Effects And Mechanism Of Hedgerows On Erosion Control In Slope Of Engineering Accumulation

Production and construction projects generate engineering accumulation including waste dump, gangue field, tailings impoundment during construction and production process. If soil and water conservation lack, soil erosion on these engineering accumulation are serious. To explore the effective soil and water conservation measures, standard runoff plots which are 20 meters long and 5 miters wide were be constructed. Effects and mechanism of hedgerows on sediment erosion of engineering accumulation was studied by using runoff scouring experiment under three flow discharges(35, 45, 55L/min) and three slope gradients(24°, 28°, 32°). The results indicated that:(1)Runoff and sediment yield of control plot and hedgerows plot increased with increasing of runoff discharge and gradient. Runoff yield of hedgerows can reduce runoff and sediment yield effectively: ①Runoff reduction benefit that reaches 4%~40% increase with increasing of plot gradient. But the relationship between runoff reduction benefit and runoff discharge is not simple linear correlativity, it increases first then decreases as increasing of runoff discharge. ②Sediment reduction benefit of hedgerows which is 15%~45% decreases with increasing of runoff discharge and gradient.(2)Runoff rate and sediment rate of control plot and hedgerows plot increase with increasing gradient and runoff discharge. Varying tendency of runoff rate with the time rapidly increases in early then level off. While sediment rate rapidly increases in early then dramatic decline in later, even it in the end of the time is less than it in the beginning under large runoff discharge(45、55L/min). Runoff rate and sediment rate of hedgerows plot is less than it of control plot. Outflow moment of hedgerows plot is delayed for 2~10min than control plot. Sediment rate of hedgerows plot is less than it of control plot in early stage, then the difference is more and more smaller in later stage even the former exceed the later.(3)Rill erosion amount has the greatest proportion in first section of slope, which is at least 40%. Rill erosion of the upper slope shows a trend of decrease after the first increase with increasing of gradient. Rill erosion has the greater proportion with increasing of runoff discharge, which shows that rill erosion improve downwards. Protective effect of hedgerows is better for lower slope and rill erosion is limited to upper slope by hedgerows. Hedgerows have more significant impact on rill distribution of 24° and 32° plot.(4)The content of sand grains in sediment increase gradually while the content of clay particles reduce with increasing gradient of and runoff discharge. Compared with control plot, sand grains content decreases while silt and clay particles content increases in sediment of Hedgerows plot. This results show that hedgerows have obvious intercept capability for sand grains. sand grains can be an index to evaluate the effect of hedgerows to slope erosion.(5)Hedgerows reduce the soil detachment rate from 3~10g·m-2·s-1 to 1.5~8g·m-2·s-1, and decrease the runoff shear stress 4~8N·m-2 to 2.5~6N·m-2, increase critical shear stress and critical stream power by 0.25 and 5 times. Hedgerows reduce the water erosion degrees by weaken the energy and erosion dynamic of slope runoff.(6)Erosion control capacity of a specific hedgerows has a critical value over time. The relationship between erosion control and scour time can be fit by quadratic function. The maximum value of sediment reduction accumulated amount appeared later than 26 th min, and it would appear in advance with increasing gradient of and runoff discharge. The direct cause for time limit of hedgerows controlling erosion is the sequential variation of the runoff sediment concentration. The ratio of sediment concentration to sediment carrying capacity show the source-sink relation of hedgerows and runoff which is underlying cause that erosion control capacity has critical value.