Analysis about Effect Rules of Underlying Surface Change to the Relationship between Rainfall and Runoff in the Chabagou Catchment

Along with the increasing degree of human activities,the impact of land cover change on water resources becomes more and more serious,especially on surface runoff.In this paper,the precipitation experiment,which controlled by mankind in field,is carried out in the Chabagou Catchment.In this experiment, different type of land cover,degree of land cover and treating methods of surface layer are all considered to analyze the influence to hydrology process.Based on this experiment,the variation law of runoff coefficient with time under the condition of different degree of land cover,different tillage measures and different underlaying surface are discussed.At the same time,the variation law of runoff coefficient following the time for the same rainfall intensity is analyzed.The result shows that the change of land use type greatly affects the relationship between precipitation and runoff in the loess hilly-gully area.Additionally,the relationship between the precipitation and runoff is influenced more by tillage measure than the change of land cover.Only when the coverage ratio is changed from 100% to 50%,variance of stabilizing runoff yield less than 10%.But only when the cultivating measurement is used-the field is ploughed from 50% to 100%,the variance of stabilizing runoff yield about is 20%.Under the same rainfall intensity,the runoff yield in different type of land cover is very distinct,the runoff yield in grass field is 50% of the runoff yield in the bare land.The relationship between runoff coefficient and rainfall intensity can be described by using linear equation.The coefficient of first order is greater in the grass land than in the bare land,but the constant coefficient is less in the grass land than in the bare land.This relationship can show,when the rainfall intensity is less,the grass land have stronger water storage ability.But the water storage ability in grass land weakened rapidly along with the rainfall intensity increasing.In the bare land,the runoff coefficient doesn't change obviously along with the rainfall intensity increasing.The relationship between runoff coefficient and the period of rain time can be described by using logarithm equation.The constant coefficient is greater in the grass land than in the bare land.The difference of the rainfall coefficient between in the grass land and in the bare land is not obvious,when the period of rain time is increasing.