Best Management Practices For Water Conservation In Jinghe River Basin Based On SWAT Model

With the continuous development of China’s economy and society,as well as the acceleration of urbanization,the impact of human activities on the natural ecological environment is gradually becoming prominent.Under the influence of long-term unreasonable development and utilization,as well as changes in climate conditions,the ecosystem function of the Jinghe River basin has been severely damaged.The uneven spatiotemporal distribution of internal flow in the basin has led to water resource supply and demand problems,which have seriously restricted the high-quality development of regional economy and society.In response to the existing problems in the Jinghe River Basin,in response to the national requirements for ecological environment protection and high-quality development of the Yellow River Basin as a whole,improving the core function of the Jinghe River Basin ecosystem-water conservation,and formulating the best management measures(BMPs)for the basin can provide reference for practical application and implementation,which is of great significance for the ecological protection and high-quality development of the basin.This study takes the Jinghe River Basin as the research area,collecting and organizing digital elevation data(DEM),land use data,meteorological data,soil data,hydrological data,etc.On this basis,a SWAT model for the Jinghe River Basin was constructed.In addition,different extreme land use scenarios were established to compare and analyze the impact of different land use types on the runoff process in the Jinghe River Basin under different level year conditions.Finally,based on the analysis results,relevant national policies,and the actual situation of the Jinghe River Basin,the best management practices for improving the water-saving capacity of the Jinghe River Basin were proposed.The main results and conclusions of this article are as follows:(1)Collect and organize DEM,land use,soil,meteorological and other data of the Jinghe River Basin,and establish a daily scale SWAT model of the Jinghe River Basin.The model divides the Jinghe River Basin into 39 subbasins,249 hydrological response units(HRUs),and selects 20 parameters that affect runoff simulation for sensitivity analysis,The SWAT model was constructed using daily measured runoff data from Zhangjiashan Station in the Jinghe River Basin from 2006～2014 for calibration and validation.The warm-up period was divided into 2006～2007,the calibration period was 2008～2012,and the validation period was 2013～2014.The applicability of the SWAT model’s daily scale runoff simulation results in the Jinghe River Basin was evaluated using three indicators:the Nash efficiency coefficient NSE,determination coefficient R~2,and deviation percentage PBIAS,In the regular daily runoff simulation rate(2008～2012),R~2=0.64,NSE=0.63,and PBIAS=8.6.In the validation period(2013～2014),R~2=0.70,NSE=0.67,and PBIAS=14.8.Considering the difficulty of the model in simulating the daily runoff of the entire watershed during the calibration process,and on the basis of appropriately relaxing the accuracy requirements,the relevant indicators of the model(R~2,NSE have both exceeded 0.5)have met the evaluation criteria of the model,And it can basically accurately reflect the changes in the runoff process of the Jinghe River Basin under relevant influencing factors.This indicates that the established SWAT model is basically suitable for daily scale runoff simulation in the Jinghe River Basin and can be used for simulating the daily runoff process in the region.(2)The Sep Hydro tool was used for basic flow segmentation of watershed runoff processes.The application effects of Petty John&Henning’s fixed interval method,sliding interval method,and local minimum method,among the basic flow segmentation methods provided by Sep Hydro,were compared in the Jinghe River Basin.Finally,the Petty John&Henning(local minimum)with better segmentation effect was adopted,Using this method,the measured and simulated runoff processes in the watershed were segmented into basic flows,and the results showed that the constructed SWAT model in the Jinghe River Basin can accurately restore the basic flow process of the watershed.(3)Three extreme land use scenarios(forest land scenario,grassland scenario,and farmland scenario)were simulated for the annual runoff process of the Jinghe River Basin in wet,normal,and dry years.The impact of different land use types on the water conservation function of the basin was quantitatively analyzed.The results indicate that the forest and grassland in the watershed have a positive and significant effect on water storage and replenishment,reducing peak flow,increasing non flood season base flow,and improving the water conservation capacity of the watershed.The maximum peak flow reduction in forest scenarios can reach 810 m~3/s.At the same time,it can increase the baseflow rate by 9.59m~3/s.The maximum flood peak reduction in grassland scenario is 376 m~3/s.At the same time,it can increase the baseflow rate by 12.6 m~3/s;The increase in arable land will lead to more drastic changes in the annual internal flow process of the basin,with an increase in peak flow and a decrease in non flood season baseflow.Among them,the highest peak flow under normal year conditions will increase by 214m~3/s compared to the original scenario.And the baseflow of the watershed has decreased by 4.79 m~3/s.This indicates that cultivated land will weaken the function of water storage and replenishment in the watershed,which means the lack of water conservation capacity in the watershed.The impact of different land use types on watershed runoff process and base flow remains consistent under wet,normal and dry years.Overall,both grassland and forest land are beneficial for watershed water conservation,with grassland increasing more base flow,forest land having a significant effect on reducing flood peaks,and cultivated land having a negative impact on watershed water conservation capacity.(4)Based on the previous analysis and conclusions,different scenarios for the best management measures in the Jinghe River Basin have been set up:land with slopes of 6°,15°,and 25°above will be converted from farmland to forests;Implement measures to cover arable land with residues.And the above scenarios were simulated for runoff under wet,normal and dry years.The results indicate that the measures of returning farmland to forests can effectively improve the water conservation capacity of the watershed.The area of returning farmland to forests is positively correlated with the baseflow under various years,and the peak flow during the runoff process of the watershed has also been significantly reduced.The maximum flood peak reduction for the scenarios of returning farmland,returning farmland to forests,and closing mountains for afforestation under the conditions of wet years is 129m~3/s,214m~3/s,418m~3/s.The increase in baseflow is 0.930m~3/s,2.09m~3/s,4.82m~3/s.The residual cover measures that can change the vegetation coverage and surface roughness of cultivated land in the watershed can also improve the water conservation capacity of the watershed to a certain extent.Under the conditions of abundant water,the maximum reduction in peak flow is 38.1m~3/s,baseflow increased by 0.883m~3/s.And compared to returning farmland to forests,it is easier to promote and implement.