrent has been -50 uniform through time. (3) Several unique problems were encountered in the -100 study of erosion at Kualoa Point. First, there were no obvious stable reference points for beach changes to be measured against. This problem was resolved by selecting points in Apua Fishpond which appeared -150 stable over the 50-year observation period. Measure- ments taken between these points on all the photo- 00 graphs had a range of 7 feet. -200 The transects for this study were established perpen-' dicular to the 1949 beach. As Kualoa Point changed shape, the orientation of transects 7 to 9 became more -250 - oblique to the shoreline. Trigonometric relations indi- cate that the largest error is about 18% for the most 15 recent measurement on transect 8. On Table 25, the -300 - shoreline changes for this transect were corrected by determining the percent error for each observation perio'd. The most recent measurements for transects 7 and 9 were off by 7% and 6%, respectively. No correc- -350 - tions were made for these measurements as the total error is under 10 feet. From 1928 to 1978, the vegetation line at Kualoa -400 Point eroded about 327 feet. Over the same interval, 1930 1940 1950 1960 1970 1980 water line retreat of 367 feet was recorded. Between October 1978 and August 1980, field and photographic Figure 5. Kualoa Beach Erosion. Graph shows the historic shoreline measurements indicate that the beach receded an addi- changes at Kualoa Point (transect 8). tional 27 feet. From the available data, an estimate of the total loss at Kualoa Point since 1928 is about 350 to 400 feet. at 8 feet per year. For the last observation period, to 1978, the rate of retreat was 17 feet per year. The cumulative movement curve for transect 8 (cor- rected for errors) shows a progressive increase in the Several factors have caused an accelerated erosion rate rate of erosion at Kualoa Point (Figure 5). From 1928 at Kualoa Point. One important variable appears to be to 1949, the vegetation line receded about 3 feet per the changing shape of the point itself. In 1928, the tip year. During the 1949 to 1975 period, erosion occurred of Kualoa protruded seaward. Sand transport from the 64 eastern shore around the protrusion to the southern (4) Along the south shore of Kualoa Beach, erosion began shore was difficult. In addition, waves hit parallel to in 1971 after a long history of accretion dating back to the beach causing minor longshore currents. By 1978, 1928. The vegetation line at transect 9 grew seaward the point had become blunted. Sand from the, north 258 feet during the 1928 to 1971 interval but receded was easily transported around the point. Furthermore, 88 feet in the next seven years. The erosion at transect trade wind waves hit the beach at a larger angle and 10 began around 1975 and is less severe. Shoreline re- therefore increased the alongshore drift. treat for this section of the beach will increase progres- sively as Kualoa Point is washed away. To the west of As sand was carried past the point, the beach narrowed transect 10, accretion has been the general trend, as il- significantly. The reduction in beach width through lustrated by the widening of the camping beach since time can be seen on the 1928 and 1978 aerial photo- the late 1970's (D. Griffin, personal communication). graphs for Kualoa Point. Without the protection of a The force delivering sand to this section of the beach is wide sloping beach, waves of less than two feet high the refracted waves from Mokolii Island. can cut back the beach scarp during periods of high tide combined with strong onshore winds (D. Griffin, The projections for Kualoa Beach are based on the assumption that personal communication). no remedial measures are taken to save the park. Of the several mea- sures that have been proposed, sand replenishment would not require Another possible factor causing the increased erosion the installation of artificial structures on the beach or offshore. This within recent years is the sandgrabber, which was in- option is not available to the public as the present regulations prevent stalled in December 1977. As the most recent aerial mining an offshore deposit that was identified as a possible donor of photographic observation period covered the interval sand. between 1975 and 1978, it cannot be determined wheth- er the high rates of erosion during this time were all Kualoa Point eroded at leas 4t 250 feet prior to the construction of the natural or partly influenced by this structure. beach park. Few people we're aware of this change, for the land had Nevertheless, the sandgrabber appears to be hoarding little value then. After the park was constructed and trees were under- sand to the north (upcurrent). This would increase mined, it was realized that the beach was unstable. Now costly remedial erosion south of the structure in a manner similar to measures will be required if the park is to be saved. the erosion downcurrent of the groins along the highway. It is also possible that the increased erosion is caused by a steady reduction in the sand supply from the north. There appears, however, to be no significant in- crease in the rate of erosion along the eastern shore of the beach park. Thus, this factor may be minor in importance. The bathhouse at Kualoa Point was 35 fee t from the vegetation line on August 9, 1980. Given the present rate of retreat, this structure has about two years before it is undermined (Plate 9). 65 Plate 9. Kualoa Point. Erosion at Kualoa Point threatens to undermine the park.comfort station. Compare the position ofthe vegetation line with the bathhouse on the 1975 and 1979 photographs. rv, - 1975 1979 66 It is not obvious why the middle portion of Kailua Beach changed the Kailua Beach way it did for these two observation periods. When the two monitoring intervals are combined, however, and net changes computed from Table 26 summarizes the historic changes in the position of the vege- 1949 to 1963, all transects show the beach growth to be more regular. tation line for the fifteen transects established at Kailua Beach. From This fact may be an important clue to the beach processes operating at the data, several interesting trends are apparent. Within the total littoral that time. Since an aerial photograph represents only a spot observa- cell known as Kailua Beach are three distinct units or subcells. Al- tion, it may be possible that the 1957 photographs recorded unstable though the sand transport processes in any of the subcells is dependent conditions for the central part of the beach. An examination of the on the others, each unit seems to behave as a separate entity. 1957 photograph shows the shoreline changing its orientation abruptly in this area. During the monitoring interval, from 1957 to 1963, the For the period from 1949 to 1957, Kailua Beach grew throughout its middle porti 'on of the beach grew about twice as much as adjacent parts entire length, except for the middle portion between transects 7 and 9 to realign itself with other sections of the shoreline. (Photomap 26). During the monitoring inte 'rval from 1957 to 1963, ac- cretion was also prevalent with especially high growth in the middle sec- For the next three observation periods, from 1963 to 1978, an inter- tion of the-beach. esting pattern of beach change is clearly seen in the data. While one end Table 26 - Kailua Beach. Changes in the Vegetation Line in Feet. Transect Number Observation Period 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Nov 22, 1949 - Sep 07, 1957 * +25 +42 +41 +32 -1 +18 -13 +23 +30 +34 +37 +30 -1 Sep 07, 1957 - Nov 20, 1963 * +20 +17 +7 +19 +34 +34 +45 +18 +3. +14 +22 +51 +77 Nov 20, 1963 - Feb 06, 1971 * -40 -13 -20 -15 +6 -3 +9 +6 +18 +40 +69 +65 +51 Feb 06, 1971 - Apr 13, 1975 +34 +45 +17 +29 +181 -3 -12 . -13 -6 +1 -23 -46 -72 -26 Apr IS, 1975 - Oct 16, 1978 +10 +17 +11 F -6 -3 +2 +3 +7 -7 +9 +7 -2 -73 -48 -14 Net Change - Vegetation Line * +61 +57 +54 +56 +39 +44 +21 +50 +59 +63 +9 +26 +87 Range - Vegetation Line * 61 63 57 56 40 52 54 50 59 88 128 146 128 Net Change - Water Line * +67 +37 +79 +60 +18 +44 +30 +65 +40 +87 +101 +104 +119 Range - Water Line * 68 63 79 69 73 57 56 65 59 115 129 170 175 *No data L 1 ' +40 L + 1 _23 .1 +7 2 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 67 Alala % tailua each i' M, Kapoho Point Transect3 Transect 8 Transect 13 +130 - 1971 +120 - +110 - '000 Feet +100 - +90 - +80 - 1975 S +70 - Photomap 26. Kailua Beach +60 1978 1963 1963 Photographs by Air Survey Hawaii: February1971 S +50 1975 - 1971 6 1963 - 1978 +40 - 1975 1957 +30 - 1957 +20 - - 1957 +10 - 1978 1971 0 - 1949 - 1949 1949 -10 - Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 68- of Kailua Beach is accreting, the other end is retreating. The middle sec- change. Since the orientation of Kailua Beach is almost tions tend to remain relatively stable. This conclusion is also supported perpendicular to the northeast trade wind direction, by the historic ranges in the position of the vegetation and water lines. any fluctuations in this wind system would have a pro- nounced effect on the direction of littoral drift. If over During the monitoring interval from 1963 to 1971, the southeast end a 10-year period, the trade winds blew from a more of Kailua Beach was in an accreting cycle while the north end of the easterly direction than usual, erosion might result at beach eroded by as much as 40 feet. For the two observation periods Kailua Beach Park and accretion at the opposite end of from 1971 to 1978, the direction of net littoral drift shifted and resulted the littoral cell. This trend might be reversed if the in significant erosion at Kailua Beach Park while the Kaneohe end of trade winds blew from a more northerly direction, the littoral cell grew considerably. when averaged over a multi-yearly period. The cyclic trend of erosion and accretion at opposite ends of Kailua According to Wentworth (1949), the trade winds shift- Beach is similar to the seasonal changes on some other Hawaiian' ed in direction from northeast to east and back to the beaches, such as Lumahi Beach on Kauai (Moberly and Chamberlain, northeast over a period of 40 years. If trade wind cycles 1964). This pattern indicates that sand eroded at one end of the beach of this periodicity are the rule, then beach changes at is transported to the opposite end. Therefore, it should be realized that Kailua Beach may also have a natural cycle of 40 years. any structures designed to hoard sand at one end of the littoral cell may starve all down-current sections of the beach. Although the two hypotheses presented have been mentioned sepa- rately, they are not mutually exclusive. For example, the long-term di- Any shifts in the trend of beach change reflect reversals in the direc- rection of littoral drift may be to the southeast for active winter wave ac- tion of littoral transport. Two possibilities are presented to account-for tivity accompanied with a northerly shift in the trade winds. these reversals. Since the littoral processes on Kailua Beach are dependent on meteo- (1) It has been suggested that the direction of littoral trans- rological factors, an accurate prediction on beac h changes would require port varies seasonally for Kailua Beach (Noda, 1977). a knowledge of future weather conditions. Although our ability to fore- During the summer months,.strong persistent trade cast trade wind directions or North Pacific swell activity is limited, it wind waves tend to transport sand to the northwest. In should be realized that the historic record for Kailua Beach shows a the winter, sand transport may be to the northwest or tendency towards cyclic erosion and accretion. Therefore, these cycles southeast, depending on the interaction of northeast may occur in the future. This means that trees, houses or any other trade waves with North Pacific swell. According to this structures must not be placed on that portion of an accreting beach that concept, the direction of littoral transport would be to may retreat many years later as part of the natural cycle. Unfortunately, the southeast if unusually strong or persistent North this practice has not been followed for several sections of Kailua Beach. Pacific swell occurred during a winter storm. For example: An examination of a 1967 photograph for north Kailua (1) During the period from 1949 to 1971 the vegetation Beach shows considerable erosion of'the vegetation line in front of transect 13 grew seaward about 128 line during the 1967 to 1971 interval. This erosion is feet. Within this time interval, two rows of trees were concurrent with similar events at Punaluu Beach Park, planted approximately 95 feet and 40 feet inland of the Swanzy Beach Park and Kaaawa Beach Park. The ero- 1971 vegetation line. Between 10I and 1978, the sion at these beaches was caused by the winter storms vegetation line retreated about 119 feet to the position of 1968 and 1969. where the 1978 vegetation line was within 10 feet of its 1949 location. As a result many trees fell in the water (2) It is also possible that a shift in the direction of the (Plate 10). trade winds causes the direction of trade wind waves to 69 VT, pgq!