US Army Corps of Engineers New Orleans District Morganza to the Gulf Systemwide Model

1. US Army Corps of EngineersNew Orleans DistrictMorganza to the GulfSystemwide Model A. Malene Henville 23 May 2008

2. Content • Systemwide Model Purpose • Data Collection Points • Boundary • Geometry • Model output • Other ongoing or planned models in the area

3. Model Purpose • To assess the impact of the proposed project on the general trend of flow distribution and salinity intrusion along the main channels and lakes, tributaries and distributaries in the project area • To develop the preliminary sizing of the Environmental Structures

4. Data Collection Points

5. USACE Data Collection Points

6. Boundary Conditions • Tidal stage fluctuations from the Gulf of Mexico • Various freshwater inflows from major waterways including Atchafalaya River, Wax Lake Outlet, Bayou Lafourche, and GIWW East of Larose • Saltwater boundary at the Gulf of Mexico • Data used collected by CEMVN and other agencies

7. How the HET Has Helped • Provided information on types of predominant vegetation in particular marsh areas to help determine Manning’s n values • Provided data (flow, stage, salinity) for existing and possible additional boundary conditions or points to verify or calibrate to. • Provided bathymetry data in areas that we did not collect data or have existing data available • Provided known facts about marsh areas that are part of the model • Had joint meeting to go through geometry in detail to find errors or erroneous details that did not match field observations

8. Model Geometry • Two-dimensional elements in X,Y plane • 48, 960 elements • 171, 289 nodes • Element material properties • Peclet control or Eddy viscosity control • Roughness by depth or wetting and drying by marsh porosity • Bathymetry in Z plane • Results are depth averaged

11. What the model does… • The model will be able to track general changes in the velocity, stage, and salinity intrusion by directly comparing data at specific points • The environmental structures will be modeled as simulated openings in order to determine if the initial flows and locations are appropriate to maintain current conditions

12. Establish Discharge Capacity of Environmental Structures • Artificial openings are created where the environmental structures are proposed • Flows with and without project, inside and outside the levee will be compared. • Openings can be resized and/or relocated so that the flow distribution remains about the same in areas that become hydraulically isolated due to project • Any parameter can be compared at any point between different scenarios.

13. Initial Alternatives • Alternative 1- Model all environmental and navigational structures in open position during typical spring conditions. • Alternative 2- Model all environmental structures in closed position and all navigational structures in open position during typical spring conditions. • Alternative 3- Model all environmental structures in open position and model all navigational structures in open position with the exception of the Houma Navigational Canal (HNC) Lock Complex floodgate and lock in closed position during typical spring conditions. • Alternative 4- Model all environmental and navigational structures in open position during typical fall conditions. • Alternative 5- Model all environmental structures in closed position and all navigational structures in open position during typical fall conditions. • Alternative 6- Model all environmental structures in open position and model all navigational structures in open position with the exception of the HNC Complex (floodgate and lock) in closed position during typical fall conditions.

14. Status of Systemwide Model • Being verified by the Engineer Research and Development Center in Vicksburg, MS • Hydrodynamics are verified • Salinity runs but is not yet verified • Contract set up to run alternatives • Contract being set up to do ITR

15. Other Work in this area • Ad Circ Storm Modeling • Localized Interior Drainage (HEC RAS) • Systemwide Interior Drainage (UNET, HEC-RAS) • CH3D Modeling for the Houma Navigation Canal Deepening Feasibility Study • Physical Modeling of the Lock Complex

16. Interior lakes and project alignment

17. Localized Interior Drainage Models Grand Bayou Canal Bayou du Large Bayou Pointe aux Chenes Bayou Terrebonne Montegut G-1

18. Status of Localized InteriorDrainage Models Bayou Terrebonne was eliminated because of existing local levees, MTOG will not impact interior drainage Completed • Bayou Pointe aux Chenes • Montegut Wetland Area • G-1 Area Pending Completion • Bayou Du Large • Grand Bayou Canal @ GIWW

19. CH3D Model The model was used assess the effects of the HNC being deepened from -14 ft NAVD88 (-15 ft MLG) to -18 ft and -20 ft NAVD88 Specifically: 1. The impact on the flow distribution at the junction of the GIWW and HNC during low and high freshwater flow events. 2. The impact on the flow distribution at the Bayou Grand Caillou (BGC) and HNC junction during low and high freshwater flow events. 3. The impact on salt water intrusion along the HNC and HNC’s tributaries and distributaries. 4. The operation of the HNC Lock Complex to increase flow along the BGC during low flows. Current effort is complete but utilized along with average flow year salinities and high flow month salinities will provide a broad range of conditions and information that is critical to developing the Houma Navigation Canal Lock Structure Operating Plan to minimize salinity intrusion at the Houma Water Treatment Plant.

20. Localized ADH 2-D Structure Modeling Completed Bayou Pointe aux Chenes Bush Canal Pending Completion Bayou Terrebonne Bayou Petit Caillou Lapeyrouse Canal? Bayou Du Large Falgout Canal GIWW West of Houma GIWW East of Larose Grand Bayou Humble Canal