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

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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.