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CIA& RECOMMENDATIONS FOR Jf FRESHWATER DIVERSION S TO LOUISIANA ESTUARIE EAST OF THE MISSISSIPPI RIVER .1V Tc 425 .M66 .L8 DEPARTMENT OF NATURAL RESOURCES R46 1982 COASTAL MANAGEMENT SECTION Cover: A pigme of turbid water emanates from Bayou Lamoque as freshwater is diverted from the Mississippi River into the Breton Sound estuary to control salinity levels and enhance oyster production (p.-2). This document was published at a cost of $ 3.17 per copy by the Louisiana Department HT O@F IV@ of Natural Resources, P.O. Box 44396, Baton Rouge, Louisiana, for the purpose of carrying out the requirements of the Louisiana Coastal Zone Management Program under the authority of Act 361 of 1979. This material was printed in accordance with the standards for printing by state agencies established pursuant to R.S. 43:31 and was M Ln purchased in accordance with the provisions of Title 43 of the Louisiana Revised Statutes. This project was financed through a grant provided under the Coastal Management Act of 1979,, as amended, which is administered by the U.S. Office of Coastal Zone Management, National Oceanic and Atmospheric Administration. RECOMMENDATIONS FOR FRESHWATER DIVERSION TO LOUISIANA ESTUARIES EAST OV. THE MISSISSIPPI RIVER by J. L. van Beek D. Roberts D.. Davis D. Sabins S. M. Gagliano Db Coastal Environments, Inc. Baton Rouge, LA This study was funded by: Office of Coastal Zone Management National Oceanic and Atmospheric Administration Department of Commerce prepared f or: Coastal Management Section Louisiana Department of Natural Resources Baton Rouge, Louisiana JUNE 1982 TABLE OF CONTENTS List of Photos ........ iii CHAPTER IV: SUPPLEMENTAL FRESHWATER REQUIREMENTS ............... 13 List of Figures ....... iii List of Tables ...................... .............. o........... ....... iii Method of Analysis .......... ...... o.............................. 13 Acknowledgements ........... o................... o................... o .... iv Freshwater Inflow Data ..... o ....... o ...o...... o ....................... 13 Freshwater and Salinity .... o............ o.................... o ......... 16 CHAPTER 1: INTRODUCTION ...................... o ....................... 1 Results of Analysis ............. o ....... o.............................. 16 Freshwater Needs ................................. o.. o............ o ... 17 Review of Past Work ........................... o .............. 2 Diversion Volumes ..................................................... 18 Scope of Present Work ....... o .......o .......... o...................... 2 CHAPTER V: PROPOSED SITES FOR FRESHWATER DIVERSION ............. 23 CHAPTER H: ANALYSIS OF SALINITY-INDUCED HABITAT CHANGE, 1955-1978 ........................................... o............... 3 General Considerations ................................................. 23 Site Analysis ........... o............. o ............ o ................... 24 Pontchartrain Watershed ........ ......... o.......... 4 Pontchartrain and Lake Borgne Watersheds ............................. o.. 26 Lake Borgne Watershed ....................... o... o.................... 4 Breton Sound Watershed ....... o ............ o ........................... 29 Breton Sound Watershed ............... ...... ...... o ....... 4 CHAPTER VI: PREDICTED RESULTS AND POSSIBLE IMPACTS ................ 31 CHAPTER III: GOALS FOR ENVIRONMENTAL RESOURCE MANAGEMENT ...... 5 Pontchartrain Watershed ......... ................... - .............. 31 Habitat Types and Optimum Salinity Regimes ....................... 5 Lake Borgne Watershed ................... o ............ o ............ 32 Environmental Units and Management Goals .............................. 9 Breton Sound Watershed ....... o ........... o ...... 33 Pontchartrain Watershed ........ o... o .............................. 9 Effect on Salinity Regimes of the Capture of Mississippi Lake Borgne Watershed ............... o........... o............. o.. 9 River Flow by the Atchafalaya River ................................... 35 MRGO Marsh Unit ....................................... o.. o...... 10 Breton Sound Watershed .......................................... 11 CHAPTER VII: SUMMARY AND CONCLUSIONS ............. o................ 37 REFERENCES .......... o ....... o......................................... 39 PLATES ....... .................................................... 42 LIST OF PHOTOS LIST OF TABLES Oyster boat returning to dock ............................................... I Table 2-1. Approximate Acreages of Salinity-induced Habitat Dead cypress swamp in St. Bernard Parish .................................... 3 Change in the Lake Pontchartrain, Lake Borgne, and Healthy cypress typelogum swamp ........................................... 5 Breton Sound Watersheds ................. ....................... 4 Fresh marsh dominated by cattail ............................................ 7 Table 3-1 Percentage Habitat Utilization by Puddle Ducks in Louisiana trapper skinning muskrat .......................................... 8 Coastal Louisiana .............................................. 6 Ecotone of cypress swamp and fresh marsh, St. Charles Parish ................... 9 Table 3-2 Estimated Fur Catch Per 1000 Acres of Coastal Marsh .............. 6 MRGO at Southern Natural Gas pipeline looking south .......................... 10 Table 3-3 Summary of Life History and Habitat Data for the Intermediate marsh near Caernarvon ......................................... 11 American Oyster ............................................... 9 Industry with river frontage, wetlands in the background ........................ 23 Table 3-4 Summary of Wetland Habitats, Salinity Regimes, and Freshwater siphon at Violet, St. Bernard Parish ................................ 24 their Associated Wildlife and Fisheries Resources ................... 9 Freshwater siphon at Whites Ditch, Plaquemines Parish ......................... 25 Table 4-1 Key to Salinity Stations Used in the Study ......................... 13 Bayou Lamoque Structure #2 ................................................ 26 Table 4-2 Hydrologic Unit I ............................................... 17 Caernarvon Canal, Big Mar, and Braithewaite Park and Table 4-3 Hydrologic Unit H .............................................. 17 Golf Course ............................................................. 28 Table 4-4 Monthly Exceedanee Discharges, Gaged and Corrected Louisiana's renewable wetland resources ...................................... 31 Total ......................................................... 19 Three-eornered grass marsh near Lake Lery ................................... 33 Table 4-5 Mississippi River Stages Near Existing and Proposed Freshwater plume from the Bayou Lamoque diversion structures ................. 35 Diversion Sites for 5.0% and 80% Exceedanee Discharges .................................................... 19 Table 4-6 Estimated Discharges at Bonnet Carre and Resultant Salinities at Bayou St. Malo for Various Structure Sizes (50% exceedanee) ......................................... 19 Table 4-7 Estimated Discharges at Bonnet Carre and Resultant Salinities at Bayou St. Malo for Various Structure Sizes (80% exeeedanee) ......................................... 19 Table 4-8 Predicted Discharges at Bonnet Carre and Resultant LIST OF FIGURES Salinities at Middle Causeway for Various Structure Sizes (50% exceedance) ......................................... 20 Table 4-9 Predicted Discharges at Bonnet Carre and Resultant Figure 4-1 Freshwater sources base map for Hydrologic Units Salinities at Middle Causeway for Various Structure I and H ....................................................... 14 Sizes (80% exceedanee) ......................................... 20 Figure 4-2 Mean monthly predicted salinities for Bayou St. Table 4-10 Predicted Discharges at Caernarvon and Resultant Malo and Middle Causeway with and without the Salinities at Bay Gardene for Various Structure Bonnet Carre diversion for 50% exceedance Sizes (50% exceedance) ......................................... 21 criteria ...................................................... 21 Table 4-11 Predicted Discharges at Caernarvon and Resultant Figure 4-3 Mean monthly predicted salinities for Bay Gardene Salinities at Bay Gardene for Various Structure and Lake Petit with and without the Caernarvon Sizes (80% exceedance) ......................................... 21 diversion for 50% exceedance criteria ............................ 22 Table 4-12 Predicted Discharge at Caernarvon and Resultant Figure 5-1 Proposed diversion plan for Hydrologic Unit I Salinities at Lake Petit for Various Structure at Bonnet Carre ............................................... 27 Sizes (50% exeeedance) ......................................... 22 Figure 5-2 Proposed diversion plan for Hydrologic Unit 11 Table 4-13 Predicted Discharges at Caernarvon and Resultant at Caernarvon ................................................ 29 Salinities at Lake Petit for Various Structure Figure 6-1 Predicted mean fall salinity gradient with 50% Sizes (80% exceedanee) ......................................... 22 exceedance criteria for various Bonnet Carre Table 6-1 Existing Water Quality Near Proposed Sites in the structure sizes ................................................ 33 Mississippi River and Stations in Lake Pontchartrain Figure 6-2 Predicted mean fall salinity gradient for 50% and Breton Sound ............................................... 32 exceedance criteria for various Caernarvon Table 6-2 Annual Operating Schedule of the Louisiana Oyster structure sizes ................................................ 34 Fishery ....................................................... 34 ACKNOWLEDGEMENTS This study was funded by the Office of Coastal Zone Management, National Oceanic and Atmospheric Administration, U.S. Department of Commerce, through the Coastal Management Section of the Louisiana Department of Natural Resources. We wish to thank Mr. Joel Lindsey, CMS Administrator, and Mr. David Chambers, CMS Project Officer, for their support in realizing this study. Execution of this present study would not have been possible without the cooperation of a number of Federal, state, and local agencies and the help of their staff in acquiring hydrologic data, formulating management objectives and review of the final draft. In this regard, we wish to extend our sincere thanks to and acknowledge the contributions of Dr. Robert Muller, State Climatologist; Dr. James Geaghan, Department of Experimental Statistics, Louisiana State University, Messrs. Harry E. Schafer, Jr., John Tarver, Ronald J. Dugas, Robert Ancelet, L. Brandt Savoie, and John F. Burdon of the Louisiana Department of Wildlife and Fisheries; Mr. George Robichaux, Louisiana Department of Health and Human Resources; Mr. Clark Lozes and Dr. Ray Varnell of the Plaquemines Parish Mosquito Control District; Messrs. Cecil W. Soileau, Bill Garret, Robert Buisson, Peter Hawxhurst, Paul Rasmus, and Ms. Nancy Powell, U.S. Army Corps of Engineers; and Mr. Max Forbes, Water Resources Division USGS. Within Coastal Environments, Inc., we are indebted to Dr. Charles Wax for his contribution to water balance analyses and to Douglas O'Connor for data compilation and processing. Susan Pendergraft was responsible for editing and report production and Curtis Latiolais for cartography and drafting. Typing was done by Bettye Perry and layout by Nancy Sarwinski. 1V )6L UL *%ww ows wo, *IWAWOW "W"NOW0, "O'Nomw .0wo -00"04# CHAPTERI INTRODUCTION Oyster boat returning to dock. In recent years, a growing awareness of the directed, preparation of a freshwater diversion plan recommended for consideration by the Senate and environmental problems in coastal Louisiana has under the State and Local Coastal Resources Man- House Committees on Natural Resources include increased interest in implementing major agement Act. It is under this mandate that the the Caernarvon Freshwater Diversion Project in diversions of freshwater and sediment from the present study has been authorized. Plaquemines Parish. This same project has Mississippi River into rapidly deteriorating wetland received renewed local support. Varnell and Lozes areas. This interest is evident at Federal, state Implementation of at least one major freshwater (1981) produced a working draft plan for a and local levels. In recognition of the state's diversion structure was brought a step further in diversion at that location, striving to overcome interest in such projects, in 1979 the Louisiana 1981 when Governor David C. Treen and the State most of the problems associated with the diversion Legislature enacted an amendment to Section Legislature established the Coastal Environment projects at Scarsdale and Bohemia authorized in 213.10 of Title 49, adding Subsection F, which Protection Trust Fund. Associated projects 1964. Review of Past Work (USACE) Mississippi River. and Tributaries Project. and productivity of the outfall area. Such diver- .The report recommended four diversion sites: the sions shall incorporate a plan for monitoring and Barataria Waterway and Empire on the west bank reduction and/or amelioration of the effects of of the river and Scarsdale and Bohemia on the east pollutants present in the freshwater source" The concept of diverting freshwater from the bank of the river. At that time, the total imple- (Louisiana Department of Natural Resources Mississippi River into the surrounding swamps and mentation cost for the plan was estimated at $8.7 [DNRI 1980). marshes is not a new one. In 1906, the second million, with a favorable benefit/cost ratio of 1.65. biennial report of the Oyster Commission of These four diversions were authorized by Congress, This report constitutes Phase I of a planning effort Louisiana recommended that gaps be permitted in however, the state and local governments did not by DNR, Coastal Management Section, directed at the east bank levee in Plaquemines Parish to revi- agree to grant the $741,000 as local assurance, and implementation of a freshwater diversion plan for talize oyster beds made extinct by salty water. the plan was never implemented. For the purposes the Louisiana coastal zone. This phase deals with Ahead of his time in many ways, Percy Viosca, of this study, it should be mentioned that the 1964 the estuarine environments to the east of the Jr. (1927, 1928) described the dependence of plan was only intended to meet the needs of the Mississippi River as combined into Hydrologic Louisiana's fisheries and wetlands on the fresh- Barataria Basin and the Breton Sound Estuary Units I and II, respectively. Unit I comprises the water resources of the Mississippi River. He (Hydrologic Units IV and 11, respectively). estuarine systems, inclusive of directly contribu- foresaw a great problem in the harnessing of the ting watersheds, associated with Lakes Maurepas, river and suggested irrigation of the wetlands with Pontchartrain, Borgne, and the Chandeleur and siphons, as well as conservation of rainfall and In order to quantify the freshwater needs through- Mississippi Sounds. Unit II is made up of Breton groundwater for wetland management. Of the out coastal Louisiana, a series of studies were Sound and surrounding wetlands and levee ridges. conflict between flood control and wetland funded through the USACE in the late 1960s. resources, he states, "It should be considered a These studies, together with contributions by other state and national problem equal in significance to Federal and state agencies, documented salinity The primary objective here is to make detailed agricultural development, to the end that the state regimes, defined salinity goals considered desirable recommendations as to location, manner, and and nation may enjoy a more balanced diet, more from a wildlife (primarily furbearer) and fisheries quantity of discharge diversion from the Mississippi healthful recreation, and enduring prosperity" (primarily oyster) point of view, and determined to River into adjacent estuaries to the east. In (Viosca 1928). what extent freshwater requirements to meet attaining this objective, recommendations, con- defined goals could be met by available surpluses cepts, and data developed in previous work were (Gagliano et al. 1971). Requirements and surplus utilized as a basis and built upon. Partially for determinations were based on continuous monthly that reason the time period considered relative to water balance calculations (Gagliano et al. 1970) salinity regimes extends from 1967 to 1979. The Twenty years later, the economic consequences of and statistical analyses of relationships between present report is further intended to supplement inadequate freshwater supplies to the oyster- calculated freshwater inflow and measured salin- parallel studies by the USACE as part of the producing areas of Plaquemines Parish had become ities in each of Louisiana's estuaries (Light and Louisiana Coastal Areas Study (1982) and the severe enough to warrant action. In 1956, the Alawady 1970). Louisiana Wildlife and Fisheries Commission com- Louisiana and Mississippi Estuarine Areas Study pleted construction of the Bayou Lamoque Diver- (1981a). sion Structure on the east bank of the river. Discharges from this structure have been responsi- Recommendations as set forth in this report are ble for maintaining oysters on several thousand based on the following major elements: acres of water bottoms since that time (Dugas 1981, personal communication). Another structure 1. Analysis of habitat changes and relation- was built in 1977 at Bayou Lamoque to more than Scope of Present Work ship to hydrologic and salinity regimen. double the capacity, and both are presently oper- 2. Development of management goals for the ated solely to meet the needs of the oyster indus- various environmental units as related to try in Breton Sound. The present study re-emphasizes the interest of past and present uses and as affected by the State of Louisiana in the development and freshwater inflow. implementation of a comprehensive freshwater 3. Development of workable statistical diversion plan for its afflicted coastal wetlands. models that define present relationships The state's position is described in Guideline 7.4 of between salinity and freshwater inflow. The first comprehensive plan for freshwater diver- the Louisiana Coastal Resources Program: "The 4. Analysis of possible diversion sites and sion to benefit waterfowl and furbearers, as well as diversion of freshwater through siphons and con- scenarios including structure size vs. commercial fisheries, through habitat enhance- trolled conduits and channels, and overland flow to needs, delivery systems, and outfall plans. ment, was published through the U.S. Fish and offset saltwater intrusion and to introduce nutri- 5. Discussion of expected beneficial results Wildlife Service (FWS) (1964) and was included in ents into wetlands shall be encouraged and utilized and possible adverse impacts of freshwater volume V of the U.S. Army Corps of Engineers whenever such diversion will enhance the viability diversion. 2 4, A@j 4@i CHAPTERII ANALYSIS OF SALINITY AM. 7-4. -.Af1 =Jc- INDUCED HABITAT CHANGE, 1955-1978 Overlays of FWS habitat maps (Wicker et al. 1980) produced at a 1:24,000 scale for the years 1955 and 1978 were compared to assess and map changes in low,* wetland habitat types due to salinity intrusion during the 23-year period. Types of habitat change between the two years that were considered -fresh included transitions of fresh habitats to non types, and baldcypress swamps to fresh- -;4k intermediate marsh. Areas where wetland habitats showed transition to developed types, including urban and agricultural, were not mapped. Areas of change were first mapped at a scale of 1:24,000 then generalized onto 1:125,000-scale maps. Dead cypress swamp in St. Bernard Parish. in addition, areas of b;aldcypress swamp that appeared to be in the early stages of deterioration intermediate to brackish or brackish to saline and transition due to salinity intrusion were map- On the FWS 1955 habitat maps (Wicker et al. 1980) ped. These stressed baldcypress swamps were marshes were classified as either fresh or non- marsh. identified from 1978 color infrared imagery by the fresh. The non-fresh marshes were not further presence of a white mottled pattern, representing defined by salinity level such as intermediate, The map of the Louisiana coastal marsh types by a dead or stressed condition of the ground cover, brackish, and saline as was done for the 1978 O'Neil (1949) was used as an important data base showing through a thinned, sparse canopy cover. habitat maps. Therefore, it was impossible to by Wicker et al. (1980) in producing the 1955 habitat maps. Because O'Neil's map is somewhat Swamps being stressed by continual impoundment delineate salinity-induced changes between the more generalized than later efforts, such as the rather than by salinity intrusion were not mapped. years within the non-fresh marsh type, such as 3 coastal marsh vegetative type map of Cbabreck climatic events in southeast Louisiana, such as the Although not mapped, changes have also occurred and Linscombe (1978), the intermediate marsh occurrence of hurricanes, waters of salinities of in the marsh types classified as non-fresh in 1955. type, an ecotone between fresh and non-fresh 5-10 ppt have been driven into the baldcypress Much of the brackish marsh in 1955 was dominated marsh habitats, was delineated more accurately on swamps surrounding Lake Maurepas. By increasing by three-cornered grass (Scirpus olneyi), a pre- the 1978 habitat maps. As a result, some of the soil salinities, such events have been a major ferred marsh plant species for furbearers and, in transitions from fresh to non-fresh habitats that factor in the gradual transition of these wetlands particular, muskrat (Ondatra zibethicus) (O'Neil are shown may be due, in part, to this dif f erence in from swamp to marsh. Other exacerbating factors 1949). With increased mean salinities and tidal detail between data bases, in addition to the actual include general subsidence of the land surface, amplitudes due to the MRGO, the brackish marshes changes transpiring during the period considered. disruption of the natural runoff pattern from the have reverted to large expanses of predominantly Pleistocene terrace through the baldcypress wiregrass (Spartina patens), which is a less valuable swamps by canal development, and in some in- species for both furbearers and waterfowl (CEI stances impacts from the cypress logging industry. 