- W Fq t '41, R 1949 1975 _4 LT ZIF-. m IQ k W As Aft 1971 1978 Plate 10. Kailua Beach Park. This sequence of aerial photographs and 1971, the vegetation line grew seaward 128 feet. Over the next seven show the accretion-erosion cycle at Kailua Beach Park. Between 1949 years,'a net erosion of 119 f6et wa's recorded. 70 (2) From 1949 to 1978, the net -change in the position of the vegetation line for transect 8was +44feet. During Lanikai Beach this period a house was built 35 feet inland of the 1978 vegetation line. If the beach retreats to its 1949 posi- The patterns of shoreline change at Lanikai are similar to those of tion, this house will be undermined. Kailua Beach. Lanikai can be separated into three major subcells, con- sisting of a stable middle and two end sections that change differently. (3) Between transects 5 and 6, the vegetation line ad-, The approximate boundary of the subcells, as interpreted from the vanced seaward about 54 feet over the 29-year obser- data, appears on Table 27. vation period. Five houses have been built along this stretch and are located from 47 to 40 feet inland of the During the 1961 to 1971 period, the vegetation line at the south end 1978 vegetation line. of Lanikai grew seaward by 139 feet. From 1971 to 1980, the trend reversed, and the vegetation line eroded,I 11 feet at a rate of about 12 (4) Approximately 300 fee It south of transect 3, the vegeta- feet per year (Photomap 27, Plate 11). This accretion-erosion cycle tion line advanced seaward about 61 feet over the coincides in timing and magnitude with the one for Kailua Beach Park. 29-year monitoring period. A house was constructed at this location about 32 feet inland of the 1978 vegeta- Over the 30-year observation period, the* middle section of Lanikai tion line. In fact, this house is situated within 10 feet of remained relatively stable (transects 6 and 7). This inflection point the 1949 land-water boundary. If the vegetation re- separates opposite ends of the beach that change differently. cedes 40 feet as it did during the 1963 to 1971 interval, this house will be undermined. A field check in For north Lanikai, four of the five observation periods show changes August 1980 shows the accretion trend at North that differ from those at the'south end. During the 1950 to 1961 period, Kailua has reversed. Erosion during the winter of 1980 north Lanikai eroded while the opposite end grew slightly. Between has threatened to undermine this house. 1961 and 1967, sections of north Lanikai experienced severe erosion (transects 4 and 5) while the south end grew by up to 105 feet. From It cannot be predicted whether any section of the beach will retreat to 1967 to 1971, the north end was stable while the opposite end was still its 1949 position. The data for most of the transects at the beach indi- laccreting. The photographic data prior to 1971 indicate that the long- cate a general increasing trend. The Kailua Beach Park area, however, term direction of littoral transport may have been from north to south. showed a general increasing trend for 22 years until rapid erosion began This trend reversed during the 1971 to 1975 interval when north Lani- without any forewarning. Since our knowledge of the littoral cycles at kai showed its maximum accretion while the south end began to erode. Kailua Beach is imperfect, it would be wise to keep all future develop- Only during the 1975 to 1980 period was a net erosion at both ends of ment well inland of the most withdrawn historic position of the vegetaz. the beach experienced. tion line, as determined by aerial photographs. If this practice is fol- lowed, extensive property damage may be avoided in the near future, The pattern of erosion and accretion at opposite ends of Lanikai sug- for the historic record indicates that Kailua Beach is a dynamic zone gests that major beach changes are determined by the direction of sand that will continue to change through natural cycles of erosion and transport along the shoreline. As explained for Kailua Beach, this is accretion. determined by the direction of the northeast trade waves, and the inter- action of these waves with North Pacific swell. Although shoreline changes at Kailua and Lanikai are similar, three important differences exist: (1) The beach changes within and between subcells at Lanikai are not always transitional but sometimes fluctuate unpredictably. 71 Table 27 - Lanikai Beach. Changes in the Vegetation Line in Feet. Transect Number Observation Period 1 2 3 4 5 6 7 8 9 10 11 Apr 19, 1950 - Jan 20, 1961 -151 01 -13 +3 -26 -4 +14 +8 -8 +10 -4 Jan 20, 1961 - May 08, 1967 +152 +82 -4 -2) -353 -1 -5 +18+105 -6 May 08, 1967 - Feb 06, 1971 -4 -1 +10 +4 * 0 -7 +19 +34 +5 -6 Feb 06, 1971 - Apr- 13, 1975 +9 +73 +20 +83* 0 +6 +9 -46 -30 +10 Apr 13, 1975 - Jan 19, 1980. -23 -8 * +18 +2 -323 -65 -16 -11 Net Change - Vegetation Line -18 +14 +5 -14 -61 +13 +10 +22 +20 +25 -17 Range - Vegetation Line 23 14 30 29 61 18 14 54 139 71 17 Net Change - Water Line -54-304 -8 -534 -394 +15 * +405 -86 Range - Water Line 54 314 37 714 394 57 * 1515 1476 *NoData April 19, 1950 - July 23, 1959 2July23,1959-May8 1967 3 To seawall 4 From 1950-1980 5 From 1967-1980 6 From 1961-1980 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 72 W 4'v 4, t4' S, % 7 8 10- 0 5 4 V-1 A Transectl Transect 6 Transect 9 +140 - +130 - 1971 +120 - +110 - [email protected]' M +100 - 1967 +90 - 4k 1975 W +80 +70 +60 - +50 - +40 - Photomap 27. Lanikai Beach +30 - Photographs by Air Survey Hawaii: April 1975 4-20 - 1980 - 1980 +10 - 1975 0- 1950 1950 - 1950 -10 1967 7- 1961 - 1961 1971 1967 1961 1971 -20 - 1980 197S -30 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 73 S Aak- M W Ak 1950 1980 Plate 11. Lanikai Beach. The accretion-erosion cycle at south Lanikai Beach is depicted in these aerial photographs. Between 1950 and 1971, the vegetation line had a net change of +131 feet. This accretion was concentrated during the 1961 to 1971 interval. Over the next nine years, erosion of III feet occurred. 7" 1971 74 .(2) The maximum variation in the position of the vegeta- With few exceptions, practically all of Lanikai has had a history of al- tion line at*Lanikai is not. found at the ends of the littor- ternating erosion and accr6tiow it is. not'po Issible to predict the long- al cell. For Lanikai, the maximum range is recorded at term trend for it is partly or wholly dependent on meteorological fac- ,transects 5 and 9.. tors.- In such a case; planners should use the historic range in the posi- tion, of the vegetation. line.to estimate the *inland extent of prohibitive (3) Even though the middle and south sections of Lanikaie development. record changes in phase with Kailua, the north end dif- fers slightly. In particular, during,the, period from 1950 Severe erosion problems exist at north Lanikai and many houses are to 1961, the.north end of Kailua grew appreciably at, the water's edge. As a result, several isections of ´┐Żeiiwall were con- while north Lanikai eroded. structed during the summer of 1980., If,the [email protected] treats in the winter, both access and recreation of this shoreline will be limited or nonexis- Several factors could account for the differences between the two tent. This has been the trend for much of Oahu's shoreline in the last beach systems. Wave diffraction between Mokulua Islands and reftac- 30 years. tion around them would give Lanikai a wave regime different from Kailua's. Another factor i 's the shape of the two beaches. Kailua Beach is concave seaward, whereas Lanikdi:has three,´┐Żea)6rd protruding points separating linear beach segments (Photomap 27). Finally, Lani- kai may not be a closed littoral cell. It has been suggested that sand transport to the horth may occur around Alala Point (Noda, 1977). This could explain the difference in the,patterns of beach change be- tween the north ends of Kailua and Lanikai. Significant erosion at north Lanikai occurred during the 1975 to 1980 period. It is unlikely that the sewage pipe constructed on the beach was the cause of the recent erosion, as field checks show no sand hoarded to either side of the structure. Erosion for the entire beach,during the 1975 to 1980 period is unusu- al compared to that of previous observation periods. The....sand. from Lanikai Beach may have been transported around Alala Point but it ap- pears that a major portion was temporarily lost offshore. Field checks in- April and August of 1980 showed a large seasonal change that exposed and then covered a section of beachrock. Since Lanikai is developed, little can be done.to alleviate the prob- lems that exist or may occur. Nevertheless, no structures or trees should be established seaward of the present houses for any part of the beach. Even if accretion occurred, the aerial photographs show that the trend may reverse quickly, given the cyclic nature of the beach. 75 for these transects appear on Table 28 (transects 1-11) and Table 29 Waimanalo Beach (transects 12-20). A summary of the major findings appears below. The Waimanalo Beach system is bounded by Wailea Point on the Over a 30-year period, the north section of Waimanalo Beach near north and, the Pahonu Fish Pond to the south. Along this crescent- Bellows Air Field has experienced chronic erosion (Photomap 28). Be- shaped beach are found the following sections: Bellows Air Field tween 1950 and 1962, the retreat of up to 53 feet in the vegetation line Beach, Waimanalo Beach Park, and Kaiona Beach Park. threatened to undermine several cabins. As a result, a 350-foot boulder wall was installed for protection. Over the next 13 years, erosion to Nineteen transects were established perpendicular to Waimanalo either side of the wall resulted in the construction of 1,650 feet of stone Beach. One transect was established to the south of this beach. The data revetment. In 1978, a sandgrabber was placed south of these structures. Table 28 - Waimanalo Beach. Changes in the Vegetation Line in Feet. Transect Number Observation Period 1 2 3 4 5 6 7 8 9 10 11 Apr 19, 1950 - Apr 06, 1962 -33 -53 -35 * +26 -19 +3 +34 +34 Apr 06, 1962 - May 29, 1967 +6 -6 -8 -12 * +32 +15 +17 +4 +112 +182 May 29, 1967 - Feb 06, 1971 -161 -171 -24 -32 +2 -28 +2 -36 -12 -952 -342 Feb 06, 1971 - Apr 13, 1975 -7 + 1 +26 +2 -9 -6 -5 +36 +8 Apr 13, 1975 - Jan 09, 1980 +27 * +3 -2 -16 * +2 -28 -40 Net Change - Vegetation Line -43 -76 -12 -78 +31 +30 -27 -22 +23 -76 -14 Range - Vegetation Line 43 76 39 79 31 58 27 42 38 95 66 Net Change - Water Line -723 -823 -934 -57 -12 +44+111 +72 +63 -44 +74 Range - Water Line 723 823 934 60 23 61 124 100 63 80 78 *NoData I To rock barrier 2 1967photographs taken on April 23 3From 1950-1975 4 From 1962- 1980 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in theposition ofa beach index line. 76 Table 29 - Waimanalo Beach (cont.). Changes in the Vegetation Line in Feet. Transect Number Observation Period -12 13 14 15 16 17 18 19 20 Apr 19, 1950 - Apr 06, 1962 +5 +66 -25 -25 -48 -62 -20 +7 Apr 06, 1962 - Apr 23, 1967 +60 -10 0 -7 -2 + 1 +26 + I + I Apr 23, 1967 - Feb 06, 1971 -47 -13 +16 +45 -2 +8 -13 -7 + I Feb 06, 1971 - Apr 13, 1975 +7 + 1 +8 +2 -6 +16 +15 +15 -1 Apr 13, 197 5 - Jan 19, 1980 -9 -9 -20 -34 +6 -11 -9 Net Change - Vegetation Line +16 +35 -21 -19 -4 -34 -43 -11 +8 Range - Vegetation Line 65 66 21 47 10 48 62 26 9 Net Change - Water Line -19 +50 + 1 +14 +9 +18 +41 +15 +10 Range - Water Line 102 90 38 53 85 73 601 18 39 No Data From 1962-1980 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. The stone revetment at north Waimanalo may have reduced the rec- The middle section of Waimanalo Beach (transects 6-13) expe- reational value of the beach. In 1950, the beach was continuous and rienced alternate periods of erosion and accretion. Generally, the major about 60 feet wide. Now only a narrow strip of sand fronts the revet- erosion events occurred during the 1967 to 1971 and 1975 to 1980 peri- ment. Access along the shore is limited and the beach cannot be used ods. During the 1967 to 1971 interval, the vegetation line at transect 10 for sunbathing or picnics. receded 95 feet. Erosion for much of Waimanalo occurred during this period, possibly because of the high waves of December 196 8 and Janu- At north Waimanalo Beach, sections to the south of the artificial ary 1969, which damaged other sections on the windward coast. From structures have had a history of erosion (transects 3-4). This suggests 1975 to 1980, the vegetation line for transect 11 receded 40 feet, and that more remedial measures will be required in the future. From 1975 again, erosion occurred along most of the beach (Photomap 29)-. Other to 1980, erosion south of the sandgrabber began to undermine a public than these, two periods of erosion, accretion at middle Waimanalo bathhouse. Over the same interval, the stretch of shoreline between Beach was recorded for most of the time. transects 3 and 4 grew slightly. The long-term trend for these transects, however, has been shoreline retreat. 