Data Collection and Analysis In Support of The Mid-Breton Sediment Diversion Project

Since the Mississippi River was leveed in the 1930s, the Mississippi River Delta, which includes the Barataria and Breton Basins, has lost approximately 1,800 square kilometers (km) of land, representing one of the highest rates of land loss in the world. This is attributed to sediment deprivation, hydrologic alteration, subsidence, sea level rise, and saltwater intrusion. Recognizing the need for an innovative approach to restore and sustain land, the State of Louisiana’s Coastal Master Plan has proposed multiple sediment diversions along the Mississippi River as cornerstone projects essential to creating and sustaining coastal land. Controlled sediment diversions offer a unique opportunity to strategically re-establish hydrologic flows, carry land-building sediment, nourish marshes, and sustain land. CPRA decided in fall 2015 to recommend that the Mid-Breton and Mid-Barataria diversions move forward to preliminary engineering and design.

The Mid-Breton project will be located at River Mile 68.0 AHP on the left descending bank of the river near the community of Wills Point. It is being designed for a peak flow of approximately 1,415 cms (50,000 cfs) when the river is flowing at 28,316 cms (1,000,000 cfs). Extensive data collection and modeling has been completed to support planning and hydraulic design of the diversion. Prior to field data collection, a thorough examination of existing public data was conducted. This included existing historical bathymetry, water surface elevation, discharge, current, salinity, sediment data, and turbidity. This data was supplemented with a robust field data collection program that included Acoustic Doppler Current Profiling (ADCP) to collect current and backscatter, iso-kinetic water sampling for determination of suspended sediment concentration and grain size, Laster In-Situ Scattering and Transmissometer (LISST) and Conductivity-Temperature-Depth (CTD) to supplement suspended sediment and turbidity data, bed sediment grab samples for grain size determination, and repeated multi-beam bathymetric surveys to track morphologic change. This data was ultimately used to input into numerical and physical models to optimize diversion location size, shape and orientation to maximize hydraulic efficiencies and sediment capture. The discussion in this session will focus on the data collection techniques, results and key observations that were used to inform the subsequent analyses and design.