US Army Corps of Engineers ® Engineer Research and Development Center West Bay Diversion Evaluation 1-Dimensional Modeling CWPPRA Technical Committee and Peer Review Team Presentation 2 December 2009 Freddie Pinkard ERDC - CHL

US Army Corps of Engineers ® Engineer Research and Development Center West Bay Diversion Evaluation 1-Dimensional Modeling Purpose Model Capabilities, Limitations, & Requirements Modeling Approach MVK Regional HEC-6T Base Model ERDC HEC-6T Model Results and Conclusions Sensitivity Analyses

US Army Corps of Engineers ® Engineer Research and Development Center West Bay Diversion Evaluation 1-Dimensional Modeling Purpose ● The 1-dimensional modeling provides the means of assessing the long term impacts (50 year simulations) of the diversion as well as providing upstream sediment boundary conditions for the multi dimensional models. ● The results of the 1-dimensional modeling will be integrated with the results of the geomorphic assessment and the multi dimensional models in order to provide a complete evaluation of the impacts of the West Bay Diversion.

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling Model Capabilities, Limitations, and Requirements HEC-6T Sedimentation In Steam Networks ● is a 1-dimensional movable boundary open channel flow numerical model designed to simulate and predict changes in river bed profiles resulting from scour and/or deposition over moderate time periods ● provides computed total sediment discharge passing each cross section and the volume of deposits or scour accumulated at each cross section from the beginning of the simulation

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling Model Capabilities, Limitations, and Requirements HEC-6T Advantages ● Allows for long term simulations ● Ability to simulate dredging activities ● Allows for the diversion of both water and sediment and calculates that impact on downstream sediment transport HEC-6T Disadvantage ● Uses average hydraulic and sediment parameters to simulate 3-dimensional processes in 1 dimension

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling Model Capabilities, Limitations, and Requirements Input Requirements ● Channel Geometry ● Upstream Boundary Conditions ● Flow ● Sediment Loads ● Bed Material Gradations ● Distributary / Diversion Outflow and Sediment Concentrations ● Water Temperature ● Downstream Boundary Conditions Water Surface Elevations ● User Defined Sediment Transport Function

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling Model Capabilities, Limitations, and Requirements Two Phased Calibration ● Water Surface Profiles ● Sediment Observed Deposition and/or Erosion Measured Loads Dredging Records

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling - Modeling Approach ● Utilize MVK developed regional HEC-6T model ● Add cross sections through study reach to better define channel geometry ● Compare ERDC collected diverted flow, sediment concentration, and bed material gradation data to model values ● As model input parameters are modified, check model calibration ● Determine subsidence and sea level rise rates

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling Modeling Approach ● Develop typical discharge hydrograph ● Develop downstream water surface elevations to match the discharge hydrograph ● Develop composite dredge template ● Run hydrograph for 4 alternative scenarios West Bay Diversion Closed + No PAA Dredging West Bay Diversion Closed + PAA Dredging West Bay Diversion Open + No PAA Dredging West Bay Diversion Open + PAA Dredging

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling Modeling Approach ● Compare sediment deposition locations and quantities and dredging locations and quantities through the PAA for the 4 50-year simulation scenarios to determine the impact that the West Bay Diversion has on the PAA

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling MVK Regional HEC-6T Model ● Model Limits - Vicksburg, MS (RM ) to Pilots’ Station in Southwest Pass (RM -18) ● Channel Geometry Comprehensive Hydrographic Survey ● Cross Section Distribution

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling MVK Regional HEC-6T Model ● Bed Material Gradations ● Nordin and Queen samples collected in 1989 ● 2 year frequency discharge run for 30 days to rework bed material gradations. ● Water Temperature – monthly averages from measured values at Tarbert Landing ● Downstream Water Surface Elevations – monthly average stages for the NOAA gage at Grand Isle East Point

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling MVK Regional HEC-6T Model ● Diversion / Distributary Locations

