Abstract
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 in a 3.0 m long and 0.5 m wide flume using four well sorted sands (0.230, 0.536, 0.719, 1.022 mm). Unit discharges ranging from 0.07 to 2.07 × 10−3 m2 s−1 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.
Highlights
Soil erosion has become a major global environmental problem (Lal, 1998)
Sediment detachment rate depends on the potential of rainfall and a thin layer of overland flow to detach soil particles from the soil matrix as well as on the resistance of the soil against detachment
The objectives of this research were (i) to study the effect of unit discharge, mean flow velocity and slope gradient on sediment transport capacity and how these relations vary in the presence and absence of bed irregularities; and (ii) to evaluate the potential of different composite force predictors for the estimation of transport capacity under overland flow conditions
Summary
Soil erosion has become a major global environmental problem (Lal, 1998). Several process-based soil erosion models have been developed to estimate sediment yield at the catchment scale (KINEROS2, Smith et al, 1995; LISEM, De Roo et al, 1996; EUROSEM; Morgan et al, 1998; WEPP, Flanagan et al, 2001). Soil erosion is a combination of detachment and transport of sediment particles. Sediment detachment rate depends on the potential of rainfall and a thin layer of overland flow to detach soil particles from the soil matrix as well as on the resistance of the soil against detachment. The potential of rainfall and thin layer of flow is separately ascertained by using different equations during soil erosion modelling Most of the existing models estimate sediment detachment rate of flowing water by using the concept of Foster and Meyer (1972). According to this concept, the detachment rate is calculated as the difference between the sediment transport capacity and actual sediment load. Sediment transport capacity plays a pivotal role in the physical description of soil erosion processes
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