77 Transect 2 Transect 4 Transect 11 Point 1967 1962 1975 1971 1950 1950 1950 1980 0 < 1962 -3 1967 1962 1967 C", 1971 1975 Bellows Field Beach Park 1971 .6 4 8 ML 10 Photdmap 28.- Waimanalo Beach Photographs by Air, Survey Hawaii: February 1971 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 78 7W 771 [email protected] 1000*Feet M", V q '4V W a 'All i4U, zpr X la/o Beath Park W 17 2 16 15 !Yt A, 4 [email protected] Ni" 4 n A- f Transect 14 Transect 18 +10 0 1950 1950 1975 -10 1971 -20 1980 1962 Photomap 29. Waimanalo Beach (cont.) -30 - 1967 1975 Photographs by Air Survey Hawaii: February1971 -40 - 1967 1980 -50 - 1971 -60 1962 -70 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. I rs 79 When averaged over a 30-year period, some sections of middle Waimanalo grew while others receded. No clear pattern is seen from Makapuu Beach Park the data. For planning purposes, 'the transect closest to the point of interest should be chosen to indicate the past shoreline change. The stable reference points at Makapuu Beach were located in unfa- vorable positions. In order to obtain data for this beiich, a connecting It is possible that the net change of the vegetation line for middle line was drawn between the stable reference points. Measurements to Waimanalo records the combined effects of storm wave damage and the beach were then made from a point on the stable line. Although the migration of large beach cusps in the direction of littoral drift. Stud- this procedure introduces inaccuracies, it does provide a first approxi- ies indicate that small beach cusps are stable over a period of a few mation of the historic changes at Makapuu over a 25-year period. months, but no measurements were made over a multi-yearly period (Gerritsen, 1978a). Data on the water line *from 1950 to 1980 give no Analyses of the aerial photographs for Makapuu Beach show that the clear indication of a migrating sand wave. vegetation line at mid-beach advanced seaward 14 feet during the 1950 to 1967 period (Photomap 30, Table 30). During the next eight years, Along the middle section of Waimanalo, stone jetties have been built the vegetation line at mid-beach receded 48 feet. The major loss oc- perpendicular to the beach to constrain the flow of two streams. Both curred during the 1967 to 1971 interval. This erosion is concurrent with the jetties near transect 5, and the one near transect 10 have a slight similar events experienced for many of the beaches on the windward buildup of sand at the south end. This indicates that the direction of lit- coast. The vegetation line at Makapuu Beach may have been cut back toral drift for these beach sections is from south to north. during the winter storms of December 1968 and January 1969. The southern section of Waimanalo Beach (transects 14 to 19), has Over a 25-year observation period, the water line grew seaward 72 experienced periods of alternate erosion and accretion. Unlike middle feet. On the aerial photographs, several rocks that were in the water on Waimanalo Beach, this section eroded significantly during the 1950 to April 19, 1950 were covered by sand on April 13, 1975. It is possible 1962 period. The maximum loss was at transect 18 where the vegetation that the apparent accretion is due to a variation in the seasonal change. line receded 62 feet. Between 1950 and 1980, the data indicate that ero- Surveys taken during the 1962 to 1963 period indicate a seasonal varia- sion for this stretch predominates in terms of time and net change. tion of 50 feet (Moberly' and Chamberlain, 1964). Field surveys taken over a 10-year period indicate that Makapuu may have actually been re- Transect 19 was established at Kaiona Beach Park. The pattern of duced in volume (Campbell, 1972). change for this beach is similar to that of other sections of southern Waimanalo. Since it is difficult to separate the seasonal and long-term changes from the water line, the vegetation line should be used as an indicator The shoreline changes at transect 20 indicate that the northwest end of the long-term trend. In this case, Makapuu has had a long history of of Kaupo Beach is stable. This beach system is separated from the slight accretion offset by shorter erosion events. Waimanalo littoral cell by Pahonu Fishpond. When averaged over a 30-year period, data show that the north and south sections of Waimanalo have eroded. Some sections in the middle. grew, while others receded. If this pattern is representative of the the long-term trend, then the crescent shape of Waimanalo Beach should become less distinct with time. 80 W, Oil On 4X V A W. W, Photomap 30. Makapuu Beach Park Photographs by Air Survey Hawaii: April 1975 81 Table 30 - Makapuu Beach Park. Changes in the Vegeta- tion Line and Water Line in Feet. Observation Period Vegetation Water Apr 19, 1950 - Apr 23, 1967 +14 +8 Apr 23, 1967 - Mar 17, 1971 -35 +13 Mar 17, 1971 - Apr 13, 1975 -13 +51 Net Change -34 +72 Range 48 72 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 82 SECTION III - SOUTH SHORE The south shore extends from Makapuu Point on the east to Barbers Keahi Point is located at the west end of Iroquois Point. From 1928 Point on the west (Figure 6). Along much of this stretch a shallow to 1976, the vegetation line and water line receded about 180 feet. fringing reef absorbs incoming wave energy. As a result, the beaches on this shore have been stable or have grown slightly. Some exceptions Erosion at Ewa Beach was concentrated during the 1958 to 1967 are listed below. period. Many of the seawalls at Ewa were installed during that time. Paiko Peninsula is a barrier spit projecting into Maunalua Bay. Be- tween 1928 and 1961, this spit grew over 800 feet to the east while the arm thinned considerably. During the 1967 to 1971 period, erosion was experienced at Sandy Beach Park, Hanauma Bay, Paiko Peninsula and east Kahala Beach. It appears that high waves during this interval inundated the backshore area. '0W OW 8 40 39 VzM 41 43 42 31 35 32 36 37 Figure 6. Photomap Arrangements - South Shore. 83 Sandy Beach Park Table 31 - Sandy Beach Park. Changes in the Vegetation Over a 30-year period, the water line at Sandy Beach receded about Line in Feet. 13 to 16 feet (Table 3 1). As Sandy Beach may have an annual variation in width of at least 25 feet (Moberly and Chamberlain,'1964), it cannot be determined if this represents a significant long-term loss in the Transect Number beach system. The changes in the vegetation line for transect I are small, partly be- Observation Period 1 2 cause rocks protect the vegetation in front of this transect (Photomap Oct 29, 1949 - Nov 20, 1963 -1 +51 31). Nov 20, 1963 - Apr 23, 1967 +8 -3 Transect 2 is located at the west end of the parking lot. Between 1949 and 1963, the vegetation line grew seaward 51 feet. During the 1967 to Apr 23, 1967 - Dec 18, 1971 -9 -71 1971 interval, the vegetation was cut back 71 feet, perhaps by high wave runup onto the backshore. Dec 18, 1971 - Apr 13, 1975 +6 Since 1971, the vegetation at Sandy Beach has not recovered. This Apr 13, 1975 - Apr 03, 1979 +3 makes the parking lots more susceptible to wave inundation. Part of Sandy Beach has no offshore reef structure and therefore receives the Net Change - Vegetation Line +7 -23 full energy of the ocean waves. Range - Vegetation Line 9 74 Net Change - Water Line -16 -13 Range - Water Line 41 17 *N6 data Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 84 el W4 7 Transect 2 +60 +50 1963 1967 +40 - +30 - +20 - Photomap 31. Sandy Beach Park +10 - Photographs by Air Survey Hawaii: ApHI1975 0 1949 -10 -20 - 1971 -30 - Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 85 Hanauma Bay Beach Park Table 32 - Hanauma Bay Beach Park. Changes in the Hanauma Bay may be a natural sediment sink. Over a 47-year period, Vegetation Line in Feet. the water line grew seaward by as much as 41 feet. While part of this change is attributed to artificial sand replenishment, much of the accre- tion occurred prior to 1967. Transect Number At transect 1, the vegetation line receded 26 feet during the 1928 to Observation Period 1 2 3 1949 period (Photomap 32, Table 32). This change was localized. Generally, the vegetation for the east end of the beach had a net gain over this interval. The vegetation line for much of the beach also grew 1928 - Oct 29, 1949 -26 from 1949 to 1967. Oct 29, 1949 - Nov 20, 1963 -2 +39 +9 The severe erosion at Hanauma Beach in the late 1960's was partly Nov 20,1963 - Apr 23, 1967 -2 +4 +8 influenced by man. In 1949, the shallow fringing reef at Hanauma Bay was continuous. Much of the wave energy was dissipated on the reef Apr 23, 1967 - Dec 18, 1971 -5 -58 +9 flat instead of on the beach. As a result, the trees and vegetation grew within a few feet of the water. Dec 18, 1971 - Apr 13, 1975 0 +7 +2 In 1957, a 250-foot-wide channel was cut through the reef. The artifi- Net Change - Vegetation Line -35 -8 +28 cial channel allowed waves to cross the reef flat more readily. On the Range - Vegetation Line 35 58 28 1967 aerial photograph, wave sets over the reef are found only where Net Change - Water Line +41 +8 +27 the channel had been dredged. Range - Water Line 59 37 63 Sometime between 1967 and 1971, many beaches on the south shore *No data experienced erosion. This suggests a high amount of wave energy Net change is the total change in the position of a beach index line between the during that period. At Hanauma Bay, large waves coupled with a high earliest and most recent observation year Range is the difference between the observed extremes in the position of a tide may have crossed the reef channel and run up tfie'beach. This wave beach index line. action undermined the vegetation and coconut trees.which had pre- viously grown within 10 feet of the water. In April of 1970, the City and County of Honolulu, Department of Parks and Recreation, constructed a wave barrier and placed 4,100 cubic yards of sand on'the beach. 86 V, A- R "3 r V QW, *A +40 - 1963 -a!. +30 - E- Photomap 32. Hanauma Bay Beach Park +20 - Photographs by Air Survey Hawaii: April 1975 +10 - 949 0 -10 1975 1971 -20 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 87 Paiko Peninsula Table 33 - Paiko Peninsula. Changes in the Vegetation Paiko Peninsula is the most unstable coastal feature on Oahu. A Line in Feet. Hawaiian government survey map taken of the Maunaula Bay area in 1884 indicate that this feature did not exist. Over the past century the peninsula has grown approximately 2,000 feet to the east. Transect Number Geomorphologists would classify Paiko Peninsula as a barrier spit, an Observation Per .iod 1 2 3 elongate sand body that extends from the coastline in a roughly parallel trend and is separated from. the land by a lagoon. The peninsula changes in the following manner. Wave action transports sand from the 1928 - Oct 29, 1949 +554 fringing reef to the beach along two distinct sand plumes. One is located Oct 29, 1949 - Jan 20, 1961 +359 +18 +7 to the east of Niu Peninsula and the other is near transect 1 (Photomap 33). Jan 20, 1961 - Aug 29, 1967 -2 +11 Once on the beach, the sand is carried from west to east by longshore Aug 29, 1967 - Jan 04, 1971 -2 -12 currents. As the sand passes the tip of Paiko, two results may occur that are dependent on the relative amounts of wave energy. If the wave Jan 04, 1971 - Apr 13, 1975 +4 +14 action is strong, sand is deposited in a fork-shaped washover fan ex- tending -into Paiko Lagoon. When the wave energy is low, the spit Net Change - Vegetation Line +913 +18 +20 grows to the east. Range - Vegetation Line 913 18 20 Net Change - Water Line +865 +2 +34 Between 1928 and 1949, the tip of Paiko Peninsula grew eastward Range - Water Line 865 19 34 about 550 feet (Table 33, Plate 12); This extension to the east occurred at an average rate of over 25 feet per year. Meanwhile, the arm of the No data spit thinned considerably. If not for a rock wall built along the shore- Net change is the total change in the position of a beach index line between the line, the eastern end of the peninsula might have separated and earliest andmost recent observation year become a barrier island. Range is the difference between the observed extremes in the position of a beach index line. From 1949 to 1961, Paiko Peninsula grew an additional 350 feet to the east. Since then, the shape of Paiko has been influenced by a nearby artificial channel and extensive dredging operations. In the early 1970's, several channels were dredged within Paiko Lagoon to increase water circulation. Dredged material was deposited in the lagoon to create is- lands for wildlife habitation. Paiko Peninsula is an extremely unstable geomorphic feature. There- fore, it may be wise to keep the eastern portion of Paiko a, wildlife pre- serve before additional interference with natural processes occcurs. 