1982; Palmisano 1971a). Concurrently, St. Pontchartrain Watershed Bernard Parish has experienced a substantial Rising salinity levels in Lake Pontchartrain and reduction in harvestable furbearer populations. In Lake Maurepas have caused substantial transitions addition, marshes occurring along the northeast of habitats in this watershed (Plate 1). 'Approxi- side of the MRGO are exposed to ship wake wash mately 25,000 ac of formerly fresh habitats, in- as well as increased salinities and tidal amplitudes. cluding fresh marsh and baldcypress swamp, were Lake Borgne Watershed The result has been severe erosion of marsh along converted to non-fresh habitats by 1978 this side of the MRGO and the conversion of about (Table 2-1). This occurred predominantly in the The completion of the Mississippi River-Gulf 6250 ac of brackish marsh to salt marsh dominated lower Pearl River drainage near the Rigolets and in Outlet (MRGO) in the mid-1960s broug ht about by oystergrass (Spartina alternifora) (CEI 1982). the vicinity of Pass Manchac. In the lower Pearl substantial changes within the wetlands of St. River, fresh marsh changed to intermediate marsh, Bernard Parish in the vicinity of Lake Borgne. In while south of Pass Manchac baldcypress 1955, baldcypress swamps existed at the base of (Taxodium distichum) swamp also showed transition the Mississippi River natural levee and graded into Breton Sound Watershed to intermediate marsh. fresh marsh and brackish marsh toward Lake Borgne (O'Neil 1949). Relatively low salinity con- Almost 21,000 ac of baldcypress swamp showed ditions were maintained due to the protection In 1955, a substantial acreage of fresh marsh transition to marsh classified as fresh by the 1978 afforded the area by the natural ridge of Bayou La existed along the flank of the natural levee of the habitat maps. The large majority of this transition Loutre. When the MRGO breached this ridge an Mississippi River in Plaquemines Parish (Wicker et took place between Lake Maurepas and Lake avenue was provided for higher salinity Gulf waters al. 1980). By 1978, about 20,000 ac of fresh marsh Pontchartrain along Pass Manchac. About to intrude into these wetlands. Natural drainage here and along the northern perimeter of the Lake 36,000 ac of baldcypress swamp were interpreted patterns were disrupted, part of the area was semi- Lery marsh (Plate 3) had transformed to non-fresh as being in a stressed condition. Such stressed impounded by the large spoil deposition, and tidal marsh, predominantly brackish (Wicker et al. 1980). swamp occurs over substantial areas on both the amplitudes increased. In short, the MRGO became north and south shores of Lake Maurepas. Addi- the major hydrologic force. As a result of the Several factors interacting concurrently apparently tional stressed swamp occurs southeast of the increased salinities, approximately 9705 ac of have precipitated these changes. Construction of Bonnet Carre Spillway in St. Charles Parish, while formerly fresh marsh and baldcypress swamp have back levees along the Mississippi River tended to only a small bit occurs along the north shore of been changed to brackish marsh (Plate 2) deny marshes outside the levees freshwater runoff Lake Pontchartrain. (Table 2-1) in the area now termed the Central that before had helped to moderate salinities. A Wetlands of St. Bernard Parish (CEI 1976). About rather severe drought in the early 1960s, coupled Generally, the baldcypress swamps flanking Pass 914 ac of baldcypress swamp still exist but are in a with hurricane Betsy in 1965, brought higher Manchac, Lake Maurepas, and the western end of decidely stressed condition (Plate 2). salinity water into the upper reaches of the Breton Lake Pontchartrain have been subjected to slight Sound Watershed. In addition the expansion of the increases in salinity during the last 25 years Table 2-1. Approximate Acreages of SaUnity-4nduced Habitat Change in the Lake oil and gas industry in the area produced an in- (Wicker et al. 1981). The fall months of Pontchartrain, Lake Borgne, and Breton Sound Watersheds. crease in the number of rig cuts and pipeline September, October, and November produce the Habitat Change Lake Pontetntrtrain Lake Borgne Breton Sound canals. The maze of canals and spoil banks worked lowest discharge from the Tickfaw and Tangipahoa Fresh to non-fresh 24,934 9,705 23,090 both to accelerate saltwater intrusion into the Rivers, yet the highest water stage at Pass formerly well-protected fresh marshes and, Jn Manchac is due to predominant east to northeast Swamp to fresh-marsh 20,925 a other cases, impounded some marsh areas with winds that push water from Lake Pontchartrain Strewed Swamp 36,010 914 subsequent deterioration. The result was a into the Lake Maurepas Basin (Wicker et al. 1981). transition from fresh marsh to brackish marsh and As a result, the highest mean salinities for Pass Source: Wicker et aL 1980. major transitions from marsh to open water Manchac also occur during these months. During (Wicker et al. 1980). 4 Salinity tolerance in swamp forest has not been studied thoroughly. However, in the study of the baldcypress swamps in Tangipahoa Parish in the vicinity of Pass Manchac, severe impacts were evident where over several years water salinities reached 2 ppt or greater for 50 percent of the time the swamp was inundated (Wicker et al. 1981). It appears then that salinities must be kept below 2 ppt continuously for maintenance of the health of the forest. Baldcypress swamps in Louisiana serve as impor- CHAPTER III tant nesting, brood rearing, roost sites, and winter- ing areas for the Wood Duck (Aix spons ), a resi- dent species dependent on tree cavities for nest sites (Bellrose 1976, Sincock et al. 1964). Other GOALS FOR waterfowl, in particular Mallards (Anas platyrbynchos), also utilize swamp forest as win- ENVIRONMENTAL tering areas. As overflow bottomland hardwood areas, which are high-qualtiy waterfowl habitats RESOURCE P lor these species, continue to become reduced in MANAGEMENT areal extent in Louisiana (FWS 1979), baldeypress swamps will increase in importance to waterfowl. Wetland habitats of southeast Louisiana are recent Other avian species utilizing swamp forests to a environments formed for the most part within the great degree include wading birds such as herons, last 5000 years as a direct result of Mississippi Healthy cypress tupelogurn swamp. egrets, and ibises that feed largely on small fish River alluvium (Kolb and van Lopik 1958). Through and crustacean populations in shallow water areas. the shifting course of the Mississippi River, delta Great Egrets (Casmerodius albus) and Great Blue progradation created the deltaic plain and Herons (Ardea herodias) i-E-m-only nest in swamp associated swamp and marsh habitats. Overbank Habitat Types and Optimum forests, and !tie -White Ibis (Eudocimus albus) is flooding of the Mississippi River mainstem and its Salinity Regimes known to nest in substantial numbers in the distributaries resulted in deposition of fine sands, baldcypress swamps of Tangipahoa Parish (Lowery silts, and clays into marine and paludal basins. Baldcypress swamps are relatively low-energy, 1974a, Portnoy 1977). Baldcypress swamps formed on the back slope of essentially freshwater environments located on the natural levees and extended over large inter- predominantly clay soils. Plant associates in addi- Other important wildlife species utilizing swamp distributary basins in areas protected from waters tion to baldcypress often include tupeloguni (Nyssa forests include furbearers, such as raccoon influenced by encroaching Gulf salinities. Marsh aquatica), swamp red maple (Acer rubrurn var. (Procyon lotor) and mink (Mustela vison), which habitats tended to be formed farther seaward of drummondii), black willow (@Sali@F_ - n ash take advantage of abundant crayfish populations as a!Ei@aT,-g-ree prey. During the early part of this century, mink the baldcypress swamps in areas of increased tidal (Fraximus pennsylvanica), and swamp black gum fluctuation and higher water salinities. The dis- @-syl-y-at-ica var-.biflora) (Penfound 1952, were particularly numerous and heavily trapped in tribution of wetland environments is governed by a Conner and Day 1976, Conner et al. 1981). Al- the cut-over swamps around Lake Maurepas number of interrelated factors such as soil com- though baldcypress swamps are inundated for much (Palmisano 1971b). Populations have since declined position, water level regime, tidal energy, and soil of the year, water levels must recede below the considerably. Along ridge-swamp interfaces sport and water salinities. Each habitat also has its soil surface periodically for normal functioning and hunting for white-tailed deer (Odocoileus particular intrinsic fish and wildlife resources for maintenance of productivity (Conner et al. 1981). virginianus) and squirrel (Sciurus sp.) is common. which environmental factors theoretically can be Permanent flooding, which does not allow germina- optimized. Although salinity is only one of many tion of seeds of baldcypress and many of its Fresh marsh occurs at slightly lower elevations and elements which tend to define the wetland hab- associates (Mattoon 1915, Demaree 1932, Penfound is subject to more frequent flooding than swamp itats, in the context of freshwater diversion it will 1952), results in lowered productivity and loss of forests. Water salinities in the fresh marsh vege- be the parameter most directly affected. Thus, recruitment (Conner et al. 1981). Seasonal flood- tative type have been reported to range up to 6 ppt optimum salinity regimes are discusse or t e ing an raining are vi 0 (Chabreck 1972), but typically average less than 2 various habitats to formulate goals for resource species diversity and for proper functioning as ppt (Palmisano and Chabrecl@1972). Organic con- management. nursery and spawning grounds and nesting sites. tent is quite high, generally averaging over 50 5 percent (Palmisano and Chabreck 1972). Fresh waterfowl that annually winter in Louisiana have In summary, swamp and fresh-marsh habitats rem- marsh exhibits the highest diversity of plant varying food preferences, water depth require- quire salinity regimes under 2.0 ppt almost contin- species of all marsh types, with 93 species reported ments, and pond size needs. However, the fresh uously to maintain community structure, species by Palmisano and Chabreck (1972) to occur in this marsh type appears to meet the various require- diversity, and productivity. Wading birds, water- type along coastal Louisiana. The major species of ments to the greatest extent. fowl, furbearers, and the alligator are among im- these include paille fine (Panicum hemitomum), portant wildlife resources utilizing these habitats comprising 25.62 percent, bulltongue (SagittArla in substantial numbers. lancif olia) with 15.15 percent, spikerush The fresh marsh vegetative type is also important (Eleocharis sp.) with 10.74 percent, alligator weed as commercial furbearer habitat. Although catch The protected inland waters of less than 2 ppt are (Alternanthera philoxeroides) with 5.34 percent, records are not always completely indicative of inhabited by characteristic freshwater fishes and ii5d -wiregrass with 3.74 percent (Chabreck 1972). population levels due to variations in trapping invertebrates. Some of the most common are techniques and intensity of effort, fresh marsh crawfish (Procambarus clarkii), river shrimp The high diversity of plant species and low salini- evidently produces the highest means and maxi- (Macrobrachium ohioni-eT, -gars (Lepisosteus sp.), ties make the fresh marsh vegetative type valuable mum harvests of nutria (Myocastor coypus) and bream (Lepomis sp.), crappie (Pomoxis sp.), largem- wildlife habitat. The coastal marshes of Louisiana mink, as well as the highest maximum harvests of mouth bass (Micropterus salm des), hannel cat- in some years may winter up to 4,000,000 ducks raccoon (Palmisano 1973) (Table 3-2). The nutria fish (Ictalurus punctatus athead catfish and 500,000 geese (Sanderson 1976, Bellrose 1976), is now the most important furbearer in Louisiana in (PY10(fic-tis olivaris). In Louisiana, the primary which account for more than two-thirds of the terms of number of animals harvested and total fa-c-to-rsthat influ nce population size of these migratory waterfowl population in the Mississippi monetary value to the trapper, having overtaken species are dissolved oxygen, overflow regime, and Flyway. During the 1975-76 waterfowl season, the muskrat in this regard in the early 1960s salinity. Low dissolved oxygen is a primary cause Louisiana hunters accounted for about one-third of (Lowery 1974b). of mass mortalities (fish kills) in the Pontchartrain the 2,083,831 birds harvested in this flyway Basin (W. C. Dixon, personal communication 1982) (Sorenson et al. 1977). The value of fresh marshes and is fostered by the combination of an in southeastern Louisiana is exemplified by the Since the 1960s, alligator (Alligator overabundance of organic matter and sluggish fact that about 65 percent of the puddle ducks mississippiensis) populations have increased water movement. Man affects both through recorded here in some years utilize this vegetative continually through protection, research, and nutrient loading (Craig and Day 1977; Seaton 1979) type (Palmisano 1973) (Table 3-1). Major environ- management efforts of the Louisiana Department that promotes growth of aquatic vegetation and mental factors influencing waterfowl usage of win- of Wildlife and Fisheries (O'Neil and Linscombe channeliziation that slows water movement during ter habitat include water depth, food availability, 1977). A legal harvest season now takes place each dry periods. The highest productivity of distribution of aquatic habitat, climatic conditions, fall throughout coastal Louisiana. The estimated freshwater species is correlated with flooding of and soil and water salinity (Chabreck et al. 1974, population by 1977 was about 92,000 in the sub- swamps and bottomland hardwood forests in the Chabreck 1979). Tradition also plays an important delta marshes, with fresh marsh holding 13.8 spring (Bryan and Sabins 1979, Sabins 1977). This part in selection of winter habitat in that areas percent of the alligators present (McNease and overflow situation provides an abundance of that are used presently are generally those that Joanen 1978). The substantial nutria populations in spawning habitat and food and protection for fry have been used in the past. However, continued fresh marsh are an important - food source for and juveniles. As floodwaters recede, the use during the winter is dependent upon habitat alligators (McNease and Joanen 1977) and numerous organisms become concentrated in the quality and particular preferences of individual contribute to the value of this vegetative type as permanent waterbodies, increasing feeding species (Chabreck 1979). The several species of alligator habitat. efficiency and facilitating rapid growth. Table 3-2. Estimated Fur Catch Per 1000 Acres of Coastal Marsh. Table 3-1. Percentage Habitat Utilization by Puddle Ducks in Coastal Louisana. SALINE BRACKISH INTERMEDIATE FRESH Southwestern La. Southeastern La. Entire Coast Species Mean a Maximum Mean maximum Mean Maximum Mean Maximum Puddle Ducks Habitat Puddle Ducks Habitat Puddle Ducks Habitat Muskrat b b 84.4 6477.7 97.5 513.9 78.5 646.8 Vegetative Type Recorded Sampled Recorded Sampled Recorded Sampled Nutria b b' 96.4 191.1 284.9 499.6 512.7 884.4 Mink b b 1.1 12.8 0.9 11.9 2.1 14.2 Saline Marsh 0.60 1.19 5.33 24.90 1.67 8.66 Raccoon b b b 15.6 b 6.3 b 31.0 Brackish Marsh 29.28 19.92 21.59 35.49 27.66 24.82 Otter b b 0.2 0.7 0.4 1.3 0.5 1.3 Intermediate Marsh 33.05 15.15 8.04 7.59 27.03 12.77 Fresh Marsh 26.82 15.67 65.04 32.02 35.91 20.82 a Mean values determined from recent records. Maximum valuies are an average of long term maximum catch figures. Agricultural 10.25 48.06 -0- -0- 7.73 32.93 b Inadequate Records Source: Palmisano 1973. Source: Palmisano 1973. 6 Salinities below 2 ppt not only promote the growth Verret 1980, Hinchee 1977). During this life stage, wide range of salinities, with Chabreck (1972) re- of swamp and fresh marsh, but also are ideal for vegetative cover is of utmost importance to sur- porting a range for Hydrologic Units I and 11 of most freshwater fauna. Catfish are important vival and growth. In this salinity range, the about 5-15 ppt. For purposes of this report this commercial species that tend to prefer river and dominant vegetation is intermediate marsh and vegetative type has been broken into low-salinity shallow, intermediate-salinity lake habitats. beds of submerged aquatic weeds and grass, which brackish marsh (5-10 ppt) and high-salinity brack- Salinity greater than 2 ppt apparently causes are generally low-energy environments with little ish marsh (10-15 ppt). Although similarities are competition between blue catfish (Ictalurus, daily water level fluctuation. Consider the bene- apparent between the two, relative value for parti- furcatus) and channel catfish and their estuarine fits of stable waters and gentle currents to very cular fish and wildlife species can be differen- counterpart, the sea catf ish (Arius felis). small and fragile organisms. Even with an abun- tiated, primarily on the basis of tidal influence and Commercial fishermen around Pass anchac re- dance of food, energy expenditures in maintaining water level fluctuation. portedly move their trotlines from western Lake a desired position detract from the growth rate of Pontchartrain in the spring, to Lake Maurepas in the animal. Where water levels fluctuate greatly, An assemblage of estuarine species different from the summer, and finally remove them entirely by the protection and food source of marsh vegetation the low-salinity assemblage mentioned previously fall as their catch becomes dominated by the are not as continuously accessible, promoting utilizes the low-salinity brackish marsh (5-10 ppt) unmarketable sea catfish (Tangipahoa Parish greater predation and lower survival. Desirable, during early post-larval and juvenile stages, pre- Coastal Advisory Committee, personal low-energy hydrologic conditions have occurred sumably for similar hydrologic reasons. Brown communication 1981). historically in low-salinity areas of estuaries, shrimp (Penaeus aztecus), spot (Leiostomus where the residence time of freshwater is longer xanthurus F,-s-potted seatrout (Cynoscion nebulosus), Marshes of intermediate salinities represent an and the tidal energy lower than other parts of the and red drum (Sciaenops ocellata) tend to prefer ecotone or transition zone between the fresh and estuary. From this, it might be concluded that nursery habitats above 5--p-p-t-TF-ruge and Ruelle non-fresh marshes and usually make up only a these post-larval estuarine organisms have evolved 1980). Juvenile spotted seatrout are found in small percentage of the total wetland acreage, to seek low salinity regimes for the better pro- low-salinity brackish nursery in the summer, and especially in Hydrologic Units I and II (Chabreck tection typically afforded there. If so, then the red drum utilize the area in late fall and early 1972). Water salinities in intermediate marshes acreage of intermediate marsh nursery is more winter. Rapid decreases in water temperature vary somewhat across the state in different important to production of white shrimp, blue crab, during frontal passages can cause mortality of the hydrologic units, but a typical range of values is 2- croaker, and menhaden than the absolute salinity juvenile red drum. Post-larval brown shrimp enter 5 ppt (Palmisano and Chabreck 1972). values of surrounding open water bodies. the area in early spring and are also adversely Intermediate marsh vegetation includes a large affected by low water temperature (less than 20* C number of species indicative of both fresh and or 680 F). Before leveeing of the Mississippi River, brackish environments (Palmisano and Chabreck annual overbank flooding in the spring not only 1972). Wiregrass is the dominant species in south- reduced salinities, but also decreased the temper- eastern Louisiana, with three-cornered grass, bull- ature of the water in the estuary. Larval brown tongue, and dwarf spikerush being important shrimp seeking low-energy nursery areas probably associates (Chabreck 1972). The low salinity encountered low temperatures in the 2-5 ppt range values and high plant diversity of this marsh type and therefore evolved to utilize higher energy contribute to its value as wildlife habitat. On a nursery in the 5-10 ppt range. In the late spring per-acre basis, intermediate marsh receives high and summer, overbank flooding subsided and water utilization by waterfowl in southeastern Louisiana temperatures rose sufficiently to encourage white (Table 3-1) and also produces high yields of nutria shrimp immigration into 2-5 ppt intermediate nur- and mink (Table 3-2) (Palmisano 1973). In addition, sery. This system allowed maximum utilization of intermediate marsh supported the highest densities the marsh resources, less competition, and maxi- of alligator (1 alligator per 7.9 ac) in 1977 on a mum secondary productivity. coastwide basis (McNease and Joanen 1978). The dominant vegetative species in both low- and