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling MVK Regional HEC-6T Model ● Diversion Flow Distributions – percentage of Mississippi River flow upstream of diversion estimated from measured data or calculated ● Sediment Concentration Diversion Ratios – ratio of sediment concentration in the diverted flow compared to sediment concentration in the Mississippi River derived by grain size for a range of flows from measured data or estimated using the Rouse equation ● Sediment Transport Function – Toffaleti / Meyer-Peter Muller

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling MVK Regional HEC-6T Model ● Impact of Salinity – approximated by varying the silt and clay shear threshold deposition coefficients ● Water Surface Profile Calibration – gage stations

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling MVK Regional HEC-6T Model ● Sediment Calibration ● observed deposition downstream of the Old River Complex ● observed erosion at Smithland Crossing ● measured sediment transport at Tarbert Landing and at Belle Chasse ● reported dredge volumes in Southwest Pass and Above Head of Passes

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling ERDC HEC-6T Model ● Model Limits - Vicksburg, MS (RM ) to Pilots’ Station in Southwest Pass (RM -18) ● Cross Section Distribution

US Army Corps of Engineers ® Engineer Research and Development Center ● Analyze ERDC Collected Data / Compare With MVK Model Input / Revise Input As Required ● Flow Distribution At Diversions / Distributaries ● Sediment Concentration Ratios Between Diversions / Distributaries And The River ● Bed Material Gradations From RM 19.6 to RM Dimensional Modeling ERDC HEC-6T Model

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling - ERDC HEC-6T Model Flow Distribution – Baptiste Collette Bayou, Grand Pass, West Bay Diversion, and Cubits Gap

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling - ERDC HEC-6T Model Flow Distribution – West Bay Diversion

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling ERDC HEC-6T Model

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling - ERDC HEC-6T Model West Bay Diversion Sediment Concentration Diversion Ratios Derived From ADH 2-D Model

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling ERDC HEC-6T Model West Bay Diversion Sediment Concentration Diversion Ratios

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling ERDC HEC-6T Model

US Army Corps of Engineers ® Engineer Research and Development Center Bed Sample Locations Grand Pass West Bay Diversion

US Army Corps of Engineers ® Engineer Research and Development Center River Mile 5.5 ERDC Bed Sample Locations BSS-18 BSS-17 Looking Downstream

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling ERDC HEC-6T Model Bed Material Gradations At Site BSS-17

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling ERDC HEC-6T Model Bed Material Gradations At Site BSS-18

US Army Corps of Engineers ® Engineer Research and Development Center Bed Sample Locations West Bay Diversion Cubits Gap Head Of Passes

US Army Corps of Engineers ® Engineer Research and Development Center River Mile 2.5 ERDC Bed Sample Locations BSS - 23 BSS - 26 Looking Downstream

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling ERDC HEC-6T Model Bed Material Gradations At Site BSS-23

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling ERDC HEC-6T Model Bed Material Gradations At Site BSS-26

US Army Corps of Engineers ® Engineer Research and Development Center 1-Dimensional Modeling ERDC HEC-6T Model Subsidence Rates Derived From NOAA Technical Report NOS/NGS 50

US Army Corps of Engineers ® Engineer Research and Development Center Typical Hydrograph At Vicksburg BSS Dimensional Modeling - ERDC HEC-6T Model

US Army Corps of Engineers ® Engineer Research and Development Center ● Develop Downstream Boundary Condition ● Daily 8:00 AM Stage At Grand Isle, East Point Gage ● Rectify Datum Issues ● Sediment Transport Function – Toffaleti ● Extended the moveable bed limits and utilized a realistic dredging template (750 feet wide at -50 feet, MLG minus 1 foot overdepth / advance maintenance dredging) 1-Dimensional Modeling - ERDC HEC-6T Model

