Mitigating land loss in coastal Louisiana by controlled diversion of Mississippi River sand

Abstract

After the 1927 flood of record on the Mississippi River, the Bonnet Carré Spillway in Louisiana was constructed as a flood control operation. When it is opened, the spillway diverts floodwaters from the Mississippi River to Lake Pontchartrain1, to reduce the water discharge flowing past New Orleans. During the 2011 Mississippi River flood, which had the highest peak discharge since 1927, the Bonnet Carré Spillway was opened for 42 days, from 9 May to 20 June. During this period, the average spillway discharge of 6,010 m3 s−1 amounted to 10–20% of the total river flood discharge. Here we present measurements of the areal extent and thickness of new sediments in the floodway, following the 2011 Mississippi flood. Only the upper 10–15% of the river water column was skimmed into the floodway. Yet, we conservatively estimate that 31–46% of the total sand load carried by the Mississippi River during the period of spillway opening was diverted. We find that local river conditions led to increased concentrations of suspended sand in the upper water column and thus led to diversion of sand from the river into the spillway. We conclude that an appropriate design of engineered river diversions in Louisiana can help mitigate coastal wetland loss.

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Figure 1: Map overview of survey location.
Figure 2: Sand deposits in the BCS.
Figure 3: Summary of grain-size data and predicted and measured sand-deposit volumes.

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Acknowledgements

This research was supported by the National Science Foundation (NSF) through the RAPID grant EAR 1140198. J.A.N. was partially supported by NSF post doctoral grant EAR 0948224. M.C. and G.P. were partially supported by the Office of Naval Research, N00014-10-1-0617. G.P. was partially supported by the National Center for Earth-Surface Dynamics, an NSF Science and Technology Center, EAR 0120914. The authors acknowledge T. Sawyer and E. Prokocki for providing valuable field assistance and the sedimentology lab at the Jackson School of Geosciences at the University of Texas, Austin, for facilities support. The logistical support of the United States Geological Survey and the USACE are gratefully acknowledged.

Author information

J.A.N. led the field studies, laboratory work and data analysis, and was the primary author of the manuscript. J.L.B. was part of the intellectual development of the project and contributed to subsequent analysis of the data and writing of the paper. C.B. took part in the field studies and provided USACE data while assisting with the analysis. R.W.C. participated in the field studies. M.C. participated in the field studies and also assisted in the orthophoto analysis. P.K. and G.P. were part of the intellectual development of the project and also contributed to writing of the manuscript.

Correspondence to Jeffrey A. Nittrouer.

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Nittrouer, J., Best, J., Brantley, C. et al. Mitigating land loss in coastal Louisiana by controlled diversion of Mississippi River sand. Nature Geosci 5, 534–537 (2012) doi:10.1038/ngeo1525

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