Aquatic habitat of 2-5 ppt salinity supports many high-salinity brackish marsh is wiregrass, which species of freshwater fish as well as a low- was found by Palmisano and Chabreck (1972) to salinity- tolerance estuarine faunal assemblage, comprise 55 percent of the vegetation in all brack- some of commercial importance. In late winter ish marshes. Other important species include salt- through early summer, postlarval forms of white Fresh marsh dominated by cattail (Typha sp.). grass (Distichlis spicata), three-cornered grass, shrimp (Penaeus setiferus), blue crab (Callinectes dwarf spikerush, and oyster grass in southeastern sapidus), Atlantic croaker (Micropogonias Louisiana (Chabreck 1972). Brackish marshes his- undulatus), and menhaden (Brevoortia patronus) Seaward of intermediate marsh higher water salin- torically have been the major producer of muskrat actively seek nursery habitat iWfiere salinity is less ities and increased tidal energy lead to establish- (O'Neil 1949), which constituted the real strength than 5 ppt (Fruge and Ruelle 1980, Thompson and ment of brackish marsh. This marsh type has a of the trapping industry in coastal Louisiana for 7 has the greatest density of ponds and lakes areas of the estuary in search of f ood is the (Chabreck 1972) that aids in its attractiveness for southern oyster drill (Thais haemostoma) (Pollard waterfowl. Widgeon grass (Ruppia maritima) is an 1973). Predation by the oyster drill, along with important waterfowl food and is most prolific in parasitism by marine fungi (Dermodestidium sp.) conditions of low turbidity and stabilized water and boring sponges (Cliona sp.), pro uces natural levels in shallow, brackish-water ponds (Chabreck limits on the expansion of the American oyster into and Condrey 1979). Such conditions can be found saline environments. In Louisiana, the oyster drill in both low- and high-salinity brackish marshes, is considered a nuisance on private oyster leases in but the lesser tidal influence in low-salinity brack- the lower estuary because its predation is a direct ish marsh may make it somewhat more amenable economic loss to oystermen. More importantly, to widgeon grass propagation. heavy predation of the easily penetrated seed oysters (1 to 3 in) on the public grounds represents -salinity brackish marsh (10-15 ppt) is utilized e additional effort High an indirect economic loss becaus by all major estuarine species at some life stage, is necessary to gather seed oysters for either as larval forms moving into the estuary or as transplanting. It is therefore advantageous to juveniles and immature adults moving out. The exclude the drill from the oyster grounds by hydrologic regime promotes export of plant mater- keeping the salinity at or below 15 ppt. However, ial into water bodies to serve as a food source. oyster reproduction occurs only above 10 ppt The flux of organisms and organic matter through (Galtsoff 1964), larval development of oysters in Louisina trapper skinning muskrat. this environment provides abundant food for the summer is most favorable at 25 ppt, and mature adult fish, and it is therefore a prime metamorphosis (spatfall) peaks in waters of 20 ppt sportsfishing area. The majority of effort during (Tabony 1972). For lower salinity tolerance, many years until the nutria took its place in the the inshore shrimping seasons is spent in the high- concentrations less than 5 ppt when temperatures 1960s (Lowery 1974b). Three-cornered grass salinity brackish marsh. This area is also the most are greater than 209C are fatal to all life stages marshes produce the highest densities of muskrat, productive for the American oyster (Crassostrea (Lindall et al. 1972). Optimum conditions for with 80 percent of the harvest coming from these virginica). In short, the aquatic productivity of an increased oyster populations should include a short marshes in some vears (Table 3-2) (ONeil 1949). estuarine system as a whole is best displayed in the period of 20 ppt salinity in the midsummer on the Management for three-cornered grass, which is 10-15 pt salinity range where there is intense seed grounds for spatfall, with salinities below but also considered a good waterfowl food (Palmisano interaction among many species, including man. near 15 ppt for the rest of the year. Commercial 1971a), is dependent primarily on water levels and oysters grow better and have a more desirable secondarily on salinity regime (Ross 1972), with In areas with greater tidal energy and salinities flavor at salinity greater than 10 ppt (Dugas 1977), annual burning used to retard competition from above 15 ppt for much of the year, the saline making the optimum range for private leased areas wiregrass (O'Neil 1949). Ideally water levels should marsh type is dominant. The salt marsh has less 10-15 ppt. A description of oyster life history be maintained a few inches above the soil surface plant diversity, with oyster grass the dominant stages and salinity requirements is presented in (Palmisano 1967), and although three-cornered species (Palmisano and Chabreck 1972). Other Table 3-3. grass occurs in a wide range of salinities, Ross common species include saltgrass, black rush (1972) reported that a salinity range of 5-10 ppt (Juncus roemerianus), and wiregrass. Although may provide for best growth. Considering the saline marsh does support furbearers such as rac- lower tidal influence with this type as compared to coon, mink, and muskrat, pelts from this vegeta- Table 3-3. Summary of Life History and Habitat Data for the American Oyster. the high-salinity brackish marsh, management tive type are of poor quality and are seldom sought potential for three-cornered grass appears sub- (Palmisano 1971b). Waterfowl usage of this marsh Reproduction Larval Larval Metamorphosis stantially greater in the low-salinity-regime type is slight (Table 3-1) (Palmisano 1973), and (spawning) Development -_ (Spatfall) May - October June - November June - October brackish marsh. The lower salinity regime also alligators cannot tolerate its high salinity regime Waters greater than Most favorable in waters Peak in late August in 10 ppt and near WC of 25 ppt and 29*C; waters greater than favors alligator production, with population densi- (Joanen and McNease 1972). The salt marsh is Growth inhibited below 20 ppt and 299C; No 12 ppt; No survival survival below 10 ppt ties here about equal to the fresh marsh (McNease valuable habitat for shorebirds, seabirds, and below 10 ppt and Joanen 1978). Newly hatched alligators cannot Clapper Rails (Rallus longirostris) and serves as a Seed Oysters* Commercial Oysters* Adult tolerate salinities above 10 ppt for extended buffer to the more inland marshes against extreme (1-3 in) (greater than 3 W Oysterso periods (Joanen and McNease 1972). salinities and storm tides (Palmisano 1971b). AD year All year All year Most favorable Most favorable General tolerance waters between 5-15 ppt waters between 10-25 ppt for waters between 5-30 ppt Waterfowl usage of brackish marshes is not as great as fresh or intermediate types on a per-acre Aquatic habitats above 15 ppt are not only utilized Oyster drill predation, incidence of disease, and competition of fouling organisms increase significantly for seed, commercial, and adult oysters when salinities exceed basis (Table 3-1) but still is important due to the by estuarine- dependent organisms but are fre- 15 ppt. Also, tolerance to salinities below 10 ppt is reduced when temperatures large expanse of the brackish type present quently invaded by true marine species. One exceed 23*C. (Palmisano 1973). The brackish vegetative type marine species that frequently invades 15-18 ppt 8 In summary, animal resources are related to the Manchac where swamp has been replaced by marsh water levels from June through August for aeration wetland habitat types found in an area. Differen- habitats within the last 20 years. Goals for this of the substrate and seed germination. tiation of wetland habitat types is determined by unit include providing a salinity regime of 0-1 ppt hydrological conditions such as salinity and tidal for as much of the year as is realistically possible St. Charles Marsh Unit energy. The description of optimum hydrological and to keep salinities at Pass Manchac below 2 ppt conditions, habitat types, and biological resources continuously. This would allow maintenance of a This environmental unit is comprised of brackish is presented in Table 3-4. healthy swamp system and increase the potential and intermediate marsh grading into baldcypress for restoration of the stressed and dead swamp swamp that shows evidence of salinity stress. areas. A healthier swamp system would benefit a Goals here are to moderate salinities such that diverse array of wildlife species -including water- salinities less than 2 ppt exist for the swamp and Environmental Units and fowl such as Wood Ducks and Mallards, various most inland marsh, grading into a regime of 2-5 ppt Management Goals wading birds such as ibises, egrets, and herons, and near Lake Pontchartrain. This would improve the commercially important furbearers such as mink, condition of the swamp habitat and potentially PONTCHARTRAIN WATERSHED nutria, and raccoon. increase diversity in the marsh. Wiregrass is now dominant in the marsh environments, and lowering Wetland areas in the Pontchartrain Watershed were Freshwater aquatic organisms are dominant over salinities would facilitate structural management partioned into environmental units on the basis of most of the Lake Maurepas Freshwater Wetlands to induce establishment of plant associations more historic conditions and intrinisic suitability for Unit. Suitable salinity goals would be maintenance valuable for wildlife. The St. Charles Marsh Unit is a very important nursery area for estuarine- environmental management. The environmental of 0-1 ppt in the winter and spring and prevention del)endent organisms in Lake Pontchartrain. This units are delineated on Plate 1. of salinities above 2 ppt in the summer and fall. Other goals for localized management would in- area has historically accommodated the low Lake Maurepas Freshwater Wetlands Unit clude structural control of water levels approxi- salinity estuarine assemblage, as well as a resident freshwater fish assemblage. Salinity goals should mately 1-2 ft above the swamp floor from Febru- be to maintain 2-5 ppt over the year. A more This unit is predominated by baldcypress- ary through May for spawning and recruitment with important goal would be to protect the remaining tupelogum swamps except in the vicinity of Pass subsequent release and possible draw-down of marsh and create new marsh whenever possible. Table 3-4. Summary of Wetland Habitats, Salinity Regimes, and Their Associated Wildlife and Fisheries Resources. OPTIMUM WILDLIFE AND FISHERY RESOURCES HABITAT SALINITY WATER LEVEL TYPE (ppt) REGIME TERRESTRIAL AVIAN AQUATIC A@ Swamp 0-2 Seasonal flooding due Mink,raccoon, Wood Duck " Mallard Crawfish, bream, to heavy precipitation, white-tailed White Ibis, Great largemouth bass; Jir very slight tidal influence deer, swamp rabbit Blue Heron crappie 6- Fresh Marsh 0-2 Frequent and seasonal Nutria, mink Mallard, Teal, Pintail Blue catfish, channel flooding, some tidal raccoon, alligator Little Blue Heron catf ish, nathead influence river otter catf ish Intermediate 2-5 Low amplitude tidal Alligator, nutria, Mallard, Gadwall, White shrimp, Marsh fluctuation, low river otter Teal, Pintall blue crab, croaker, daily water exchange menhaden, Rjn&!a clam Low-Salinity 5-10 Medium amplitude Muskrat, nutria Gadwall, Brown shrimp, Brackish Marsh tidal fluctuation, Widgeon, Shoveler spot, red drum, significant daily spotted seatrout, water exchange oysters High-Salinity 10-15 High amplitude tidal Muskrat Gadwall, Lesser Scaup, Commercial oysters, Brackish Marsh fluctuation, almost Red Head duck, adult brown and complete daily Louisiana Heron, white shrimp, water exchange shorebirds adult sportfish L Saline Marsh Above 15 Highest amplitude Terns, gulls, Seed oysters on tidal fluctuation, Louisiana Heron, Brown Pelican, public grounds, adult virtually total daily Clapper Rail, brown and white shrimp, water exchange Lesser Scaup, Snowy Egret, adult sportfish Ecotone of cypress swamp and fresh marsh, St. shorebirds Charles Parish. Al., r Goose Point and North Shore Marsh Units for establishing productive marsh types (e.g., MRGO Marsh Unit three-cornered grass for muskrat management) and Both these units of marsh habitat are presently aquatic vegetation (e.g., widgeon grass to attract Water salinities and tidal amplitudes in this unit valuable for fish and wildlife, although they showed waterf owl). have increased substantially since construction of losses of fresh marsh habitat between 1955 and the MRGO in the 1960s, with a corresponding loss 1978. Goals here are to moderate salinities slight- Orleans Parish Marsh Unit of baldcypress habitat and conversion of marsh ly to possibly increase areas of fresh and inter- Water salinities in this unit also are controlled to types to higher salinity regimes. The value of mediate marsh, especially in the Goose Point Unit, some extent by amount of discharge from the Pearl these wetlands as wildlife habitat has declined and thus increase the diversity of habitat types and bstantially as a result. Substantial reduction of River as well as salinities in Lake Borgne, the su increase the value as wildlife habitat. Brackish salinities may not be possible under existing condi- marshes, in particular the North Shore Marsh Unit, Intracoastal Waterway, and the MRGO. Goals for tions dictated by the MRGO. However, establish- should be maintained in the low-salinity brackish this unit are to maintain the habitat as low-salinity ment of low-salinity brackish marsh (5-10 ppt) in range (5-10 ppt) for maximum value to fish and brackish marsh to maximize its potential as fur- areas most protected from MRGO waters may be wildlif e. bearer and waterfowl habitat. feasible, with high-salinity brackish marsh (10-15 The Goose Point Marsh and ad acent submerged Salinity goals for aquatic organisms in the Orleans ppt) being maintained near the channel. One goal i should be to reverse the trend along the MRGO grass beds are very important nursery areas, espe- Parish Marsh Unit should be in the range from 2-10 whereby brackish marsh is presently being con- cially for juvenile blue crabs. Salinity goals in the ppt. This would provide nursery habitat for brown verted to salt marsh due to high salinities and tidal 2-5 ppt range are optimum here. Protection of the shrimp, red drum, spotted seatrout, and other amplitudes. Marshes in this unit west of the grass beds from shoreline modifications should be members of the typical, high-salinity estuarine as- MRGO spoil exist in a semi-impounded condition another environmental management goal. Grass semblage during times of low Pearl River dis- due to this large spoil barrier. During periods of beds could be expanded on the exposed, south- charges, and nursery habitat for white shrimp and heavy rains, water levels here may rise to 2-3 ft facing shoreline of Goose Point near Bayou blue crab during high Pearl River discharges. above marsh level and salinities are reduced to Lacombe by construction of artificial reefs to Because of the unique location of these marshes below 1 ppt. These conditions usually exist for absorb wave energy. between two large natural tidal passes, they are only short time periods such as 1 or 2 days, after probably utilized by all estuarine organisms as a which water levels recede and salinities may again staging area for immigration into Lake Pontchar- reach as high as 15 ppt due to the influence of the train. The discharge of the Pearl River probably MRGO. Such rapid and extreme fluctuations in LAKE BORGNE WATERSHED dictates which species will utilize these nursery marsh conditions are not conducive to, and can be areas in a particular year. The salinity goals are detrimental to, establishment of high-quality wild- Environment correspondi ngly broad. is to implement structural management to moder- al unit delineations for the Lake life habitat. The only recourse in such a situation Borgne Watershed appear on Plate 2. ate extreme conditions. Pearl River Wetlands Unit T The MRGO Marsh Unit experiences an unnaturally his valuable wetlands unit has a diversity of steep salinity gradient because of the strong verti- habitats ranging from baldcypress swamps to cal stratification in the navigation channel. A brackish marsh. Pearl River discharge dictates to complete description of the nursery value of these a large degree the salinity regimes of these envi- ronments, but there was a substantial conversion marshes is found in the St. Bernard Marsh anag EI 1982). Following completion of from fresh marsh to non-fresh marsh between 1955 ment Plan (C the MRGO, oyster leases became established in and 1978. Goals for this unit are to moderate salinities, especially during the fall months, to western Lake Borgne between Bayou Bienvenue and Martello Castle where salinities were formerly maintain the present habitat diversity, and to in- much 1 hibit any further loss of fresh habitats to non-fresh 7 ower. These leases are presently the most marsh. The brackish marsh near the Rigolets productive in St. Bernard Parish, indicating a -15 ppt. However, coliform salinity regime from 10 should be maintained as low-salinity brackish New Orleans is often on pollution emanating from marsh (5-10 ppt) due to its higher potential for management for furbearers and waterfowl. The the verge of exceeding criteria for shellfish har- implementation of structural management tech- MRGO at Southern Natural Gas pipeline looking vest. Growth of New Orleans could increase niques, such as weirs and flapgates for water level south. coliform concentrations, causing these leases to be control, can be successful in this salinity regime closed to harvest. 10 Realistic salinity goals for aquatic habitat adjacent BRETON SOUND WATERSHED valuable aquatic plants such as widgeon grass in to the MRGO would be maintenance of 10-15 ppt, ponds for waterfowl. Salinity goals to promote and for parts of the unit farther from the MRGO, The Breton Sound Watershed environmental units low-salinity brackish marsh in the Upper River aux 5-10 ppt. Another goal would be to prevent are shown on Plate 3. Chenes and Terre aux Boeufs Marsh Units will additional marsh loss by stabilizing the northeast increase the nursery value to brown shrimp, spot- bank of the channel that has eroded extensively ted seatrout, and red drum. (CEI 1982). 'X Lower River aux Chenes: Marsh Unit Biloxi Marsh Unit Higher tidal energy and salinities make this unit Historically, this environmental unit provided high- less amenable to management for wildlife. Goals quality wildlife habitat, but due to salinity intru- here are to moderate salinities slightly and possibly force some seaward movement of the 15 ppt iso- sion from the MRGO its value has declined. Goals haline. Any tendency towards landward movement for this unit are to reinstate as closely as possible of this isohaline should be inhibited. In addition, the salinity regimes present prior to MRGO con- the elimination of salinity extremes above 15 ppt struction. This would result in an extensive area of during the fall months is an important goal. This low-salinity brackish marsh more amenable to should strengthen the present value of this unit for management for furbearers and waterfowt. fish and wildlife, as well as insure its role as a buffer against extreme salinities and tidal energy Salinities ranging from 5-10 ppt would produce Intermediate marsh near Caernarvon. for wetlands farther inland. optimum conditions for aquatic organisms in the Biloxi Marsh Unit, providing nursery areas for A high density of private oyster leases in the brown shrimp and other species in the high-salinity Caernarvon Crevasse Marsh Unit Lower River aux Chenes Marsh Unit dictates that assemblage. Construction of weirs for waterfowl 10-15 ppt salinities be maintained for oyster pro- management in the late 1950s created low energy This environmental unit was subject to extensive duction. conditions in these marshes and promoted growth transition of fresh marsh to non-fresh marsh, es- of extensive beds of submerged grasses. Because pecially between 1955 and 1978 along the of a lack of maintenance, most of the weirs have Mississippi River. Goals for this unit are to re- Reggio Canal Marsh Unit been breached or cut around (Beter 1980, personal establish where possible some of the freshwater communication). However, the structures probably wetlands that have proven to be among the most The location of the Reggio Canal Marsh Unit still dampen tidal energy to some extent, producing valuable habitats for waterfowl and furbearers, and between the natural levee ridges of Bayous Terre good, low-salinity, brackish nursery potential. to broaden the extent of the low-salinity, fresh-to- aux Boeufs and LaLoutre has historically made intermediate marsh habitats in the upper reaches these low-energy marshes. However, the levee of the Breton Sound Watershed to more closely ridges also have .shielded the area from freshwater Outer Biloxi Saline Marsh and LaLoutre Marsh approximate historical conditions. Salinity goals of inDut from the MiSSiSSiDDi River and Lake Borgne Unift. 