US Army Corps of Engineers ® Engineer Research and Development Center ● Composite Dredge Template – extended dredging width to add an end area equivalent to match the PAA dredging. Width varied from 940 to 970 feet depending upon PAA dredging elevation (-41, -44, or -48 feet) at -50 feet, MLG ● Model under estimates reported dredging quantities in Southwest Pass but responds well in other reaches. Computational analysis instead of computational model. 1-Dimensional Modeling - ERDC HEC-6T Model

US Army Corps of Engineers ® Engineer Research and Development Center River Mile 2.46 – West Bay Diversion Open 1-Dimensional Modeling – ERDC HEC-6T Model Navigation Dredge Template vs. Composite Dredge Template Utilized Option Of Filling Dredge Cut First, Then Deposits Equally Across The Cross Section

US Army Corps of Engineers ® Engineer Research and Development Center Total Sediment Load for the Ms River Between RM 80 and RM -20 Relative to Total Sediment Load at RM Dimensional Modeling – Results

US Army Corps of Engineers ® Engineer Research and Development Center Total Sediment Load for the Ms River Between RM15 and RM -5 Relative to Total Sediment Load at RM Dimensional Modeling – Results Baptiste Collette Bayou Grand Pass West Bay Diversion Cubits Gap Head Of Passes

US Army Corps of Engineers ® Engineer Research and Development Center River Mile 2.46 – West Bay Diversion Closed 1-Dimensional Modeling – Results

US Army Corps of Engineers ® Engineer Research and Development Center River Mile 2.46 – West Bay Diversion Open 1-Dimensional Modeling – ERDC HEC-6T Model

US Army Corps of Engineers ® Engineer Research and Development Center River Mile 2.46 West Bay Diversion Open / No PAA Dredging 1-Dimensional Modeling – Results

US Army Corps of Engineers ® Engineer Research and Development Center River Mile 2.46 West Bay Diversion Open / With PAA Dredging 1-Dimensional Modeling – Results

US Army Corps of Engineers ® Engineer Research and Development Center BSS - 23 Average Dredging Per Cycle Upstream of Head of Passes During 10 Year Periods 1-Dimensional Modeling – Results

US Army Corps of Engineers ® Engineer Research and Development Center BSS - 23 Percentage of Dredging Due to Opening West Bay Diversion 1-Dimensional Modeling – Results

US Army Corps of Engineers ® Engineer Research and Development Center Sensitivity of Model Modifications ● Dredging Template Dimensions and Moveable Bed Width ● Sediment Concentration Diversion Ratios ● Subsidence Rates ● Daily Downstream Stages ● Increased Cross Sections to Better Define Channel Geometry

US Army Corps of Engineers ® Engineer Research and Development Center Sensitivity Analyses (Recommended For 12 Month Effort) ● Future Flows (Typical Hydrograph) ● Future Development of West Bay Diversion ● Different Transport Functions ● Impact of Different Diversions / Distributaries

US Army Corps of Engineers ® Engineer Research and Development Center BSS - 23 ● West Bay Diversion can not be analyzed in isolation. ● Approximately 40% - 50% of the total sediment load at RM 12.5 is diverted and/or deposits upstream of Head of Passes. ● The 1-D model performs well in reproduction of deposition and dredging locations but under estimates the best available estimates of dredging quantities in Southwest Pass. ● From Cubits Gap downstream to Head of Passes, the channel functions as an efficient sediment trap. 1-Dimensional Modeling – Conclusions

US Army Corps of Engineers ® Engineer Research and Development Center BSS - 23 ● Although the West Bay Diversion diverts only 7% of the total flow, the computed impact on dredging is disproportionably large. The 1-D model indicates that the West Bay Diversion accounts for 20% – 25% of the dredging required above Head of Passes including the PAA. ● Due to the influence of salinity and tides, a 3-D or laterally averaged hydrodynamic / salinity / sedimentation model may be required to resolve the sedimentation processes in Southwest Pass. 1-Dimensional Modeling – Conclusions

US Army Corps of Engineers ® Engineer Research and Development Center West Bay Diversion Evaluation 1-Dimensional Modeling Questions / Comments