Study On The Effects Of Different Surface Water Drainage Patterns On The Characteristic Of Runoff And Soil Loss Under Simulated Rainfall Condition

No matter on the non-continuous slope formed of natural terrace or continuous slope formed in the process of excavation, runoff and soil loss is the inevitable result of the slope erosion. During the process of rainfall, under certain rainfall intensity, there will be different patterns of slope runoff and soil loss response mechanism with the different soil infiltration rate and aggregate structure effected by soil particles fractal characteristic. It will cause the result of soil particle and sediment transport and the influence of soil nitrogen and phosphorus nutrient output which is an quite interactive process. In the current study, it was well proved that reasonable drainage structure with supporting system of reservoir has make great significance on the control of soil erosion and regulating effect on the seasonal agricultural water. But during intense rainfall, the quite not an ideal dewatering and sediment settlement effect is the man problem of slope drainage system. And In order to improve intercepted regulation effects of slope drainage on the runoff and sediment, with in-depth knowledge of effluent process in the natural hydrological system, two different layout modes of level trench were designed to change effluent process of surface runoff on the slope. And in contrast with the slope without any drainage layout(CK), rainfall simulation experiment was used to study the different characteristics of runoff and soil loss under two different slope drainage layout measures which were respectively designed to lead water flow in concentration (T1) and shunt in a form of "swallow" (T2), the result shows that the layout of drainage helps change the process of slope runoff per minute by the way of periodic dewatering time regulation and intercepting water in section, keep slope soil micro-aggregate structure by separation characteristics and handling mechanisms of soil particle size, and resulting in the decrease of nitrogen and phosphorus output concentration in runoff and sediment and the shunt effect have significant differences between T1 and T2 on the slope with different gradient and land use types by the interactive test study. The main themes of the paper are as follows:(1) On the cultivated land slope, T1 and T2 can significantly reduce runoff rate. Compared with the CK treatment, the runoff rate more slowly increased in a longer period of time, its increasing duration delayed to 21 minute after the beginning the runoff and fitting coefficient with time was increased above 0.85 with fact of T1 and T2. Besides they also can bring a more stable distribution of runoff process and with the result of the reduce of the runoff carrying capacity, the critical fraction size of soil micro-aggregate particle decreased into 5um and the range of sediment enrichment rate reduced within 0.576 and 1.563, which helps reduce the effect of gradient on the output of nutrient. But the output concentration of total nitrogen and phosphorus in runoff were shown as T1>T2 which means that Tl makes more effect on the reducing the loss of nutrient in sediment while T2 helps more for the decrease value nutrient loss in runoff and its output concentration regulation by the change of volatility degree.(2) Due to the change of soil structure and increase of soil erosion resistance, deposition of the soil particles become more obvious during the process of runoff on the waste-grassland slope which works into different dynamic process of runoff and soil loss. On the slope of 5 °and 10 °, T2 could not only diminished the micro-aggregates with relative large size to change the " Soil Coarseness" phenomenon on the slope but also resulted no effect on the sharply decrease of the small size particle amount. T1 and T2 could respectively weaken the collapse and migration of 1000-50um micro-aggregates particles by 11.31% and 11.31%, and T2 (51.72%) have more obvious effect on the change of runoff than Tl (58.95%) in contrast with CK. But when the slope gradient is increased to 15 °it presented opposite regularity which means there exists no corresponding relations between the mechanism of flow and sediment reduction on the waste-grass land slope. But the T1 is more beneficial to reduce the interaction effect of drainage factor and gradient factor on runoff which explain the reason of lower loss of total nitrogen and phosphorus while T2 have more advantageous to greater reduce amount of available nitrogen and phosphorus in the runoff and sediment.(3) On the forest land with a gentle slope of 5 °and 10 °, regulation of distribution benefit on soil runoff effect was more apparent for T1 and T2 with greater fitting degree of rainfall runoff rate than 15 °, but no obvious significant of the effect of reducing the peak value of sediment content effect was founded between the two type of control drainage layout ways. Under the condition of the heavier forest soil particles itself, it also was easy for the small and medium-sized micro-aggregate to exist a differentiated settlement so that the process of slope runoff and sediment yield process will appear obvious consistency under the effect of dewatering factor of T1 and T2. While by contrast, T1 works greater to regulate the change of available nutrient output concentration thanks to the excellent fact of periodic and cross settlement or supplement of compound grain and single grain. So the stability of the water and sediment regulation depends on the reasonable intercepting drainage layout way on slope based on its gradient and land use type.