| In recent years,the urbanization process of the Yangtze River Economic Belt has accelerated,the coordination between regional economic development and resource and environmental carrying capacity has changed,and various phenomena of first destroying and then repairing and unreasonable construction behaviors in the development of water and soil resources are increasing,resulting in serious water and soil erosion in the river basin,ecosystem degradation,and decline in ecological services.This paper selects the Fujiang River Basin in the upper reaches of the Yangtze River as the research area,and analyzes the characteristics of runoff and sediment changes in the Fujiang River Basin over the years;by constructing the SWAT model of the Fujiang River Basin,and on the basis of examining the relationship between runoff erosion power and sediment transport,combined with runoff erosion The concept of power,in-depth analysis of the spatial distribution characteristics of runoff,sediment and runoff erosion power in the Fujiang River Basin,and explored the spatial scale effect of runoff erosion power in areas with severe water and soil erosion in the Fujiang River Basin;further applying the SWAT model in different scenarios,quantitatively analyzed The main research conclusions of this paper are as follows:(1)The annual distribution of precipitation and runoff and sediment in the Fujiang River Basin from 1960 to 2018 is extremely uneven.The annual precipitation,annual runoff and annual sediment transport are all concentrated in the June-September of the flood season,all of which are unimodal.The characteristics are basically the same.The interannual variation of annual precipitation and annual runoff is relatively gentle,the extreme value ratio of the annual sediment transport sequence is large,the coefficient of variation is high,and the interannual variation is severe.The results of trend test and mutation test show that there is no significant trend change in the precipitation series from 1960 to 2018.Both the runoff sequence and the sediment transport sequence have a significant decreasing trend,and show a positive continuity.The runoff sequence has a sudden change in 1994,and the sediment transport sequence has a sudden change in 1985.(2)The SWAT model of the Fujiang River Basin was established,and a total of 143 subbasins and 1943 hydrological response units were divided to distribute in the 4 hydrological stations Jiangyou Station,Santai Station,Shehong Station and Xiaoheba in the upper,middle and lower reaches of the Fujiang River The calibration of runoff and sediment data measured at the station verified the applicability of the SWAT model in the Fujiang River Basin.The Nash efficiency coefficient NS and the correlation coefficient R2 of the runoff and sediment inspection results of the regular and verification periods at each station were higher than 0.5,passing the index test.Based on the overall verification results of each station,it is believed that the constructed SWAT model is suitable for the Fujiang River Basin and can better reflect the real hydrological situation of the Basin.(3)Based on the runoff and sediment data measured by four hydrological stations from 2007 to 2018,the relationship between runoff depth-sediment volume and runoff erosion powersediment volume of Fujiang River was compared and analyzed,and the correlation between runoff erosion power and sediment volume was found Higher,indicating that the runoff erosion power can more accurately reflect the sediment transport in the Fujiang River Basin.Based on the simulation results of the SWAT model,runoff,sediment transport,and runoff erosion power have similar spatial distribution characteristics in the Fujiang River Basin.larger.Select the control area of the outlet section of each sub-basin as the spatial scale factor,and fit it with the corresponding erosion power.For the whole Fujiang River Basin,it can be seen that the erosion power decreases with the increase of the area,and the high mountain terrain with serious erosion is uplifted.The spatial scale threshold of runoff erosion power in the change area is 1030km~2.(4)From the analysis of land use changes in different years in the Fujiang River Basin,it can be seen that there are large areas of woodland and grassland in the upper mountainous areas of the Fujiang River Basin;the low mountains and hilly plains in the middle and lower reaches are mainly dry land and paddy fields.In the past 30 years,the forest land,urban,rural and construction land in the Fujiang River Basin have increased,while the area of dry land and shrubs has gradually decreased.Based on the SWAT model analysis of the water and sediment production characteristics of the main land use types,it can be known that the annual average runoff modulus of paddy fields,dry land,forest land,shrubland,and grassland in the watershed are similar,and grassland has the highest sand transport modulus affected by the slope of the mountain,followed by dry land.The simulation results of the model scenarios show that the measures of returning slope land to forests,fully converting dry land to paddy fields,and fully converting grassland to shrub and forest land all have a reduction effect on runoff and sediment production in the watershed,but the overall reduction is relatively small.From the perspective of spatial distribution,for areas with severe erosion,all scenario measures can produce strong soil and water conservation effects,which can greatly reduce soil and water loss in severely eroded areas. |
