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Title: Sediment transport and soil detachment on steep slopes: I. Transport capacity estimation

item Zhang, Xunchang

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2008
Publication Date: 7/1/2009
Citation: Zhang, G., Han, Y., Liu, Y., Zhang, X.J. 2009. Sediment transport and soil detachment on steep slopes: I. Transport capacity estimation. Soil Science Society of America Journal. 73(4):1291-1297.

Interpretive Summary: Correct estimation of the maximum sediment load (namely sediment transport capacity) is important for developing computer erosion models, because sediment transport capacity plays a pivotal role in determining soil erosion rates. The goal of this study was to evaluate the effects of flow discharge, flow velocity, slope gradient, flow shear force, and flow stream power on determining sediment transport capacity and to further develop predictive equations. The experiment was conducted under different flow discharge rates and slope gradients using river bed sediment in a laboratory hydraulic flume. The results indicated that either flow stream power, flow shear force, or a combined function of flow discharge and slope gradient is capable of predicting sediment transport capacity under the experimental conditons, but the stream power is preferred for its simplicity and easiness to measure. The results are useful to erosion modelers to develop better soil erosion prediction tools, which can be used by soil conservationists for soil and water resources conservations.

Technical Abstract: Precise prediction of sediment transport capacity (Tc) is pivotal to develop physically based erosion models. Few data are available for predicting Tc on steep slopes. The objectives of this study were to evaluate the effects of unit flow discharge (q), slope gradient (S), and mean flow velocity on Tc of shallow flow and to investigate the relationship between Tc and flow shear stress, stream power, and unit stream power on steep slopes using a 5-m-long and 0.4-m-wide non-erodible flume bed. Unit flow discharge ranged from 0.00063 to 0.005 square meter per second, and slope gradient from 8.8% to 46.6%. The diameter of the test riverbed sediment varied from 0.02 mm to 0.84 mm with a median diameter of 0.280 mm. The results showed that Tc increased as a power function with discharge and slope gradient with the Nash-Sutcliff model efficiency (NSE) being 0.95. The influences of q and S on Tc increased as q and S increased, with Tc being slightly more sensitive to q than to S. The Tc was well predicted by shear stress (NSE=0.97) and stream power (NSE=0.98) but less satisfactorily by unit stream power (NSE=0.92) for steep slopes. Mean flow velocity was also a good predictor of Tc (NSE=0.95), as flow velocity increased as q and S increased in this study. Overall, stream power seems to be the preferred predictor for estimating Tc for steep slopes. However, the predictive relationships derived in this study need to be further evaluated using a range of soil materials on eroding bed and steep slopes.