88 A, "'Cu, j, -4, A % @7 14, x A, All 21 -P @@Oon 0 Ali PR 0 500 WWI Transect 3 Photomap 33. Paiko Peninsula +30 - Photographs by Air Survey Hawaii: January 1971 1975 +20 - 1967 +10 - 1961 1971 0 1949 -10 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 89 - - - - - - - - - - M 1928 1975 Plate 12. Paiko Peninsula. During the 1928 to 1961 interval, Paiko Peninsula grew over 900 feet to the east (left). Since 1961, the shape of the peninsula has been modified artificially. Along the residential section of Paiko, the vegetation line grew sea- ward about 20 feet during the 1949 to 1975 period. Accretion pre- dominated over the 26-year interval, although the vegetation line at transect 3 receded 12 feet between 1967 and 1971. This erosion is con- current with the losses recorded at Sandy Beach Park and Hanauma Bay. 1961 90 Niu Beach to Wailupe Peninsula Table 34 - Niu Beach to Wailupe Peninsula. Changes in The shoreline between Niu Beach and Wailupe Peninsula underwent the Vegetation Line in Feet. small changes during the 1949 to 1975 period. The net changes in the vegetation line indicate slight growth or stability for the beach section covered by transects I and 2 (Photomap 34). Transect 3 showed a Transect Number tendency toward long-term accretion. Over a 26-year observation period the vegetation line grew seaward 23 feet (Table 34). The water Observation Period 2 3 line had a net change of + 21 feet. This stretch of shoreline has a shallow fringing reef between 1,000 Oct 29, 1949 - Jan 20, 1961 +4 +11 +8 and 1,800 feet offshore; the reef absorbs wave energy and supplies sand Jan 20, 1961 - Aug 29, 1967 +14 -3 +7 to the beach. Aug 29, 1967 - Jan 04, 1971 -5 +2 +13 Jan 04, 1971 - Apr 13, 1975 -6 0 -5 Net Change - Vegetation Line +7 +10 +23 Range - Vegetation Line 18 11 28 Net Change - Water Line +10 +21 +21 Range - Water Line 23 30 37 Net change is the total change in the position of a beach index line between. the earliest and most recent observation year Range Is the difference between the observed extremes in the position of a beach index line. .91 1006 Feet [email protected] 141 'A [email protected] @4, A W upe Peninsula ail IM Photomap 34. Niu Beach to Wailupe Peninsula Photographs by Air Survey Hawaii: January 1971 92 Wailupe Beach Park and Residential Area The 2,000-foot stretch of beach west of Wailupe Peninsula has grown Table 35 Wailupe Beach Park and Residential Area. or remain ed stable over a 26-year period. From 1949 to 1975, the net Changes in the Vegetation Line in Feet. change in the position of.the vegetation line at transects 1 and 2 were + 14 feet and -I feet, respectively (Photomap 35, Table 35). Transect Number The fringing reef along this beach is about 1,500 feet offshore. Numerous channels and sand plumes extend from the reef to the beach. Observation Period 1 2 Oct 29, 1949 - Jan 20, 1961 +2 +4 Jan 20, 1961 - Aug 29, 1967 +5 +3 Aug 29, 1967 - Jan 04, 1971 -2 -2 Jan 04, 1971 - Apr 13, 1975 +9 -6 Net Change - Vegetation Line +14 -1 Range - Vegetation Line 14 8 Net Change - Water Line +16 -8 Range - Water Line 30 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 93 0 500 1000 Feet .7 A [email protected]' I'G 44 V, Al A Nx Or 4 it All -OV4 Photomap 35. Wailupe Beach Park and Residential Area Photographs by Air Survey Hawaii: January 1971 94 Kahala Beach Table 36 - Kahala Beach. Changes in the Vegetation Line The net change in the vegetation line for the five transects estab- in Feet. lished at Kahala Beach indicate beach stability or growth. During the 1967 to 1971 period, however, the vegetation line at transect 2 receded 26 feet (Photomap 36, Table 36). This loss is concurrent with other ero- Transect Number sion events on the south shore. Despite the brief period of erosion, the vegetation line for this transect had a net change of +31 feet over a Observation Period 1 2 3 4 5 26-year interval. The net loss in the water line for all the transects is difficult to inter- Feb 16, 1949 - Jan 20, 1961 +12 +14 0 pret because of problems with tidal fluctuations, seasonal changes, and Jan 20, 1961 - Aug 29, 1967 +3 +16 +2 01 -21 light reflection on the aerial photograph. Field surveys conducted in 1962 and 1972 show an increase in the vegetation line and water line Aug 29, 1967 - Jan 04, 1971 -4 -26 0 +2 -3 for Kahala (Campbell, 1972). Jan 04, 1971 - Apr 13, 1975 -11 +27 +9 + I + I Net Change - Vegetation Line 0 +31 +11 +3 -4 Range - Vegetation Line 15 31 11 3 5 Net Change - Water Line -21 -5 -7 -19 -21 Range - Water Line 43 51 28 21 *Nd data 1 Change from 1949- 196 7 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 95 0 500 .1006 '-Feet t 'Black Point A/ A6 A.- Tran WIC +40 1975 Photomap 36. Kahala Beach +30 1967 A Photographs by Air Survey Hawaii: January 1971 W to +20 1961 +10 1971 0 1949 -10 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 96 Kaalawai Beach and Kuilei Cliffs Beach Park Table 37 - Kaalawai Beach and Kuilei Cliffs Beach Park. Measurements of the vegetation line over a 26-year period indicate Changes in the Vegetation Line in Feet. that Kaalawai Beach is stable. Transects I and 2 record net changes of 0 and +3 feet, respectively (Photomap 37, Table 37). At transect 3, the vegetation line receded 7 feet over a 26-year period. Erosion of 15 feet Transect Number during the 1949 to 1967 period may be an overestimate as the stable reference point used for the measurement was the inner edge of bea- Observation Period 1 2 3 chrock. This rock may have been covered by sand, altering the exact po- - sition of the suppo .sedly stable point. Feb 06, 1949 - Aug 29, 1967 -5 -15 The interpretation for the change of the water line at transects I and 2 is complicated by seasonal changes, tidal fluctuations, and problems Aug 29, 1967 - Jan 04, 1971 -3 +21 +7 in locating the water line on the aerial photograph. Jan 04, 1971 - Apr 13, 1975 +8 +1 + I Net Change - Vegetation Line 0 +3 -7 Range - Vegetation Line 8 3 15 Net Change - Water Line -27 -20 Range - Water Line 32 20 *No data Change from 1949-19 71 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 97 WIN kaalawa -Bea6h-.-", Al, A 7W 4", 41 Photomap 37. Kaalawai Beach and Kuilei Cliffs Beach Park Photographs by Air Survey Hawaii: January 1971 98 Iroquois Point Table 38, - Iroquois Point. Changes in the Vegetation Line in Feet. Iroquois Point is located to the west of the Pearl Harbor entrance. Over a 48-year period, the shape of the point has changed significantly. Along the eastern sections of the beach, between transects 2 and 4, ac- cretion has been the general trend. At Keahi Point, however, transects Transect Number 5 and 6 record a history of severe erosion (Photomap 38). Due to the development of the residential section in the 1950's, tra"_ Observation Period 1 2 3 4 5 6 7 sect 6, had to be relocated to give a continuous record of the shoreline 1928 - Sep 23, 1950 change. On the photographs preceding 1961, transect 6 is 40 feet to the -86 -98 west of its present position. Still, the combined changes for this transect Sep 23, 1950 - Jan 20, 1961 -34 are believed to give a reasonable estimate of the net loss at Keahi Point. From 1928 to 1976, the vegetation line and water line receded about Jan 20, 1961 - Jun 20, 1967 +4 +21 -3 +76 -8 +11 180 feet (Table 38, Plate 13). The rates of erosion for the vegetation Jun 20, 1967 - Feb 12, 1976 -4 +23 -6 +5 -41 -34 line were not constant but varied from 1.2 feet per year during the 1961 to 1967 period, to 4.7 feet per year between 1967 and 1976. Net Change - Vegetation Line 0 +44 -9 +81 -86 -181 -23 Range - Vegetation Line 4 44 9 81 86 181 34 On the 1976 photograph for Keahi Point, several exposures of rock' Net Change - Water Line -10 +47 +32 +36 -48 -183 -14 are found along the shore. This rock has not stabilized the beach. Range - Water Line 54 32 65 48 183 13 During a field check in September 1980, the algae-covered rock was under several feet of water.- This suggests that the erosive trend, which *NoData dates back to at least 1928, is still in process. Net change is the total change in the position of a beach index line between the earliest and most recent observation year One of the homes at Keahi Point is within 60 feet of the 1976 vegeta- Range is the difference between the observed extremes in the position of a beach index line. tion line. If the beach continues to recede, some type of remedial mea- sure will be required if the property is to be saved. It appears that sand is transported along the shore from Keahi Point to the eastern sections of Iroquois Point where accretion was expe- rienced. Therefore, any erosion-control structures that may hoard sand updrift may cause erosion downcurrent on other portions of the beach. Several of the homes at Keahi Point have sand bags and plastic bar- riers placed along the vegetation line. As the beach diminishes in size, these remedial measures will provide meager protection to the back- shore area. According to one resident, 20 sand bags were washed away during the wave activity ftorn May to June 1980. 99 0 500 1000 feet %.-.- Keahi Poik 6 6 2 [email protected] 'M OM A IV 3 0 [email protected] 7% .0 Hammer Poi 7* N J, lie -4, Ab, , nt 4- tl A Transect 6 ..,W7 +20 - AM"M* 0 -- 1928 Y -20 - -40 - -60 - -80 - -100 -- 1950 Photomap 38. Iroquois Point .2 0 -120 - .0 1961 Photographs by Air Survey Hawaii: febfuayyl97(, < -140 1967 -160 -180 1976 [email protected] Absolute change is the change in the position of the vegetation line compared to the earliest or base year. -200 100 0 cz 0 U 0 (1) -Q CL 00 cd 03 to [email protected] > ca > 0 cn [email protected] cz 00 00 C4 r @x-!i -Tif pa, 1Y, A I Ald w 44 20 feet. This erosion threatened to undermine several coconut trees. Ewa Beach From 1967 to 1979, the vegetation line had a net change of + 5 to + 22 feet. Ewa Beach is two miles long and has an average width of about 50 feet (U.S. Army Engineers, 1971). Along this stretch are found the The beach along the residential section of Ewa is about 1.3 miles Puuloa Rifle Range, Ewa Beach Park and the Ewa residential area. long. In 1950, there were few if any seawalls along this stretch. Between 1950 and 1958, the vegetation line was stable or grew seaward. At tran- At east Ewa Beach, transects I to 3 were established near the rifle sect 9, however, erosion along a 400-foot-section was experienced. range (Photomap 39). Over a 26-year period, the vegetation line has been stable or has grown seaward. One exception is the erosion record- Sometime during the 1958 to 1967 period, erosion along much of the ed at transect I during the 19 5 8 to 1967 period (Table 3 9). beach occurred. The losses were especially noticeable along a 3,000- foot-stretch to the west of the beach park. Many of the seawalls at Ewa Transects 4 and 5 record the shoreline changes at Ewa Beach Park. were installed during that time. Between 1958 and 1967, the vegetation fronting the park receded about Table 39 - Ewa Beach. Changes in the Vegetation Line in Feet. Transect Number Observation Period 1 2 3 4 5 6 7 8 9 10 Sep 23, 1950 - Jun 19, 1958 +11 +15 +15 +8 +20 +2 -26 + I Jun 19, 1958 - Jun 13, 1967 -12 0 +33 -19 -21 01 01 0 +12 -5 Jun 13, 1967 - Feb 12, 1976 -1 +16 -2 +5 -3 -8 +11 -31 Feb 12, 1976 - Jul 19, 1979 -1 +17 +8 Net Change - Vegetation Line -2 +31 +45 +3 -16 +8 +20 -6 -3 -7 Range - Vegetation Line 13 31 48 22 24 8 20 8 26 8 Net Change - Water Line -21 +4 -18 +6 +2 +42 -163 -8 +5 -21 Range - Water Line 25 20 19 