--> ABSTRACT: Sediment Flux into Lake Pontchartrain from the Mississippi River via the Bonnet Carré Spillway: Implications for Land Building in South Louisiana, by Fabre, Jeff; Bentley, Samuel J.; Li, Chunyan; Walker, Nan D.; Smith, Emily; #90142 (2012)

Datapages, Inc.Print this page

Sediment Flux into Lake Pontchartrain from the Mississippi River via the Bonnet Carré Spillway: Implications for Land Building in South Louisiana

Fabre, Jeff *1; Bentley, Samuel J.1; Li, Chunyan 2; Walker, Nan D.2; Smith, Emily 2
(1) Geology & Geophysics, Louisiana State University, Baton Rouge, LA.
(2) Oceanography & Coastal Sciences, Louisiana State University, Baton Rouge, LA.

Recent studies indicate that up to ~ 10,500 sqkm of land may be lost in the lower Mississippi Delta by 2100, due to decreased sediment supply, sea level rise, and channelization. Man-made diversions of sediment-laden river water are being considered as a primary mechanism for building land to combat this problem. To date, no study has documented the sediment-delivery potential of a large man-made river diversion. In the spring of 2011, historic flooding on the Mississippi River delivered record river and sediment discharge to the Delta, and the US Army Corps of Engineers opened floodways, including the Bonnet Carré Spillway, to keep levees from being overtopped between Baton Rouge and New Orleans. The Bonnet Carré Spillway connects the Mississippi River upstream from New Orleans to Lake Pontchartrain. We studied river-sediment flux from the spillway into Lake Pontchartrain as an analog for future river-sediment diversions under study at present. The spillway was open from May 9 to June 20, 2011, reaching peak flows > 8,000 m3/s, at the upper end of diversion flow considered for land-building, making the spillway for a short time one of highest discharge rivers in North America. To study sediment flux and fate, we examined time-series satellite imagery, recorded flow with acoustic current meters, measured suspended-sediment concentrations, and collaborated with others to gain additional flow measurements. To develop a sediment budget, sediment deposition was measured in sediment cores collected across the ~900 sqkm lake before, during, and after the operation of the spillway. Cores were analyzed for the cosmogenic radionuclide Be-7, for grain size, and sedimentary structures, via X-radiography. Initial results suggest that the plume rapidly dispersed across most of the lake, and deposited a sediment layer mm to tens of cm in thickness across the lake floor, with a total mass estimated at 1-4 MT. This suggests that such diversions, if operated on a regular basis during high flows when both sediment concentration and discharge are highest, may provide an important tool for conserving and building land in the shrinking Mississippi Delta.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California