Analysis Of Runoff Variation In Qujiang River Basin Based On SWAT Model

With the rapid development of socioeconomic,the whole ecosystem is affected more and more seriously by human disturbances,especially on water resources and water environment in some regions.Therefore,it is of great significance to study the ecohydrological processes on large-scale in order to evaluate the water quantity and water quality accurately.As a mature distributed hydrological model,SWAT model has been widely used in the research of many regions in the world.In China,more and more attention has been paid to the influence of land use /cover change on water cycling and flood disaster.In recent years,the contradiction between supply and demand of water resources in Zhejiang province has becoming increasingly serious,besides,soil erosion has also been very serious,which not only affects the development of local industry,but also on the production of human life.In this context,this study chose Qujiang basin as the research object.Based on the data of vegetation,climate,soil,hydrology and map of Qujiang Basin,the SWAT model of Qujiang River Basin was established based on Arc GIS10.3 platform.After the simulation operation was completed,the sensitivity analysis and calibration of the model parameters is conducted using SWAT-CUP,finally we obtained the parameters of runoff sensitivity and readjusted the parameters with high sensitivity.In the met step,R2 and Ens were selected as indicators to calibrate and validate the simulation results using runoff data of Kaihua County from hydrological observation station of2008-2014.Then GIS technology was used to converse farmland into woodland and orchard land respectively,to establish runoff of the two types under simulation and compare the status of land use types of map,type 1 and type 2 so that to investigate the effects of two kinds of situation of returning farmland to forests and artificial economic forest on runoff output changes in the region.Main conclusions including:1 Through the simulation of Qujiang basin runoff and using SWAT-CUP,we selected parameters with higher sensitivity,such as SOL_Z,CH_K2,ALPHA_BF,GWQMN,ESCO,and SOL_AWC.Then the model was calibrated with the monthly measured runoff data of Kaihua from 2009 to 2011 to verify the monthly runoff flowrate of 2012~2014 the results showed that average monthly net flow error was less than 10%,and the correlation coefficient of the calibration and verification period were greater than 0.90,besides,the Nash coefficient was greater than 0.80,which had a certain credibility so that the model simulation in Qujiang basin was reliable.2 We discussed the effects of different land use scenarios on runoff and found that type one decreased surface runoff by 16.64 mm when all arable land were transferred into forest land,the flow measurement increased 1.44 mm and the reflux increased 13.43 mm,besides,the transpiration sporadic content was increased by 1mm.The above results showed that the conversion of cropland into forest could reduce surface runoff and increase the ability of water conservation by plants,and to achieve the effect of soil and water conservation.In the case of type two,the surface runoff was reduced by 10.90 mm and the flow rate was increased by 4.66 mm,meanwhile,the reflux was increased by 12.08 mm and the transpiration was reduced by 6mm.Transferring economic forestland into forest and orchard reduced the runoff and also increased the absorptive capacity of soil water,and plant transpiration was decreased,which indicated that part of the hilly terrain with relatively slow slope could be transferred into economic forest in some cases in order to benefit the soil and water conservation and to improve the water conservation capacity of soil.