Calculation Model Of Sediment Loads For Medium And Small Rivers In Yunnan Province

There are many medium and small rivers in the mountainous areas of Yunnan Province.However,there are few hydrological stations in many basins,and few sediment observations are carried out,which brings some difficulties to the design and construction of water conservancy projects.At present,most of sediment loads for design medium and small reservoirs are approximately estimated based on soil erosion amount,which are much more than the actual sediment loads and increase engineering cost.Therefore,it's urgent to find a method with more accurate to estimate river sediment loads in medium and small rivers.Based on sediment transporting mechanism,we investigate the relationship between suspended sediment data from 20 hydrological station in Yunnan and land-use,soil distribution and some other environmental factors,obtain data of each factors by RS and GIS,established suspended sediment calculation model.The accuracy of the model is verified by the measured sediment data in Chahe reservior.The main results are as follows:(1)Based on six factors,such as soil erodibility(k),percentage of sloping farmland(P),percentage of sloped farmland with a degree above 25(P_k),catchment area(F),percentage of vegetation area in basin(V)and the frequency of rainstorm(R),Calculation model of the sediment transport for unit runoff depth of small and medium rivers in Yunnan Province is established as8)=^{0.4210.227-0.09}(1^-0.030.406.Then annual suspended sediment loads in the river can be calculated associated with runoff data.(2)Comparing the calculation results of the model with the measured sediment data,it is found that the measured sediment transport modulus per unit runoff is less than 2 t/(km~2·mm),the hydrological stations with error less than 30%account for 86%.In the basins of Irrawaddy River,Nujiang River and Lancang River in western Yunnan,hydrological stations with the error less than 30%account for 75%.(3)Using the model to calculate the sediment volume of the Chahe Reservoir,it's found that the annual sediment load calculated by the model of Chahe reservoir is 8.64×10~4 tons,much less than that is estimated as 18.39×10~4tons estimated by soil erosion amount.Our results are in close proximity to gauging value 5.97×10~4 tons at Chahe hydrological station.The research results provide sediment reference for the construction of water conservancy projects in medium and small rivers in Yunnan Province,and are of great significance for the reasonable planning of reservoir capacity and the saving of project cost,also act as a reference for the study of soil and water loss in Yunnan Province.