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 T 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 × 10 −3 to 5 × 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 μm, with a median diameter of 280 μm. 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.