Louisiana Coastal Protection and Restoration Authority

Lower Barataria Basin and Lower Breton Sound Sediment Diversion Feasibility Study

Duration:
Completed 2016
In support of feasibility planning for the construction and operation of a sediment diversion located along the bank of the lower-most Mississippi River, the Institute conducted a series of studies related to site selection using both field-based and numerical methods. Diversion site selection was based on multi-criteria analyses, such as land building potential and impact to natural ecosystem services and fisheries. Studies were conducted using a diverse range of methodologies including environmental monitoring reliant on the deployment of fixed-station instruments and vessel-based sensors and hydrodynamic and sediment transport modeling.

The Challenge

Diversion site selection required new in-depth knowledge of the morphodynamic and water constituent transport properties in both the lower river system and within the surrounding estuaries and marshes. The Institute developed multi-dimensional morphodynamic models using the Delft3D platform covering the river channel, receiving basins, and diversion channels at multiple resolutions and time scales. To calibrate the modeled land building processes, in the absence of any currently operational diversion structure in a coastal environment, a high-resolution morphodynamic model was developed and parameterized using an analogous existing uncontrolled diversion (i.e., the West Bay diversion located 5 miles upstream of the Mississippi River ‘Head of Passes’). A high-resolution computational fluid dynamics (CFD) model was developed of the analogue diversion to explore the control of sediment transport patterns through the diversion channel and receiving basin. In additional to evaluating land building potential and the environmental effects, numerical modeling was used to explore the predicted hydraulic environment in and around diversion inlet and outfall structures and their potential impact on local reach-scale sediment erosion and deposition. 

The Approach

Field data collection in support of this project included monitoring a range of processes (e.g., flow velocities, sediment transport, turbidity, salinity) distributed through a range of complex environments. Sediment tracer particles were employed to monitor how river sediment was diverted through the diversion analogue and advected through the downstream receiving-basin. Receiving basin bathymetry was characterized using multiple integrated methods of data collection (e.g., multibeam sonar, terrestrial RTK GPS survey, airboat-mounted LiDAR) in response to the vast range of water depths that were present which stymied traditional survey methods.

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