STUDY ON ANALYTICAL MODEL OF RUNOFF-EROSION DUE TO RAINFALL IN BRAZILIAN SEMI-ARID REGION

本文用物理模式分析了巴西东北部半干旱地区降雨径流侵蚀的特征。本研究分为三个部分：径流侵蚀模型、模型参数最优值的确定、模型的现场应用。主要结论如下：1.坡面径流-侵蚀数学模型的研究用运动波理论分析了多雨条件下的面流和沟流，在模型参数选取合理的情况下，可以较好地模拟出坡面径流和沟流对土壤的侵蚀速率.模型参数最优值的确定研究用改进的遗传算法对模型参数中的四个主要参数：降雨冲击可分离性Ki、剪应力可分离性Kr、挟沙系数a和土壤水张力参数Ns进行了优化，并结合现场实测资料进行了验证.用改进的遗传算法优化模型参数，对巴西试验田和Matuyama Ishle河流域的径流冲刷资料进行了较好的分析。

THE CHARACTERISTICS OF RUNOFF-EROSION DUE TO RAINFALL IN THE SEMI-ARID REGION OF NORTH-EAST BRAZIL, WERE ANALYSED BY A PHYSICAL MODEL. THIS STUDY CAN BE DIVIDED INTO THREE PARTS: RUNOFF-EROSION MODEL, DETERMINATION OF THE OPTIMAL VALUES OF MODEL PARAMETERS, APPLICATION OF THE PROPOSED MODEL TO THE FIELDS. MAIN COCLUSIOS ARE AS FOLLOWS:1. STUDY ON PYSICAL RUNOFF-EROSION MODELSURFACE FLOW AND CHANNEL FLOW OF EXCESS RAINFALL ARE ANALYSED BY THE KINEMATIC WAVE THEORY AND THE EROSION RATE OF SOIL SURFACE WITH THE FLOWS ARE SIMULATED WELL IF THE MODEL PARAMETERS ARE PROPERLY GIVEN.2. STUDY ON DETERMINATION OF THE OPTIMAL VALUES OF MODEL PARAMETERSVALUES OF FOUR MAIN PARAMTERS OF THE MODEL PARAMETERS, SOIL DETACHABILITY BY RAINFALL IMPACT Ki, SOIL DETACHABILTY FOR SHEAR STRESS Kr, COEFFICIENT FOR SEDIMENT ENTRAINMENT a, AND SOIL MOISTURE-TENSION PARAMETER Ns ARE OPIMISED WELL BY A MODIFIED GENETIC ALGORISM WITH OBSERVED DATA IN THE TEST FIELD.3. STUDY ON APPLICATION OF THE PROPOSED MODEL TO THE FIELDSRUNOFF-EROSION DATA FROM THE TEST FIELD IN BRAZIL AND ISHlE RIVER BASIN IN MATUYAMA ARE ANALYSED WELL BY THE PROPOSED MODEL WITH PARAMETERS OPTIMIZED BY THE MODIFIED GENETIC ALGORISM.