|Ramirez-Avila, John -|
|Mcanally, William -|
|Ortega-Achury, Sandra -|
Submitted to: Joint Federal Interagency Sedimentation and Hydrologic Modeling
Publication Type: Proceedings
Publication Acceptance Date: May 15, 2009
Publication Date: February 1, 2010
Citation: Ramirez-Avila, J.J., Mcanally, W.H., Langendoen, E.J., Ortega-Achury, S.L. 2010. A sediment budget for Town Creek watershed: Suspended sediment transport analysis. Joint Federal Interagency Sedimentation and Hydrologic Modeling. 12 pages. Interpretive Summary: Stream channels in the Town Creek watershed in northeastern Mississippi were channelized in the early 20th century to improve drainage of the adjacent floodplain for cultivation and increase transport of sediments eroded from the adjacent hill slopes. The consequent unnatural channel form has caused an acceleration of erosional processes, especially eroding fine-grained sediments from streambanks causing navigation problems downstream on the Tennessee-Tombigbee Waterway. In order to develop practices to reduce the detrimental impact of the increased stream bank loadings on downstream habitat and infrastructure, it is necessary to understand the sources of sediment and sediment transport rates. Researchers at the U.S. Department of Agriculture-Agricultural Research Service-National Sedimentation Laboratory and the Department of Civil and Environmental Engineering of Mississippi State University are developing a sediment budget for the watershed by monitoring and analyzing flow and suspended sediment transport at selected sites on Town Creek. Relations between suspended sediment load and water discharge derived from this data set show: (1) suspended sediment loads much larger than those estimated from empirical regional relations; (2) significant impact of channel gradient and channel form across the watershed, and (3) a reduction in suspended sediment load for a given discharge between 1981 and 2009. The results indicate that conservation measures to reduce suspended sediment loads should focus on stabilizing actively eroding reaches in the northern headwaters due to channelization and riparian zone management practices.
Technical Abstract: The Town Creek watershed is located in the Southeastern Plains Ecoregion in Mississippi. Its total area covers 1,769 km2 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-1 of deposition in Aberdeen pool, where annual dredging averages 310,000 T yr-1. To develop 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 km2) within the watershed is under development by means of flow, streambank, streambed, and suspended sediment monitoring, GIS applications, and modeling methods. Tiers 1 and 2 from Sharp’s (2007) sediment budget template were adopted in order to identify suspended sediment transport trends and possible general conditions driving sediment supply and exportation within and from Town Creek watershed. A suspended sediment transport rating curve was established using 1,401 records of suspended sediment concentration and flow discharge at the USGS station 02436500 (Town Creek near Nettleton, MS) between 1981 and 1995 and between May 2008 and April 2009. Average annual suspended sediment load at this USGS station over a 29-yr period was about 1,000.000 T yr-1. Estimated suspended sediment yield at the effective flow discharge was 80 T d-1 km-2. Suspended sediment yield at the last studied year 2008-2009 was about 40 T d-1 km-2. Suspended sediment loads and yields for Town Creek estimated by regional relations were significantly lower than the above-mentioned numbers. Temporal analysis of suspended sediment transport rating curves from 1981 to 2009 showed a reduction in the amount of suspended sediment load contributed by Town Creek watershed at a specific instantaneous flow. Further, the suspended sediment transport rating curve’s parameters (slope and intercept) reflected 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. Conservation measures to reduce 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 km2 of Town Creek watershed. Analysis of bed material transport by incorporating Tier 3 of the analysis proposed by Sharp (2007) is necessary for a more comprehensive understanding of the sediments transported from Town Creek watershed, its sediment budget, and the stage of channel evolution in the different subareas of the watershed.