2-5 .,pt are desirable, especially for white slirIMP9 1 11 L IL and during recent times the proximity of the blue crab, menhaden, and croaker nursery habitat. MRGO has caused increases in the salinity regime. Historically, the area of highest oyster production These marshes have historically provided the low- The marshes are best suited to become low-salinity in Hydrologic Unit I has been in the Outer Biloxi energy hydrologic conditions for these species in brackish nursery with salinity goals of 5-10 ppt. Saline Marshes and the LaLoutre Marsh bordering Breton Sound. This salinity regime also would be most suitable for It Chandeleur Sound. A significant portion of the this unit to enhance brackish marsh wildlife habitat water bottoms in this area is leased for oyster Upper River aux Chenes and Terre aux Boeufs for increased furbearer productivity and greater production today. However, large tracts in Bay Marsh Units attractiveness for migratory waterfowl. Boudreau, Indian Mound Bay, Three-mile Bay, and others are not leased. Possible reasons include These two units border the previous low-salinity heavy oyster drill predation and lack of easily Caenarvon Crevasse Marsh Unit and comprise the obtainable seed oysters, both of which are related next step in the salinity gradient toward Breton Outer Breton Saline Marsh Unit to salinities above 15 ppt. Goals for this area Sound. These units represent extensive areas of would be to maintain a salinity regime of 10-15 ppt potentially low-salinity brackish marsh. Goals for The primary public and seed oyster grounds for to encourage oyster production. CuItch planting these units are to establish a salinity regime of southeastern Louisiana are situated in the Outer and controlled harvest on some unleased areas 5-10 ppt over this large marsh area to increase Breton Saline Marsh Unit. Salinity goals for seed could then be practiced to create a reliable source management potential in particular for establish- oyster production are generally 15-20 ppt as dis- of seed oysters. ment of three-cornered grass for muskrats and cussed previously. and also it is believed that effects of antecedent conditions other than available freshwater are of- Table 4-1. Kev to Salinity Stations Used in the Study. ten important in controlling salinities -during a ABBREVIATION STA71ON 11) SOURCE COMMEN75 given month. For example, sustained winds may change water levels and accelerate or reduce Hydrologic Unit I freshwater release into the estuary. For these two PM Pass Manchac at US 51 USACE Daily 1961 - present reasons, the lagged freshwater inflows were re- Bridge, CE 85420 placed by a single variable in the form of average NC North Causeway, USAC E Weekly 1972 - present salinity for the preceeding month. The basic model CE 85575 thus became MC Middle Causeway, USACE Weekly 1972 - present CE 85600 SC South Causeway, USACE Weekly 1972 - present ST,L = f(ST-1,L,F,E) CE 85624 IC ICWW at Paris Road, USACE Twice weekly 1967 - present in which STL is the average salinity for a given CE 76042 month (T) @i a given location (L); ST-1 1. is the CM Chef Menteur, USACE Daily 1967 - present CHAPTER IV average salinity for the preceeding monih Jat that CE 85750 RL Rigolets, CE85700 USACE Daily 1967 - present same location; F is the freshwater introduction BL Bavou LaLoutre at from one or more sources; and E is the error term Alluvial City, CE 85775 USACE Daily 1975 - present FRESHWATER due to factors not incorporated, such as meteoro- Sm Bayou St. Malo LDWF Intermittent 1968 - present logic and oceanographic conditions during the NM Ninemile Bayou LDWF Intermittent 1968 - present SUPPLEMENTAL month T. Hydrologic Unit U REQUIREMENTS As stated earlier, interest and scope of work BG Bay Gardene LDWF Weekly 1968 - present extended primarily over the period from 1967 to LP lAke Petit LDWF Weekly 1968 - present A Special Stations LDHHR 1979. Data requirements thus were for that period from oyster water Combined data-.stations and included the monthly average of salinity values surveys 1 62, 63, 64 - Area 11 Assuming that freshwater inflow is the primary B Lomted at centroid LDHHR 60, 61 at representative locations throughout Hydrologic of 5 tions listed 2 variable controlling salinity variation in Louisiana!s C 1 2 LDHHR 68 Units I and 11 and estimates of freshwater inflows D 1:2 LDHHR 66 69, 70 estuaries, the estimation of inflow needed to E 1 2 LDHHR 51 that controlled these salinities. F 1:2 LDHHR 32 achieve a particular salinity regime requires three G 12 LDHHR 33 52,74 H 1 2 LDHHR 30 31 elements. These are: data characterizing fresh- 8: water inflow conditions, data characterizing salin- Salinity data were obtained mostly in the form of 1,2 LDHHR 2,29 ity conditions, and a numerical description of the daily observations from a number of sources and relationship between the two. That is, some kind reduced to monthly means. To the extent possible, and Breton Sound. While monthly river discharges of numerical model that expresses salinity as a the stations utilized extended over the full range for the Mississippi River were available from the function of at least freshwater inflow, and of other of habitats and related resource uses prevalent USACE, the remaining sources were partially or variables if needed. within each of the hydrologic units. Station char- totally ungaged and required further computations. acteristics are listed in Table 4-1. A number of stations necessitated further data processing. To Freshwater soureas for HwIrn1c) c Unit T nr#-. thp Method of Analvqiq complete the salinity record for some irregularly sampled stations or stations created after 1967, Pontchartrain, Pearl, and Lake Borgne watersheds Objectives, as well as limitations relative to mod- linear regression could sometimes be employed. To (Figure 4-1). The Pontchartrain watershed source eling and available salinity data, necessitated the obtain adequate coverage for Hydrologic Unit 11 combined the gaged discharges of the Amite, use of a relatively simple statistical model. It was required that data from closely spaced stations of Tickfaw, Natalbany, Tangipahoa, and Tchefuncte therefore decided basically to continue the ap- the Oyster Water Survey, Louisiana Department of Rivers' drainage areas, rainfall surpluses generated proach taken in the earlier work (Gagliano et al. Health and Human Resources (DHHR) be lumped. over the ungaged portions of those areas and 1970, Light and Alawady 1970) and utilize 6 multi- In that event the centroid was plotted as the new receiving lakes, and the occasional diversions of ple linear regression model expressing average sal- station's position. A total of 20 salinity stations (9 flow from the Mississippi River through the Bonnet inity in a given month as a function of total in Unit I and 11 in Unit II) were utilized. Carre Spillway. The gaged and ungaged drainage freshwater inflow during that month and of some areas of the Bogue Chitto and Pearl Rivers com- additional variables to account for the effect of prise the Pearl watershed source. The Lake Borgne antecedent conditions. Freshwater Inflow Data watershed source is the totally ungaged rainfall surpluses generated on Lake Borgne and the sur- Previous studies only incorporated antecedent con- Freshwater inflows into Hydrologic Units I and II rounding wetlands. ditions in so far as they concerned freshwater were divided into a number of sources to be inflow. This was done by lagging monthly fresh- evaluated separately. They included the Missis- To estimate monthly freshwater contributions from water inflows by as much as six months and intro- sippi River, the presently operational diversion the ungaged areas of each watershed, continuous ducing the successive, lagged inflows as indepen- structures, and four major watersheds designated daily water balance computations were undertaken dent variables. This procedure is very cumbersome respectively Pontchartrain, Pearl, Lake Borgne, for the period of 1967 to 1979 for each watershed. 13 legend GAGED UPLAND UNGAGED UPLAND UNGAGED WETLAND MAJOR WATERSHED BOUNDARY RIVER BASIN BOUNDARY CLIMATOLOGICAL STATION PEARL RIVER Sloe--Index number GAGING STATION 40 EXISTING DIVERSION STRUCTURE POSSIBLE DIVERSION SITE PROPOSED CAERNARVON AMITE ANGIPAHOA DIVERSION STRUCTURE Franklinton SSW 0 5 10 A TICKFAW 3327 a a I k. B.g.lu.. NATALBANY 0945 Amite nonn 0 New Roads SESE 6686 ogue Chitto near Bush. 1210 m12 Tchefuncte River n , Folsom 00 .5.5 M12 am Baton Rouge-Ryan Airport mond 0549 W Covington 4NNW * 4034 2151 Tickfaw River Netalbany River Tanqlpa oa River t Holden at Baptist at Robert) Amite River at 247 mJ2 79.5 M12 646 mi Denham Springs 1280 ml 2 @8* Springville Fire Tower L.S.U.-Ben Hur Rd. 8.715 5620 matchline Lake Maurepas LAKE PONTCHARTRAIN Figure 4-1. Freshwater sources base map for Hydrologic Units I and 11. 14 S.U. Hur Rd. Springville Fire Tower -13 47 Sb C9 Matchline 4 Lake Maurepas LAKE PONTCHARTRAIN Carville 25w 1585 Donaldsonville W:_- Reserve 7767 ISSIPPI 1A SS Now Orleans Int. 6660 Lac des Affemends S. Be 8 08 Thibodaux Paradis South 0 9013 7096 IQ zz., Houma 4407 Plaqu E.p.-S 73 Gaillano C2 433 It 0 I low 1P k. zZ Figure 4-1. (continued) The ungaged areas were mapped and divided into Essentially the same procedure was followed for At this point, the one month lagged salinity' was categories. upland/drained fastland and wetland/open water Hydrologic Unit II. Sources here are the ungaged introduced as an additional independent variable in Using the Thiessen method, each un- Breton Sound watershed, the ungaged freshwater semi-logarithmic function. The result was a dra- gaged area was further divided into polygons to diversion from the Mississippi River through the matically increased R2 value for almost all of the define the area represented by each of the clima- White's Ditch, Bohemia, and Bayou Lamoque struc- 20 salinity stations. Accordingly, it was decided to Aologial stations for which rainfall and temperature tures, and the indirect effects from the Mississippi define relationships between freshwater inflow and data were available since 1967 (Figure 4-1). For River via dilution of nearshore waters. Water salinity by the general model: each polygon the size of the wetland/open water balance computations as described were applied to and upland/fastland. areas was determined using a the, Breton Sound watershed, while Mississippi St = a St-1 + b log Q, + c-109 Q2 + d log Q3 + e (2) digitizer. These areal measurements, together River discharges were obtained from the USACE, with the daily precipitation and temperature read- New Orleans District. where: St = predicted average monthly salinity, ings from the climatolgical stations, formed the Absence of operational records prevented reliable St-1 = average salinity during the preceeding data base for the water balance computations. estimates for the small ( 500 cfs) diversions at month, Ql-Q3 'are freshwater contributions; a-d' White's Ditch and Bohemia. However a diversion are model coefficients, and e is the intercept A modified version (Stone et al. 1971; Wax 11.981) of record for Bayou Lamoque could be constructed. value. the continuous daily water balance method Discharge equations had been calibrated by the (Thornthwaite and Mather 1955) was used to obtain USGS for Bayou Lamoque Structures No. 1 and No. Result of Analysis monthly runof 'f and surplus values for each of the 2 (USGS 1978) in the general form: F or all Hydrologic Unit I stations except Bayou ungaged watershed areas. The employed water balance model utilizes a two-layer soil storage Q =C - A (2 - 9 - ISMR-Stl )0_5 (1) LaLoutre, the Pearl watershed discharge is found to be the dominant factor in controlling salinity. component for uplands in which an upper layer exhibits equal availability for water loss and re- The coefficients to the models for each salinity charge, and a lower layer exhibits a decreasing where: Q = discharge in cfs, C = discharge coeffi- station in Hydrologic Unit I are given in Table 4-2. availability proportional to content. Values for cient (0.65 for No. 1 and 0.72 for No. 2) ' A = R-square values, or correlation coefficients, shown upper and lower soil capacities for each polygon cross-sectional area of gates (400 ft2 - No. 1 and in the table represent the percentage of the were calculated from vegetation and. soils maps. 576 ft2 - No. 2), g = acceleration of gravity, SMR variation in salinity that is accounted for by the Parish soil surveys made by the Soil Conservation = stage of Mississippi River in ft, and St = stage of models. The model for Chef Menteur (Table 4-2) Service JSCS), U.S. Department of Agriculture the outfall area in feet. in order to generate mean accounts for 82% of the variation, while the South monthly discharges at Bayou Lamoque, it was (USDA), were used to calculate soil storage capa- assumed that all gates were fully opened (except Causeway model accounts for only 55%. All sta- cities in inches per foot. Average rooting depths for known periods of closure) from 1967 to 1979 tions in Table 4-2 have R-square values greater were estimated for the various vegetative cover and that the mean tidal stage was +0.76 ft MSL than 0.50. The coefficients for the discharge types, and multiplied by the soil storage capacities during this period. Data on daily Mississippi River variables (B, C, and D) logically should be negative to obtain a weighted average of total available discharge and stage near Bayou Lamoque were in the equation form used because freshwater in- water storage capacity for each polygon. Ten analyzed using the general form of the quadratic flow should reduce salinity. However, the coeffi- millimeters was used as the upper soil layer capa- equation to derive a relationship between stage cients for the Lake Borgne discharge (c) are posi- city in each case, with the remainder of the total and discharge. The resulting equation (R2 = 0.96) tive. This is probably related to the small magni- making up the lower layer. For wetland areas was substituted for SMR in equation (1). Finally, tude and irregularity of rainfall surpluses in the (swamps and marshes), soil storage was not con- mean monthly Mississippi River discharges were small watershed. sidered, the assumption being that the soils are entered into equation (1) to generate estimated continuously saturated. mean monthly discharges for Bayou Lamoque. The model for the Intracoastal Waterway at Paris The results were stored as a variable called Road gave a very poor correlation and questionable The output of the water balance program was Lamoque in the same data set with Mississippi coefficients and is not included in Table 4-2. The stored in data files and converted to mean monthly cause is probably related to the strong vertical discharge (cubic f eet per second, cfs) using the River and Breton Sound discharges. stratification (salt wedge) in this channel and the acreage values previously entered. Surplus values Freshwater and Salinity MRGO. For this reason it may be difficult to were used in wetland/open water areas, while run- accurately predict salinities near the MRGO. off from the soil storage component was used in The salinity and discharge data sets for Hydrologic Otherwise the models for Pontchartrain and Borgne ungaged.upland/fastland areas. The ungaged dis- Units I and II were concatenated using the Statisti- adequately describe the majority of the variation charge estimates were then added to the gaged cal Analysis System (SAS) so that various forms of in salinity and are significant at the 0.0001 level. river discharges obtained from the USGS, Water salinity/discharge functions could be explored. In Resources Division. The discharges of the Bonnet each case, this involved the station salinities as the The R-square values for stations in Breton Sound Carre Floodway were added to the appropriate dependent variable and discharges as the indepen- (Table 4-3) are slightly lower, with stations C and monthly values for the Pontchartrain watershed. dent vari&bles. Linear, semi-log, log-log, and in- H below 0.50. This is probably a reflection of the Accordingly, all freshwater sources entering verse function forms were tried. Correlation longer interval of time between salinity measure- Hydrologic Unit I were documented as three vari- coefficients were highest for semi-log and log-log ments in this basin (weekly, at best, vs. daily in ables, Pontchartrain, Pearl, and Lake Borgne, in models (112 = 0.32 to 0.65), with the semi-log form Pontchartrain/Borgne). The two most influential terms of mean monthly inflows. giving slightly higher values overall. discharge variables in Breton Sound are the 16 Mississippi River (B) and Bayou Lamoque (D) (Table 4-3). The coefficients for the Breton Sound Table4-2. Hydrologic Unit 1. Pontchartrain/Borgne Basin Salinity/Discharge Models. watershed surplus (C) are negative, but many could become positive within the range of the standard STATION NAME A* B C D E R-square error (� S.E.), indicating a negligible influence on salinity within. Again, this is attributed to the small magnitude and variability of rainfall sur- Chef Menteur 0.691 +0.038 -2.242 +0.372 0.376 +0.226 -0.862 +0.409 13.021 +1.304 0.818 pluses associated with theBreton Sound watershed. Bayou La Loutre 0.588 +0.049 -2.274 +0.621 0.561 +0.379 -2.598 +0.682 22.578 +2.317 0.712 Freshwater Needs Pass Manchac 0.741 +0.050 -0.628 +0.184 0.047 +0.133 -0.166 +0.215 3.413 +0.646 0.734 With valid salinity/discharge models, the next step Middle Causeway 0.734 +0.044 -1.109 +0.262 0.276 +0.164 -0.497 +0.296 6.403 +0.876 0.738 in the analysis was to determine freshwater needs North Causeway 0.741 +0.050 -0.696 +0.236 0.003 +0.149 -0.174 +0.273 4.099 +0.776 0.625 to attain the salinity goals outlined in Chapter 111. It is apparent that goals for salinity include both Nine Mile Bayou 0.565 +0.048 -4.673 +0.685 0.643 +0.401 -0.573 +0.737 22.984 +2.376 0.726 spatial and temporal components (location and sea- Rigolets 0.608 +0.042 -3.653 +0.481 0.620 +0.286 -0.648 +0.516 17.347 +1.639 0.795 son) that may cause conflicts between resource Bayou Saint Malo 0.519 +0.056 -2.304 +0.523 0.237 +0.315 -1.126 +0.570 17.916 +1.918 0.611 uses. In those cases it must be determined what South Causeway 0.532 +0.059 -1.127 +0.342 0.246 +0.212 -1.008 +0.380 9.250 +1.124 0.549 resource uses are most important and, corres- pondingly, which goals should govern freshwater diversion. This must be done, however, within the *coefficients and standard error for the general form: constraints of structure parameters, including size and location, and of the Mississippi River hydro- Salinity = A (Previous Month Salinity) + B (log Pearl discharge) + C (log Lake Borgne discharge) + D (log Pontchartrain logic regime. discharge) + E .. . .......... .. ...... In determining freshwater needs, the desired loca- tion of the 15 ppt isohaline for average conditions during the fall became the most important para- meter. Various 15 ppt isohalines also were used in Table 4-3. Hydrologic Unit 11. Breton Sound Salinity/Disebarge Models. previous studies (USACE 1970) as goals relative to oysters (Ford isohaline) and furbearers (Palmisano isohaline). Our analysis of salinities and habitats STATION NAME A* B C D E R-square indicated that average fall salinities of 15 ppt separated brackish from saline marshes and A 0.637 +0.066 -3-040 +1.291 -0.354 +0.551 -1.561 +1.654 25.880 +6.269 0.552 productive from drill-infested oyster grounds. In the study area, a normal seasonal salinity pat- B 0.650 +0.065 -2.323 +1.208 -0.513 +0.515 -2.046 +1.571 24.372 +5.886 0.580 tern of lowest salinities in the late winter and C 0.519 +0.075 -1.560 +1.080 -0.541 +0.458 -2.374 +1.400 22.788 +5.226 0.435 spring and highest salinities in the late summer and D 0.620 +0.062 -2.026 +1.010 -0.703 +0.432 -2.658 +1.317 26.424 +5.038 0.611 fall is evident. The mean fall salinity at a point is E 0.618 +0.064 -1.247 +0,967 -0.624 +0.414 -3.061 +1.283 23.722 +5.023 0.616 therefore an estimate of maximum mean salinity F 0.591 +0.062 -3.036 +1.056 -0,578 +0.454 -2.826 +1,379 33.842 +5.519 0.630 that is tolerated by the vegetation, wildlif e, and fisheries species. Short-term influxes of higher G 0.580 +0.061 -4.217 +1.274 -0.052 +0.546 -3.121 +1.614 39.486 +6.521 0.624 salinites are doubtless important, especially with H 0.445 +0.071 -3.699 +1.380 -0.023 +0.591 -4.083 +1.760 43.062 +7.263 0.498 regard to vegetation, but sufficient data do not 0.540 +0.068 -3.881 +1.306 -0.130 +0.559 -3.497 +1.653 42.763 +6.938 0.566 exist on short-term vegetative salinity tolerance, and the resolution of the salinity models does not Lake Petit 0.636 +0.063 -1.300 +1.142 -0.918 +0.485 -3.416 +1.516 25.973 +5.607 0.613 allow prediction of short-term fluctuations in sa- Bay Gardene 0.650 +0.056 -4.037 +1.186 -0.484 +0.509 -2.737 +1.537 39.406 +6.203 0.692 linity. Therefore the desired position of the mean fall 15 ppt isohaline was used as a goal. *coefficients and standard error for the general form: Having determined the desired location of the 15 ppt mean fall isohaline in each of the hydrologic Salinity = A (previous salinity) + B (log Mississippi River discharge) + C (log Breton discharge) + D (log Bayou Lamoque units on the basis of resources and resource uses discharge) + E within the seaward portion of each unit, the cor- 17 Discharges, Gaged and Corrected Total. ppt isohaline were obtained (Bayou St. Malo and responding salinities for stations closest to the 15 Table 4-4. Monthly Exceedance Bay Gardene). This in turn allowed computation of % freshwater diversion required to attain the identi- Exceed- Mississippi Pontchartrain Pont.* Pontchartrain Pearl Gaged Pearl Pearl Total Month ance River Q (efs) Gaged Q (cfs) factor Total Q (efs) Q (cfs) factor Q (efs) fie@d salinities by use of the regression models. Subsequent use of the specified diversion need as January so 272,734 2556 2.114 7959 7708 0.165 8980 input. into the models for the upper estuarine 50 437,979 4588 14,287 13,974 16,280 stations provided mean fall isohalines for the February 80 336,405 3133 2.064 9600 11,094 0.165 12,924 brackish to fresh part of the estuary. Comparison so 521,614 5452 16,705 18,704 21,790 of these isohalines With identified goals showed March 80 493,048 3048 1.696 8230 13,718 0.108 15,200 that meeting goals relative to location of the mean so 66 8,631 5390 14,526 22,191 24,588 15 ppt isohaline in all cases satisfied or exceeded April 80 551,309 2458 1.088 5132 10,944 0.093 11,962 requirements for the fresher stations. It was 50 734,914 4555 9511 19,383 21,186 May 80 495,012 1780 2.201 5698 7181 0.150 8258 furthermore established that fall requirements did 50 656,714 2957 9465 12,856 14,784 indeed exceed requirements during the remaining June 80 321,778 1166 2.252 3792 3517 0.185 4168 seasons. 