Sediment Transport and Soil Detachment on Steep Slopes: I. Transport Capacity Estimation

Precise estimation of sediment transport capacity (T-c) is critical to the development of physically based erosion models. Few data are available for estimating T-c 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 I c in shallow flows and to investigate the relationship between T-c and shear stress, stream power, and unit stream power on steep slopes using a 5-m-long and 0.4-m-wide nonerodible flume bed. Unit flow discharge ranged from 0.625 x 10(-3) to 5 x 10(-3) m(2) s(-1) and slope gradient from 8.8 to 46.6%. The diameter of the test riverbed sediment varied from 20 to 2000 pm, with a median diameter of 280 mu m. The results showed that T-c increased as a power function with discharge and slope gradient with a coefficient of Nash-Sutcliffe model efficiency (NSE) of 0.95. The influences of S on T-c increased as S increased, with T-c being slightly more sensitive to q than to S. The T-c 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 the slope range of 8.8 to 46.6%. Mean flow velocity was also a good predictor of T-c (NSE = 0.95). Mean flow velocity increased as q and S increased in this study. Overall, stream power seems to be the preferred predictor for estimating T-c for steep slopes; however, the predictive relationships derived in this study need to be evaluated further in eroding beds using a range of soil materials under various slopes.