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Little Topashaw Creek - Sediment Transport
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Effects of rehabilitation measures on bed-material sediment transport were estimated by applying SAM to a data set comprised of 11 cross sections. The total force option was used for determination of composite hydraulic properties, and the Yang equation was used to compute bed-material sediment load. Manning n values were set at 0.07 for vegetated banks and 0.04 for the central portion of the channel. These values reflect increases of about 30% to allow for effects of sinuosity. At 0.4 times the estimated two-year discharge, the computed sediment transport capacity of the existing channel upstream from the project was about 1,200 kg s-1, increased in the reach containing a 0.8-m high headcut, and then declined to about 800 kg s-1 . This pattern is consistent with the channel evolution model proposed by Simon. The influence of LWDS was simulated by increasing the Manning n values to 0.15 for segments of the cross section covered by LWDS. Resulting composite n-values computed by SAM were consistent with values obtained using the approach of Shields and Gippel. This modification influenced only a small fraction of the wetted perimeter, but reduced computed sediment transport for the reach by 50%. Effects for greater discharges were slightly less.

 Little Topashaw Creek Sediment Rate