50 471,647 1661 5402 5318 6302 In order to solve the regression equations for the July 80 251,240 1255 4.034 6318 3029 0.341 4062 Bayou St. Malo and Bay Gardene stations for 50 357,094 1738 8749 4342 5823 August 80 177,952 1141 4.146 5972 2929 0.416 4147 maximum supplemental freshwater needs, it was 50 240,396 1576 8110 4001 5665 necessary to decide which discharge variable in September 80 148,107 1026 3.329 4442 2491 0.352 3368 each hydrologic unit to solve for and what values 50 189,274 1569 6792 3534 4778 to assign to the remaining discharge variables in October 80 136,173 911 2.725 3393 2154 0.232 2654 the models. In Hydrologic Unit I, the Pontchar- 50 195,987 1262 4701 3140 3868 -.train watershed variable was chosen even though the Pearl watershed variable exerts more influence 50 213,760 1542 7556 3746 5057 November so 144t931 944 3.900 4626 2307 0.350 3114 in the model. This choice was made because December 80 195,708 1734 2.776 6548 4264 0.255 5351 diversion from the Mississippi River would repre- . 50 300,209 3168 11,962 8263 10,370 sent a direct input into the Lake Pontchartrain *The correction factor is applied as: Total gaged + (factor) (gaged) Watershed. Similarly, in Hydrologic Unit II, the Bayou Lamoque discharge variable was chosen to be'solved for. Mean monthly discharges from the appropriate regression models for the Pontchar- For each location, monthly rates of freshwater water balance analysis were used as the Lake train variable and Bayou Lamoque variable respec- diversion were computed for various structure Borgne and Breton watershed variables. These tively, and subtracting the 80% exceedance dis- sizes and for 50% and 80% exceedance discharges variables exert very little influence in the model. charges calculated to be available from these of the Mississippi River. Necessary stages were However, it was decided to determine long-term sources, the maximum supplemental water require- obtained from rating curves at Bonnet Carre and discharge characteristics for the Mississippi River ments are obtained. Those are 33,000 cfs for Caernarvon as presented together with those for and the Pontchartrain and Pearl watersheds Hydrologic Unit I and 9000 cfs for Hydrologic Unit the Bayou Lamoque structure (Table 4-5). From because the period of record from 1967 to 1979 can Ii. the obtained monthly diversion rates, it soon be@- be described as "wetter than averagell in Louisiana. came apparent that the diversion goals of 33,000 In order to eliminate this bias, gaged river dis- Diversion Volumes cfs and 9000 cfs into Hydrologic Unit I and Hydro- charges for the major watersheds from 1945-1979 In order to optimize plans for freshwater diversion logic Unit II, respectively, could not be met during were analyzed, using a Log-Pearson distribution, to in relation to a broad spectrum of environmental the fall months because of head constraints. This determine discharges for 50% and 80% exceedance units and related goals and needs, it was decided to meant that goals could be met only by diverting frequencies on a monthly basis. Monthly correc- sufficient water during the spring months to the tion factors were calculated from the water bal- formulate feasible diversion scenarios and evaluate extent that its ef feet would last into the fall. ance. data to convert gaged discharge to total resultant annual salinity regimes for the various discharge for the Pontchartrain and Pearl water- estuarine stations. This procedure necessarily in- To determine optimum structure size for attaining sheds. The results appear in Table 4-4. cluded specific locations'for the diversion struc- the salinity goals in the above manner, the stages tures since location determines available head and, and discharges of Table 4-4 were entered as a data Using the above method, maximum freshwater re@- consequently, discharge for a given structure size. set along with mean monthly discharges of the quirements thus were defined for Hydrologic Unit I Given the location, various diversion discharges Lake Borgne and Breton watersheds and the model and Hydrologic Unit II as the volume of freshwater can be expressed in terms of structure size. On co-efficients for each salinity station. Computer inflow required to maintain the 15 ppt isohaline in the basis of the analysis results presented in processing of this data using equations (1) and (2) the desired location during the fall under condi- Chapter V, freshwater was assumed diverted into provided predicted salinities for selected structure tions of a drought having a probability of occur- Hydrologic Unit I at Bonnet Carre and into'Hydro- cross sections. Discharges through the structure rence of once every five years. By solving the logic Unit II at Caernarvon. and predicted salinities were calculated for each 18 station on a monthly basis using various structure Table 4-6. Estimated Discharges (Q) at Bonnet Carre and Resultant Salinities (S) at Bayou St sizes under 50% and 80% conditions. Each model was allowed to stabilize as required by use of the 0 ft2 500 ft2 1000 ft2 1500 ft2 200ft2 2500ft 3000ft2 previous month's salinity. Stabilization never re- quired more than 24 monthly iterations. Q S Q S Q S Q S Q S Q S Q S Table 4-5. Mississippi River stages Near Existing and Proposed Diversion Sites for 50% and MONTH (cfs) (ppt) (cfs) (ppt) (cfs) ((ppt) (cfs) (ppt) (cfs) (ppt) (cfs) (ppt) (cfs) (ppt) 80% Exceedance Discharges. Mississipii River Stage (ft) June 0 10.0 7,981 9.6 15,963 9.3 23,944 9.2 31,925 9.1 39,906 9.0 47,888 8.9 Month Exeeedence Bonnet Carre caernarvon Bayou Lamoque July 0 10.6 6,109 10.3 12,219 10.1 18,328 9.8 24,438 9.7 30,547 9.6 36,656 9.4 August 0 11.3 4,001 10.9 8,002 10.6 12,003 10.4 16,004 10.2 20,005 10.1 24,006 9.9 January 3 62 2.55 1.94 7.71 5.00 2.82 September 0 11.8 2,836 11.4 5,673 11.1 8,509 10.9 11,346 10.8 14,182 10.6 17,019 10.5 February So 5 3.52 2.39 October 0 12.5 2,979 12.0 5,958 11.7 8,937 11.4 11,916 11.2 14,895 11.1 17,875 11.0 50 10.03 6.19 3.20 November 0 12.4 3,408 11.9 6,815 11.6 10,223 11.4 13,631 11.2 17,038 11.0 20,446 10.9 March 80 9.30 5.78 3.07 December 0 11.3 5,192 10.9 10,384 10.6 15,576 10.4 20,768 10.2 25,960 10.1 31,152 9.9 50 13.57 8.31 3.86 6.63 3.32 January 0 10.2 7,460 9.8 14,921 9.5 22,381 9.3 29,841 9.1 37,301 9.0 44,762 8.8 April go 10.90 50 15.00 9.25 4.18 February 0 9.4 8,654 8.9 17,309 8.6 25,963 8.4 34,618 8.2 43,272 8.0 51,926 7.9 May 5o 9.38 5.80 309 March 0 8.8 10,211 8.3 20,422 8.0 30,632 7.7 40,843 7.5 51,054 7.4 61,265 7.2 13.32 8.13 3.92 April 0 9.0 10,776 8.2 21,552 7.8 32,328 7.5 43,104 7.3 53,880 7.5 60,653 7.3 June so 4 71 3.30 2.30 so 9.68 5.49 99 May 0 9.5 10,109 8.6 20,218 8.2 30,326 7.9 40,435 7.7 50,544 7.5 60,653 7.3 July so 3.16 2.21 1.67 June 0 10.7 7,981 9.7 15,963 9.3 23,944 9.0 31,925 8.8 39,906 8.6 47,888 8.4 50 5.50 3.84 2.48 July 0 11.2 6,109 10.4 12,219 10.0 18,328 9.7 24,438 9.5 30,547 9.3 36,656 9.2 August 1.73 1.03 0.45 August 0 11.6 4,001 10.9 8,002 10.6 12,003 10.3 16,004 10.1 20,005 10.0 24,606 9.8 80 2.93 2.04 1.51 September 50 1.12 0.50 September 0 11.9 2,836 11.4 5,673 11.1 8,509 10.9 11,346 10.7 14,182 10.6 17,019 10.4 50 1.97 1.22 068 October 0 12.5 2,979 12.0 5,958 11.7 8,937 11.4 11,196 11.2 14,895 11.1 17,875 10.9 October 5o 0.7 0.29 November 0 12.3 3,408 11.9 6,815 11.6 10,223 11.4 13,631 11.2 17,038 11.0 20,446 10.9 go 2. 7 1.32 0.79 November 80 1.06 0.46 50 2.40 1.59 1.0 December 2.07 132 0.7 80 4.25 2.99 Table 4-7. Estimated Discharges (Q) at Bonnet Carre and Resultant Salinities (S) at Bayou St. Malo for Various Structure Sizes (80% Exceedance). 0 ft2 500 ft2 1000 ft2 1500 ft2 2500 Structure size as used in the following paragraphs refers to the cross-sectional area of the structure Q S Q S Q s Q s opening through which flow is passed from the MONTH (cfS) (ppt) (cfs) (cfs) (cfs) (ppt) (cfs) 28 Mississippi River to the wetlands. For the present determination of structure size, it was assumed June 0 10.6 5,547 10.2 11,095 9.9 16,642 9.8 that the structure would consist of multiple, gated, July 0 11.6 4,233 11.2 8,465 10.9 12,698 10.7 concrete box culverts of 2 x 2 feet with a August 0 12.2 2,461 11.8 4,921 11.5 7,382 11.3 discharge coefficient C = 0.72 (equivalent to the September 0 12.8 2,057 12.4 4,113 12.2 6,170 11.9 Bayou Lamoque #2 Structure); the implied length October 0 13.5 2,057 13.0 4,113 12.7 6,170 12.5 being approximately 300 feet. The culverts are November 0 13.6 2,057 13.1 4,113 12.9 6,170 12.6 assumed to be totally submerged at all times. No December 0 12.9 2,979 12.5 5,958 12.2 8,937 12.0 consideration is given to resultant velocities and January 0 11.9 4,662 11.5 9,323 11.2 13,985 11.0 head requirements at the outflow point. February 0 11.0 5,767 12.2 11,534 10.2 17,302 10.2 Accordingly, the actual required structure size- March 0 10.4 8,297 9.8 16,594 9.5 24,892 9.5 may be larger depending on structure design, April 0 10.5 9,016 9.7 18,032 9.3 27,047 9.3 including length and shape, and on design criteria May 0 11.0 8,337 10.1 16,674 9.7 25,011 9.3 for the outflow channel. June 0 12.0 5,547 11.1 11,095 10.7 16,642 10. Four stations are selected as examples of the July 0 12.4 4,233 11.7 8,465 11.3 12,698 11.0 above analyses. These are Bayou St. Malo, and August 0 12.6 2,461 12.1 4,921 11.7 7,382 11.5 Middle Causeway for Hydrologic Unit I and Bay September 0 13.0 2,057 12.6 4,113 12.3 6,170 12. Gardene and Lake Petit for Hydrologic Unit II. October 0 13.6 2,057 13.1 4,113 12.8 6,170 12.5 Tables 4-6 and 4-7 display predicted salinity re- November 0 13.6 2,057 13.2 4,113 12.9 6,170 12.7 gimes for Bayou St. Malo under 50% and 80% exceedance conditionsp respectively. In essence, Table 4-8. Predicted Discharges (Q) at Bonnet Carre and Resultant Salinities (S) at Middle CauseWay for Various Structure Sizes (50% Exceedance). 50% exceedance is average conditions, or the situ- ation expected to occur one out of two years, while 0 ft2 500 ft2 1000 ft2 1500 ft2 2000 ft2 2500 ft2 3000 ft2 80% exceedance describes a "low water" or drought situation expected to occur once in five years. Q 8 Q S Q S Q S Q S Q S Q 3 MONTH (efs) (ppt) (cfs) WO (efs) WO (cfa) WO (cfa) WO (efs) WO (cfs) WO Two conclusions can be drawn from the tables: 1) June 0 2.9 7,981 2.7 15,963 2.6 23,944 2.5 31,925 2.5 39,906 2.4 47,888 2.4 there is very little difference between the 50% and July 0 3.4 6,109 3.1 12,219 3.0 18,328 2.8 24 i438 2.8 30,547 2.7 36,656 2.6 80% fall month discharges for a particular struc- August a 3.7 4,001 3.5 8,002 3.3 12,003 3.2 16,004 3.1 20,005 3.0 24,006 2.9 ture size, and 2) there is less difference in dis- September 0 4.1 2,836 3.8 5,673 3.7 8,509 3.5 11,346 3.4 14,182 3.3 17,019 3.2 charge from small to large structures in the fall October 0 4.5 2,979 4.2 5,958 4.0 8,937 3.8 11,916 3.7 14,895 3.8 17,875 3.5 than in the spring. This points to the paradox of November 0 4.6 3,408 4.3 6,815 4.1 10,223 4.0 13,631 3.8 17,038 3.7 20,446 3.0 freshwater diversion. The fall months are the most December a 4.3 5,192 4.0 10,384 3.8 15,576 3.8 20,788 3.5 25,960 3.4 31,152 3.3 critical with regard to salinity goals, but the majority of the freshwater must be diverted in the January 0 3.8 7,460 3.5 1.4,921 3.3 22,381 3.1 29,841 3.0 37,301 2.9 44,702 2.8 spring when it is available. February 0 3.3 8,654 2.9 17,309 2.7 i5,963 2.5 34,618 2.4 43,272 2.3 51,926 2.2 March 0 2.8 10,211 2.5 20,422 2.2 30,632 2.1 40,843 1.9 51,054 1.8 61,265 1.7 To satisfy the 15 ppt fall isohaline location, fall April 0 2.6 10,776 2.2 21,552 1.9 32,328 1.7 43,104 1.6 53,880 1.4 64 656 1.3 salinities at Bayou St. Malo should remain limited May 0 2.7 10,109 2.2 20,218 1.9 30,326 1.7 40,435 1.6 50,544 1.4 60,853 1.3 to about 12.5 ppt. This is seen to require approxi- June 0 3.2 7,981 2.7 15,963 2.4 23,944 2.1 31,925 2.0 39,906 1.9 47,888 1.7 mately a 1500 ft2 structure under the dry condi- July 0 3.6 6,109 3.1 12,219 2.8 18,328 2.6 24,438 2.4 30,547 2.3 36,656 2.1 August 0 3.9 4,001 3.5 8,002 3.2 12,003 3.0 16,004 2.8 20,005 2.7 24,008 2.5 tions. (80% exceedance). Mucb larger size September 0 4.2 2,836 3.8 5,673 3.6 8,509 3.4 11,346 3.2 14,182 8.1 17,019 3.0 structures give only small additional benefits. A October 0 4.6 2,979 4.2 5,958 3.9 8,937 3.7 11,916 3.6 14,895 3.4 17,875 3.3 diversion of 50,000 efs produces a decrease from November 0 4.7 3,408 4.3 6,815 4.1 10,223 3.9 13,631 3.7 17,038 3.0 20,446 3.5 10.5 to 8.5 ppt in the spring, whereas 26,000 cfs reduces 10.5 to 9.0 ppt (Table 4-7). Hydrologic Unit I is very large, and large amounts of fresh- - water are required to reduce salinities. However, Table 4-9. Predicted Discharges (Q) at Bonnet Carre and Resultant Salinities (S) at Middle Causeway for Various Structure Sizes (80% Exceedanee). by establishing a more stable salinity regime with 0 ft2 500 ft2 1000 ft2 1500 ft2 2000 ft2 salinities several ppt fresher and without extreme 2500 ft2 3000 ft2 maxima, benefits may be greater than the reduc- tion in monthly mean salinities would indicate. Q S Q S Q S Q S Q S Q 8 Q S MONTH (cfs) (ppt) (efs) (ppt) (cfa) (ppt) (efs) (ppt) (ds) (ppt) (ds) (PPO (Cfs) (ppt) information for Middle Causeway in Lake Pontchartrain is shown in Tables 4-8 and 4-9. A June 0 3.2 5,547 3.0 11,095 2.9 16,642 2.8 22,189 2.8 27,736 2.7 33,284 2.7 similar pattern is evident at this station. The large July 0 3.8 4,233 3.5 8,465 3.4 12,698 3.3 16,931 3.2 21,164 3.1 25,396 3.1 volume of the lake tends to buffer changes in August 0 4.3 2,461 4.0 4,921 3.9 7,302 3.7 9,843 3.6 12,303 3.6 14,764 3.5 salinity. Also, as expected, the amount of salinity September 0 4.8 2,057 4.5 4,113 4.3 6,170 4.2 8,227 4.1 10,284 4.0 12,340 3.9 decrease per volume of freshwater added is less at October 0 5.2 2,057 4.9 4,113 4.7 6,110 4.6 8,227 4.5 10,284 4.4 12,340 4.3 low salinities than at higher ones. At no time did November 0 5.5 2,057 5.2 4,113 5.0 6,170 4.9 8,227 4.7 10,284 4.6 12,340 4.5 the investigated structure sizes and discharges December 0 5.4 2,979 5.1 5,958 4.9 8,937 4.7 11,916 4.6 14,895 4.5 17,875 4.4 result in the lake becoming totally fresh. The January 0 5.0 4,662 4.7 9,323 4.5 13,985 4.3 18,647 4.2 23,308 4.0 27,970 3.9 identified requirement for a salinity range of 2 to '5 February 0 4.5 5,767 4.2 11,534 3.9 17,302 3.8 23,069 3.6 281836 3.5 34,603 3.4 ppt at the Middle Causeway station is estimated to March 0 4.1 8,297 3.7 16,594 3.4 24,892 3.2 33,189 3.1 41,486 3.0 49,783 2.9 be met by a structure of between 1000 and 1500 April 0 4.0 9,016 3.4 18,032 3.1 27,047 2.9 36,063 2.8 45,079 2.6 54,095 2.5 ft2 cross section. May 0 4.1 8,337 3.5 16,674 3.2 25,011 3.0 33,348 2.8 41,685 2.6 50,023 2.5 June 0 4.5 5,447 3.9 11,095 3.8 16,642 3.3 22,189 3.1 27,736 3.0 33,284 2.9 The above analysis procedure was followed for all July 0 4.8 4,233 4.2 8,465 3.9 12,698 3.7 16,931 3.5 21,164 3.4 25,396 3.2 stations and resulted in a selection of a 1500 ft2 August 0 5.0 2,461 4.5 4,921 4.2 7,382 4.0 9,843 3.8 12,303 3.7 14,764 3.6 cross-sectional area for the diversion structure September 0 5 *3 2,057 4.9 4,113 4.6 6,170 4.4 8,227 4.2 10,284 4.1 12,340 4.0 assuming realization of the estimated delivery October 0 5.6 2,057 5.2 4,113 4.9 6,170 4.7 8,227 4.6 10,284 4.4 12,340 4.3 rate. This structure size was found to most closely November 0 5.8 2,057 5.4 4,113 5.2 6,170 5.0 8,227 4.8 10,284 4.7 12,340 4.6 attain the goals for all stations within the 20 Pontchartrain-Borgne estuary. The near maximum diversion of 32,000 cfs associated with this size is Table 4-10. Predicted Discharges (Q) at Caernarvon and Resultant Salinities (S) at Bay Gardene for Various Structure Sizes (50% Exceedance). in the same range as that identified by the USACE 0 ft2 200 ft2 400 ft2 500 ft2 600 ft2 700 ft2 goo ft2 goo ft2 1000 ft2 (1981, personal communication). Annual hydro- graphs representing the predicted salinity regimes for a 1500 ft2 structure are shown for Bayou St. Q S Q S Q S Q S Q s Q S Q S Q S Q S Malo and Middle Causeway in Figure 4-2. MONTH (efs) (ppt) (efs) (ppt) (efs) (ppt) (efs) (ppt) (efs) (Ppt) (cfs) (Ppt) (efs) (ppt) (efs) (ppt) (efs) (ppt) Expected environmental changes are discussed in Chapter VI. June 0 11.7 2,441 11.4 4,882 11.1 6,103 11.0 7,323 10.9 8,544 10.8 9,764 10.8 10,985 10.7 12,205 10.6 July 0 12.3 1,941 11.8 3,883 11.4 4,853 11.3 5,824 11.1 6,795 11.0 7,766 10.8 8,736 10.7 9,707 10.6 PREDICTED AVERAGE HALOGRAPHS August 0 13.9 1,175 13.3 2,350 12.8 2,937 12.6 3,524 12.4 4,112 12.3 4,699 12.1 5,287 11.9 5,874 11.8 NO DIVERSION STRUCTURE September 0 17.9 540 16.7 1,081 15.9 1,351 15.6 1,621 15.3 1,891 15.1 2,161 14.8 2,432 14.6 2,702 14.4 1 00 ft2 CROSS SECTION AT October 0 19.9 652 18.5 1,303 17.6 1,629 17.2 1,955 16.9 2,281 16.6 2,607 16.4 2,933 16.1 3,258 15 .9 :ONNET CARRE November 0 19.6 885 18.4 1,770 17.5 2,212 17.2 2,655 16.9 3,097 16.6 3,539 16.3 3,982 16.1 4,424 15 .9 25 - December 0 20.1 1,625 18.1 3,250 17.0 4,063 16.6 4,875 16.2 5,688 15.9 6,500 15.6 7,313 15.3 8,125 15.0 First Year January 0 17.3 2,304 15.7 4,608 14.8 5,760 14.4 6,912 14.0 8,064 13.7 9,216 13.4 10,368 13.2 11,520 12.9 20 - February 0 15.1 2,624 13.8 5,249 12.9 6,561 12.5 7,873 12.2 9,186 11.9 10,498 11.6 11,810 11 .4 13,122 11.2 March 0 13.1 3,115 11.9 6,229 11.0 7,787 10.7 9,344 10.4 10,901 10.1 12,459 9.8 14,016 9.6 15,573 9.4 is - BAYOU ST. MALO April 0 11.7 3,309 10.5 6,618 9.7 8,272 9.4 9,927 9.1 11,581 8.8 13,235 8.5 14,890 8.3 16,544 8.1 May 0 10.9 3,076 9.8 6,152 9.0 7,690 8.7 9,228 8.4 10,766 8.1 12,304 7.9 13,842 7.7 15,380 7.4 t E June 1 11.3 2,441 10.3 4,882 9.5 6,103 9.2 7,323 8.9 8,544 8.7 9,764 8.4 10,985 8.2 12,205 9.0 110 July 0 12.1 1,941 11.1 3,883 10.4 4,853 10.1 5,824 9.8 6,795 9.5 7,766 9.3 8,736 9.1 9,707 8.9 MIDDLE CAUSEWAY August 0 13.7 1,175 12.9 2,350 12.2 2,937 11.9 3,524 11.6 4,112 11.3 4,699 11.1 5,287 10.9 5,874 10.7 5 September 0 17.8 540 16.4 1,081 15.5 1,351 15.1 1,621 14.8 1,891 14.5 2,161 14.2 2,432 13.9 2,702 13.7 October 0 19.9 652 18.3 1,303 17.3 1,629 16.9 1,955 16.6 2,281 16.2 2,607 15.9 2 933 15.7 3,258 15.4 0 . . . . November 0 19.5 885 18.2 1,770 17.3 2,212 17.0 2,655 16.6 3tO97 16.3 3,539 16.1 3,982 15.8 4,424 15.6 J J A S 0 K D J F M A U J J A S 0 N 0 J F M A M Figure 4-2. Mean monthly predicted salinities for Table 4-11. Predicted Discharges (Q) at Caernarvon and Resultant Salinities (S) at Bay Gardena for Various Structure Sizes (80% Exceedance). Bayou St. Malo and Middle Causeway with and without the Bonnet Carre 0 ft2 200 ft2 400 ft2 500 ft2 600 ft2 Too ft2 800 ft2 goo ft2 1000 ft2 diversion for 50% exceedance criteria. In Hydrologic Unit II, predicted discharges and Q S Q S Q S Q S Q S Q S Q S Q S Q S salinities at Bay Gardene for 50% and 80% exceed- MONTH (efs) (ppt) (efs) (ppt) (cfs) (ppt) (efs) (ppt) (efs) Wit) (efs) Wt) (efs) Wt) (efs) Wt) (efs) WO ance conditions are shown in Tables 4-10 and 4-11, respectively. Bay Gardene is located near the June 0 12.6 1,747 12.3 3,494 12.1 4,368 12.0 5,241 11.9 6,115 11.8 6,988 11.7 7,862 11.7 8,735 11.6 important public oyster grounds where the majority July 0 13.9 1,267 13.4 2,534 13.1 3,168 12.9 3,802 12.8 4,435 12.6 5,069 12.5 5,702 12.4 6,336 12.3 of seed oysters for the region are produced. De- August 0 18.0 200 17.4 399 16.8 499 16.6 599 16.4 698 16.2 798 16.1 898 15.9 998 15.7 velopment of seed oysters requires a particular September 0 21.0 115 20.4 230 19.8 288 19.6 346 19.4 403 19.2 461 19.0 518 18.8 576 18.7 seasonal salinity regime. Salinities should not be October 0 22.6 115 22.0 230 21.6 288 21.4 346 21.2 403 21.0 461 20.8 518 20.7 576 20.5 below 10 ppt during the late spring and early November 0 22.0 885 21.3 1,770 20.8 2,212 20.5 2,655 20.3 3,097 20.1 3,539 19.9 3,982 19.7 4,424 19.6 summer months for spawning, larval development, December 0 22.4 652 21.4 1,303 20.6 1,629 20.3 1,955 20.0 2t281 19.8 2,607 19.5 2,933 19.3 3,258 19.1 and spatfall. Salinities above 15 ppt in the summer January 0 20.0 1,434 19.0 2,868 18.3 3,586 18.0 4,303 17.8 5,020 17.5 5,737 17.3 6,454 17.1 7,171 16.9 and fall lead to increased predation on the develop- February 0 17.9 1,829 17.0 3,657 16.3 4,572 16.0 5,486 15.7 6,401 15.5 7,315 15.3 8,229 15.0 9,144 14.8 ing seed oysters by the oyster drill (Dugas 1977). March 0 15.6 2,519 14.7 5,037 14.0 6,297 13.7 7,556 13.4 8,815 13.2 10,075 12.9 11,334 12.7 12,593 12.5 Table 4-10 shows that under average conditions April 0 14.0 2,733 13.0 5,467 12.3 6,834 12.0 8,200 11.8 9,567 11.5 10,934 11.3 12,300 11.0 13,667 10.8 these goals are best served with a structure size May 0 13.0 2,524 12.1 5,048 11.4 6,310 11.1 7,572 10.9 8,834 10.6 10,096 10.4 11 358 10.1 12,620 9.9 somewhere between 500 ft2 and 600 ft2 (assuming June 0 13.6 1,747 12.7 3,494 12.1 4,368 11.8 5,241 11.5 6,115 11.2 6,988 11.0 7,862 10.8 8,735 10 .6 Bayou Lamoque is fully opened), although both July 0 14.5 1,267 13.7 2,534 13.1 3,168 12.8 3,802 12.5 4,435 12.3 5,069 12.0 5,702 11.8 6,336 11.6 criteria cannot be fulfilled simultaneously. To August 0 18.4 200 17.5 399 16.8 499 16.5 599 16.2 698 16.0 798 15.7 898 15.5 998 15.3 maintain salinity near 15 ppt in the fall, when September 0 21.3 115 20.5 230 19.8 288 19.5 346 19.3 403 19.0 461 18.8 518 18.6 576 18.4 freshwater is less available, it must dip below 10 October 0 22.8 115 22.1 230 21.6 288 21.3 346 21.1 403 20.9 461 20.7 518 20.5 576 20.3 ppt in late spring when freshwater is more avail- November 0 22.1 885 21.4 1,770 20.8 2,212 20.5 2,655 20.3 3,097 20.0 3,539 19.8 3,982 19.6 4,424 19.4 able. It is possible that the Bayou Lamoque 21 structures could be operated to "fine tune" the Table 4-12. Predicted Discharge (Q) at Caernarvon and Resultant Salinities (S) at Lake Petit for Various Structure Sizes (50% Exceedance). salinity during the spawning season, but even this could cause higher salinities the following fall. 0 ft2 200 ft2 400 ft2 500 ft2 600 ft2 700 ft2 800 ft2 goo ft2 1000 ft2 Under drought conditions, oyster drills would be subdued from March to August with the 500-600 ft2 structure and from March to September with a Q s Q S Q S Q S Q s Q S Q S Q S Q S 1000 ft2 structure (Table 4-11). This indicates that MONTH (efs) (ppt) (cfs) (ppt) (efs) (ppt) (efs) (Ppt) (efs) (ppt) (efs) (ppt) (efs) (ppt) (efs) (ppt) (efs) Wt) larger structures would not aid significantly in reducing drill populations. June 0 7.3 2,441 7.0 4,882 6.6 6,103 6.5 7,323 6.4 8,544 6.3 9,764 6.2 10,985 6.1 12,205 6.0 Under average conditions predicted salinities at July 0 7.0 1,941 6.4 3,883 5.9 4,853 5.7 5,824 5.5 6,795 5.3 7,766 5.1 8,736 5.0 9,707 4.8 Lake Petit meet the goals for low-salinity brackish August 0 7.6 1,175 6.9 2,350 6.3 2,937 6.0 3,524 5.8 4,112 5.6 4t699 5.4 5,287 5.2 5,874 5.0 marsh (5-10 ppt) with a 400 ft2 structure September 0 11.3 540 9.8 1,081 8.8 1,351 8.5 1,621 8.1 1,891 7.8 2,161 7.5 2,432 7.3 2,702 7.0 (Table 4-12). In addition, it should be kept in mind October 0 13.1 652 11.4 1,303 10.2 1,629 9.8 1,955 9.4 2,281 9.0 2,607 8.7 2,933 8.4 3,258 8.1 that the diversion discharges are entered in the November 0 12.2 885 10.7 1,770 9.7 2,212 9.3 2,655 8.9 3,097 8.6 3,539 8.3 3,982 8.0 4,424 7.7 Bayou Lamoque discharge variable of the models. December 0 13.1 1,625 10.7 3,250 9.3 4,063 8.8 4,875 8.4 5,688 7.9 6,500 7.6 7,313 7.2 8,125 6.9 In other words, predicted salinities are based on January 0 10.4 2,304 8.5 4,608 7.3 5,760 6.8 6,912 6.4 8,064 6.1 9,216 5.7 10,368 5.4 11,520 5.1 freshwater input at the seaward end of the estuary. February 0 8.5 2,624 6.9 5,249 5.8 6,561 5.4 7,873 5.0 9,186 4.7 10,498 4.4 11,810 4.1 13,122 3.8 With introduction at Caernarvon it is likely that March 0 7.0 3,115 5.5 6,229 4.5 7,787 4.1 9,344 3.7 10,901 3.4 12,459 3.1 14,016 2.8 15,573 2.5 Lake Petit salinities will be somewhat less than April 0 6.0 3,309 4.7 6,618 3.7 8,272 3.3 9,927 2.9 11,581 2.6 13,235 2.3 14,890 2.0 16,544 1.8 those in Tables 4-12 and 4-13. May 0 5.4 3,076 4.1 6,152 3.2 7,690 2.8 9,228 2.5 10,766 2.1 12,304 1.8 13,842 1.5 15,380 1.3 June 0 5.7 2,441 4.5 4,882 3.6 6,103 3.2 7,323 2.9 8,544 2.5 9,764 2.2 10,985 2.0 12,205 1.7 Analysis of the predicted salinity conditions indi- July 0 5.9 1,941 4.8 3,883 3.9 4,853 3.6 5,824 3.2 6,795 2.9 7,768 2.6 8,736 2.4 9,707 2. 