Regional Different Of Runoff And Sediment Yield In The Wei River Basin

As the largest tributary of the Yellow River, the Wei River is the 'Mother River' of Guanzhong region in Shaanxi province. It plays a very important role in the development of West China and the health of the ecosystem of the Yellow River. Runoff and sediment problem has been complicated in the downstream area of the Wei River Basin in the last several decades because of the Sanmen reservoir that rising the outlet water level, the excessive demand of the channel water resources and the precipitation reduction caused by the global climate change, and so on. The severe sedimentation and the frequent flood do not only affect seriously the Wei River healthy development, but threaten directly the people life and the property security of its lower reaches area. Therefore the Wei River already becomes one of the hot spot areas drawing wide social and study attention.The integrated management including of the runoff and sediment regular is the key method to solve the runoff and sediment problems of the whole Wei River. Soil and water conservation may reduce soil erosion on the slope and sediment load of the river that would alleviate the sedimentation and the water to flush the sediment into lower stream of the river; furthermore, the water cost of sediment control (the ratio of runoff reduced and sediment reduced in the same time) of different soil and water conservation practices varied greatly that water or runoff would increase when reducing the same weight of sediment through the distribution of different practices of water and soil conservation in different region of the basin. It is necessary to study the regional difference of the runoff and sediment yield rate and contribution of each units for better understanding of runoff and sediment yield pattern in the Wei River basin, and the results would also be scientific reference of river basin management and soil and water conservation planning in the Wei River basin.The dataset covers precipitation, runoff and sediment of 28 main hydrology stations from 1971 to1986, DEM with 90 meter resolution and vegetation are used to study the runoff and sediment yield and to divide the whole basin into different runoff and sediment generation units with GIS. The regional difference of runoff and sediment are analyzed. The main results are as following.(1) Hydrology regions and erosion sub-regions in the Wei River basin Based on the distribution of existing hydrology observation stations, topography, climate, vegetation, river system characteristic, the different indicator systems are selected to divide the hydrology and soil erosion sub-regions in the Wei River basin. The indicators for hydrology sub-regions include mean annual precipitation, runoff depth, runoff yield rate, runoff coefficient,and soil erosion sub-regions division using mean annual precipitation, sediment modulus, ground slope, mean drop slope and drainage density. With the fuzzy clustering analysis, the Wei River basin would be divided 3 one level of hydrology regions, and 11 two level of hydrology sub-regions, and then 3 one level of erosion regions and 13 two level of erosion sub-regions in the Wei River basin respectively.(2)Runoff and sediment simulation models and their suitability in the Wei River basinSCS-CN (runoff curve model of Soil Conservation Service, USDA) model is selected to simulate runoff in different hydrology sub-regions in the Wei River basin. The simulation shows that results of 20 of rainfall events, accounting for the total rainfall simulation 83%, are good and the SCS-CN model could be used to simulate the runoff in the Wei River basin.Mean annual precipitation P selected take as quantitative index of rainfall factors, ground slope, drainage density and NPP (Net Primary Pproductivity) are selected as variables of land surface in the Wei River basin, and the statistics model of sediment yield rate are regressed in different erosion and sediment regions. The model were tested with 28 field actual sediment data and 24 of field simulation results were good that the regression model could simulate sediment yields very well in the Wei River basin.(3) Unit of Runoff and Sediment production Divided in the Wei River basinThere are 46 runoff yield units of and 280 sediment yield units in the Wei River basin when using"hydrology- landform"composition and ARC GIS 9.0.Centralization of runoff was distributed to the lower Wei River and some branches of nanshan areas. Runoff production shows clearly zonal features, that is, from north to south, runoff process shows from small to large - smaller - larger process. Runoff yield rate of the northeast region located in the Wei River basin (above the Hongde stations) was the smallest, its produces yield rate runoff were less than 10,000 m3/km2·a. Runoff yield rate of the south region located in the Wei River basin, especially the south Wei River, was the biggest, its produces yield rate runoff were more than 200,000m3/km2·a.Sediment yield shows clearly zonal features slso, that is, from north to south, Sediment yield shows from small to large - smaller - larger process. Sediment yield rate of the northeast region located in the Wei River basin (above the Hongde stations), beiluo river catchment (below the liujiahe stations) was the smallest, its sediment yield rate was less than 1,000 t/km2·a. But between yangjiaping station,yuluoping station and hongde station in the jing river catchment, above of tianshui station in the main stream weihe catchment, above of liujiahe station in the beiluo river catchment were the biggest, its sediment yield rate was more than 5,000 t /km2·a.(4) Regional different of runoff and sediment in the Weihe River BasinThe annual mean runoff yield rate was equal to 53,700 m3/km2a, the annual runoff was 7,443,000,000 m3 in the Wei River basin. Runoff yield rate of about zhuangtou station in the beiluo river catchment was 47,100 m3/km2a, for 11.38% of the total output. Runoff yield rate of about zhangjiashan station in the jing river catchment was 37,600 m3/km2a, for 21.89% of the total output. Runoff yield rate of about huaxian station in the main stream of weihe catchment was 76,400 m3/km2a, for 66.73% of the total output. Contribution rate of runoff displayed that the beiluo river is the smallest, the main stream of weihe is the biggest, and the jing river is the next biggest. Its values were respectively 21.48%, 52.64%, 25.89%.The average annual erosion intensity in the Wei basin was 2796.03t/km2·a, and the total amount of annual sediment yield was 330,637,900 t; at the above of zhuangtou station in the beiluo river basin, which sediment yield yield rate was 2888.48t/km2·a, the total amount of annual sediment yield was 42,882,300t, for 12.97%; at the above of zhangjiashan station in the jing river catchment, which sediment yield yield rate was 3225.85t/km2·a, the total amount of annual sediment yield was 139,898,600 t, for 42.31%; at the above of huaxian station in the main stream of weihe catchment, which sediment yield yield rate was 2273.78t/km2·a, the total amount of annual sediment yield was 147,857,000 t, for 44.72%.The contribution rate of sediment yield per unit area was the smallest in beiluo river basin, for 22.3 percent, and jing river basin was the largest for 45.58 percent, followed by the main stream of the weihe basin for 32.13%, which further clarified the major regional of sediment yield was concentrated in the jing river watershed and the main stream of the weihe, for more than 77%.