Soil Erosion And Sediment Yield Characteristics And Check Dam Construction Demand In The Yellow River-Huangshui River Valley

Yellow River-Huangshui River Valley（YHV）is located in the transitional zone between Qinghai-Tibet Plateau and Loess Plateau in the middle and upper reaches of the Yellow River Basin.It is of great significance to grasp the characteristics of soil erosion and sediment yield of the YHV for the national key control area of soil and water loss in the Ganqingning Loess Hills and the erosion control function in the upper reaches of the Yellow River.In recent years,under the joint development of ecological restoration and urban construction,land use has changed dramatically in the YHV,but how will soil erosion change,whether the check dam can meet the local demand,and whether the check dam should be built vigorously in the future have not been clearly answered.Therefore,this study takes YHV as the research object and the recent 20years of grain for green and the develop-the-west as the research period.By using the investigation of sediment information of typical dam-controlled watershed and soil erosion evaluation based on RUSLE model and SEDD model,the spatio-temporal variation characteristics and the key areas of soil erosion and sediment yield of the study area in the past 20 years were analyzed,and the matching relationship between sediment retention demand and supply measures was determined on the small watershed scale based on the type,distribution and sediment retention function of the check dam.,which can provide a scientific basis for the design of local water and soil conservation scheme.The main conclusions are as follows:1.The characteristics of sediment yield in six typical dam-controlled watersheds in the YHV are significantly different.The sediment yield modulus ranged from 6.92to 634.30 t/（km²·a）,and the average annual precipitation events were 0.6 to 7.5 times/a.The sediment yield intensity in six typical dam-controlled watersheds all showed an increasing trend with the increase of rainfall and PI₃₀.However,the sensitivity to rainfall among small watersheds because of the vegetation coverage and terrace proportion,which was manifested as the higher the vegetation coverage and terrace proportion,the lower the sediment yield intensity of small catchments.2.The regression analysis of the simulated sediment yield in the YHV and the average annual sediment deposition amount and the total amount in six typical dam-controlled watersheds in the past 20 years shows that the method combined with RUSLE model and SEDD model in this study has high accuracy.The soil erosion modulus and sediment yield modulus gradually decreased by 21.98%and 36.25%respectively during the past 20 years in the YHV.In terms of spatial distribution,the erosion modulus and sediment yield of the river valley slope within 3～5 km from the Yellow River and Huangshui River were weakened both inward and outward.The project of grain for green had a significant controlled effect on soil erosion in the YHV.The two modes of returning farmland to forest land and grassland both led to positive benefits of soil conservation.The soil conservation efficiency is higher in returning farmland to forest land,and the Chuanshui area is better than the Qianshan area.3.There are 928 dams in the YHV,with a density of about 0.03/km²,which are mainly medium dam and dam with only dam body.In terms of spatial distribution,there are more dams in the central part and less dams in the south and north,The relationship between each dam and its dam-controlled watershed is that the sediment retention capacity is greater than the sediment yield capacity.About 97.88%of the dam sediment retention function fails to play,and the sediment yield within the control watershed of dam only accounts for 4.54%of the YHV.This indicates that the spatial distribution pattern of dam and erosion-sediment yield is quite different,and dam still need to be built.4.With soil erosion intensity greater than 1000 t/（km²·a）as the scope of treatment,about 2531 small watersheds need to be controlled in the YHV.Without taking other measures into consideration,it is estimated that 2943 dams need to be built in the YHV,including 73 key dams,255 medium dams and 2615 small dams,which are mainly distributed in the Qianshan areas along the banks of the two rivers,according to the sediment yield of the small river basin and the sediment holding capacity of the dam reservoir measures.It is necessary to adjust the proposed siltation dam by considering the economic cost and ecological construction results.