WEPP模型中细沟可蚀性参数估计方法误差的理论分析

Theoretical analysis of estimation error of soil erodibility for rill erosion in WEPP model

细沟土壤侵蚀在坡面土壤侵蚀占有重要地位。土壤可蚀性参数是WEPP模型中计算预报/计算细沟土壤侵蚀中极其重要的参数。WEPP模型现在采用的可蚀性参数是用长的细沟/径流小区试验以细沟侵蚀产沙估计得到的最大可能剥蚀率为基础获得的。该文分析了细沟侵蚀产沙随沟长的变化关系,分析了可蚀性参数估计误差的来源。从理论上推导出了计算现有WEPP可蚀性参数估计误差的计算方法。理论分析表明,对于限定性细沟,可蚀性参数的估计误差主要来源于细沟最大可能剥蚀率的估计值。最大可能剥蚀率的理想估计值是水流载沙量与细沟长度的函数关系在细沟长度为0时的导数,而不是全沟长的平均剥蚀率。理论计算表明,已有方法估计得到的WEPP模型可蚀性参数,其误差可以高达90%以上,最低也在50%以上。从而,估计WEPP可蚀性参数的方法和可蚀性参数需要加以重新考虑。提出了减少误差方法的建议。

Rill erosion is of great significance in hill-slope erosion. Soil erodibility for rill erosion is a very important parameter for soil erosion prediction with Water Erosion Prediction Project (WEPP) model. The estimation of the soil erodibility needed by WEPP was based on the potential detachment rate of rill erosion, measured with long rill channel. The dynamical erosion processes along a rill caused estimation error of the erodibility. Theoretical algorithm was given for determining the estimation error of the present method. Theoretical analysis indicated that for a well-defined rill channel, the estimation error of erodibility was mainly from the error of potential detachment estimation. The ideal estimated value of the potential detachment rate was the derivative value, at the initial position, of the function between sediment load and rill length. Computated results showed that the error in erodibility presently used in WEPP model was as high as 90% with the lowest value being higher than 50%. Therefore, it was suggested that both the method and the erodibility data for the WEPP model need to be reexamined and reevaluated. Possible ways for reduction of estimation error of the parameter were suggested.