Caesar Model-based Soil Erosion Research

Soil erosion is an environment problem in the whole world,and one of the most serious environment problems in China.Soil erosion can cause siltation of fiver, floods,soil degradation,nutrient loss and many other problems,which will significantly influence the global environment and social sustainable development.At present,soil erosion models have draw great attentions,but the models capable of simulating soil erosion at a catchment scale are relatively lacking.CAESAR, developed by Tom Coulthard of the Hull University,is an automaton model which can simulate the evolution of fiver channel and watershed terrain.So far it has been successfully used overseas,but without applications in China yet.In this paper, take the Longhekou reservoir catchment,Anhui Province as an example,the environmental settings specific for the hill lands in southern China are discussed for running the models first.Then the relationship between slope,vegetation coverage, rainfall and soil erosion are explored in a quantitative way,and some threshold values for the above factors are obtained.Using scenario analysis,soil erosion under a future rainfall increase and increased seasonality are modeled.The main conclusions are:According to the digital elevation model(DEM)analysis,slope in the studied catchment varies between 0-63°.Under the condition of 80mm rainfall and 50% vegetation coverage,the critical slope in the studied area is about 25°The areas with slope greater than 25°occupy 11%of the total catchment.Under the condition of slope with 18°,which is the average slope of the catchment,the model results show decreased soil erosion amount with increasing of vegetation coverage.Soil erosion declines dramatically when the vegetation coverage reaches 35-65%and show little decrease when the vegetation coverage exceeds 70%. It suggests that a 65%vegetation coverage can keep the soil in good conversation state.Rainfall is the key factor to soil erosion.In the studied area,the effects of rainfall amount and intensity are directly related with vegetation coverage.If the vegetation coverage is middle(55%)or low(30%),significant correlations are found between rainfall amount,rainfall intensity and soil erosion amount.But if the vegetation coverage is high(70-90%),the correlations between them are not very significant.Longhekou reservoir is located at the rainy center of Dabieshan mountain, annual precipitation is high and mainly concentrated in summer,in the past,many floods have happened.Under the trend of global warming and increased precipitation,soil erosion will be more severe in the study area.The scenario analysis shows that soil erosion will reach to the grade of 'serious erosion' 4727t/km~2/a if the rainfall is 3%larger than the present mean value(less than 4050 t/km~2/a)and more concentrated in the summer season.If there are extreme weather events,the soil erosion grade will be 'intensive erosion' that is:if the vegetation Cover is 20%,the erosion modulus will be 6554.47 t/km~2/a;if the vegetation Cover is 55%,the erosion modulus will be 4904.60 t/km~2/a,when the erosion modulus reaches to 90%,the erosion modulus will be 3550.06 t/km~2/a.The vegetation can relieve the soil erosion caused by the increased rainfall.So vegetation coverage can be increased to protect the soil from erosion.Many other measures,such as warping dam,ponds and reservoirs,can be used to decrease the soil erosion damage caused by increased rainfall.