Applicability Assessment And Application Of WEPP Model In Beijing Mountainous Area

Soil erosion is a worldwide environmental hot spots. Soil and water conservation measures can protect, improve and rationally allocate the water and land resources through changing the local micro-topography, finally achieve the objective to prevent and control soil erosion. Current studies indicate that development and application of the erosion models contribute to soil erosion research. For assessing and applying the WEPP model in Beijing mountainous area, this study was conducted to calibrate and validate the WEPP model based on rainfall-runoff-erosion data of experimental plots, which placed at Soil and Water Conservation Science and Technology Demonstration Park, Yang Qing County. And then, combined with the analysis of WEPP model impact factors, we can simulate the erosion of the slope configured with different kinds of soil and water conservation measures. The main results are as follows:(1)The applicability assessment of WEPP model includes sensitivity analysis of soil parameters, model calibration and model validation. Under the premise of the establishment of the model database, the sensitivity analysis of soil parameters showed that the simulation value of runoff and erosion yield are sensitive to effective hydraulic conductivity, soil critical shear and rill erodibility parameters. By randomly selecting 14 rainfall events’(with different rainfall intensity) rainfall-runoff-erosion data and computing the accumulated error of simulated values and measured values, sensitive parameters were calibrated. Then, Nash-Sutcliffe efficiency and the coefficient of determination were used to perform model validation. The calibrated values of effective hydraulic conductivity, soil critical shear, and rill erodibility were 1.400 mm·h-1,2.750 Pa and 0.020 s·m-1, respectively. For the validation, the WEPP model presented a higher simulated accuracy for bare slope runoff than for bare slope erosion yield according to Nash-Sutcliffe efficiency of 0.731 and 0.674.(2) The impact analysis of slope length, rainfall and regional dimension factors can promote the understanding of the WEPP model simulation results. For the impact analysis of slope length factor, three kinds of runoff plots, which have different slope length but same condition, were selected for simulated values and measured values comparison. Results showed that the measured values of runoff decreases with the increasing of the slope length neither do the simulated one; however, both of the measured and simulated values of erosion yield increase with the increasing of slope length. For the analysis of rainfall factors, correlation analysis and path analysis were carried out to analyze the mutual impact among the runoff, erosion yield and rainfall factors. Rainfall factors include rainfall, rainfall duration, and maximum 30min rainfall intensity. Analysis results demonstrate that maximum 30min rainfall intensity has largest effects on runoff and erosion yield, followed by rainfall. Duration of rainfall has little correlation with runoff and erosion yield. The results of model applicability of five different regions shows that soil parameters of each region is substantially in line with the local soil characteristics, and applicability of model in each study depending on the number of samples and methods of obtaining soil parameters.(3) The WEPP model can be applied to simulate the erosion yield of slope emplaced with conservation measures, based on the results of elevation applicability and factor analysis. In view of the good validation results, we select horizontal bar slope and grassland measure to apply the WEPP model to simulating the soil erosion. There are two kinds of terrain file, one was horizontal bar slope with different slope length and different size, the other one was grassland slope with different coverage and different position. The results showed that, under 14 rainfall conditions, the erosion yield of horizontal bar slope, whose ratio of ramp potion and horizontal potion was 1:1, increased firstly and then decreased with the change of bar size. And the maximum erosion field appeared at the slope with 4 bars. However, the erosion yield of horizontal bar slope, whose ratio of ramp potion and horizontal potion was 1:2, gradually increased with the change of bar size. For the three different coverage grassland (with coverage of 10%,50%,90%), there are six kinds of configuration on different position on horizontal bar slope. Different configurations model simulated values showed that, the maximum erosion yield emerged at the slope whose low coverage grassland laid on the bottom; oppositely, the minimum erosion yield emerged at the slope whose low coverage grassland laid on the top.