Effect of hydraulic parameters on sediment transport capacity in overland flow over erodible beds

Abstract

Sediment transport is an important component of the soil erosion process, which depends on several hydraulic parameters like unit discharge, mean flow velocity, and slope gradient. In most of the previous studies, the impact of these hydraulic parameters on transport capacity was studied for non-erodible bed conditions. Hence, this study aimed to examine the influence of unit discharge, mean flow velocity and slope gradient on sediment transport capacity for erodible beds and also to investigate the relationship between transport capacity and composite force predictors i.e. shear stress, stream power, unit stream power and effective stream power. In order to accomplish the objectives, experiments were carried out using four well sorted sands (0.230, 0.536, 0.719, 1.022 mm). Unit discharges ranging from 0.07 to 2.07 × 10<sup>−3</sup> m<sup>2</sup> s<sup>−1</sup> were simulated inside the flume at four slopes (5.2, 8.7, 13.2 and 17.6 %) to analyze their impact on sediment transport rate. The sediment transport rate measured at the bottom end of the flume by taking water and sediment samples was considered equal to sediment transport capacity, because the selected flume length of 3.0 m was found sufficient to reach the transport capacity. The experimental result reveals that the slope gradient has a stronger impact on transport capacity than unit discharge and mean flow velocity due to the fact that the tangential component of gravity force increases with slope gradient. Our results show that unit stream power is an optimal composite force predictor for estimating transport capacity. Stream power and effective stream power can also be successfully related to the transport capacity, however the relations are strongly dependent on grain size. Shear stress showed poor performance, because part of shear stress is dissipated by bed irregularities, bed form evolution and sediment detachment. An empirical transport capacity equation was derived, which illustrates that transport capacity can be predicted from median grain size, total discharge and slope gradient

Modelling the sediment transport capacity of flows in steep nonerodible rills

“…The soil median particle diameter used in our test was set to 0.79 mm, which is 1,870% higher than that (0.04 mm) used by Wu et al The results show no significant effects of sediment size on T c . Ali et al () and Zhang et al () also showed that sediment size has less of an affect than slope steepness and flow rate. However, the soil median particle diameter used in our test (0.79 mm) is more similar to that used in Zhang et al model (0.28 mm) than to that used in Wu et al model (0.04 mm).…”

“…Transport capacity is also heavily affected by sediment size, the effects of which are elucidated in some equations of T c (Agarwal & Dickinson, ; Ali, Sterk, Seeger, & Stroosnijder, ; Ferro, ; Govers, ; Low, ; Zhang, Wang, Tang, Luo, & Zhang, ). Agarwal and Dickinson () observed an inverse relationship between T c and particle size, with D 50 ranging from 0.015 to 0.75 mm, and Zhang et al () reported that T c decreases as a power function of sediment size with D 50 ranging from 0.10 to 1.16 mm.…”

“…Govers () found that flow velocity has no clear influence on T c , because the influence of slopes on flow velocity is nonsignificant owing to feedback observed between rill bed morphologies and flow conditions in erodible beds (Di Stefano et al, ; Di Stefano, Ferro, Palmeri, & Pampalone, ; Giménez & Govers, ; Govers, ). Additionally, Govers and Rauws () concluded that shear stress is not a good predictor for estimating T c under erodible bed conditions, as part of shear stress is dissipated by bed irregularities, bed form evolution, and sediment detachment (Ali et al, ). They thus suggest that unit stream power can be used to predict T c for erodible beds (Govers, ; Govers & Rauws, ), as unit stream power in terms of slope and unit discharge is independent of bed conditions (Govers & Rauws, ).…”

Nondimensional sediment transport capacity of sand soils and its response to parameter in the Loess Plateau of China

“…However, the dissipation of the flow energy by separating and transporting sediment accounts for a major part of the flow energy, apart from the energy to increase flow velocity, which leads to the flow velocity being not very sensitive to slope gradient in the erodible bed (Ali et al, 2012;Giménez & Govers, 2002). The poor correlation between the mean flow velocity and the sediment transport capacity is due to the fact that the sediment transport capacity is greatly influenced by slope gradient, and the flow energy increases as the slope increases.…”

“…Soil erosion is a major contributor to land degradation and has become a heated issue globally (Ali, Sterk, Seeger, Boersema, & Peters, 2012;Lal, 1998;Zhao et al, 2013). In the process of converging along the uphill to the foot of the slope, overland flow erodes the soil and forms a flow with the sediment, which is called "sedimentladen flow".…”