【Objective】The research was conducted to generate a hydrologically correct DEM in Shaanxi and evaluate the DEM's accuracy.【Method】How to deal with original data rapidly and effectively was studied.From the presentations of terrain,river net and crossing validate,the Hc-DEM and DEM were assessed based on TIN(TIN-DEM).【Result】Hc-DEM can present topography well,and correctly present physiognomy,girder and chimb and stream network,the presentation for topography is better than TINDEM.【Conclusion】The DEM which uses ANUDEM to generate can well represent the real topography,while the quality of this DEM is better than TIN-DEM.For generating the DEM,three main parameters of ANUDEM including resolution,iteration number and 2nd roughness are 50,40,and 0.8 respectively.

It's the only way to extract slope and slope length based on low resolution DEMs for the studies of regional scale soil erosion modeling.But the slope will reduce and the slope length will enlarge.Based on the hydrologically correct DEM of 50 m and 10 m resolution using AUNDEM software in Yan'an and its surrounding areas of Shaanxi Province with the 1∶250 000 digital topographic maps and the typical area of this areas with the 1∶50 000 digital topographic maps,the derived slope and slope length from 50 m resolution DEM were re-scaled to similar to the slope and slope length from 10 m resolution DEM using histogram matching principle.Then the effects of the slope and slope length of pre and post of re-scaling on soil erosion intensity was evaluated and analyzed.Results show that re-scaled slope gradient becomes steep and the re-scaled slope length becomes short with similar histograms to high resolution's slope length when this method can promises space structure steadiness.Meanwhile,four datasets of soil erosion intensity are calculated with Chinese Soil Loss Equation(CSLE),including(a) slope and slope length unre-scaling,(b)slope re-scaling,(c)slope length re-scaling,(d)slope and slope length re-scaling.Results show that the(a) can obviously increase soil erosion intensity,the(b) can decrease soil erosion intensity,but the(c) can finally increase soil erosion intensity,which can provide more accurate data support for the soil erosion assessment.

It is essential for regional soil erosion survey and monitoring to calculate LS factor at the watershed and regional scales. Based on the theories of slope hydrology and soil erosion and the technologies of digital terrain analysis,the principles for slope and length factor are summarized and the methods and flowchart are suggested. By taking Xiannangou as an example,the LS themes are extracted and the characters are analyzed statistically and cartographically. The issues that should be studied urgently are discussed at last.

This study collected the daily precipitation data from 35 gauges in the period of 1953 to 2006,soil type map,a digital elevation model(DEM),data of soil and water conservation measures,land use maps interpreted from Landsat TM images acquired in 1986,1997 and 2006 and NDVI maps calculated from the images of the same period.Then we used the CSLE model to calculate soil loss amount of every grid unit with the soil erosion factors map layers,simulated soil erosion of 1997 and 2006 based on the state of soil and water conservation measures in 1986,and analyzed the impacts on soil erosion by soil and water conservation measures.Change of soil and water conservation measures from 1986 to 1997 and to 2006 decreased soil erosion amount by 960 000 t and 6 280 000 t in 1997 and 2006 respectively.Considering special rainfall character in 2006 different from the ordinary rainfall character in a long period,the decreased soil loess amount in 2006 by soil and water conservation is 1 400 000 t.This result would provide some references for benefit assessment of soil and water conservation.

This article inquired into talked about the improvements in calculating slope gradient,vegetation coverage and the working processes and working styles for soil erosion assessment,taking the Ansai County as an example.The results showed that: There were great change in slope gradient after re-scaling of slope gradient calculated from DEM with 50m resolution.Slope gradient in 98% of the studied area became larger with a varied extent.Mean slope gradient in the studied area increased by 14.5°.There was an increase in steep areas and a decrease in flat areas.The results of the slope gradient calculated were much more near the practical.The result of vegetation coverage calculated dy the improved method was smaller compared with the method by current method.Based on the improved method,the average of vegetation coverage decreased by 11.8%.Soil erosion assessment was calculated by computer automatically by the AML program.The assessment process was easy to repeat and the result was more impersonal and reasonable.

The purpose of this study is to explore the mapping methods for quantitative assessment of soil erosion in the provincial scale with the hoping of providing some technical support to the 4th national soil erosion survey by quantitative assessment of soil erosion in Shaanxi province. We collected the daily precipitation data, soil type map, land use map, digital evaluation map(DEM) and vegetation cover graphs of Shaanxi province, with the using of CSLE model to calculate the soil loss of this study area in 2006, and compared the results with the standard evaluation results of Ministry of Water Resources. We also explored the impact of transformation of slope and slope length in soil erosion. The results of quantitative assessment can reflect the influence of soil, climate and measures of soil and water conservation on soil erosion more accurately than the standard evaluation results of Ministry of Water Resources. There was a significantly effect after the slope and slope length had been transformed. The quantitative assessment by a soil erosion model and with the support of GIS, can reflect the soil erosion and its key impact factors efficiently and objectively. There is an extremely important reference value in regional governance and decision-aking. In order to reflect the true extent of soil erosion accurately, we must transform the slope and slope length during the evaluation.