Simulation Of Sand Production And Its Mechanism Analysis In The Small Sandstone Basin Based On The AnnAGNPS Model

The Pisha Sandstone Region among Shanxi,Shannxi and Inner Mongolia is the source of the coarse sand in the Yellow River.The coarse sand comes from this area accounts for 69.2%of the total sediment load.The erosion amount is as high as 30000 to 40000 ton per squarekilometer a year.Zhungeer,with a large area of bare sandstone.is the most highly erodible area in China.Because it is hard for field monitoring,we decide to use the model to simulate the runoff and sediment of the ravine.By comparing different characters of the models,we choose AnnAGNPS and build the data base of the studied area to simulate the runoff and sediment yield in the area in different time scales. We used the method provided by Morse to analysis the sensitivity of different parameters to the runoff and sediment.Adjust parameters of the model before export the result. We get the best management by comparing two different soil and water conservation measures.In the end,we analysis the mechanism of the runoff and sediment yielding and give several countermeasures.The main achievements of this study are as follows:(1) We build the date base of the studied area and anaylsis the sensitivity of different parameters. We find that the most sensitive parameter for runoff is the value of CN,then is the soil available water content and the last is the field capacity.The sensitivity order of paramers for the sediment is vegetation coverage,CN,yearly root biomass,K,MN of the ravine, LS.Adjust parameters to get better simulation effect.(2)We simulated the runoff and sediment of different time scales from 2007 to 2012.Simulations in day scale showed that the sediment and runoff is directly proportion to precipitation.The ways of runoff yielding is different in different precipitation situations.When the daily precipitation is larger than 40mm,The sediment yielding changes greatly. Simulations in monthly scale showed that the runoff and sediment were different monthly.The erosion mainly took place in June to September,which account for 88.45% and 88.62%of the year respectively.The average amount of runoff and sediment yielding in August was higher than other months,accounting for 26.28% and 26.7% of the year respectively. Simulations of year scale showed that the runoff and sediment changes greatly among years.The average amount of runoff and sediment was 7.44million m3 and 2.382million ton respectively.The average runoff of per area was 30.77mm.The maximum sediment yielding is 4times greater than the minimum year.(3)The distribution of runoff and sediment is greatly different in this area,the northwestern area is higher than the southeastern area.The runoff depth was deepest inthe sandstone area,then was the grassland and the last was forest land.The most intensivily erosion area was also in the sandstone area,which yielding 15000 to 20000 ton per km~22 a year.(4)The Simulation result showed that returning farmland to grassland kept water more effectively and reduced 25.7% of the runoff.while growing the sea-buckthorn performed better in reducing sediment with a 20.1% reduction.But taken together,growing the sea-buckthorn is the best choice.(5)There are several erosion forms in the studied area consist of wind erosion,gravitational erosion,freeze-thaw erosion and water erosion.Water erosion is the mian form in this area.We buildt the overland flow erosion mechanical model and discussed the affect of different factors to the sediment yielding.In the end,we put forward several soil and water conservation measures.