54 47 172 163 11 5 31 *No Data 1 Built Sea wall 2 From 1950-1979 3 From 1950- 19 76 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index 11ne. 109 ';-,@'1000 Feet Fl!" 1, 7-1 AV, 1, "Z, Ir- 0 77' U @j Transect 5 Photomap 39. Ewa Beach +1o - Photographs by Air Survey Hawaii: February 1976 S 0 1958 -10 V 1979 S -20 1967 1976 -30 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 103 Between 1967 and 1979, the vegetation line along much of Ewa Beach was stable or grew slightly. The historic data indicate that this Oneula Beach may be the long-term trend. Over a 29-year observation period, dccre- tion predominated for 20 of the years. Field surveys taken during 1962 Oneula Beach has changed little over the 26 years covered by the and 1972 indicate accretion of both the water line and vegetation line aerial photographs; net changes for the vegetation line are under 10 (Campbell, 1972). feet for all three transects (Photomap 40, Table 40). Data for transect 3 exist for only an eight-year period. The brief period of erosion during the 1958 to 1967 interval resulted in the construction of many of the seawalls. If some allowance had been made for small fluctuations in the shoreline prior to beach develop- ment, such remedial measures should have been unnecessary. Table 40 - Oneula Beach. Changes in the VegetationLine in Feet. Transect Number Observation Period 1 2 3 Sep 23, 1950 - Jun 19, 1958 +11 +5 -4 Jun 19, 1958 - Jun 13, 1967 +2 +4 Jun 13, 1967 - Feb 12, 1976 -5 -9 Net Change - Vegetation Line +8 0 -4 Range - Vegetation Line 13 9 Net Change - Water Line +24 -7 -23 Range - Water Line 24 7 *No data Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 104 7P N -=v ga @A 51 ,NN N A N-,@ _A2, 54 N tv A CL di bo Nimitz Officers Beach Table 41 - Nimitz Officers Beach. Changes in the Vegeta- Nimitz Officers Beach has had large fluctuations in the position of tion Line in Feet. the vegetation line. Between 1950 and 1958, the vegetation at the east end of the park was cut back 16 feet (Photomap 41, Table 41). During the 1958 to 1967 interval, sparse vegetation grew seaward. This accre- Transect Number tion was lost during the next nine years when the vegetation line reced- ed 40 feet. It is likely that the vegetation recedes when high waves inun- Observation Period 1 2 date the backshore. Over a 26-year period, the water line has had a net change of +60 Sep 23, 1950 - Jun 19, 1958 -16 feet. Although the water line data are complicated by numerous factors, Jun 19, 1958 - Jun 13, 1967 +37 accretion of the beach seems to be the long-term trend. Beach growth was recorded during all three of the observation intervals. Jun 13, 1967 - Feb 12, 1976 -40 -9 Net Change - Vegetation Line -19 -9 Range - Vegetation Line 40 9 Net Change - Water Line +60 +9 Range - Water Line 60 9 *No data Net ch6nge is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 106 4 4 -A* 2 V 4 4 7 J, 0 250 Transectl +30 - Z +20 - 1967 Photomap 41. Nimitz Officers Reach Z +10 - Photographs by Air Survey Hawaii: February1976 0- 1950 -5 -10 - 7 1958 -20 - 1976 -30 - Absolute change is the change in the position of the vegetation line compared to the earliest or base year. L -------------j----------------i 107 Nimitz Beach Table 42 - Nimitz Beach. Changes in the Vegetation Line The artificially constructed Nimitz Beach consists of alternating in Feet. stretches of sand and rock. Over a 26-year period, this beach has had a history of accretion. The data from the vegetation line show a seaward growth of up to 27 feet. Over the same period, the water line grew sea- Transect Number ward by as much as 57 feet. Accretion of the vegetation was concentrat- ed during the 1950 to 1958 period whereas the water line grew seaward Observation Period 1 2 3 4 5 6 between 1967 and 1976. Although accretion is the predominant trend, brief erosion events Sep 23, 1950 - Jun 19, 1958 +27 +32 +19 +19 +17 have occurred. During the 1967 to 1976 period, the vegetation line at Jun 19, 1958 - Jun 13, 1967 -4 -7 +11 -7 -3 +12 transect 2 receded 17 feet (Photomap 42, Table 42). This loss may have been caused by high-wave runup onto the backshore. Jun 13, 1967 - Feb 12, 1976 +4 -17 -7 +5 +7 -6 Net Change - Vegetation Line +27 +8 +23 +17 +4 +23 Range - Vegetation Line 27 32 30 19 7 29 Net Change - Water Line +9 +24 +28 +27 + 1 +57 Range - Water Line 10 41 28 31 12 57 *No data Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 108 'V#- .4, v, L Transect 2 Photomap 42. Nimitz Beach +40 - Photographs by Air Survey Hawaii: FebruarV1976 +30 --. 1958 1967 +20 - +10-- 1976 0-- 1950 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 109 Barbers Point Table 43 - Barbers Point. Changes in the Vegetation Line in Feet. Although the aerial-photographic record for Barbers Point is scant, the measurements indicate that the beach is suprisingly stable. Over a period of observation between 8 and 18 years the net change in the posi- tion of the vegetation line at the point has been under 10 feet (Pho- Transect Number tomap 43, Table 43). Barbers Point Beach consists of alternating stretches of sand and Observation Period 1 2 3 rock. The rock may prevent major shoreline changes by absorbing wave energy. Sep 23, 1950 - Jun 19, 1958 +6 +4 Jun 19, 1958 - Feb 12, 1976 0 Net Change - Vegetation Line +6 +4 0 Net Change - Water Line -18 -12 +12 No data Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range -is the difference between the observed extremes in the position of a beach index line. 110 1000 -Feet 7 [email protected]_ Wf. IM Photomap 43. Barbers Point Photographs by Air Survey Hawaii: February 1976 1% - SECTION IV - LEEWARD COAST On the leeward coast (Figure 7), the south end of Kahe Beach and 7 the two ends of Maili Beach experienced chronic erosion between 1949 and 1979. Most other beaches showed no obvious long-term change % when data were averaged over a multi-yearly period. Neverth eless, MA 7 a__ -OU winter surf inundation from large Kona Storm waves or refracted North 5k Pacific swell may cause periodic damage to the backshore area. Beaches that appeared susceptible to inundation between 1949 and 1975 include [email protected] [email protected] mid- okai Bay, Papaoneone Beach (Turtle Beach), Makaha Beach and 7", 53 Keaau Beach. [email protected]' 52 _5 @t' Xi, M, 51 7 %@w Tz'im- 7 -t 'WA 1A ,a:i R S"M M" t&X`[email protected]_` 50 49 "'S [email protected] Uk -a' lwt-""t 9!ri" A"I"t"I"'IN 48 "MI WL 47 AM a 10- 46 45 44 [email protected] 7. Photomap Arrangements - Leeward Coast. 113 Lanikuhonua Beach Table 44 - Kahe Beach. Changes in the Vegetation Line The pocket beach at north Lanikuhonua is about 100 feet long. Be- in Feet. tween 1949 and 197 1, the vegetation line for the beach had a net loss of 42 feet. Over the same period, there was no significant change in the water line. Transect Number On the 1971 photograph, several trees are located seaward of the line Observation Period 1 2 3 4 of scrub vegetation. This suggests that the lower vegetation was covered by thin sand or temporarily killed by high-wave inundation. There ap- pears to be no long-term erosion. May 08, 1949 - May 19,1959 +16 -10 During the 1971 to 1975 period, the vegetation line advanced sea- May 19, 1959 - Dec 22, 1965 -10 ward 16 feet. Over a 26-year period, the net change in the position of Dec 22, 1965 - Feb 06, 1971 -11 -5 the vegetation line was -26 feet. Feb 06, 1971 - Mar 30, 1975 -4 -14 -4 +942 Kahe Beach Mar 30, 1975 - Mar 13, 1979 -4 -1 +8 0 Net Change - Vegetation Line +7 -40 +4 Kahe Beach is located to the west of the Hawaiian Electric power Range - Vegetation Line 16 40 8 plant. The south end of this beach has a 30-year history of chronic ero- Net Change - Water Line -28 -42 +16 +25 sion. Between 1949 and 1979, the vegetation line and water line for Range - Water Line 43 73 18 32 transect 2 receded 40 and 42 feet (Photomap 44, Table 44). Erosion of the vegetation line was recorded during all five observation intervals. *No data I Change from 1959-1971 Although it does not show in the data, the north section of Kahe 2 Artificial change - vegetation str1poed by man Beach has receded also. An examination of the 1949 and 1979 aerial Net change is the total change in the position of a beach index line between the photographs reveal that exposed rock and basalt cobbles have replaced earliest and most recent observation year a former sandy shoreline. Much of this change occurred prior to 19,71. Range is the difference between the observed extremes in the position of a The data from the water line and vegetation line indicate that the north beach index line. end (Manners Beach) has been stable since 197 1. The sand at Kahe Beach is lost offshore. It appears that no sand is lost to adjacent coastal sections, for Kahe Beach is bounded by a jetty to the south and several rock points to the north. Some beach sand is sucked into the intake basin of the Hawaiian Electric Company where it is deposited offshore. Occasionally, HECO removes sand from the intake basin and deposits it at the north end (U.S. Army Engineer District, 1980). This may account for the stability at the north end of the beach within recent years. 114 "o 2 3 4 +10 - 0 --1949 Photomap 44. Kahe Beach -10 --1959 Photographs by Air Survey Hawaii: March 1975 -20 1965 1971 '5 -30 - 1975 -40 - 1979 -50 - Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 115 Nanakuli Beach Park Table 45 - Nanakuli Beach Park. Changes in the Vegeta- The 1,300-foot-long pocket beach at south Nanakuli appears to have tion Line in Feet. a 26-year history of accretion, Data on the vegetation line for transect 2 show a seaward growth of up to 37 feet (Photomap 45, Table 45). From the small changes in the water line, no conclusions can be drawn. Transect Number Observation Period 1 2 May 08, 1949 - May 19, 1959 +27 +16 May 1911959 - Dee 22, 1965 +3 +9 Dee 22, 1965 - Mar 30, 1975 +3 +12 Net Change - Vegetation Line +33 +37 Range - Vegetation Line 33 37 Net Change - Water Line +14 -5 Range - Water Line 37 41 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the diffetence between the observed eytremes in the position of a beach index line. 116 1000 Feet Wan Beach 2 OV na, _7 In ft 'A Photomap 45. Nanakuli Beach Park Photographs by Air Survey Hawaii: March 1975 Absolute change is the change in the position of the vegetation line compared to the earliest or base* year. 117 tation line at transect 3, however, advanced seaward 55 feet during the Ulehawa Beach Park 1959 to 1975 period (Photomap 46, Table 46). This accretion was localized. Over a 30-year period, the 1.5-mile-long beach at Nanakuli has been stable. Between 1949 and 1979, the net change in the position of the Uelehawa Beach has alternating stretches of sand and beachrock; this vegetation line at four of the five transects was under 3 feet. The vege- rock may serve to stabilize the beach. 0 1000 Feet 3 @4t Z Ask. Photomap 46. Ulehawa Beach Park Photographs by Air Survey Hawaii: March 1975 118 Table 46 - Ulehawa Beach Park. Changes in the Vegeta- Maili Beach tion Line in Feet. Offshore of Maili Beach is a dead reef flat that is sufficiently deep to allow high waves to break on the shore. As a result; sand on the beach is constantly shifting over the seasons and years in response to the Transect Number changing wave regime. Observation Period 1 2 3 4 5 Field surveys taken between 1962 and 1963 indicate that north Maili Beach has a seasonal variation of about 75 feet. During the winter, the foreshore slope is fairly steep, whereas in the summer it is flat (Moberly May 08, 1949 - May 19,1959 -7 -6 +8 -5 and Chamberlan, 1964). These seasonal changes indicate an onshore- offshore sand exchange between the beach and the nearshore area. May 19, 1959 - Mar 30, 1975 +3 +5 +55 -6 -1 Mar 30, 1975 - Mar 13, 1979 +5 +3 -4 0 +5 Over a long-term period, the middle section of Maili has grown while the two ends have experienced chronic erosion. At north Maili Beach Net Change - Vegetation Line + 1 +2 +51 +2 -1 erosion along a 2,500 stretch appears continuous. During the 1949 to Range - Vegetation Line 8 8 55 8 6 1979 interval the vegetation line at transect 8 receded by as much as 72 Net Change - Water Line +191 +31 -10 -1 +13 feet (Photomap 47, Table 47). The major erosion was concentrated Range - Water Line 611 51 29 68 73 during the 1949 to 1959, 1965 to 1971 and 1975 to 1979 intervals. The retreat during the 1965 to 1971 period was partly caused by the winter No data waves of 1968 and 1969. During this time, erosion undermined a Change from 1959-1979 shower facility and threatened the park comfort station (U.S. Army Net change is the total change in the position of a beach index line between the Engineers, 1971). The erosion during 1975 to 1979 may have been earliest and most recent observation year caused, in part by the Kona Storm of January 1979. Range is the difference between the observed extremes in the position of a beach index line. A continuation of the erosion trend at North Maili would undermine more coconut trees and jeopardize the park bathhouse. The data from the vegetation line suggest that this is likely. It is always possible that the sand mining operation at Maili caused a delayed retreat in the vege- tation line. Unfortunately, it is not possible to determine the full impact of the mining operation on the beach because of the large sea- sonalchanges. At south Maili Beach, the vegetation line receded 32 feet over a 30-year period. The erosion at transect I was recorded during four of the five observation intervals. -This indicates that shoreline retreat for that beach section predominates through time. In the future the resi- dential areas at south Maili may become susceptible to winter wave inundation. At transect 2, the vegetation line has had a small net change in its po- sition but a range of about 20 feet. This beach section has an alternating history of erosion and accretion. 