Runoff And COD Pollution Load Of Different Land Use Types Based On SCS Model In Jianshan Small Watersheds

The study area locates in the upstream of Fuxian Lake, Jianshan River watersheds which is one of the main rivers into the Fuxian Lake. Based on the monitoring system of Jianshan River watershed during flood season of 2013-2014 and chooses the 4 land use types as the research objects: secondary forest, slope farmland, plantation, grassland of Jianshan River watershed. Based on the SCS model and the SPSS regression analysis, the article makes simulation study on the experimental zone of surface runoff and COD pollution load regularity by monitoring and analysis within Jianshan Riverwatershed.The results of the study are as follows:(1)If we directly use the CN value which is provided by American engineering han dbook and predict the rainfall surface runoff in the studied area based on SCS mo-del, t he effect is not ideal, relative error is very big and distribution is uneven. Most of the ru noff depth predicted value is higher than the measured values.(2)Based on the basic principle of SCS model, by the use of S inversion algorithm and SPSS curve regression tore-rate 8)′,get MSCS model.The results show that the prediction accuracy of model of MSCS was obviously higher than that of the original model of the SCS.(3)In order to improve the prediction accuracy of MSCS model, try to adjust rainfall early loss coeffic ient λ in the model, but it is hard to get a fixed λ to make the relative error between prediction value and measured values of MSCS model below 30% or smaller.When λ=0.2,MSCS model in prediction accuracy is the most accurate in the study area.(4)Analyzed separately AMCIII λ, under the condition of rainfall events, except irrigation lawn the rest of the class of λ values are unified, secondary forest of λ = 0.19, farmland λ= 0.17, plantation λ= 0.18. In the following order : secondary forest, slope farmland, plantation, grassland, the average relative error was 11.68%, 9.58%, 16.29%, 9.58%, and the model efficiency coefficient of 0.946, 0.992, 0.969, 0.975, respectively,by correcting the λ value of MSCS model.The revised MSCS model, despite of some short comings, the regulation of rainfall in the early damage need further study and validation, but for research trials of the runoff,it is still an effective exploration.(5)By using the method of mathematical calculation, it build a model based on MSCS surface runoff under COD pollution load model(abbreviation for MSCS-COD model), Through the verification, the average relative error in COD simulation value of the model in secondary forest, slope farmland, plantation, grassland is 12.03%, 3.39%, 6.80%, 9.29% respectively. The model of correlation coefficient R2 is 0.750, 0.881, 0.777, 0.764.MSCS-COD model validation and debugging need further research, but the building methods can provide the reference for the model building of widespread pollution output on other surface runoff.