1 cates that a structure at Caernarvon with a cross- August 0 6.9 1,175 5.9 2,350 5.1 2,937 4.7 3,524 4.4 4,112 4.1 4,699 3.8 5,287 3.5 5,874 3.3 sectional area between 500 ft2 and 600 ft2 would September 0 10.9 540 9.2 1,081 8.1 1,351 7.6 1,621 7.2 1,891 6.8 2,161 6.5 2,432 6.2 2,702 5.9 provide the volume of freshwater that most nearly October 0 12.8 652 11.0 1,303 9.7 1,629 9.3 1,955 8.8 2,281 8.4 2,607 8.1 2,933 7.8 3,258 7.4 attains the salinity goals in the Breton Sound November 0 12.0 885 10.5 1,770 9.4 2,212 8.9 2,655 8.5 3,097 8.2 3,539 7.9 3,982 7.6 4,424 7.3 estuary. A 576 ft2 cross section was therefore - used (this is the size of the four 12 by 12 ft gates in the Bayou Lamoque No. 2 diversion structure) to Table 4-13. Predicted Discharges (Q) at Caernarvon and Resultant Salinities (S) at Lake Petit for Various Structure Sizes (80% Exceedance). develop the predicted average halographs for Bay Gardene and Lake Petit shown in Figure 4-3. a ft2 200 ft2 400 ft2 500 ft2 600 ft2 700 ft2 800 ft2 goo ft2 1000 ft2 Q S Q S Q s Q S Q 8 Q S Q S Q S Q S PREDICTED AVERAGE HALOGRAPHS MONTH (efs) (ppt) (efs) (ppt) (efs) (PP0 Ids) (Ppt) Ids) (ppt) (efs) (Ppt) (efs) (PP0 (efs) (PPO (efs) (PP0 ,P-:O DIVERSiO: STRUCTURE , 76 ft2 CRO S SECTION AT June 0 7.8 1,747 7.5 3,494 7.2 4,368 7.1 5,241 78.0 6,115 6.9 6,988 6.8 7,862 6.7 8,735 6.6 25 - CAERNARVON July 0 8.0 1,267 7.4 2,534 7.0 3,168 6.8 3,802 6.6 4,435 6.4 5,069 6.3 5,702 6.1 6,336 6.0 FIrst Year -I August 0 11.6 200 10.8 399 10.1 499 9.9 599 9.6 698 9.4 799 9.2 898 9.0 998 9.8 20 - BAY GARDENE September 0 14.0 115 13.2 230 12.5 288 12.2 348 12.0 403 11.8 461 11.5 518 11.3 576 11.1 October a 15.0 115 14.3 230 13.8 288 13.5 346 13.3 403 13.1 461 12.9 518 12.7 576 12.5 November 0 13.6 885 12.8 1,770 12.1 2,212 11.9 2,655 11.6 3,097 11.3 3,539 11.1 3,982 10.9 4,424 10.7 CL is December 0 14.3 652 13.0 1,303 12.1 1,629 11.7 1,955 11.3 2,281 11.0 2,607 10.7 2,933 10.5 3,258 10.2 January 0 11.8 1,434 10.7 2,868 9.8 3,586 9.5 4,303 9.1 5,020 8.8 5,737 8.6 6,454 8.3 7,171 8.1 'CIO - ca February 0 10.0 1,829 8.9 3,657 8.1 4,572 7.7 5,486 7.4 6,401 7.1 7,315 6.8 8,229 6.6 9,144 6.3 March a 8.3 2,519 7.2 5,037 6.3 6,297 6.0 7,556 5.7 8,815 5.4 10,075 5.1 11t334 4.8 12,593 4.6 LAKE PETIT April 0 7.2 2,733 6.1 5,467 5.3 6,834 4.9 8,200 4.6 9,567 4.3 10,934 4.0 12,300 3.7 13,667 3.5 May 0 6.5 2,524 5.5 5,048 4.6 6,310 4.2 7,572 3.9 8,834 3.6 10,096 3.3 11,358 3.0 12,620 2.8 of June 0 6.9 1,747 5.9 3,494 5.1 4,368 4.7 5,241 4.4 6,115 4.1 6,988 3.8 7,862 3.5 8,735 3.3 J J A S 0 N 0 J F M A M J J A S 0 N 0 J F M A M July 0 7.4 1,267 6.4 2,534 5.6 3,168 5.3 3,802 4.9 4,435 4.7 5,069 4.4 5,702 4.1 6,336 3.9 Figure 4-3. Mean mont hly predicted salinities for August 0 11.2 200 10.1 399 9.3 499 8.9 599 8.6 698 8.2 798 8.0 898 7.7 998 7.4 Bay Gardene and Lake Petit with and September 0 13.7 115 12.8 230 12.0 288 11.6 346 11.3 403 11.0 461 10.8 518 10.5 576 10.3 October 0 14.8 115 14.0 230 13.4 288 13.1 346 12.8 403 12.8 461 12.4 518 12.1 576 11.9 LAKE PET@IT@@ without the Caernarvon diversion for November 0 13.5 885 12.6 1,770 11.9 2,212 11.6 2,655 11.3 3,097 11.1 3,539 10.8 3,982 10.6 4,424 10.3 50% exceedance criteria. 22 +* CHAPTER V Aw PROPOSED SITES FOR FRESHWATER DIVERSION The analysis of possible diverison sites includes the Industry with river frontage, wetlands in the background. east bank of the Mississippi River from the northern boundary of lberville Parish to Baptiste Collette Bayou. The area upstream of Poydras in 4) Results of USACE diversion studies - The When further analyzing the feasibility of imple- St. Bernard Parish contains all possible diversion USACE.has evaluated 12 possible diversion sites menting a large number of small structures, it sites for Hydrologic Unit 1, while sites for Hydro- in Hydrologic Unit 1. Three of these were becomes readily apparent that constraints tend to logic Unit II must be selected downstream from recommended for detailed studies (USACE outweigh opportunities along nearly the entire east this point. Siting of potential diversion structures 1981a). Results of the USACE feasibility de- bank; the two major related reasons being cost and is based on four major considerations: terminations are incorporated in the present existing development. site selection. 1) Goals of the diversion - This concerns the Based on detailed analyses of topography, drainage, volume of water needed, where it is needed, General Considerations present and near future development, and con- and when it is needed. Before dealing with the specifics of Hydrologic straints posed by these elements on freshwater 2) Delivery structures and existing drainage pat- Units I and II, some general comments are in order diversion, it was decided that a limited number of terns - For specific diversion needs consider- relative to the selection of size, type, and number large structures should be favored as being most ation must be given to the requirements for of structures. It may be argued that with the feasible and cost-effective. Major considerations conveying freshwater from the river to the objective being the diversion of freshwater for the are summarized in the following paragraphs. estuary in terms of structures and channels. purpose of a managed salinity regime, diversion Alteration of drainage patterns and flooding should mimic overbank flow to the greatest extent potential must be evaluated. possible. This would provide a greater retention of water within the wetlands, which in turn provides The identified magnitude of the freshwater diver- 3) Existing and proposed land uses - Agricultural, for temperature adjustments, natural treatment, sion requirement (Chapter IV) is on the order of urban, and industrial development are concen- and a more gradual release into the estuarine 30,000 to 40,000 cfs. It may safely be assumed trated along the river because of land suit- water bodies. Accordingly, it would be desirable to that small structures, if selected, would be siphons ability and transportation. These and future have a large number of small structures. The of the type presently operational at the Lake land uses, local priorities, market values, and implementation of such a plan could be incre- Borgne Canal because siphons do not involve ownership patterns of the land are primary mental and would facilitate initiation and partici- breaching the levee, thereby creating a potentially factors in siting. pation by local governments. weak link in the flood protection chain. Having a 23 would be needed. At a per structure cost of some late summer and fall. Yet diversion of freshwater 2.5 million dollars this would more than double the into this lower part of the basin is not viewed as capacity of about 500 efs, tens of such structures western and southwestern Lake Borgne during the first cost for the diversion when compared with either very feasible or desirable for a number of USACE cost estimates for large structures provid- reasons. Near Lake Borgne, the east bank of the ing a similar total discharge. The structure- river is fronted by metropolitan New Orleans. related cost differential becomes even greater Only two potential diversion sites remain in this when taking into account operation and mainte- reach: the Inner -Harbor Navigation Canal (IHNR) nance. and the Lake Borgne Canal. The IHNC was elimi- nated from consideration by the USACE because of The second major consideration, existing develop- interference with navigation and problems with ment, involves a number of aspects. One is that water quality. The canal is separated from Lake the rapid expansion of industrial development along Pontchartrain by a navigation lock for which en- the Mississippi River banks has eliminated nearly largement has been proposed. Space at this loca- all vacant river frontage. At the same time urban tion is already at a premium, and it is doubtful that WO t"A development is forced to expand away from the a 33,000 cfs structure could be included in the lock river into adjacent wetlands. The results are design. Industrial contamination of the canal A!4 limited opportunity for gaining access to river waters is considered another major constraint in frontage without expropriation and increased dis- that diversion discharges would carry these con- Ir"n tance over which diverted water must be confined taminants into presently less polluted areas. prior to release into wetlands. Resultant cost in outfall provisions would be multiplied in case of a large number of smaller structures. The Lake Borgne Canal site was recommended for A third aspect concerns the topographic and drain- detailed studies in the USACE evaluation, although Freshwater siphon at Violet, St. Bernard Parish. age characteristics. In Hydrologic Unit I, a major a number of problems are apparent. A freshwater constraint is posed by the presence of U.S 61 which diversion siphon presently operates in the Lake Borgne Canal at Violet. It is part of the marsh Potential sites upstream from New Orleans can be is entirely on grade and by Interstate 10, part of management program in St. Bernard Parish and has divided into two groups, those which would dis- which is on grade. The highways would tend to a maximum capacity'of 500 cfs. The siphon was charge into Lake Pontchartrain and those that impound water in the area confined between these installed at a cost of approximately $2.5 million. would discharge into the swamps drained by Lake highways and the river if water were diverted In order to obtain 33,000 cfs at this site, the Lake Maurepas. A dividing line between the groups is through numerous small structures and introduced Borgne Canal and Bayou Dupre would have to be U.S. 51 at LaPlace. The USACE evaluated six into the nearest wetlands. Any such proposal enlarged greatly. The existing control gate in the possible sites upstream from U.S. 51 in LaPlace. would be expected to generate significant hurricane protection levee would have to be All were eliminated from further consideration due opposition because of anticipated deterioration of enlarged or a new one constructed. Local plans to engineering costs and disruption of community already marginal drainage. call for structural surface water and marsh aesthetic and social concerns. Within Hydrologic Unit 11, analysis of topography management in the wetlands surrounding the siphon revealed that interior drainage is largely controlled outfall. Any further freshwater diversion plans in The drainage patterns around Lake Maurepas are by natural levee ridges that more or less parallel this area should consider the public investment in influenced strongly by backwater effects at the the Mississippi River. Accordingly, a better distri- the siphon and management plans. A small portion only outlet, Pass Manchac. Because of wind set- bution of freshwater and greater benefit to exist- of the needs could be met by enlarging the existing up, mean tide stages at Pass Manchac are approxi- ing wetlands could be achieved by introduction of structure at Violet. mately +1.5 ft MSL in the spring and +2.0 ft MSL in water at the upper end of the unit, rather than the fall (Wicker et al. 1981). Water levels in Lake through multiple structures along its margin. Maurepas are elevated during floods on the Amite, Tickfaw, and Natalbany Rivers. In combination A third consideration is the benefit derived from with existing development these conditions result Site Analysis introduction of a given quantity of freshwater. in chronic backwater flooding problems in at least Diversion into the upper end of the basin would the Amite River basin. Proposed drainage projects result in the fullest use of the freshwater, sedi- in this area, which only consider channel excava- HYDROLOGIC UNIT I ments, nutrients, and dissolved minerals because of tions and enlargements, will not completely solve The maximum freshwater need for Hydrologic Unit longer retention. In the lower basin retention is the present problems of poor drainage. Conse- adversely affected by water exchange through the quently, delivery systems for diverted freshwater 1. was determined to be approximately 33,000 cfs MRGO. Also, the overall pollutant concentrations would experience the same gradient problems and (Chapter IV), that need being most apparent in in the river are less upstream from New Orleans. further contribute to backwater f looding. 24 (Although the Mississippi River stage is progres- proposed Interstate 410 also would require an ad- HYDROLOGIC UNIT 1[ sively higher upstream, stages in the outfall area ditional bridge. Flowage easements would have to also increase.) More importantly, the addition of be purchased from the land owners for overbank 10,000 to 30,000 efs to the system would respec- flows. Local priorities furthermore include a hur- tively double to quadruple the average discharge at ricane protection levee with floodgates to be built Pass Manchac. from Kenner along the lake to the Bonnet Carre Maximum freshwater needs for Hydrologic Unit 11 Floodway to protect new development in1he area. were estimated to be approximately 9000 cfs to Of further concern is projected development. The relatively small a-mount of water treatment maintain the desired positions of the mean fall t5 Acreage of urban and industrial land use is pro- and marsh buildup do not outweigh the cost of the ppt isohaline. The area of greatest need appears to jected to increase 45% in the area drained by Lake railroad and highway relocations and public be in the marshes north of a line from Belair to Maurepas by the year 2020, replacing present agri- opposition. Therefore, the site within the Bonnet Delacroix that includes the last acreage of culture and forest land uses on the natural levee Carre Floodway remains as the least expensive and intermediate marsh in the basin; this marsh is (USACE 1981b). It is likely that industry will most compatible alternative. There are. no slowly becoming saltier. The low-sahnity brackish continue to occupy lands with river frontage, caus- conflicts with development, no cost for flowage marshes bordering Lake Lery are also becoming ing commercial and residential development to easements, and an existing levee and borrow canal more brackish. The encroachment of salinities progress down the toe of the natural levee. Agri- already form two components of a delivery greater than 10 ppt in the fall is the primary cause cultural lands that now experience occasional channel. of the changes. flooding with little consequence will be replaced with residences which cannot tolerate flooding. One large (or several small) diversion structure(s) would not only compete with industry for river frontage but also encumber anticipated subdivision development by requiring additional drainage later- als, back levees, and pumping stations. Potential sites that would discharge directly into Lake Pontchartrain appear to be the most feasible. V_ Two of three sites evaluated by the USACE were AW ve recommended for detailed studies: the canals along the north guide levee of the Bonnet Carre Flood- way and the borrow canal within the floodway Law itself. A site at the Walker and St. Charles Canals was eliminated from further consideration because of the need to relocate a sand mining company, two highways, and two railroads and because of community aesthetic and social concerns. Of the two remaining site the one within the spillway was favored over the north guide levee alignment be- cause the latter required relocation of U.S. 61. 401 From an environmental standpoint, the St. Charles site has some appeal. A lar e delivery channel 9 without spoil banks would allow overflow into the marshes and provide for natural water treatment. Presently deteriorating wetlands would be revital- ized and new wetlands created in the large, open water bodies'near Lake Pontchartrain. However, in view of the required discharge (30,000 cfs), a continuous channel would still be required from the K river to Lake Pontchartrain, and the majority of the diverted water would remain in the channel. Freshwater siphon at Whites Ditch, Plaquemines Parish. View from crest of river levee. Bridges would be required at intersections of the channel with the highways and railroads., The 25 There are four diversion structures already operat- ing in Breton Sound: the Whites Ditch siphon, Bohemia, and the two gated structures at Bayou Lamoque. To protect and expand the remaining '77 0 intermediate marsh, new diversion sites should be located upstream from Whites Ditch. The area in Breton Sound upstream from Whites Ditch is essen- J@t tially a wetland cul-de-sac lying between the natural levees of the Mississippi River and Bayou Terre aux Boeufs. It is therefore protected from tidal and marine forces and exhibits the lowest a mplitude tidal fluctuation and slowest water ex change rates in the Breton Sound Unit. Diversion rn A. into this area would provide maximum use of the freshwater by temporarily retaining it in the wet- lands where chemical and thermal changes could take place prior to mixing with waters in lower areas of the Sound. In this manner, suspended sediments nutrients, and dissolved minerals (along N with possible contaminants) could be taken up and contribute to plant growth, the cooler river water would be warmed, and stored freshwater would be slowly released to moderate salinity during the low 40 river stage fall months when the diversion rates are minimal. The best location in terms of opti- mizing utilization of diverted water while accommodating local plans and priorities is at Caernarvon near the Plaquemines - St. Bernard Parish line. This si te of f ers the best possibility f or conveying water from the river to the wetlands without affecting existing development and forced lot, drainage systems or flood protection works. The river frontage is under single ownership, facilitating simple purchase or acquisition of flowage easements. In addition, a large open water area, known as Big Mar, offers an opportunity for Bayou Lamoque Structure #2, courtesy of Plaquemines Parish. outfall management of the diverted water and sediment. purpose, namely flood control. Operation of the diately upstream or downstream of the Bonnet floodgates, therefore, is regulated and authorized Carre structure with outfall directed into the only for relief of flood conditions. Second, con- floodway. Assuming a structure similar in type and tinued use of the floodway for its intended purpose efficiency to that at Bayou Lamoque, the cross- and at the necessary capacity requires that sedi- sectional area required would be approximately Proposed Diversion Sites mentation in the floodway is kept to a minimum. 15002 to provide the necessary 33,000 cfs during Sedimentation poses a problem even at the infre- average annual flood conditions. quent level of present use. Third, to allow diver- PONTCHARTRAIN AND LAKE BORGNE sion of Mississippi River water through the Without further detailed surveys, recommendations WATERSHEDS structure other than during flood stages would as to whether to place the structure on the up- require major modifications to the structure. stream or downstream side cannot be more than Since the Bonnet Carre Floodway's intended use is preliminary. It is on that basis that location of the for diversion of water from the Mississippi River at Operational and structural constraints posed by the diversion structure on the upstream end of the rates up to 250,000 cfs, selection of this site may Bonnet Carre structure presently require that Bonnet Carre intake structure is proposed as shown in many ways seem a foregone conclusion. This is diversion of Mississippi River water be accom- in Figure 5-1. Considerations reflected in the not the case for several reasons--the main one plished by means of an ancillary structure. In proposed location include river processes, land use, being that its present use is defined as single principle such a structure could be placed imme- and sedimentation associated with the diversion. 