Study Of Slope Erosion And Control In Zhaigou Basin At Water Catchment Region Of Central Route For South-to-North Water Diversion Project

To improve the current situation of the worsening ecological environment in the water source area of the South-to-North Water Diversion Project and ensure the quality of transferred water, the Water and Soil Conservation Committee of the Upper Reaches of Changjiang River started a project "Protecting Water Source Area Project of the Central Route for South-to-North Water Diversion Project". Some counties such as Chenggu, Yangxian, Ningshan and Zhenping are classified as the first batch major construction county in this project. Zhaigou basin was located in Ningshan County of Shaanxi Province, and it was one of the first batch major construction counties in this project.Nine typical areas including sloping land, abandoned farmland, plantation and natural forest in the area with a degree above 25 in Zhaigou basin were chosen and studied in 2004. In this study, the parameters of rainfall, soil and water loss, runoff and sediment yield of river were observed and some conclusions were drawn as following:Ⅰ. Difference of the soil character and the vegetation existed in the different land use type. The soil granule and nutrient loss was serious in the surface layer of the sloping land and the soil quality was poor. The' abandoned farmland had a moderately thick humus horizon and the vegetation diversity was better. The soil quality was improved in the abandoned farmland which was deserted for about three years. The content of the different soil size fraction in the abandoned farmland which was deserted for more than five years leveled off and the granule content closed to that of the natural forest. The humus horizon thick in grassland reached up to 2.7cm and the vegetation was better. The plantation had a thicker litter and vegetation was better. The percentage of forest cover of the Virgin forest land was above 95%.Ⅱ. The vegetation and the soil and water conservation measures are favorable to soil conservation. For this reason, even the smaller rainfall can cause serious soil erosion in sloping land where the vegetation was poor and the soil and water conservation measure was lacked. However, this did not happen in the natural forest and the grassland which was deserted for more than six years. Even the heavy rainstorm, the soil erosion was slight. The soil and water loss varied greatly with the different land use and the order from the biggest down to the smallest was the sloping land, abandoned farmland, open woodland, grassland and natural forest. The soil and water loss of the sloping land was far more than the others'. Water and soil loss wasn't appeared in natural forest and grassland which was deserted for ten years. The artificial factor has an insignificant effect on the forest water and soil conservation. The field layer of plantation was favorable to the sloping field conservation and soil renew. The abandoned farmland which was deserted for three years had little water and soil loss and the vegetation restored well. The abandoned farmland which was deserted for more than seven years could form the grassland.Ⅲ. The rainfall has an influence on the soil erosion. There was a correlation between the rainfall and the soil erosion. The more the rainfall, the more the soil erosion. The correlation between the rainfall intensity and the soil erosion in the study area was lower. It could be concluded by analyzing the rainfall intensity and the soil erosion that there was no soil and water loss in the abandoned farmland which was deserted for more than three years, chinquapin forest and natural forest when the rainfall was smaller than 2mm/h.Ⅳ. The Annual rainfall erosivity in the Zhaigou basin was 1603.01 MJ·mm/hm~2·h and mainly concentrated on May, June, August and September in a year. Special attention to the water and soil loss and the debris flow in the slopping area should be paid especially in June and September when rainfall and soil erosion were strongest.Ⅴ. The main types of grain for green in Zhaigou basin were the living contour hedge technology, agro forestry model, forest-crop intercropping and enclosure. The agro forestry model and forest-crop intercropping can improve the yield capacity and accelerate the development of local economic. The sloping land and terrace which widely distributed in Zhaigou basin were suitable for living contour hedge. Eucommia which adapted to the local environment were planted as hedge which could hold soil and water better. At the same time, the eucommia was the high quality economic crops and can improve the farmers' income. The Imperata cylindrical, Artemis subdigitata, Artemisia lavandulaefolia and Setaria viridis were suitable for cultivating in the Zhaigou basin.