A Sediment Budget for Town Creek Watershed: Suspended Sediment Transport Rates Analysis

The Town Creek watershed is located in the Southeastern Plains Ecoregion in Mississippi. Its total area covers 1,769 km and represents approximately 50% of the upper Tombigbee River basin area contributing to the Aberdeen Pool on the Tennessee-Tombigbee Waterway. The sediment yield from the watershed attributes to the estimated 320,000 T yr of deposition in Aberdeen pool, where annual dredging averages 310,000 T yr. To produce remedial measures and future BMPs in Town Creek watershed for reducing water quality impairment and dredging costs (expressed in terms of a percent reduction of sediment loads), it is necessary to know the current sediment sources and loads transported within the watershed. A sediment budget for a partial sub-basin (1606 km) within the watershed is under development by means of flow, streambank, streambed, and suspended sediment monitoring, GIS applications and modeling methods. In order to identify suspended sediment transport trends and to start identifying possible general conditions driving sediment supply and exportation within and from Town Creek watershed, the present paper presents results from a study which adapts Tiers 1 and 2 steps from Sharp’s sediment budget template. A suspended sediment transport curve was determined using 1,401 records of suspended sediment concentrations and flow discharges at the USGS station 02436500 (Town Creek near Nettleton, MS) between 1981 and 1995 and between May 2008 and April 2009. Average suspended sediment loads at the USGS station of Town Creek over a 29-yr period were about 1,000.000 T yr. Estimated suspended sediment yield at the effective flow (Q1.5) was 80 T d km. Suspended sediment yield at the last studied year 2008-2009 was about 40 T d km. Suspended sediment loads and yields for Town Creek estimated by regional relations were significantly lower than estimations obtained by the local expression. Temporal analysis of suspended sediment transport relations from 1981 to 2009 showed a reduction in the amount of suspended sediment loads contributed by Town Creek watershed at a specific instantaneous flow. Analysis in time of suspended sediment transport curves parameters (slope and intercept) showed active geomorphic processes and differences in stages of channel evolution caused by changes in channel gradient and channel morphology in different sections along the Town Creek. Tier 2 integration of the suspended sediment rating curve overestimated annual suspended sediment loads from years with low annual average daily flow. The reduction of suspended sediment loads should be focused on the attenuation of geomorphic processes and stabilization of reaches and agricultural lands near streambanks at the northern 320 km of Town Creek watershed. Analysis of bed material transport by incorporating Tier 3 of the analysis proposed by Sharp (2007) will result in a more comprehensive understanding about the discharge of sediments from Town Creek watershed, its sediment budget, and the stage of channel evolution in the different subareas of the watershed.