119 P (IQ 'r ep 40h eb Al eD OU > 14 4F Absolute change in feet 0 0 0 0 0 '4 -4 a, V- 41 U"m 10 Table 47 - Maili Beach. Changes in the Vegetation Line in Feet. Transect Number Observation Period 1 2 3 4 5 6 7 8 9 10 May 08 ' 1949 - May 19, 1959 -11 +14 -11 +17 -13 -33 -25 -42 May 19,1959 - Dec 22, 1965 -3 -11 +3 +37 +19 +18 +9 -8 -6 -1 Dec 22, 1965 - Feb 06, 1971 +7 0 +41 +16 +44 +67 -35 -36 -1 -9 Feb 06, 1971 - Mar 30, 1975 -17 -6 +27 +16 +9 + 1 +2 +34 -20 -12 Mar 30, 1975 - Mar 31, 1979 -8 +20 -10 -19 -4 -4 * -29 -5 +9 Net Change - Vegetation Line -32 +3 +75 +50 +57 +99 -37 -72 -57 -55 Range - Vegetation Line 32 20 85 69 72 103 39 77 57 64 Net Change - Water Line -1 -15 +12 -52 +25+150 +52 -61 -100 -39 Range - Water Line 33 37 49 65 57 150 53 81 138 98 * No Data Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. Over a period of up to 30 years, the section of Maili covered by tran- PokaiBay sects 3 to 6 experienced accretion. Between 1949 and 1979, the vegeta- tion line for the middle of the beach grew seaward by as much as 99 Several artificial structures are found along Pokai Bay. A breakwater feet. The sand for this stretch is possibly delivered from the eroding and launching ramp to the south, a retaining wall in the center, and ends. stone jetties in the middle and north have modified the natural pro- cesses of this beach system. Because of the retaining wall along much of From an inspection of the incoming wave orientations on the aerial the beach, a photographic analysis of the vegetation line was conducted photographs, it appears that two currents may be set up. At the north only for the south end of the bay. end, refracted North Pacific swell would induce a southerly littoral drift. Near the south end of Maili, waves refract around an offshore Data from 1965 to 1977 show the vegetation line near the beach park shoal and strike the beach at an opposite angle. Although the described advanced seaward 58 feet. This is to be expected as the south end of wave directions are seen on only a few of the photographs, they may ex- Pokai Beach has been accreting ever since the breakwater was con- plain the pattern of long-term changes shown in the data. More studies structed in the 1950's. Before this structure was built, the north end,of are required to test this hypothesis. Pokai Beach was much wider than the south end. 121 Studies on the present configuration of Pokai Bay indicate accretion in the south, erosion along the center section where the retaining wall Table 48 - Mauna Lahilahi Beach, Park. Changes in the has been undermined and stability in the north (U.S. Army Engineers, Vegetation Line in Feet. 1971). Occasionally, sand from the accreting southern section has been transferred to the center. The artificial transfer of sand complicates in- terpretation of the water line data. From a qualitative analysis of the aerial photographs between 1965 and 1977, it appears that north Pokai Transect Number Beach has been stable while the center section has varied in width. As the beach at mid-Pokai Bay is narrow, large waves can easily run Observation Period 1 2 3 up the foreshore and break against the retaining wall. Therefore, more Nov 22, 1949 - May 19, 1959 +5 -3 -2 problems with deterioration of this structure may occur. May 19, 1959 - Dec 22, 1965 -13 +2 +3 Mauna Lahilahi Beach Park Dec 22, 1965 - Feb 06, 1971 +13 +5 +4 Data from the vegetation line for Mauna Lahilahi Beach Park indicate Feb 06, 1971 - Mar 30, 1975 +11 0 +5 beach stability or accretion over a 28-year period. Between 1949 and Mar.30, 1975 - Dec 20, 1977 +6 0 + 1 1977, the vegetation line for transect I grew seaward 22 feet (Photomap 48, Table 48). Net Change - Vegetation Line +22 +4 +11 Range - Vegetation Line 30 7 13 It is unusual @Ihat the changes in the vegetation line and water line Net Change - Water Line -1 -63 -46 show opposite trends. Over the study period the water line receded by Range - Water Line 19 63 50 as much as 63 feet. This loss, which was concentrated during the 1949 to 1959 period, has exposed rock at the ends of the beach. It is not Net change is the total change in the position of a beach index line between the known how much of this change is seasonal. In addition, wave runup earliest and most recent observation year and light reflection complicate the measurements of the water line. Range is the difference between the observed extremes in the position of a beach index line. Although the vegetation line has grown seaward over a long-term period, the narrow beach and steep offshore bottom may make the park property susceptible to erosion by high waves. Fortunately, Lahilahi Point may block some of the wave energy refracting from the north. 122 Lahilahi Point 0 250 500 750 1000 Feet k, N 3 If 2 40 4 q, Photomap 48. Mauna Lahilahi Beach Park Photographs by Air Survey Hawaii: March 1975 123 Papaoneone Beach (Turtle Beach) Table 49 - Papaoneone Beach (Turtle Beach). Changes in Papaoneone Beach is a closed littoral cell bounded on the south by the Vegetation Line in Feet. Lahilahi Point and on the north by exposed rock (Photomap 49). The offshore reef is not sufficiently shallow to absorb much of the incoming wave energy. As a result, this beach may receive high winter surf that Transect Number could form strong rip currents and beach cusps. Observation Period 1 2 3 Between 1949 and 1977, the vegetation line for the south and north ends of the beach grew seaward (Table 49). Over the same period the water line had a small net change in its position but a large range. This Nov 22, 1949 - May 19, 1959 +43 -20 +21 indicates that the major changes at Papaoneone Beach are seasonal. May 19, 1959 - Dec 22, 1965 -14 +11 Limited data were obtained for the center of the beach where two tall Dec 22, 1965 - Feb 06, 1971 +8 -3 buildings are located. These structures obscure the position of the vege- tation line on the aerial photographs. Before these structures were Feb 06, 1971 - Mar 30, 1975 + 1 -9 built, the vegetation line at mid-beach receded 20 feet during the 1949 to 1959 period. Meanwhile the water line had a small change. This sug- Mar 30, 1975 - Dec 20, 1977 +7 +3 ests that Papaoneone Beach may be stable over a long-term period but may erode temporarily during a large winter storm. Net Change - Vegetation Line +45 -20 +23 Range - Vegetation Line 45 32 As the buildings at Papaoneone Beach are located close to the shore- Net Change - Water Line +4 -7 +21 line, the potential exists that high winter waves may run up onto the Range - Water Line 80 75 beach and inundate the lower patios. *No Data Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 124 0 250 500 750 A Lahilahi Point 4 [email protected] 01- 6 -4i @J* 3 A, Transectl Photomap 49. Papaoneone Beach (Turtle Beach) +50 - 1977 -1--1, 1959 Photographs by Air Survey Hawaii: March 1975 +40 - 1975 1971 Z +30 1965 +20 +to X 0 1949 C Absolute change is the change in the position of the vegetation line compared to the earliest or base year. 125 Makaha Beach Table 50 - Makaha Beach. Changes in the Vegetation During the 30-year period from 1949 to 1979, the vegetation line at Line in Feet. the south section of Makaha Beach grew seaward. Nevertheless, ero- sion was recorded for transects I and 2 during the 1975 to 1979 time in- terval. This change can be attributed in part to the Kona Storm of Janu- Transect Number ary 1979. The north section of Makaha Beach Park (the bathhouse to transect Observation Period 1 2 3 3) may be retreating slowly. On the 1949 photograph, an old railroad track running parallel to the Farrington Highway is seaward of the vege- Nov 22, 1949 - May 19, 1959 +24 +10 -20 tation line. Between 1949 and 1979 the vegetation line at transect 3 May 19, 1959 - Dec 22, 1965 0 +18 +16 receded 22 feet (Photomap 50, Table 50). The bathhouse at Makaha Beach Park was damaged by high winter Dec 22, 1965 - Fe .b 06, 1971 +9 + 1 -5 surf in the early'1960's and late 1970's. Apparently no allowance was Feb 06, 1971 - Mar 30, 1975 +12 @-5 + I made for the large seasonal changes on the beach. During the June 1962 to January 1963 period, Makaha Beach varied in width by 145 Mar 30, 1975 - Mar 13, 1979 -13 -9 -14 feet. These variations are believed to be caused by North Pacific swell refracted around the island (Moberly and Chamberlain, 1964). Net Change - Vegetation Line +32 +25 -22 Range - Vegetation Line 45 34 22 Although the bathhouse at Makaha was under repair during Septem- Net Change - Water Line -1 +10 +5 ber 1980, it is still in the same location and therefore subject to the Range - Water Line 63 32 46 same forces that damaged it previously. Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. 126 WWke,Ouhi,Poin* 01 [email protected] C. ;X J 3 2 41 t j Transect 3 Photomap 50. Makaha Beach +10 - Photographs by Air Survey Hawaii: March 1975 0 1949 1965 -to 1975 1971 2 1959 1979 < -30 Absolute change is the change in the position of the vegetation.line compared to the earliest or base year. 127 Keaau Beach Table 51 - Keaau Beach. Changes in the Vegetation Line The vegetation line at Keaau Beach has had a history of alternating in Feet. erosion and accretion. No clear pattern is seen from the changes. Most likely there is a tendency for the vegetation to grow seaward. Transect Number Occasionally, the vegetation is cut back when high winter surf runs up onto the beach. The degree of erosion may vary from place to place Observation Period 1 2 3 4 depending on incoming wave parameters, the location of reefs or ex- posed beachrock and the offshore bathymetry. Nov 22,1949 - May 19, 1959 +3 +23 -9 +14 The major erosion at Keaau Beach occurred during the 1965 to 1971 May 19, 1959 - Dec 22, 1965 -8 +107 -7 -8 period. This loss was probably caused by North Pacific swell which was refracted around the, island. In particular, the large waves during the Dec 22, 1965 - Feb 06, 1971 -10 -37 0 -26 winter of 1968 to 1969 and December 1969 may have been an important factor. Feb 06, 1971 - Mar 30, 1975 -2 -22 -2 -16 Transect 2 marks an especially unstable portion of the beach (Pho- Mar 30,1975 - Mar 13, 1979 +11 -6 +8 +11 tomap 51). The large changes are partly due to the growth of sparse vegetation that is occasionally cut back by high surf inundation. It ap- Net Change - Vegetation Line -6 +65 -10 -25 pears that this beach section may experience greater than average Range - Vegetation Line 20 130 18 50 winter wave runup. Net Change - Water Line -40 -41 -34 -51 Range - Water Line 77 67 74 57 The data from the water line at Keaau Beach show a net loss of 34 to 51 feet over a 30-year period (Table 51). Much of this change may be Net change is the total change in the position of a beach index line between the seasonal. earliest and most recent observation year Range is the difference between the observed extremes in the position of a beach index line. -128 0 500 1000 Feet A Transect 2 d2 ri +140 - 3' 71 +130 1965 4 +120 +110 "-Irrington +100 - 1971 +90 - +80 - +70 1975 +60 1979 +50 - Photomap 51. Keaau Reach +40 - Photographs by Air Survey Hawaii: March 1975 +30 - 1959 +20 - +10 - 0 1949 Absolute change is the change in the position of the vegetation line compared to the earliest or base year. -10 1.29 Makua Beach Table 52 - Makua Beach. Changes in the Vegetation Line Generally, the vegetation line at Makua Beach has had small changes in Feet. over a 26-year period. The net