|Thomas, Robert - UNIVERSITY OF MISSISSIPPI|
Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 5, 2008
Publication Date: June 1, 2009
Citation: Langendoen, E.J., Wells, R.R., Thomas, R.E., Simon, A., Bingner, R.L. 2009. Modeling the Evolution of Incised Streams: III. Model Application. Journal of Hydraulic Engineering. 135(6): 476-486. Interpretive Summary: The 1992 National Water Quality Inventory of 642,881 miles of US rivers reported that 44 percent of stream miles inventoried were in a degraded state, mainly caused by excess sediments and nutrients. Fine-grained sediment problems result from soil erosion from watersheds and stream banks. In the midsouth and midwestern United States up to 80% of the sediments eroded from the stream channel may originate from the banks of the channel. The U.S. Department of Agriculture-Agricultural Research Service has been developing the CONCEPTS (Conservational Channel Evolution and Pollutant Transport System) model to study the effects of riparian forests and in-stream restoration measures on stream stability. CONCEPTS is a computer model that simulates flow and sediment transport in open channels such as rivers, and their ensuing evolution. The model has been tested on the Yalobusha River and James Creek in North-Central Mississippi. It accurately predicts the changes in channel geometry and stages in channel evolution if the forces acting on the channel boundary and the resistance of boundary materials are adequately characterized. The tests also show that the model produces reasonable results if the availability of input data is limited. CONCEPTS is therefore a tool that can be used by the U.S. Army Corps of Engineers and the U.S. Department of Agriculture-Natural Resources Conservation Service to assess the impact of instream hydraulic structures to control channel erosion and quantify sediment transport rates.
Technical Abstract: Incision and ensuing widening of alluvial stream channels is widespread in the midsouth and midwestern United States and represents an important form of channel adjustment. Two accompanying papers have presented a robust computational model for simulating the long-term evolution of incised and restored or rehabilitated stream corridors. These papers showed that sediment transport and streambank erosion mechanics were adequately simulated by testing the model against data obtained from controlled laboratory and field experiments. This paper presents the application of the model to two incised streams in northern Mississippi, James Creek and the Yalobusha River, to determine: (1) its capability to simulate the temporal progression of incised streams through the different stages of channel evolution; and (2) model performance when available input data regarding channel geometry and physical properties of channel bouondary materials are limited. Model results show that temporal changes in channel geometry of James Creek and the Yalobusha River are satisfactorily simulated. Comparing final observed and simulated thalweg elevations, the r2 value is 0.976 for the Yalobusha River and 0.986 for James Creek. The r2 value of final channel top width comparison is 0.838 for the Yalobusha River. The observed and simulated changes in channel top width along James Creek compare less favorably. This is mainly due to unknown initial channel geometry along its upper part. Model application also shows the importance of accurate characterization of channel boundary materials and geometry.