--> ABSTRACT: Discharge-Sediment Dynamics of Lower Mississippi River, by Joann Mossa; #91036 (2010)

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Discharge-Sediment Dynamics of Lower Mississippi River

Joann Mossa

Temporal and spatial variations of processes in the lower 315 mi (507 km) of the Mississippi River were investigated using a data base consisting of several instantaneous measurements of discharge, suspended sediment concentration, suspended sediment load, and percent sand in the suspended load. Data were collected periodically by the Corps of Engineers at Tarbet Landing (n = 460) between 1972 and 1985, at St. Francisville (n = 84) between 1977 and 1986, and at Belle Chasse (n = 93) between 1976 and 1986.

Physical factors contributing to seasonal and annual variations in sediment load and concentration include the magnitude, duration, number, and timing of floods, and the background flow conditions. During high-flow years, sediment peaks precede discharge peaks by several months and depletion occurs during and after the maximum discharge. During low-flow years, sediment peaks occur only shortly before or coincide with discharge peaks. Unexplained sediment peaks during both falling and rising stages may be caused by bank failures or turbulent fluctuations of stream velocity.

Most differences in the discharge/sediment-load regime along the lower Mississippi River can be explained by the downstream decrease in grain size of the bed and bank material. Silt-clay and sand concentrations follow different functions with discharge. At upstream stations, the silt-clay concentration was depleted and showed a strong nonlinear relationship with discharge; however, the sand concentration showed a linear relationship with discharge. Downstream, the silt-clay concentration showed a more linear relationship with discharge.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.