黄土高原小流域考虑坡度影响的径流曲线数优化

Optimization of Runoff Curve Number Considering the Effect of Slope on Small Watershed in Loess Plateau

坡度对产流过程有重要影响,将SCS-CN模型中的径流曲线数进行坡度修正对于提升模型预测精度具有重要意义,为了进行流域平均坡度在产流过程中的影响探究,以Huang坡度修正公式为基础,利用王家沟流域1955-1981年期间70场降雨径流实测资料中的前40场作为验证期资料,重新率定了Huang坡度修正公式中的a1,a2两个参数,提出了适用于王家沟流域的3种不同前期土壤湿度条件下的CN值坡度修正公式,以此建立了具有良好区域适用性的SCS-WJG方法并与SCS-CN查表法和直接移用Huang坡度修正公式的SCS-Huang方法进行比较。结论如下:使用遍历法确定的降雨初损率λ值为0.09,故标准值0.2不适用于王家沟流域。对比3种方法求出的CN值大小后发现使用SCS-Huang方法求出的CN值最大,SCS-CN查表法次之,SCS-WJG方法最小,从结果来看使用SCS-WJG方法进行模拟的精度更高,故用其计算得到的CN值更适用于王家沟流域。对比SCS-CN查表法与SCS-Huang方法后发现SCS-Huang方法纳什效率系数较低且均方根误差较高,因此提出适用于王家沟流域的CN值坡度修正公式并建立SCS-WJG方法是有必要的。当λ=0.09时,SCS-CN查表法,SCS-Huang方法的纳什效率系数分别为-2.85,-3.25,而SCS-WJG方法的纳什效率系数提高到了0.86,与前两种方法相比,SCS-WJG方法的均方根误差分别降低了77%,78%。SCS-WJG方法的模拟精度明显优于其余两种方法,说明SCS-WJG方法具有良好的区域适用性,可为小流域产流模拟提供参考。

Slope has an important effect on the runoff production process.Slope correction of runoff curve number in the SCS-CN runoff production model is important to improve the model prediction accuracy,In order to conduct an investigation of the effect of average watershed slope in the runoff production process,in this paper,based on Huang′s slope modification formula,the first 40 out of 70 rainfall runoff measurements in the study area from 1955 to 1981 were used as the validation data,and a1 and a2 parameters in Huang′s slope modification formula were re-determined,so as to propose the slope modification formula of the CN value for the study area under three different antecedent moisture conditions,and then the SCS-WJG method,which is of good applicability to the region,was established and compared to the SCSCN look-up table method,and the SCS-Huang method,which is a direct transfer of the Huang′s slope modification formula.The conclusion is as follows:theλ-value of the initial rainfall loss rate determined using the ergodic method is 0.09,so the standard value of 0.2 is not applicable to the study area.After comparing the size of the CN values obtained by the three methods,it is found that the CN value obtained by the SCS-Huang method is the largest,followed by the SCS-CN look-up table method,and the smallest is obtained by the SCS-WJG method,so the CN value obtained by the SCS-WJG method is more suitable for the study area as shown in the simulation results.Comparison of the SCSCN lookup table method and the SCS-Huang method reveals that the NSE of the SCS-Huang method is lower and the RMSE is higher;therefore,it is necessary to propose a slope correction formula for the CN value applicable to the study area and establish the SCS-WJG method.Whenλ=0.09,the NSE of the SCS-CN lookup table method,and the SCS-Huang method are-2.85 and-3.25,respectively,while the NSE of the SCS-WJG method is increased to 0.86,and the RMSE of the SCS-WJG method is reduced by 77%,and 78%,respectively,compared with the first two methods.The simulation accuracy of the SCS-WJG method is significantly better than that of the remaining two methods,indicating that the SCS-WJG method has good regional applicability and can provide a reference for the simulation of runoff production in small watersheds.