26 DOMINANT DRIFT a IN SPRING DOMINANT DRIFT IN FALL 4 jb I'b INITIATION OF 4@. DISTRIBUTARY CHANNELS FAMW lot '"SEDIMENTATION GUIDE LEVEE & SUBAQUEOUS SPOIL DISPOSAL BORROW CANALS t OVERFLOW FOR ABOVE AVERAGE DISCHARGE ? A` =00 V ---- -------- ? A 'A Delivery hannel V Containment i es -j %V 00 ER LEVEE V @'RELOCATIOH OF RIV D MONTZ PARK 14 AN IS DIVERSION STRUCTURE 01, n1ki .... . rv -ok Figure 5-1. Proposed diversion plan for Hydmlogic Unit I at Bonnet Carre. river processes may raise the question of whether that of Plaquemine ent with Location of the diversion structure as related to of floodway capacity. Assuming average dis- corridor. This recommendation is coincid charges as presented in Tables 4-4 and 4-6 an Parish (Varnell and Lozes the upstream location lies within the accretion average annual sediment load of 5.7 million tons is 1981). Furthermore, this would allow separation of zone of the Thirty-five Mile Point's bar. If so, this expected to be introduced with the diverted Missis- diversion flows from the Caernarvon canal to may result in siltation of the intake channel and a sippi River water. prevent siltation and resultant hindrance to requirement for annual maintenance. Such main- navigation. tenance must, however, be weighed against main- Consideration should be given to minimizing height tenance dredging to be expected in Lake Pontchar- of the levees. First of all, this would. allow As proposed, to satisfy the freshwater require- train if diversion outfall were to be located along ments of Hydrologic Unit 11, a structure with a the south side of the floodway. At the Lake, inclusion of the channel system as part of the cross-sectional area of approximately 550 ft2 floodway at the earliest possible time during oper- introduced sediments would be subject to a drift ation for flood control. Secondly, this would would be placed within the levee corridor at that is predominantly westward at the time of provide for some overbank flow during above aver- Caernarvon; the size of the structure would be highest diversion discharge (Gael 1980), thus caus- age diversion discharge. based on assumed similarity to Bayou Lamoque ing sediment transport across the floodway outlet. No. 2. To minimize structure size requirements a Assuming a stable channel design and limited over- channel would be excavated from the structure As shown in Figure 5-1, it is proposed that flows bank flow, the sediment load associated with the into Big Mar. The channel would be contained diverted through the ancillary structure remain between the existing west back protection levee contained within a leveed channel until reaching diverted Mississippi River water would be and a newly built dike on the east side (Figure 5-2). Lake Pontchartrain. Below U.S. 61, the alignment deposited at the mouth of the outfall channel in The latter levee would extend to the Delacroix utilizes the existing borrow pit, berm, and Lake Pontchartrain and result in development of a Canal in order to prevent shunting flows through guidelevee as project elements. New construction small lacustrine delta. As shown in Figure 5-1, an Bayou Mandeville into Lake Lery and to prevent of channel and levees would be required between embankment about 1.5 mi long and extending bare- siltation of the Caernarvon Canal. the diversion structure and highway. ly above the water surface is proposed to direct sedimentation away from the floodway outlet. The levee also would promote initial marsh establish- ment by providing protection from wave erosion. At this point, a major aspect of the diversion To promote westward deltaic development artifi- remains--that is the management of the outfall in cial initiation of distributaries is proposed through and beyond Big Mar. The management objective functional dredge-and-fill design. On the basis of must be to distribute the water into the wetlands the 5.7 million tons of sediment estimated to be adjacent to Big Mar in order to provide maximum introduced into the Lake, present bathymetry, and natural water treatment and to derive maximum ssumed 40% sediment retention (mainly silt benefits from the associated suspended sediment an a and sand), delta building would amount to 2 mi2 in loads. It does not appear desirable to utilize Big 15 years. Mar as a plenum. This would require construction of a weir in excess of 1 mi long which would BRETON SOUND WATERSHED elevate water levels, thus requiring a larger diversion structure to meet the diversion require- derived and sedimentation within Big Mar could The proposed diversion structure at Caernarvon, as ment. Furthermore, no sediment benefits would be shown in detail in Figure 5-2, utilizes a largely have an adverse effect on diversion efficiency. undeveloped, 0.25 mi wide corridor across the natural levee of the Mississippi River. Constraints on use for diversion are primarily a highway and To achieve the desired distribution of freshwater railroad crossing and the navigational use of the and sediment, use must be made of existing canals 1:71111, Caernarvon Canal connecting a small boatyard in the area adjacent to Big Mar as a distribution with Bayou Mandeville. Backwater flood- network. This network could be linked to the Caernarvon Canal (foreground), Big Mar (upper left), protection levees confine the corridor until it primary delivery channel (Figure 5-2) by means of and Braithewaite Park and Golf Course (upper reaches Big Mar, an abandoned agricultural recla- a number of branch channels. Weirs could be right). Courtesy of Plaquemines Parish. mation project that is permanently flooded. The incorporated within these channels for the purpose entire corridor is located within Plaquemines of water allocation. This type of outfall plan Parish. cannot be further defined at this point because of From the water quality point of view it would be dependence on final design of the diversion most desirable to allow dispersion of the diversion To minimize acquisition or ease m ent-related structure, tidal circulation within the area, and discharge throughout the floodway wetlands. How- problems, the required area can be limited to a hydraulics of the canal network. All of these are ever, associated decreases in flow velocities would single landowner by locating the structure and presently unknown and require site-specific data result in deposition of sediment load and decrease outfall channel within the western half of the collection and analysis. 28 5 3 2 15 J 18 j 19 16 P@t S, cw, IM21 I- 6 ----------------I-- - - - - - - - - - - 2 PROPOSED DIVERSION STRUCTURE 1. I P- Q: ---------------- FLOOD PROTECTI ON 0 '14- 11 Chapse 3 .... -- ---- - --- --- ----------- 7 Primary Delivery Cha nne 26 28 27 NAVIGATION ROUT E 25 29 6 ------------ ---------------------- ------ Containment Dike--- + BIG MAR 30 31 10 D, -------- - 12 '13 SUSPECTED PRIMARY DRAINAGE CHANNEL -14 - -- ----------------- 26 46 19 ---------- - ---------------- \. + 58 35 36 20 40 60 37 21 38 61 -T5F ------- ------------ ------------ ---------------------- 21 2 22 .... ------------------------ "kk N 23 3 20 @q- 24 4 40 25 5 41 27\ 4 6 Figure 5-2. Proposed diversion plan for Hydrologic Unit H at Caernarvon. ;Ito "A 4 J Al "@h CHAPTER VI I i PREDICTED RESULTS AND POSSIBLE IMPACTS q Olt- Iff Pontchartrain Watershed Diversion of freshwater into Lake Pontchartrain at the Bonnet Carre site will produce a lowered 'V, salinity regime throughout the Maurepas- Pontchartrain Basin. Under average conditions, or more accurately, 50% exceedance river flows, sa- linities at Pass Manchac will be continually less than 2 ppt. Even with drought conditions or 80% exceedance river flows, salinities at Pass Manchac are projected to rise to only about a 2 ppt average Louisiana!s renewable wetland resources, during the fall months of September, October, and November (Plate 4). By eliminating salinities above 2 ppt at Pass Manchac during most years, Generally, the lowered salinity regime and conver- marily determined by late winter and spring water baldcypress swamps will be protected from further sion of some areas to fresher vegetative types are levels, should expand into the North Pass-Middle salinity stress. Areas that have been in transition expected to enhance the wetlands of this water- Bayou shrub swamp (Wicker et al. 1981) and from swamp to marsh in the vicinity of Pass shed for most wildlife forms. Fresh and Manchac Wildlife Management Area. Commercial Manchac may possibly, in time, be able to reveg'e- intermediate marsh types have been shown to be catfishing will be greatly improved in Lake tate in baldcypress with this regime. The St. among the most productive habitats for nutria, Maurepas and will become more seasonally Charles marshes should convert to fresh- raccoon, and alligator (Palmisano 1973, McNease consistent in the portion of Lake Pontchartrain intermediate types with the potential for increased and Joanen 1978) and are the most heavily utilized between the diversion outfall and the Tchefuncte diversity of vegetative species and enhancement of by the various species of waterfowl (Palmisano River (Plate 4). Benthic populations within 1.5 to 2 wildlife habitat. An increase in extent of fresh and 1973). mi of the diversion outfall will be adversely intermediate marshes at the expense of some affected by sediment deposition. However, brackish marshes also is expected along the north sediment input from the diversion structures should shore of Lake Pontchartrain., particularly in the Freshwater fish habitat in Lake Maurepas and the result in the creation of significant acreages of Goose Point marshes. The majority of marsh east surrounding swamps will be improved by elimina- marsh within the first 15 years of the project of Goose Point along the north shore will remain tion of short-duration salinities greater than 3 ppt (Chapter V). The infrequent operation of the low-salinity brackish marsh. in the fall. Crawfish populations, although pri- Bonnet Carre Floodway has not created marsh 31 because much of the coarse sediment is deposited exceed EPA criteria in Lake Pontchartrain, and no be as directly affected as wetlands around Lake in the floodway and because the input is not change in concentration is anticipated. Coliforms Pontchartrain. As a result, conversion of marsh continuous. The diversion outfall area will receive should cause no impacts to Lake Pontchartrain vegetative types to less saline associations will be almost continuous sediment input into shallow shellfish because the only oyster grounds are al- less likely. There may be some expansion of the waters (2-6 ft). Distributary mouth bars and ready permanently closed to harvest. After estab- intermediate marsh type in the lower Pearl River natural levees are expected to form and become lishment of marsh vegetation, increased retention area, and a possibility of a slight seaward advance anchors for overbank deposition of finer sediments. of suspended sediments and associated contam- of high-salinity brackish marsh at the expense of During times of maximum diversion discharge in inants should improve the quality of the diverted saline marsh in the Biloxi marsh area of St. the spring, predominant southeasterly winds will water by incorporating these sediments into the Bernard Parish (Plate 5). The extent of low- tend to cause westerly longshore currents at the marsh substrate. salinity brackish marsh in the Biloxi Wildlife outfall (Figure 5-1) (Gael 1980), resulting in deflec- Management area should also increase somewhat. tion of the freshwater plume to the west and north No adverse impacts will occur from the limited towards Pass Manchae. This tends to favor distri- freshening of Lake Pontchartrain. The 2-5 ppt butary formation in that direction as planned. aquatic habitat will be displaced slightly to the During the low discharge fall months, however, east. Salinities at the Rigolets and Chef Menteur The more important effect of freshwater diversion strong, predominantly northeast winds will induce will not exceed 10 ppt, leaving the majority of the for this watershed will be a more consistent strong, southeastward longshore currents near Rud- lake to remain intermediate- to low-salinity salinity regime from year to year without the dock that decrease in strength toward Frenier brackish aquatic habitat as it is at present. extreme high salinities that occur periodically. (Gael 1980). These currents may tend to oppose The major vegetative types in this watershed are the low diversion discharge, deflecting it to the brackish marshes of both low- and high-sal 'inity east (Figure 5-1). Incoming waves from the north- regimes, with wiregrass occurring as the usual east will cause erosion of the accreted marsh at dominant plant species. Wiregrass has a wide the outer fringe. Lake Borgne Watershed range of salinities and is in fact found in every marsh type along coastal Louisiana (Chabreck The outfall area will experience increased concen- 1972). A widely fluctuating salinity range tends to trations of coliforms, phosphate, lead, arsenic, and The wetlands of the Lake Borgne watershed are favor the continued dominance of this species at cadmium (Table 6-1). Mercury and coliforms located farther from the diversion site and will not the expense of other vegetative species more Table 6-1. Existing Water Quality Near Proposed Diversion Sites in the Mississippi River and Stations in Lake Pontchartrain and Breton Sound. Coliform, fecal, Nitrogen, ammonia Phosphorus, Lead, total Mercury, total Oxygen demand Solids, residue Arsenic Cadmium, Carbon 0.7 UM-MF +organic dis. total recoverable recoverable Phenois Biochem uninhib at 105*c, sus-- total total recoverable organic total Station Name* (cols.100/ml) (mg/l as N) (mg1l as P) (ug/1 as ft) NO as Hg) NO) 5-day (mgu) pended (mgll) (ugll as As) (Ugli as cd) (mgll as C) Mississippi River at Luling Ferry 722 388 0.75 :L0.14 0.28 � 0.02 15 4 0. 04 � 0.03 2 � 0.2 2.1 t 0.7 171 :L 21 2.7 :L 1.6 2.411.0 6.6 11.2 Mississippi River at Belle Chasse 2979 970 0.75 10.09 0.24 � 0.01 41 25 0.05 ;LO.02 2.1 :L 0.2 228 k 9 3.3 �.0.4 4.1 :L 4.5 6.4 t 1.4 Lake Pontchartrain at GNO Expressway Bridge 48 146 0. 68 :L 0. 08 0.11 :tO.03 8 :L 3 0.04 � 0.01 2 10.2 1.4 :L 0.4 2117 1.2 :t 0.2 0.8 10.6 7.0 � 0.6 Black Bay near Mouth of River aux Chenes 6 11 0.84 tO.12 0.11 10.02 8 14 0.04 10.01 2.4 11.1 23 14 1.0 :L 0.2 0.3 � 0.1 11.2 0.8 EPA (1976) Quality Criteria for Water and 1980 revised criteria 142 0.81 � 7.34 0.1 0.34 251 0.0251 303 2503 5081 4.51 *all values expressed are means based on data from USGS, 1977-1980. 1 Criteria for marine organisms. 2 Criteria for harvesting of shellfish. 3 Criteria for domestic water supply. 4 No criteria, but natural range given. 32 20 1. MOUTH OF AMITE RIVER 2. PASS MANCHAC 3. MIDDLE CAUSEWAY 4. CHEF MENTEUR 5. BAYOUR ST MALO 6. PALMBANO LINE 7. FORD LINE 15 10 5 0 2000FT 1500FT 1000FT 500FT NO STRUCTURE 1 2 3 4 5 6 7 Three-eornered grass marsh near Lake Lery, St. Bernard Parish. EXISTING HABITATS PREDICTED HAVITATS EXISTING OYSTER RESOURCES PREDICTED OYSTER RESOURCS RED LINE HABITATS SWAMP FRESH MARSH MO PRODUCTION MSROHNAL PRODUCTION OYSTER RESOURCES FRESH MARSH INTERMEDIATE MARSH LOW SALNITY BRACKFISH MARSH HIGH SALINITY BRACKFISH MARSH MARGINAL PRODUCTION HIGH PRODUCTION NO PREDATION HIGH PRODUCTION HIGH PREDATION MAJOR PUBLIC AND SEED OYSTER GROUNDS SALINBE MARSH EXPANSION AND INCREASED PRODUCTION OF PUBLIC AND SEED OYSTER Public seed oyster grounds in this area have become virtualluy extinct and are shown as seaward limits of private leases. Predicted results indicate that, using management development of a new, viable seed ground is possible. valuable to wildlife. Although a variety of factors through the passes at Martello Castle and Bayou govern marsh species composition, a more consis- Bienvenue is responsible for the successful estab- tent salinity regime would tend to increase the lishment of the existing oyster leases. management potential for the more valuable species such as coco (Scirpus robustus) and three- cornered grass. Conditions for submerged aquatic The areas of high oyster production will expand in plants important as waterfowl food, such as south- the "Louisiana marsh" between Lake Borgne and ern naiad (Najas quadalupensis) and Eurasian Chandeleur Sound (Plate 6). Figure 6-1 shows the watermilfoil Myriophyllum spicaturn), which can predicted salinity gradient in Hydrologic Unit I and Optimum thrive in slightly brackish conditions (Chabreck and the corresponding shift in habitats. Condrey 1976), will also be enhanced under the oyster habitat will be expanded into the shallow slightly reduced salinity regime. bays, farther from urban influences and pollutants. This will also expand the acreage suitable for leasing. More importantly, the predicted salinity regime indicates that a new public seed oyster It is possible that some private oyster leases in the ground could be established to provide for the northwestern corner of Lake Borgne will be im- expanded production potential. At present, seed pacted by salinities below 5 ppt in the spring (Plate oysters are harvested in Breton Sound and trans- 6). As mentioned in Chapter IV, however, the ported to leases in the Lake Borgne area. Creation salinity dis charge models do not adequately and maintenance of these new seed grounds is also describe conditions in the MRGO. Salinities imme- dependent on expansion of the successful Louisiana diately adjacent to the MRGO will probably be Department of Wildlife and Fisheries program of higher than the predicted salinities shown and the cultch plantings and regulated harvest presently . Predicted meanfall salinity gradient for 50% exceedance criteria for various Bonnet Carre structure sizes (cross section of gates). Predicted results are based on 1500 ft2 cross section. Breton Sound Watershed Diversion of freshwater at the Caernarvon site will produce an area of fresh marsh in the vicinity of Big Mar that is presently of intrmediate salinities (Plate 7). The area of intermediate marsh also will be expanded below Big Mar and will extend throughout most of the marshes north of Lake Lery. Habitat for waterfowl, funbearers and the alligator should be enhanced substantially in the upper reaches of the Brenton Sound marshes. There 33 re less expensive to should be an increase in the extent of low-salinity oyster production at present under normal condi- adjacent seed grounds will make seed oysters more brackish marsh that favors growth of tions and active seeding is probably restricted to readily available and therefo' three-cornered grass, considered the most high-salinity drought years (Dugas 1981, personal obtain. Another possible benefit would be the important food plant for muskrats in coastal communication). On the other hand, optimum expansion of the public oyster reefs, if the Louisiana (O'Neil 1949, Chabreck and Condrey salinity conditions will be established in the area of Louisiana Department of Wildlife and Fisheries 1976). Although water level regime is of primary greatest lease density (Figure 6-2). Decreased cultch planting program were enlarged in scope. importance in management for three-cornered predation losses to the oyster drill on the produc- The oyster management program of the Louisiana grass (Ross 1972), areas of low tidal energy and tive leases will give oystermen a better return per Department of Wildlife and Fisheries is outlined in low-salinity brackish (5-10 ppt) conditions favor its oyster seeded. Also, decreased predation on the Table 6-2. Investments by the state to expand the establishm ent. Thus, management potential for public oyster reefs with the predicted salinity 20- regime would not only produce dividends in oyster muskrats should be increased in much of the Breton - Sound watershed. With the extension of low- No Structure, production but also might result in moderation of ft2 400 salinity brackish marsh, the range of harvestable ft2 tide and wave energy. Natural oyster reefs are Soo alligator populations should also increase since =CL 800 ft2 generally oriented perpendicular to prevailing cur- young alligators cannot tolerate salinities greater a 1000 ft2 rents allowing for passage of more water and than 10 ppt for extended periods (Joanen and suspended food over the reef. This not only McNease 1972). The expansion in extent of fresh benefits the oysters but also reduces the energy of Ic 10 CAERNARYON (A and intermediate marsh in the upper Breton Sound -1 INTERPRETED 2 EXISTING LIMITS OF the moving water. By providing new substrate INTERMEDIATE MARSH watershed should favor increases in alligator (cultch) in the form of shells, rock, or other hard Z 3STATION A numbers since these vegetative types have been C material, new natural reefs could be initiated in 4LAKE PETIT shown to support the highest nesting densities on a a a - 5 STATION F suitable areas to moderate tidal exchange and statewide basis (MeNease and Joanen 1978). 6 BAY GARDENS associated removal of freshwater and materials. In the Mississippi River near Caernarvon, coli- 0 Table 6-2. Annual Operating Schedule of the Louisiana Oyster Fishery. forms, lead, and mercury exceed EPA criteria 1 2 FAIJ SEASON (Table 6-1). Outfall management must include EXISTING HABITATS plans to remove these and other contaminants from DatsFirst Wednesday after Labor Day to December 31 (inclusive) the water. Since most pollutants are associated PREDICTED HABITATS Aetivities :: ` -, -, 1) 7ransplanting of seed oysters (1-3 inches) from public grounds to private with suspended sediments, the diversion discharge leases. should be exposed to a large surface area of marsh EXISTING OYSTER RESOURCES 2) Harvesting commercial seek oysters (greater than 3 inches) from public and .X. MEN where sediments could be incorporated in the sub- private grounds and canning oysters from private laws& strate. Assuming a successful outfall management PREDICTED OYSTER RESOUR4ES F" ----------- ........... ... . ....... plan is implemented, there should be negligible .................... ................ adverse impacts on water quality in the basin and 1) Oysters law than 3 inches emmot be marketed from public grmndL RED LINE-'J 2) Periodic closure of effWn parts of public grounds for cuitch (shell) planting substantial increases in productivity from the nu- HABiTArs OYSrER RESOURCES to improve spatfall and seed oyster production. trients and dissolved minerals in the freshwater FRESH MARSH NO PRODUCTION SPRWG BRAWN (Table 6-1). INTERMEDIATE MARSH MARGINAL PRODUCTION Dates January I to May 20 (inclusive) Acreages of intermediate- and low-salinity LOW SALINITY BRACKISH MARSH HIGH PRODUCTION NO PREDATION Activities brackish nursery will be dramatically increased as GH SALINITY BRACKISH MARSH HIGH PRODUCTION HIGH PREDATION 1) Harvesting of transplanted seed oysters from private leases for canning and a result of the Carenarvon diversion (Plate 8). This SALINE MARSH MAJOR PUBLIC AND SEED OYSTER GROUNDS Back oyster markets. should foster an increase in populations of white 2) Harvesting of canning and sack oysters from public groundL OPEN WATER EXPANSION AND INCREASED PRODUCTION Reabletions shrimp, blue crab, and menhaden, as well as other OF PUBLIC AND SEED OYSTERS 1) Certain seed ground reservations and depleted regular public grounds may be members of this low-salinity assemblage. Brown closed to harvesting. shrimp populations will not benefit as much as 2) Size limits on oysters harvested from public grounds may be Impose& white shrimp, but will have access to an expanded Figure 6-2. Predicted mean fall salinity gradient 3) Periodic closure of certain parts of public grounds for cultch planting. area of low-salinity brackish nursery. Commercial CLOSED SEAWN crabbing in Lake Lery should expand and become for 50% exceedance criteria for Date@ more consistent from year to year, giving local various Caernarvon structure sizes May 21 to the first Tuesday after Labor Day (inclusive). fishermen another reliable source of income. (cross section of gates). Predicted Activities results are based on 576 ft2 cross 1) Some harvesting of larger oysters from private leases oat were rot section. (Note: the assumption is harvested In the Spring. 2) Cultch plantings on some parts of public grounds. Some private oyster leases in the upper portion of made that the Bayou LamoWe Restrictions the watershed will be impacted by low salinities structures are kept fully opened.) No harvesting or transplanting of oysters from public gromd& (Plate 8). However, these leases exhibit marginal 34 Effect on Salinity Regimes To develop a reasonable rate and manner of flow redistribution, a graph of percent flow down the of the Capture of Mississippi Atchafal aya from 1910 to 1950 (Latimer and Schweizer 1951) was updated by plotting percent Mn River Flow by the mean annual flow from 1941 to 1963 on the same graph. The distribution of the data points between Atchafalaya River 1950 and 1963 (when the ORCS began operating) do not fit the extrapolated curve of Latimer and Schweizer (1951). Instead, the annual rate of flow Until completion of the Old River Control Structure (ORCS) in 1963, steadily increasing capture appears to be linear. The slope of the line % volumes of Mississippi River discharge were cap- of best fit through these points is 0.44% capture ima tured by the Atchafalaya River which provides a per year. By extending this line to 1982, it appears shorter route to the Gulf of Mexico. The structure that the Atchafalaya would be receiving 44% of limited discussion to approximately 30% of the the mean annual flows of the Mississippi River had Mississippi River dishcarge and interrupted a pro-- the Old River control structure not been built, or cess that was estimated to have lead to a change in approximately 14% more of the total than at the Mississippi River's course by 1975 (Latimer and present. During the 19-year life of the ORCS, the Schweizer 1951). While the ORCS effectively Atchafalaya River channel has been maturing controls the discharge distribution, channel primarily through scouring in the upper portion and development of the Atchafalaya River has con- natural levee formation in the lower portion tinued under the influence of an average annual (infilling of Grand and Six-mile Lakes, etc.). This al peak flow of 425,000 cfs and flood control has resulted in a decrease of the water slope by measures related to use of the Atchafalaya Basin decreasing stage for a given discharge in the upper as a floodway. Adjustments of the hydraulic portion and increasing stage in the lower portion. gradient have occurred that further favor the During the same time period, the Mississippi River Old River Control Structure capture of Mississippi River by the Atcbaf alaya channel below the ORCS has been deteriorating River were it not for the ORCS. Accordingly, with a resultant increase in stage per discharge at concern has been expressed as to the ability of the the ORCS. The final result has been an increase in 8260 cfs. A maximum discharge of 18,930 cfs ORCS to prevent such capture in the event of a head across the structure which is the apparent would occur in April, but no diversion will be large flood. cause of excessive scouring and possible under- possible from August - November. There will be no mining of the ORCS responsible for the recent drastic changes in the salinity regime of Hydro- Af ter the 1973 flood, during which the low sill concern and apocalyptic predictions. logic Unit I, however, due to the continued fresh- structure was damaged, many expressed fears that water input from the Pontchartrain and Pearl the Atchafalaya would become the Mississippi However, it is important to remember that the River Watersheds. Salinities at Bayou St. Malo will River in one catastrophic event. Kazmann, present problem of increased head is related to a range from 10 ppt in April to 14 ppt in October. Johnson, and Harris (1980) describe the physical natural process of maturation of the Atchafalaya The effects on Hydrologic Unit II (Breton Sound) and economic consequences of such a scenario River channel, a process that proceeded at an Will be more severe. The mean annual discharge of where 70% or so of Mississippi River flow is apparently linear rate from 1910 to 1963, and the the proposed Caernarvon structure will decrease captured in a single season. Kolb (1980) notes that same process that would have resulted in a present from 5920 cfs to 2200 efs. The maximum April although such a massive rapid diversion is unlikely, 44% diversion if no action had been taken. The the engineering constraints and economics of main- case that will be evaluated here will assume that diversion will be only 5700 cfs and no freshwater taining a 30% flow diversion over the long term the ORCS fails during a major flood and results in will be available during a 5-month period from makes his suggestions for a planned, gradual the capture of 44% of the Mississippi River flow by August - December. Discharges -from Bayou increase in Atchafalaya discharge a viable alterna- the Atchafalaya after passage of the flood condi- Lamoque will decrease even more substantially. tive to be considered. tions. It is assumed that the rate of capture will Most importantly, the decreased indirect effect of proceed at 0.44% per year from 1982 to 2030. Mississippi River discharge itself on salinity of In the context of the present study, these scenarios nearshore Gulf waters will cause detrimental raise the question of what effects a Mississippi Under these assumptions, by the year 2030 about increases in salinity in the estuary. Even assuming River course change would have on the 65% of the Mississippi River will be flowing down consistent average rainfall, salinity at Bay Gardene recommended freshwater diversion plan. Available the Atchafalaya. Discharges at Bonnet Carre will will range from a low of 14 ppt in April to 28 ppt data are used here to predict the consequences of be about half of those at present, ranging from or more in October. These salinities will result in redistribution of flow between the Atchafalaya and 367,000 cfs in April to 94,600 in September (50% total elimination of the fresh and intermediate Mississippi Rivers as this relates to salinity exceedence, average flows). Diversion rates at the marsh created by the Caernarvon project and a regimen and proposed diversion plans in the study proposed Bonnet Carre diversion structure will significant landward shift of the line between area over the standard 50-year project life. decrease from an annual mean of 19,930 cfs to saline and brackish marsh. 35 the sediment and water. A major additional con- Statistical relationships between salinity regimen tribution inherent in each is the flow of water in each of the hydrologic units and monthly fresh- through the wetland system as a basis for many water introduction from direct rainfall, runoff, and physical, chemical, and biological processes. presently operational diversion structures formed the basis for determination of freshwater volumes required to most nearly attain the desired goals. Diversion of Mississippi River water for the pur- The major constraint in attaining goals was the pose of maintaining and improving estuarine diversion feasibility during the fall as controlled by resources related to salinity is the focal point of Mississippi River discharge and stage. This this report. The area of concern includes the requires that diversions in the spring and early estuarine system associated with Lakes Maurepas, summer be sufficiently large so that their effect Pontchartrain, Borgne, and Chandeleur Sound as lasts until the fall. To achieve desired conditions Hydrologic Unit I and the wetland systems linked 80 percent of the time, a required diversion to Breton Sound as Hydrologic Unit II. capacity of approximately 32,000 cfs was Recommendations for freshwater diversion into determined for Hydrologic Unit I and a required each of the units are developed in terms of type, capacity of 9000 cfs for Hydrologic Unit II. location, volume, and seasonal need on the basis of salinity induced habitat changes, present estuarine environments and resource uses, opportunities and Associated with the identified diversion needs are goals for future use, and the salinity regimens that major structural requirements for that purpose. can be achieved by introducing given quantities of Based on detailed analysis of topography, drainage, freshwater. present and future development, and desires expressed by local government, a limited number of large structures was found most feasible and Salinity encroachment in each of the estuarine cost-effective. Further consideration of the above units has caused two types of changes. Most factors and of state and Federal interests resulted CHAPTER VII obvious has been the landward shift of the saline, in recommendation of diversion into Hydrologic brackish, and intermediate salinity wetland zones Unit I through the Bonnet Carre floodway utilizing resulting in the loss of freshwater wetlands in the an ancillary structure and through a smaller SUMMARY AND upper estuaries. Equally important are the salt- structure at Caernarvon into Hydrologic Unit II. Anticipated cross-sectional areas of the structures induced changes within a given environment that are respectively in the order of 1500 ft2 and 550 CONCLUSIONS cause a loss of desirable species of plants and ft , the latter being similar to the operating animals such as those utilized in trapping and structure of Bayou Lamoque in Plaquemines Parish. oyster production. Together these changes have The basic premise for diversion of water from the resulted in either or both the loss of resources or Mississippi River into adjacent estuaries is that the relocation of uses such as oyster production. Predicted results and adverse impacts of the Because of past adjustments in location of resource recommended diverisons are expressed in terms of continued existence of Louisiana's coastal wetland- uses the goal for freshwater diversion cannot be based resources requires the subsidy of freshwater merely the seaward displacement of all salinity salinity and related resource changes within each and associated materials that prevailed under zones. of the environm ental units. Within the natural conditions. The evidence for that argu- Pontchartrain Basin the benefits derive primarily ment is derived from the documentation of from the stabilization of the freshwater wetlands environmental change and the understanding of For the above reasons goal development for fresh- in the upper estuary, the improved quality of cause-effect relationships. The subsidy provided water diversion was guided in the first place by brackish marshes, and the reduced occurrence of by Mississippi River waters involves three major retention and improvement of present resources. salinity peaks and wide salinity fluctuations elements. These are the seasonal distribution of Primary goals therefore included ameliorating salt- experienced by the Lake Borgne environments. freshwater inflows that help regulate the distri- induced stress in the freshwater swamps and The latter will allow seaward expansion of existing bution and extent of salinity-controlled habitats marshes, improving the quality of the brackish oyster production. Primary benefits associated and biological processes, the contribution of sedi- marshes in terms of species composition, and main- with the diversion of Caernarvon will be the ments as materials that aid in maintaining required taining a salinity regime favorable for oysters in reestablishment of freshwater wetlands and wetland substrate elevation against subsidence, and the lower estuary. Major criteria in this regard optimum salinity conditions in the area of greatest the organic and inorganic materials including nutri- became the position of the 2 ppt and 15 ppt oyster lease density, and the opportunity for ents, salts, and toxicants that are introduced with isohalines, respectively, during the fall months. expanded production of public and seed oysters. 37 Conner, W. H. and J. W. Day 1976 Productivity and composition of a baldcypress-water tupelo site and a bottomland hardwood site in a Louisiana swamp. American Journal of Botany 63(l)-.1354-1364. REFERENCES Conner, W. H., J. G. Gosselink, and R. T. Parrondo 1981 Comparison of the vegetation of three Louisiana swamp sites with different flooding regimes. American Journal of Botan 68(3):320-321. Bellrose, F. C. Craig, N. J. and J. W. Day, Jr. 1976 Ducks, geese, and swans of North America. 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Louisiana State University, Baton Rouge, Coastal Studies 1973 Habitat preference of waterfowl and fur animals in the northern Gulf coast Institute. Vol. III, part I, pp. 68-95. marshes. Pages 163-190 in R. H. Chabreck (editor), Proceedings of the coastal marsh and estuir-Y management symposium. Louisiana State Lindall, W. Jr., J. Hall, J. Sykes, and E. Arnold, Jr. University, Division of Continuing Education, Baton Rouge. 1972 Louisiana Coastal Zone: Analyses of resources and resource development needs in connection with estuarine ecology. Sections 10 and 13 - fishery and R. H. Chabreck resources and their needs. Prepared for U.S. Army Corps of Engineers, New 1972 The relationship of plant communities and soils of the Louisiana coastal '5rleans District. Contract No. 14-17-003-430. National Marine Fisheries marshes. Proceedings of the Louisiana Association of Agronomists 13:72-101. Service, Biological Laboratoryq St. Petersburg Beach, Florida. 323 pp. Penfound, W. T. Louisiana Department of Natural Resources (LDNR) 1952 Southern swamps and marshes. Botanical Review 18:413-446.. 1980 Excerpts from Louisiana coastal resources program final environmental impact statement. Louisiana Department of Natural Resources, Coastal Pollard, J. F. Management Sectiong Baton Rouge. 1973 Experiments to re-establish historical oyster seed grounds and to control the southern oyster drill. Louisiana Wildlife and Fisheries Commission, Technical Lowery, G. H. Bulletin 6. 1974a Louisiana birds. Louisiana State University Press, Baton Rouge. 556 pp. Portnoy, J. W. 1977 Nesting colonies of seabirds and wading birds - coastal Louisiana, Mississippi, 1974b The mammals of Louisiana and its adjacent waters. Louisiana State and Alabama. Louisiana Cooperative Wildlife Research Unit, Louisiana State University Press, Baton Rouge. University, Baton Rouge. FWS/OBS-77/07. 40 Thornthwaite, C. W. and J. R. Mather Ross, W. M. 1955 The water balance. Publications in Climatolog 7(l):1-86. 1972 Methods of establishing natural and artificial stands of scirpus olneyi. M.S. thesis, Louisiana State University, Baton Rouge. 100 pp. U.S. Army Corps of Engineers (USACE) 1970 Fish and wildlife study of the Louisiana coast and the Atchafalaya Basin: Sabins, D. S. Report on Mississippi River flow requirements for estuarine use in coastal 1977 Fish standing crop estimates in the Atchafalaya Basin, Louisiana. School of Louisiana. U.S. Army Engineer District, New Orleans. 28 pp. Forestry and Wildlife Management, Louisiana State University, Baton Rouge. 17 pp. 1981a Mississippi and Louisiana estuarine areas study - draft reconnaissance report. Sanderson, G. C. U.S. Army Engineer District, New Orleans. 59 pp. 1976 Conservation of waterfowl. Pages 43-58 in F. C. Bellrose (editor), Ducks, geese, and swans of North America. Stackpole Books, Harrisburg, U.S. Army Corps of Engineers (USACE) Pennsylvania. 540 pp. 1981b New Orleans - Baton Rouge metropolitan area water resources study. U.S. Seaton, A. Army Engineer District, New Orleans. 271 pp. 1979 Nutrient chemistry in the Barataria Basin: a multivariate approach. M.S. U.S. Fish and Wildlife Service (FWS) Thesis. Louisiana State University, Baton Rouge. 124 p. 1964 A plan for freshwater introduction from the Mississippi River into sub-delta Sincock, J. L., M. M. Smith, and J. J. Lynch marshes below New Orleans. In USACE Mississippi River and tributaries 1964 Ducks in Dixie. Pages 99-106 in J. P. Linduska (editor), Waterfowl tomorrow. project, vol. V. U.S. Army Engineer District, New Orleans. U.S. Government Printing Office, Washington, D.C. Sorenson, M. F., S. M. Carney, and E. M. Martin 1979 Documentation, chronology, and future projections of bottomland hardwood 1977 Waterfowl harvest and hunter activity in the United States during the 1976 habitat loss in the lower Mississippi alluvial plain. Division of Ecological hunting season. Office of Migratory Bird Management, U.S. Fish and Wildlife Services, Vicksburg. 133 pp. Service. Administrative Report. 26 pp. U.S. Geological Survey (USGS) Stone, L. A., Jr., J. C. Albrecht, and G. A. Yoshioka 1978 Unpublished rating tables for determining discharge through the Bayou 1971 Computer programs for the climatic water balance. C. W. Thornthwaite Lamoque diversion structures No. 1 and No. 2. U.S. Geological Survey Water Associates Laboratory of Climatology, Publications in Climatology 24(3). Resources Division, Baton Rouge. Swenson, E. M. Varnell, R. J. and C. L. Lozes 1980 General hydrography tidal passes of Lake Pontchartrain, Louisiana. Pages 1981 Management plan for the Breton Sound Estuar Plaquemines Parish 157-215 in J. H. Stone (editor), Environmental analysis of Lake Pontchartrain, Mosquito Control District, Braithwaite, Louisiana. 17 pp. Louisiana-, its surrounding wetlands, and selected land uses. Coastal Ecology Viosca, Percy, Jr. Laboratory, Louisiana State University. Prepared for U.S. Army Engineer 1927 Flood control in the Mississippi Valley in its relation to Louisiana fisheries. District, New Orleans. Transactions, American Fisheries Society 57:49-64. Tabony, M. L. 1972 A study of the distribution of oyster larvae and spot in southeastern 1928 Louisiana wetlands and the value of their wildlife and fishery resources. Louisiana. M.S. Thesis, Louisiana State University, School of Forestry and Ecology 9(2):49-64. Wildlife Management, Baton Rouge. 70 pp. Tangipahoa Parish Coastal Advisory Committee Wax, C. 1981 Personal communication regarding the reported effects of salinity intrusion. 1981 A modified daily water budget model for coastal wetlands in Louisiana: A Hammond, Louisiana. computer program. Unpublished manuscript. 21 pp. Wicker, K. M., et al. 1980 The Mississippi Deltaic Plain Region habitat mapping stud . U.S. Fish and Thompson, B. A. and J. S. Verret Wildlife Service, Office of Biological Services. FWS/OBS-79-07. 464 maps. 1980 Nekton of Lake Pontchartrain, Louisiana, and its surrounding wetlands. Pages 711-864 in J. H. Stone (editor), Environmental analysis of Lake Pontchartrain, f-ouisiana, its surrounding wetlands, and selected land uses. 1981 Assessment of the extent and impact of saltwater intrusion into the wetlands Coastal Ecology Lab, Louisiana State University. Prepared for U.S. Army of Tangipahoa Parish, Louisiana. Prepared for Tangipahoa Parish Police Jury. Engineer District, New Orleans. Coastal Environments, Inc. Baton Rouge. 59 pp. 41 U @d@! c 7 in Is '16 N, 4; T.W01, -o. hi@chu Lefi Lit 4 9r 1.6- co@- Tch.. Light. ie@ 1, lato Lookout f --j"wr a' 7x/ tli. gil= G- Point ii A\ 4 it, R- L,&ht A LA KE Orl ePl 2@ A A1JRPPAS f Norin V4 A K E L 7 17 P 0 TCHARTRIAIN 'N@ enje, 1@ I r it 1_,W@ W-d' koafgt P, R 6 k 00 NEW ORLEANS station ftimoms station B-d Ldg4rd M!_15T pumping at k A FRESHWATER DIVERSION PLAN legend ENVIRONMENTAL UNI FOR THE LAKE MAUREPAS FRESHWATE LOUISIANA COASTAL ZONE: AREAS OF TRANSITION, 1955-1978 PHASE I FRESH TO NON-FRESH MARSH 2 ST. CHARLES MARSH HYDROLOGIC UNITS I AND 11 BALDCYPRESS SWAMP TO FRESH MARSH 3 GOOSE POINT MARSH E SnLz VIRONMENTS, INC. BALDCYPRESS SWAMP IN STRESSED CONDITION 4 NORTH SHORE MARSH 42 I I 1@ i lilt'. S;,; s do 'A 0--l __s usbt ,@'pr&Td Pw Cl-, N.,th Sho', Ap_@ 'A"le gig Fw J" 1h 41. IlAmpd, pi. r@ _cvP'isfkvb PA."* Hb_ r'.w. 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