change is under 20 feet for all the tran- sects established at this beach (Photomap 52, Table 52). The large loss at transect 1 during the 1949 to 1965 period is possibly Transect Number attributed to a clandestine sand mining operation. On the 1965 aerial Observation Period 1 2 3 4 photograph, the vegetation appears stripped and numerous tire tracks are on the beach. May 08, 1949 - Dec 22, 1965 -60 -4 -17 Dec 22, 1965 - Feb 06, 1971 +34 +3 +6 +81 Feb 06, 1971 - Mar 30, 1975 +10 -1 +9 +3 Net Change - Vegetation Line -16 -2 -2 +11 Range - Vegetation Line 60 4 17 11 Net Change - Water Line -33 +21 +50 -14 Range - Water Line 104 46 50 14 *No data 1 Change from 1949- 19 71 Net change is the total change in the position of a beach index line between the earliest and most recent observation year Range is the difference between the observed extre in the position of a beach index line. 130 500 1000 Feet 4,4" 4 A 2 3 N 'AW, AW, "I' Photomap 52. Makua Beach Photographs by Air Survey Hawaii: March 1975 1.31 Yokohama Beach (Keawaula) Table 53 - Yokohama Beach (Keawaula). Changes in the The measurements to the water line and vegetation line at Yokohama Vegetation Line in Feet. were made from a point on a stable reference line. Although this proce- dure introduces inaccuracies, it was the only way to obtain data for the beach. Therefore the data should be regarded as a first approximation, Transect Number subject to later revision. Yokohama Beach is a confined littoral cell bounded by rocky coast to Observation Period 1 2 3 either side (Photomap 53). Between 1949 and 1979, this beach lost up to 64 feet from the vegetation line and 124 feet from the water line May 08, 1949 - May 26, 1972 -9 -84 -13 (Table 53). The major change, during the 1949 to 1972 period, is at- May 26, 1972 - Mar 30, 1975 +3 tributed to an extensive sand mining operation. In 1957, 54,455 cubic yards (almost 1.5 million cubic feet) of sand Mar 30, 1975 - Mar 21, 1979 _91 +201 was removed to build Ala Moana Beach (Campbell and Moberly, Net Change - Vegetation Line -18 -64 -10 1978). The effect of sand mining is especially noticeable at the south- Range - Vegetation Line 18 84 13 east end of Yokohama. At this section, retreat of the beach since 1949 Net Change - Water Line -124. -71 -49 has exposed rock along the shoreline (Plate 14). Although this change Range - WaterLine 124 84 49 may be seasonal it appears unlikely. All the aerial photographs used in the study of Yokohama were taken during the spring months. Further- *No Data more, the rocks were exposed during the end of summer 1980, when 1 Change from 19 72- 19 79 the beach should have been in a high accretion state. Net change is the total change in the position of a beach index line between the earliest and most recent observation year It may take some time before Yokohama returns to its former width. Range 'is the difference between the observed extremes in the position of a This beach receives no sand from adjacent coastal sections or by river beach index line. runoff. An offshore reef exist, but it is uneven and slopes moderately seaward. 132 [email protected] A A [email protected] A Mli,till, M r "A V 3 V WE V 14, Photomap 53. Yokohama Beach (Keawaula) Photographs by Air Survey Hawaii: May 1972 133 Plate 14. Yokohama Beach (Keawaula). The loss to the beach from sand mining is shown on the 1949 and 1972 photographs for Yokohama. 1949 Oki," 1972 134 MANAGEMENT PROBLEMS ON OAHU Once a house.or park facility is constructed along an eroding shore- For beaches on the north shore, seawalls may provide adequate pro- Jine, the difficult question must be faced of whether to save the build- tection from normal winter waves. During a large storm or tsunami, ings or preserve the beach. For most cases in the past, artificial struc- however, these structures will eventually fail or be overtopped. When tures have been placed on the beach to protect endangered buildings. this occurs the loss to the resident may be greater than if the structure had never been built. For this situation, seawalls have two evils. Not Each year an increasing percent of Oahu's shoreline is spanned by only do they encourage development in hazard areas, but they give the seawalls, stone revetments, and boulder piles. This trend can be seen homeowner a false sense of security. on the aerial photographs for Mokuleia Beach, Kawailoa Beach, Laniloa Beach, Lanikai Beach, Bellows Air Field Beach, and Ewa Beach. In ad- The management problems presented here have one common root. dition, future problems at Kailua Beach, Iroquois Point, Kahe Beach Development was too close to the shore. No allowance was made for and Maili Beach may lead to the proposal of more erosion-control the dynamic nature of the beach. structures. To prevent problems before they begin it will be necessary to place Several problems are associated with some artificial structures. buildings sufficiently inland so that the natural changes of the beach Besides being detrimental to scenic views, structures may also reduce can take place. The 20-to 40-foot setback established by the Land Use the recreational utility of the beach. For example, a seawall may reflect Commission of the State of Hawaii will not protect homeowners or pre- wave energy, causing sand to be carried offshore. Therefore, a beach serve the beach. For example, Kualoa Point eroded 350 to 400 feet that recedes during the winter might never regain its former width in over a 50-year period. At Iroquois Point, the vegetation line and water the summer if a seawall were built in the interim. As a consequence, line receded about 180 feet between 1928 and 1976. When erosion access along the shore would be blocked and the beach could not be began at Kailua Beach Park or South Lanikai, the vegetation line reced- used for picnics or sunbathing. In this manner, seawalls have reduced ed at a rate of more than 10 feet per year. the total length of recreational beaches on Oahu. With the ever- increasing demand for limited beach resources, it is apparent that this The Coastal Zone Management Act of 1977 gives the counties juris- trend will lead to greater conflicts in the future. diction over an area extending 100 yards inland of the kahakai. The kahakai is the line of greatest annual wave reach as marked by debris Another concern with some remedial measures is the possible dis- left by the highest reaching waves with mean annual frequency, or by ruption of the littoral cell. At Mokuleia Beach, seawalls and stone revet- the seaward edge of the vegetation excluding especially salt-tolerant ments cause erosion at the flanks. Therefore, more protective struc- species (Cox, 1978). tures may be proposed. At Kualoa Beach, groins accelerate erosion to the south and appear to be the ultimate cause of erosion at the beach From the aerial photographic study of Oahu, the minimum lWyard park. If certain erosion-control structures were installed at north Kailua zone of the special management area should be sufficient to prevent Beach, sand might accumulate at one end of the littoral cell and result erosion problems on all the beaches except for Kualoa Beach Park. As in subdivision of the beach system. the counties have control on construction within this zone, new amend- ments to the setback rules and regulations should not be required. 135 MANAGEMENT STRATEGY The characteristic long-term change for a beach may vary significant- At Mokuleia Beach, several houses are less than 20 ly from one system to the next. Therefore, to generalize all beaches by feet from the edge of the vegetation line or a seawall. having one arbitrary setback for the entire island can only lead to prob- One house under construction was less than 10 feet lems in the future. from the vegetation line as of January 1981. Because of this development close to the shore, the potential for In the study for Oahu, it was found that the beaches could be placed disaster involving loss of life and property damage into five management categories based on their history of erosion and from events similar to the December 1969 storm and accretion and their susceptibility' to inundation by large winter waves. the tsunamis of 1946 and 1957 has increased These categories are presented below. enormously. (1) Hazard Areas are subject to inundation by large storm Recommendations: (A) In hazard areas, an 80-foot waves. The beaches on the north shore of Oahu have setback should be established to minimize the damage been placed in this category. Every winter, residents from large Waves. New subdivisions that require the on this coast are threatened by high surf. In addition, construction of houses within this 80-foot, zone should the north shore is particularly susceptible to tsunami not be approved. This recommendation would not re- damage, although this threat is common to all sections quire amendments to the Shoreline Setback Rules and of the island. Regulations of the City and County of Honolulu. Under the Coastal Zone Management Act of 1977, the From past history, it is apparent that a 40-foot setback counties have been given jurisdiction over an area ex- line is not sufficient to prevent problems on the north tending 100 yards inland. shore. Houses built this close to the vegetation line often require the construction of a seawall or revet- The rationale for selecting 80 feet as an appropriate set- ment for protection from large waves. These protective back is the following. During 1967 to 1971, the pho- structures may give the homeowner a false sense of tographic data indicate that the vegetation line for security. The seawall or revetment may provide ade- many of the beaches on the north shore receded more quate protection during normal winter waves, but the than 40 feet. This erosion is attributed to the winter large storm or tsunami that occurs every decade or two storm of December 1969. It would be dangerous to can cause considerable damage. place buildings within 40 feet of the vegetation line when erosion of this magnitude can occur during one During the December 1-4, 1969 storm, structural brief event. damage from large surf was experienced on every de- veloped beach on the north shore. At west Sunset The data from the vegetation line indicate none of the Beach alone, 14 homes were damaged or destroyed beaches on the north shore eroded more than 80 feet (State of Hawaii, DLNR, 1970). Yet, when property during the 1967 to 1971 interval. This does not preclude along this beach was redeveloped, several homes were the possibility, however, that erosion of 80 feet did placed closer to the shore than before the storm. Con- occur during the December 1969 storm. Significant sea- struction at this beach and the rest of the north shore ward growth of the vegetation line may have transpired has continued with no regard to the dangers involved. 