ABSTRACT
In the open pit, runoff from the platform is large discharge and rapid afflux, which often results in serious gully erosion of dump slope. The study of erosion process under catchment conditions of the platform-slope system is still backward. In this study, field scouring experiments were conducted to investigate runoff characteristics and sediment yield processes of the platform-slope system under different flow discharges (48, 60, 72 and 84 L·min-1). Our results showed that rill erosion dominated the platform-slope system under the flow discharge of 48 L·min-1, and gully was formed under 60-84 L·min-1. The flow velocity of the platform and the slope showed an abrupting-fluctuating-stable trend with the duration of discharge. The flow velocity of the platform was smaller than that of the slope, with the magnitude of reduction at 8.3%-67.1%. The highest flow velocity appeared on the up-slop/down-slope, being 18.5%-44.6% higher than that of the middle-slope. In general, the sediment yield rate of the platform and the slope varied with the duration of discharge, with the sediment yield rate of the slope being 17.4 times as that of the platform. The ratio of gully width to depth showed substantial difference between the platform and slope. The platform generally had the largest ratio than the slope. For the slope, the largest ratio appeared on the middle-slop/down-slope, being 1.36-1.93 times as that of the up-slope. The morphology of rill and gully along the platform to down-slope presented in the form of "wide and shallow-narrow and deep-wide and shallow". Rill erosion mainly concentrated in the platform and the middle slope under the flow discharge of 48 L·min-1, contributed 29.9% and 26.8% of the total erosion volume, respectively. When the flow discharge increased to 60-84 L·min-1, the largest average across-section areas (1083.25-1737.86 cm2) formed on the up-slope accounted for 36.1%-44.7% of the total erosion volume. Our results provided evidence for modelling soil and water erosion of the platform-slope system in opencast coal mine.
Subject(s)
Geologic Sediments , Soil , Coal , Water , Water MovementsABSTRACT
Ephemeral gully erosion is an important erosion type in hilly and gully regions of Loess Plateau. While previous studies mainly focused on ephemeral gullies in agricultural land, little is known about the effects of naturally restored grassland on ephemeral gully erosion. In this study, taking the bare ephemeral gullies as the baseline, we conducted in-situ flushing tests to explore runoff and sediment yield characteristics and erosion mechanism of grassland ephemeral gullies under the runoff conditions of 5, 10, 15, 20 and 25 L·min-1. Compared to the bare ephemeral gully, average flow velocity, stable runoff rate, Reynolds number and Froude number of grassland ephe-meral gullies was reduced by 25.4%-67.3%, 8.4%-26.6%, 54.9%-80.5%, 18.6%-65.1%, respectively, whereas resistance coefficient was increased by 0.09-7.18 folds. Compared to the bare ephemeral gully, the maximum sediment yield rate, stable sediment yield rate, average sediment yield rate of grassland ephemeral gullies was decreased by 55.1%-90.9%, 61.8%-95.4%, and 64.8%-92.4%, respectively. The sediment yield reduction benefit of the naturally restored grassland under the discharge flow rate of 5-25 L·min-1 could reach 65.9%-88.8%, which decreased with increasing discharge flow rate. Compared to the bare ephemeral gully, average stream power and average shear stress of grassland ephemeral gullies was reduced by 54.9%-80.5% and 12.4%-51.1%, respectively, whereas the critical stream power and critical shear stress was increased by 1.43 folds and 33.7%, respectively. The average sediment yield of grassland and bare ephemeral gullies was signifi-cantly linearly related to average stream power and shear stress. Naturally restored grassland significantly increased the erosion resistance and reduced runoff erosion potential of ephemeral gullies.
