An Approximation of the Sediment Budget for the Tombigbee River and the Mobile River Basins

Ramirez-Avila, J. J., McAnally, W. H., & Ortega-Achury, S. L. (2015). An Approximation of the Sediment Budget for the Tombigbee River and the Mobile River Basins. Federal Interagency Sedimentation Conferences (FISC). Reno, NV.

A sediment budget is an accounting of the sources and disposition of sediment as it travels from its point of origin to its eventual exit from a drainage basin. Sediment budgets are important in defining the dynamic behavior of a river system. The Mobile River Basin covers two thirds of the state of Alabama and portions of Mississippi, Georgia, and Tennessee. It is the fourth largest basin in the United States in terms of flow volume and is the sixth largest river system in the U.S. in terms of area. The lower Mobile Bay is a designated national estuary under the EPA’s National Estuary Program. The Mobile Bay and the rivers draining into it support major uses with national implications which include the Tennessee- Tombigbee Waterway, the Port of Alabama, various commercial fisheries, large industry, tourism and recreation, and abundant development. Surface water in the Tombigbee River and Mobile River Basins generally meet Federal and State drinking water standards and guidelines for protection of aquatic life.However, water quality conditions along both river basins have been reported to be adversely affected by urban and agricultural activities, as indicated by elevated concentrations of sediments, nutrients, pesticides, and other organic compounds and biological communities commonly exhibit signs of environmental stress. A study was performed to develop a sediment budget for the Tombigbee River Basin and the Mobile River Basin. A two tier analysis was developed to determine the annual sediment changes along the Tombigbee River Basin and the Mobile River Basin. Results indicate that important sedimentation processes are occurring on the impoundments distributed along the Tombigbee River Basin and the Alabama River Basin, which receives waters from the Cahaba River, Coosa River, and Tallapoosa River. Higher rates of sediment along the lower part of the Tombigbee River Basin could be related to the occurrence of river bank instability processes between the Demopolis and the Coffeeville Dams on the Tennessee-Tombigbee Waterway. Total sediment loads at the entrance of the Mobile River ranged from 0.8 to 18.75 Mg yr-1. Changes on morphological and hydrodynamic processes below the diversion of the Mobile River in two distributaries can be favoring sedimentation processes along the lower part of the basin and the Mobile Bay. Assessment of a sediment budget in the Mobile River Basin is important to increase the scientific understanding of sediment behavior and distribution within the basin, as important factors that influence water quality trough the basin itself, the Mobile Bay and the Gulf of Mexico.