Study On Hydrology And Sediment Response Based On Sensitive Area Identification Of Soil Erosion And Optimization Of Cultivated Land

In this paper,we took xixian basin upstream of the huai river as the research object,under the guidance of ecological planning theory,through the evaluation of soil erosion sensitivity（risk）,and identified the regional of soil and water loss risk in the basin in the future.Cultivated land is the land use type that is most prone to soil erosion and should be partly converted into woodland to slow basin soil erosion,therefore,ecological suitability evaluation of cultivated land in the research area is carried out in this paper.On the basis of sensitivity evaluation of soil erosion and suitability evaluation of cultivated land,three kinds of soil and water conservation scenarios compared to the current situation of land use in 2015 were constructed,and the sediment and hydrological response in various scenarios were simulated by the SWAT model,in order to verify the role of soil and water conservation scenarios in preventing soil erosion in the basin.The research conclusions obtained here are as follows:（1）The spatial database of the xixian basin was established,and after the watershed topographic analysis,the watershed digital river network was extracted with the minimum catchment area threshold of 20000 ha,and the threshold value of hydrological Response unit was 0/2/2,and the watershed was dispersed into 15 sub-basins and 265 Hydrologic Response Units（HRUs）.（2）Using the land use data in 2000 to simulate the monthly sediment and runoff on the scale of 1996-2003.The model efficiency was measured using the naxi coefficient Ens,the correlation coefficient R² and the bias percentage P_BIAS.The results showed that during calibration and validation period,the Ens of the monthly runoff rate were 0.92 and 0.79respectively,and the R² were 0.93 and 0.81 respectively,and the P_BIAS were-8.98%and-6.65%respectively,so the simulation accuracy was high.And during calibration and validation period,the Ens of the monthly sediment rate were 0.67 and 0.78 respectively,the R² were 0.69 and 0.81 respectively,and the P_BIAS was-9.27%and-16.39%respectively,so the simulation accuracy was good,which indicated applicability of the SWAT model in the research area.（3）According to the general equation of soil erosion,the influence factors of soil erosion include rainfall,slope gradient and length,soil texture and vegetation cover condition,so the sensitivity evaluation of the above four impact factors is carried out separately.The results showed that the effects of rainfall and soil texture on soil and water loss were significant,and the slope and slope length had a small effect,and the vegetation coverage was good in the study area,and the contribution to soil erosion was small.（4）Using geometric mean method to carry on the comprehensive evaluation of soil and water loss,the results show that area of soil erosion risk were mainly distributed in part of nanyang and xinyang in henan province,and xiaogan and suizhou in hubei,than easily happened soil erosion area account for 6.71%of the total basin area,area of high soil erosion risk accounted for 14.54%,moderate risk of soil erosion area accounted for27.43%,mild soil erosion risk areas account for 27.19%of the total area in this basin.（5）Four evaluation indexes,such as terrain conditions,soil conditions,weather conditions,location conditions,and ten evaluation factors such as elevation,gradient,slope direction,soil organic carbon content,ph,soil texture,soil ph,average annual rainfall,accumulated temperature greater than or equal to 10℃,the distance from the water,the distance from the town,were chosen to evaluate the farmland suitability.Using hierarchical analysis method and expert scoring method to calculate the weight of each evaluation index and evaluation factor,the sum of weighted index were cultivated to get land suitability.The analysis on the suitability of cultivated land in areas sensitive to soil and water loss shows that 64.8 km2 is not suitable for cultivated land and 1990.08 km2 is generally suitable for cultivated land.（6）Three kinds of land use situation of soil and water conservation were constructed,scenario 1 is the area both sensitive to soil and water loss and not suitable for cultivated land returning farmland to forest area,scenario 2 is all regions not suitable for arable land returning farmland to forest in the studied area,scenario 3 is all regions sensitive to soil erosion in the area study returning farmland to forest.Using the verified SWAT model,to simulate the sediment and hydrological variables during the periods from 1996 to 2003 in the above three scenarios and the existing land use conditions of 2015,maintaining topography,meteorology and soil conditions.The results showed that,in terms of the average annual sediment yield and average monthly sediment yield,land use scenario in2015>scenario 1≥scenario 2>scenario 3,largest area of farmland returning to forest in scene 3 is bad for protection of cultivated land and the development of local agriculture,farmland return to forest in scene 2 is larger than scenario 1,but resulted in same sediment reduction effect,so scenario 1 was considered the optimal situation of soil and water conservation.（7）Using the SWAT model to model the basin surface,surface runoff,vapor emission quantity and total water volume under three types of water and soil conservation scenarios,the results indicated that surface runoff and total water production gradually decrease,while the surface runoff gradually increases.Therefore,the decrease of cultivated land area and the increase of woodland area in the research area brought by the conversion of farmland to forest will play an important role in the conservation of water resources and the reduction of water loss in the river basin.At the same time,the reduction of surface runoff will play an important role in the hydraulic erosion of soil,providing an important basis for soil and water conservation and land use planning in the river basin.