汛期洪水弃水与水土流失耦合风险关系分析

Relationship Between Surplus Floodwater in Flood Season and Coupling Risk of Soil and Water Loss

暴雨洪水是导致流域水土流失的一个重要因素,水土流失又会引起径流泥沙含量的增加,使汛期洪水弃水量加大,成为汛期洪水灾害发生的重要原因。以泾河流域为例,根据信息熵理论和USLE模型,提出约束信息量因子BI和水土流失耦合风险概念及其计算式,建立汛期洪水弃水系数与水土流失耦合风险等级之间的关系式,结果表明:①泾河张家山站以上流域1986、1995和2000年的水土流失耦合风险等级呈现出递减的趋势,分别为2.544、2.542和2.472;②汛期洪水弃水系数与水土流失耦合风险等级之间存在着显著正相关关系。

Rainstorm flood is one important factor resulting in soil and water loss of watershed.The soil and water loss can cause the increase of sediment concentration in runoff,which will add more surplus flood in flood season and consequently become an important reason for the occurrence of flood disaster.A factor of binding information（BI） was presented based on the information entropy theory.The BI is able to describe the uncertainty degree（i.e.,risk value） hiding in system before events happen.According to the BI values of different controllable-observable objectives（COOs）,the changing situations of uncertainty degree that events evolve from a COO to another one can be uncovered.So the BI is convenient to test risk changing of soil and water loss and reflect its evolution trend.In addition,the Universal Soil Loss Equation（USLE） has a preferable merit to describe and maintain the details of soil and water loss.Considering these characteristics of the USLE and BI,a notion of risk,coupling risk of soil and water loss,was proposed.The coupling risk is defined as the superposition results multiplied the BI by the factors in USLE.It can not only maintain the details of soil and water loss,but also describe the evolution processes of soil and water loss risk.On the basis of the presented coupling risk,a function relationship between sediment concentration in runoff and coupling risk grade of soil and water loss is established.A maximum rating method is employed to calculate the coefficient of surplus floodwater in flood season based on the independent variable of sediment concentration in runoff.Therefore,the relation between the coefficient of surplus floodwater and the coupling risk grade of soil and water loss is achieved with the intermediate variable of sediment concentration in runoff.A case study related to Jinghe River Basin with representative characteristics of floodwater resources utilization and soil and water loss has been performed.Results demonstrate that： 1） the coupling risk grades of soil and water loss for 1986,1995 and 2000 at the upper watershed of the controlled section of Zhangjiashan Station are 2.5437,2.5421 and 2.4722,respectively,which shows a total decrease trend of the coupling risk of soil and water loss in the basin;2） there is a prominent relationship at the confidence level of 0.01 between sediment concentration in runoff（y） and coupling risk grade of soil and water loss（x） as y=0.0108exp（2.4211x）.The square of correlation coefficient R is equal to 0.4037（R 2= 0.4037）.The higher the coupling risk grade（x） is,the larger the sediment concentration in runoff（y） is,vice versa;and 3） a prominent function relationship at 0.01 confidence level exists between the coefficient of surplus floodwater in flood season（y） and the coupling risk grade of soil and water loss（x） as y =0.0229exp（0.9937 x） R 2=0.3878.The bigger the coupling risk（x） is,the larger the coefficient of surplus floodwater（y） is,the larger the amount of surplus floodwater in flood season is,and the greater the flood disaster risk is.The results can provide a reference for analysis on relationship between the risks of watershed soil and water loss and flood disaster.