Soil And Water Loss In Puhe River Basin Based On RUSLE Model And Sediment Connectivity Index

Since the implementation of the Grain for Green Project,although the total amount of sediment in the Loess Plateau has decreased significantly,the sharp decrease of sediment discharge at the drainage basin cannot indicate that soil erosion on the Loess Plateau has been effectively controlled and solved,because the sediment discharge monitored at the drainage basin outlet cannot explain the process and degree of soil erosion and sediment transport within the basin.In this case,it is particularly necessary to evaluate the temporal and spatial changes of erosion and sediment yield in the Loess Plateau in order to make up for the lack of sediment transport information in the drainage basin,and to carry out research on soil erosion and sediment transport in the Loess Plateau.Therefore,this study focuses on the prominent water and soil loss issues in the Loess Plateau watershed,taking the typical watershed of the Loess Plateau-Puhe River Basin as the research object.Based on the analysis of the spatiotemporal characteristics of land use types at different stages(1990-2000,2000-2010,2010-2019)in the study area.The revised universal soil loss equation model(RUSLE)and the revised sediment connectivity index(RIC)were used to evaluate the changes of soil erosion and sediment connectivity before and after Grain for Green.Through the analysis of soil erosion and sediment connectivity,the temporal and spatial variability of sediment yield and sediment transport before and after Grain for Green was revealed,so as to make up for the shortage of information of sediment transport at the outlet of the basin.Identifying the key areas of water and soil conservation in the basin for promoting the ecological governance process in the Puhe River Basin.The main research conclusions are as follows:(1)With the implementation of the Grain for Green Project,the erosion intensity level of the watershed has shifted from moderate or above to slight erosion,with the erosion modulus effectively reduced,and the water and soil loss situation in the watershed has been significantly improved.In the past 30 years,90.26% of the basin showed a decreasing trend,while the areas with increased erosion intensity are mainly concentrated in the widely existing hills and valleys in the basin.These areas should be paid attention to when carrying out vegetation restoration or sediment reduction projects in the future.Watershed erosion varies significantly with elevation and slope,with an elevation of 1300-1700 m and a slope of 15-25° being the zone with the largest proportion of soil erosion area and amount,which should be focused on in future prevention and control work.(2)Linear regression fitting and significance level analysis indicate that the RIC index based approach is applicable in the Puhe River basin.Over the past 30 years,sediment connectivity in the watershed has decreased over time,making sediment transport increasingly difficult.The sediment connectivity of the basin varies significantly with elevation and slope changes.In low elevation zones,the path for sediment to reach the river channel is shorter which made it easier for sediment to transport to the river channel.However,the larger the slope,the less difficult the sediment transportation is.There is no significant difference in the minimum value of RIC in different periods under different land use types.The land use type with the highest average value of RIC is residential construction land,and the minimum value is forest land.For cultivated land and grassland,the vegetation coverage varies with the seasons,and there is no significant difference in the average RIC of the two land types.(3)It is necessary to consider both soil erosion and sediment connectivity in assessing watershed water and soil loss.The results show that areas with higher elevations in the upstream of the river basin have poor connectivity and vulnerability to erosion,while the middle and lower reaches close to the river often belong to areas with high erosion and high connectivity.The implementation of the Grain for Green Project has significantly changed the coupling between soil erosion and sediment connectivity in the Puhe River basin.The decrease in erosion and sediment connectivity does not occur simultaneously,but rather decreases sediment connectivity first.High erosion and high connectivity in the Puhe River Basin are mainly concentrated in the areas around the river network,which is still the main sediment sources and needs continuous attention in the future.