137 during the time after the storm and 1971, when the may be utilized is given for Laniloa Beach on the wind- next aerial photographs of the north shore were taken. ward coast. The photographic data for hazard areas does not allow The vegetation line at Laniloa Beach has had a history a precise determination of a suitable setback for each of continuous retreat. On the 1949 aerial photograph, beach. When more data become available, this 80-foot fallen trees on the beach indicate prior erosion. Be- zone can be adjusted. As the major long-term changes tween 1949 and 1975, the vegetation line receded 70 in hazard areas occur intermittently during large storm feet. On a field check in 1980, the northeast tradewind events, a beach mobility-energy classification scheme waves broke against the base of an erosional scarp in should be considered (Nordstrom, 1979). This plan the vegetated dune field, indicating that the erosive would require the daily monitoring of beaches in the trend is still in process. hazard area category over a two-month period. Although the littoral processes at Laniloa are not fully (B) When houses or other structures are destroyed by known, the historic data allow the prediction that ero- large waves, reconstruction on the plot of land should sion will continue in the future. From the aerial pho- be carefully analyzed and in some cases advised tographic measurements, an average rate of retreat of against. If redevelopment of the land is to occur, the up to three feet per year can be expected. use of pile supports to elevate buildings should be con- sidered. It should be realized that areas inundated by In determining the inland extent of prohibitive beach large waves have a beach profile and offshore reef development at Laniloa, planners should multiply the structure that make them susceptible to damage from rate of erosion by the life expectancy of a structure and future storms. then add 40 feet as a buffer. For example, if a house has a 40-year-life expectancy, it should be placed at (C) The practice of cutting down storm berms and least 160 feet inland to preserve the beach. Placing the dunes to provide vistas for homeowners should be dis- house any closer insures that some type of remedial couraged. These beach features provide a natural pro- measure will be required to protect the building in the tection against large waves and in some areas their future. removal can accelerate erosion (K. Keller, personal communication). Recommendations: (A) Periodic field surveys or aerial photographic studies should be made to deter- mine significant changes in the rate of retreat for (2) Chronic Erosion Areas. Beaches with a long-term his- chronically eroding beaches. Kualoa Point has had a tory that indicates erosion will continue in the future steady increase in the rate of erosion from 4 feet per are here defined as chronically eroding. The beaches in year to 8 feet per year to more than 17 feet per year. this category include Iroquois Point on the south Laniloa Beach has a rate that varies from 1-4 feet per shore, Maili Beach and Kahe Beach on the leeward year. Erosion at Iroquois Point has ranged from 1-5 coast, and north Kahuku Golf Course Beach, Laniloa feet per year. Beach, Hauula Beach Park, Kualoa Beach Park, and Bellows Air Field Beach on the windward coast. (B) New subdivisions requiring the construction of buildings in the chronic erosion area should not be al- The management of chronically eroding beaches lowed. The extent of an appropriate setback should be should be based on historic studies on the rate of ero- based on the local rate of erosion and the life expectan- sion as determined by aerial photographs, maps, charts cy of the proposed structure. and field surveys. An example of how these studies 138 (3) Unstable 'Beaches have an alternating history of ero- (B) An appropriate setback may be obtained by adding sion and accretion. The long-term changes on these the historic range in the position of the vegetation line beaches are unpredictable and dependent partly on and 40 feet as a buffer. Subdivisions in which houses meteorological conditions. Areas on Oahu in this must be placed within the setback zone should not be category include Malackahana Beach, Kailua Beach, approved. Lanikai Beach, sections of Waimanalo Beach, and Makapuu Beach on the windward coast and Sandy (4) Accreting Beaches have a long-term history that indi- Beach Park, Ewa Beach and Nimitz Officers Beach on cates accretion will continue in the future. The the south shore. beaches in this category are relatively few. They in- clude Kaiaka Bay and Kawela Bay on the north shore; Development on unstable areas should be far enough Kahana Bay, Kaluanui Beach and Punaluu Beach on inland to allow for the natural changes of the beach. the windward coast and Nanakuli Beach Park on the This has not occured at Lanikai Beach and Ewa Beach. leeward coast. On these beaches, seawalls span large portions of the shore even though Lanikai may have a constant sand Generally, no major problems exist on accreting budget and Ewa appears to be accreting. beaches except at Kawela Bay, where houses were damaged by the 1946 tsunami and the December 1969 An appropriate setback to prohibit development on storm. This beach also falls in the hazard area category unstable beaches may be obtained by using the historic and management should therefore follow the guide- range in the position of the vegetation line. For exam- lines previously described. ple, the vegetation line at Kailua Beach Park has a range of about 150 feet between its maximum accre- The major issue on accreting beaches is one of land tion and erosion state. When a 40-foot buffer is added, ownership. At Kawela Bay, Kaluanui Beach and Puna- inland development at this section should be no closer luu Beach, residential dwellings are located in the back- than 190 feet. shore zone. At the north end of Kailua Beach, the range in the posi- (5) Stable Beaches have had a small net change and range tion of the vegetation line over a 29-year period was in the position of the vegetation line. No major prob- about 60 feet. Therefore, development any closer than lems exist on these areas, except for the potential of 100 feet to the edge of the vegetation line should be damage from tsunamis and storms. prohibited in order to preserve the littoral cell. Unfor- tunately, several houses were placed too close to the Areas that have been stable over a long-term period in- vegetation line on a portion of the beach that grew be- clude sections of Laie Beaeh, Kokololio Beach, sec- tween 1971 and 1978. Since 1978, erosion has set in tions of Katuanui Beach, the stretch from Mahie Point and the houses now require the protection of sand bags to Swanzy Beach Park, the stretch from Niu Beach to and tires. If the trend continues, remedial measures Kuilei Cliffs Beach Park, Oneula Beach, Barbers Point, will be proposed that could disrupt the entire beach Ulehawa Beach Park and Mauna Lahilahi Beach Park. system. On table 54, the beaches of Oahu have been placed into the five Recommendations: (A) On unstable beaches, devel- management categories. Some of these beaches may fall into more than opment on portions of the beach in an accreting cycle one category. In other cases, one section of the beach may have a dif- should be avoided because erosion can set in as part of ferent classification from another. Finally, there are some beaches that the normal sequence. await classification until more data become available. 139 The @beach -classification scheme presented here is lyased o n a ments for a particular beach were not representative of the long-term determination of historic beach trends. Although the past record gives trend. For this reason it is necessary to continuously update the data the best insight into possible future trends, there is no guarantee that file on the beaches. This could be done with periodic field surveys or these changes will occur. It may be found that the past shoreline move- aerial photographs taken every five years. Table 54 - Oahu Beach Classification. The Numbers in Parenthesis Refer to the Established Transects at the Beach. NORTHSHORE WINDWARD COAST Mokuleia Beach Hazard Kahuku Golf Course Beach Erosion (I) -Stable Kaiaka Bay Beach Hazard-Accretion Malaekahana Beach Unstable Stable (4) Haleiwa Residential Area Hazard to Alii Beach Park Laie Beach Unstable (1,2,6) Stable (3 to 5) Haleiwa Beach Park Hazard Accretion (7) Kawailoa Beach Hazard Laie Point to Pali Kilo la (Laniloa Beach) Erosion (5 to 7) Waimea Bay Beach Park Hazard-Erosion Unstable (4) Stable (1 to 3) Pupukea Beach Hazard (Pounders Beach) Unstable Sunset Beach Hazard Kokololio Beach Stable Sunset Point to West Kawela Hazard-Erosion (1,2,8) Hauula Beach to Makao Beach Erosion (2,3) Unstable (5 to 8) Kawela Bay Hazard- Accretion Stable (1,4) Turtle Bay Hazard Kalaipaloa Point to Waiono Stream Unstable (1,2,6,7,8) Stable 0 to 5) Kaihalulu Beach Hazard Accretion (between 2+3) Hanakailio Beach Hazard Punaluu Beach Park and Residential Area Stable (3,4) Accretion (1,2) Kahana Bay Beach Park Accretion 140 Mahie Point to Swanzy Beach Park Erosion (4) Ewa Beach Unstable 0,4 to 7,9,10) Stable G to 3) Stable (8) Accretion (2,3) Kaaawa Residential Area Unstable (I to 4, 7,8) to Kalaeokaoio Pt. Stable (5,6) Oneula Beach Stable Kualoa Beach Erosion Nimitz Officers Beach Unstable Kailua Beach Unstable Nimitz Beach Unstable (2) -Accretion Accretion (7 to 11) Barbers Point Stable Lanikai Beach Unstable Stable (6,7) LEEWARD COAST Waimanalo Beach Erosion Q to 4) Lanikuhonua Beach Unstable Unstable Kahe Beach Erosion (2) Kaupo Beach Stable(north) Unclassified Unclassified Nanakuli Beach Park Accretion Makapuu Beach Park Unstable Ulehawa Beach Park Stable SOUTHSHORE Maili Beach Erosion 0,7 to 10) Sandy Beach Park Unstable Unstable (2) Accretion (3 to 6) Hanauma Bay Beach Par k Unclassified PokaiBay Unstable-stable (north) Paiko Peninsula Unstable Accretion (south) Niu Beach to Wailupe Peninsula Stable-Accretion (3) Mauna Lahilahi Beach Park Unstable (1) -Stable Wailupe Beach Park and Residential Area Stable Papaoneone Beach (Turtle Beach) Unstable Kahala Beach Unstable (1,2)-Stable Makaha Beach Hazard-Unstable Kaalawai Beach and Stable Keaau Beach Hazard-Unstable Kuilei Cliffs Beach Park Makua Beach Unclassified (1) Iroquois Point Erosion (6,7) Unstable (3) -Stable Accretion (2 to 4) Stable (1) Yokohama Beach (Keawaula) Unclassified 141 SUMMARY From the aerial photographic survey of Oahu's shoreline, the follow- (4) Beaches on the south shore have been relatively stable ing conclusions may be drawn. over the study interval. The exceptions are Paiko Peninsula and Iroquois Point. A brief period of erosion (1) The most unstable beaches on Oahu are located on between 1967 and 1971 was experienced at Sandy sand bodies projecting from the coastline. Examples of Beach Park, Hanauma Bay, sections of Paiko Peninsu- these features include Paiko Peninsula, Kualoa Point la, and east Kahala Beach. Ewa Beach eroded between and Iroquois Point. 1958 and 1967. Many of the seawalls at Ewa were con- structed during this time. (2) On the north shore beaches are wide and have a large seasonal change. Generally, no permanent damage to (5) On the leeward coast, Kahe Beach and the ends of the backshore area occurs unless large waves overwash Maili Beach experienced chronic erosion. Most other the beach zone. This situation may occur during a beaches had no apparent'long-term change. Neverthe- strong winter storm or tsunami. Aerial photographs less, periodic damage to the backshore area may occur record the effects of the December 1969 storm, 1946 from refracted North Pacific swell or Kona Storm tsunami and possibly the 1957 tsunami. For -many waves. Beaches that appeared susceptible to inundation beaches on the north shore, the largest retreat in the over a 26-year period include mid-Pokai Bay, Papao- vegetation line over a period of 26 to 30 years occurred neone Beach, Makaha Beach and Keaau Beach. during the December 1969 storm. At Waimea Beach, almost half the loss in the vegetation line over a The beaches of Oahu have been placed into five management catego- 47-year period occurred during this brief event. ries based on their history of erosion and accretion, and their suscepti- bility to inundation from large waves. Beaches on the north shore have (3) Beach changes on the windward coast are caused by been placed in the Hazard Area category. It is recommended that the trade wind waves and refracted North Pacific swell. setback line on this coast be increased by the distance of 80 feet to mini- The large long-term changes at Kailua Beach, Lanikai mize the damage from large winter storms and tsunamis. Chronic Ero- Beach and Kualoa Beach are partly caused by variations sion Areas have a long-term history that indicates that erosion will con- in sand transport along the shoreline. Chronic erosion tinue in the future. On these beaches, an appropriate setback line may areas on the windward coast include North Kahuku be obtained by multiplying the rate of erosion by the life expectancy of Golf Course Beach, middle and south Laniloa Beach, the structure and then adding 40 feet as a buffer. Unstable Beaches Hauula Beach Park, Kualoa Beach Park and Bellows. have had an alternating history of erosion and accretion. The long-term Air Field - Beach. Erosion problems exist at Kalanai changes on these beaches are unpredictable and are dependent partly Point, Swanzy Beach Park, Kaaawa Beach Park, the on meteorological factors. In order to preserve the beach, planners ends of Kailua Beach, Lanikai Beach, and Waimanalo should use the historic range in the position of the vegetation line to Beach. Accretion was found at Kaluanui Beach, Puna- determine a suitable inland setback. Development on Stable Beaches is luu Beach and Kahana Bay. generally not a problem except for the threat from tsunamis. On Accret- ing Beaches the major issue is one of )and ownership. 143 BI,BLIOGRAPHY, Bretschneider, C. L. and P. G. Wybro, 1975.,Inundations and Forces Dollar, S. J. 1979. Sand Mining In Hawaii ([email protected], Restrict.ions and Caused by'Tsundmis- for. the State 'of Hawaii. Tech. Su'ppl. No. 5. Choices.for the Future). Univ. of Hawaii Sea Grant College Program Hawaii Coastal Zone Management Program.- Honolulu, 88 p.' Tech. 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