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Title: COMBINED GEOMORPHIC AND NUMERICAL-MODELING ANALYSES OF SEDIMENT LOADS FOR DEVELOPING WATER-QUALITY TARGETS FOR SEDIMENT

Author
item Simon, Andrew
item Bingner, Ronald - Ron
item LANGENDOEN, EDDY - UNIV OF MISSISSIPPI
item YUAN, YONGPING - UNIV OF MISSISSIPPI
item WELLS, ROBERT - UNIV OF MISSISSIPPI
item Alonso, Carlos

Submitted to: American Society of Civil Engineers Water Resources Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/9/2003
Publication Date: 6/15/2003
Citation: SIMON, A., BINGNER, R.L., LANGENDOEN, E.J., YUAN, Y., WELLS, R., ALONSO, C.V. COMBINED GEOMORPHIC AND NUMERICAL-MODELING ANALYSES OF SEDIMENT LOADS FOR DEVELOPING WATER-QUALITY TARGETS FOR SEDIMENT. PROCEEDINGS EWRI-ASCE WORLD WATER & ENVIRONMENTAL RESOURCES CONGRESS. 2003. 11 P. CD-ROM.

Interpretive Summary: Sediment transported by streams has been determined to be one of the major pollutants of surface waters in the United States. In an effort to alleviate problems related to excessive amounts of sediment, it is important to first determine how much sediment is transported under "natural" undisturbed conditions. This can then be compared to how much sediment is transported in other streams to evaluate if that stream is impacted by excessive amounts of sediment. James Creek, Mississippi, has been listed as being impaired due to sediment. This research was carried out to determine how much sediment James Creek transports compared to how much sediment is transported by stable streams in the region. Historical data on streamflow and sediment were used with determinations of channel stability to determine how much sediment is transported by stable streams in the Southeastern Plains. Simulations of streamflow, upland, field, and channel processes were then conducted using data collected in the James Creek watershed. Results showed that most of the sediment eroding from the watershed came from stream channel and not from agricultural fields and that the amount of sediment transported by James Creek was much greater than what is predicted for stable streams in the region.

Technical Abstract: The principle objective of the study was to determine sediment loads for James Creek, Mississippi and for similar, but stable ("reference") streams to develop water-quality targets for sediment. Without historical sediment-transport data a combination of methods was used including analysis of historic data from other sites and numerical modeling of uplands and channels. "Reference" sediment-transport loads were determined from stable streams with historical flow and sediment-transport data in the Southeastern Plains Ecoregion. Using the discharge that occurs, on average every 1.5 years (Q1.5) as the "effective discharge," an initial "general reference" of 0.3 T/d/km2 was obtained. A weighted-reference condition based on the percentage of the drainage area encompassed by the various bed-material types results in a reference yield at the Q1.5 of 2.2 T/d/km2. Similarly, a weighted-reference concentration of 160 mg/l was obtained. "Actual" sediment-transport loads were obtained by: simulations of flow and sediment transport using the model AnnAGNPS; direct comparisons of measured cross sections from 1967 and 2002; and by simulations of channel flow and sediment transport by the channel-evolution model CONCEPTS. Average sediment loads at the mouth of James Creek over the 35-year period are about 250,000 T/y with 88% emanating from channels and 12% from upland sources. However, since clearing and snagging work in 1967 sediment loads attenuated and the contribution from channels and uplands over the period 1970-2002 shifted to 70% and 30%, respectively. Following the installation of low-water crossings in 1999, loads decreased to about 39 T/D/km2. This value is more than an order of magnitude greater than the "reference" yield.