Evaluating a single-class net deposition equation in overland flow conditions

Abstract

The quantitative description of sediment transport across areas of net deposition is an essential part of assessing the off-site effects of soil erosion on hillslopes. A new approach to describing sediment deposition across areas of net deposition, the single-class Hairsine and Rose [1992a, 1992b] sediment deposition equation, is evaluated here using a series of controlled laboratory experiments. Hydraulic and sediment transport input parameters, sensitivity analysis, calibration using half the experimental data, and evaluation using the remaining data are presented. Simulations of overland flow hydraulics are evaluated using measured flow velocities. This evaluation shows that the Manning's equation gives a good estimate of flow velocities. Calibration is conducted by adjusting the fraction of stream power available for sediment (re)entrainment (F), and the threshold stream power below which no reentrainment occurs (Ωcr), to minimize the error between the simulated and the measured outflow sediment concentrations. The calibration runs show that the single-class Hairsine et al. equation is very sensitive to the characteristic settling velocity adopted. The evaluation found that good simulations are obtained if appropriate threshold values are used. Incorporation of the reentrainment term significantly improves sediment outflow simulations above the threshold value.