Study On Application Of Soil Erosion Grading Index In Small Watershed In The Middle Reaches Of The Yarlung Zangbo River

The classification index of soil erosion is the water industry standard issued by the Ministry of Water Resources of the People’s Republic of China,which plays a vital role in the evaluation of regional soil erosion in China.At present,the latest standard being used is the Soil Erosion Classification and Classification Standard(SL 190—2007),which is revised according to the“Water Resources Technical Standards Preparation Regulations”(SL 1—2002)and the Soil Erosion Classification and Classification Standard(SL 190-96).Among them,the hydraulic erosion intensity classification is divided according to the soil erosion modulus calculated by the model method,and the soil erosion intensity classification result is obtained.The classification index is applicable to most areas in China,such as the northeast black soil area,the northern soil mountain area,and the southern red soil hills area,the southwest earth and rock mountain area,northwest loess plateau area.Due to the small amount of soil loss allowed in Tibet,the application of soil erosion grading indicators in Tibet remains to be explored.This thesis takes the Zhayeba small watershed in the middle reaches of the Yarlung Zangbo River as the research object.Based on RS and GIS technology,combined with ground survey,the CSLE model and multi-factor comprehensive method are used to evaluate the soil erosion in the study area,and a comparative study was carried out.The main research contents and achievements include the following aspects:1.Different methods of soil erosion evaluation in the Zhayeba small watershed in 2017.According to the Soil Erosion Classification and Classification Standard(SL190-2007),the soil erosion modulus obtained by the CSLE model was graded,and the soil erosion of the Zhaibaba watershed was quantitatively evaluated.The results showed that the average erosion modulus of the study area was 106.32t/(km~2·a),the soil erosion amount is 7522.14t/a,the soil erosion intensity is mainly micro-degree,the highest erosion level is only strong,and the erosion area is 2.61 km~2,accounting for 3.69%of the total area.The multi-factor comprehensive method was used to qualitatively evaluate the soil erosion of the small-salt flow in Zhayeba.The results were also dominated by micro-erosion,with an erosion area of 27.10 km~2,accounting for 38.30%of the total area.It can be seen that the results of the two are quite different.Combined with the field survey,the overall layout of the multi-factor comprehensive method results is relatively consistent.2.Difference analysis between CSLE model and multi-factor synthesis method.The results of soil erosion intensity,erosion area and overall layout are compared and analyzed.The results show that the highest erosion level of CSLE model method is only strong,only four erosion intensity levels,multi-factor comprehensive method results all strength levels are included;the erosion area is CSLE,the erosion area of the study area is 2.61km~2,and the multi-factor synthesis method is 27.10km~2 of erosion area and 24.49km~2 of erosion area.The overall layout is the overall distribution.There is a significant difference,but in detail,it can be seen that the mild erosion in the CSLE results corresponds to the strong,extremely intense region of the multi-factor synthesis method.3.Experiment and analysis of soil erosion grading indicators.Correlation analysis was carried out between the CSLE model and the multi-factor integrated method for the soil erosion intensity distribution raster layer.The correlation coefficient was 0.87,which was positively correlated and strong correlation.On this basis,the research program of soil erosion grading index was developed,and 8 sets of test results were obtained.The accuracy index was analyzed by using the difference index and relative error.The best test results were selected as the middle of the Yarlung Zangbo River.Grading indicators of soil erosion in the basin,ie micro-erosion:<30 t/(km~2·a),mild erosion:30~100 t/(km~2·a);moderate erosion:100~380 t/(km~2·a)Strong erosion:380~650 t/(km~2·a),extremely strong erosion:650~1200 t/(km~2·a),severe erosion:>1200 t/(km~2·a).