Study Of Ecological Water Supplement In Beijing-Tianjin-Hebei Region Based On The SWAT Model ——Case Study Of The Yongding River Basin And The Ziya River Basin

With the continuous development of the economy of Beijing-Tianjin-Hebei region and the yearly growth of urban population,the shortage of water resources and uneven distribution of water resources have restricted the development of regional economy,and the decrease of water resources and the increase of water demand have also brought about the contradiction of water supply and demand.The water ecological environment of the river basin has been damaged.In order to ensure the ecological flow of rivers and solve the ecological degradation problem in the basin,it is important to use hydrological models to simulate the hydrological cycle and recharge scenarios in the basin,and to find a scientific and reasonable ecological recharge plan for the ecological restoration of the basin.As a distributed hydrological model,SWAT model has a wide range of applications in runoff simulation and scenario change analysis.In this study,the SWAT model was constructed and its applicability was verified in the Hai River basin in Beijing-Tianjin-Hebei region,and the ecological replenishment simulation objectives were proposed for the problems of river disconnection in the Hai River basin of the Beijing-Tianjin-Hebei region.This study provides a theoretical basis and reference for the development of a reasonable and scientific ecological replenishment plan in the Beijing-TianjinHebei region to improve the water ecology of the river basin.1.In this study,based on the digital elevation model,land use type data,soil type data,and meteorological and hydrological data in the Beijing-Tianjin-Hebei region,the SWAT model for the Beijing-Tianjin-Hebei region was constructed,and 21 hydrological stations in the basin were selected,and the SWAT-CUP tool was used to perform sensitivity analysis,rate determination,and validate the simulation results for the model water parameters based on the runoff observation data of the hydrological stations from 2008 to 2016.The results show that the R2 of the simulation results for 18 of the 21 hydrological stations in the basin are greater than 0.6,the results of NSE are greater than 0.5,and the annual runoff errors of the remaining three hydrological stations are within the acceptable range,and the simulation results meet the simulation accuracy requirements,indicating that the constructed SWAT model applies to the study area.By analyzing the spatial distribution of basin runoff,combined with the Tennant ecological baseflow calculation method,we obtained that the ecological baseflow of the Ziya River and the Daqing River is smaller and the ecological water demand is lower,while the ecological baseflow of the the Luan River basin and the South Canal basin is larger and the average ecological water demand of the basin is higher.2..In this study,From the current situation of ecological water replenishment project in Beijing-Tianjin-Hebei region,we can see that the main sources of ecological water replenishment in the basin are water conservation project,South-North Water Transfer Project,Yellow River and Luan River Diversion Project,local reservoir storage,etc.Through the analysis of the actual river breakage situation in Beijing-Tianjin-Hebei region,it is concluded that the main river breakage in the basin is distributed in Yongding River Basin and Ziya River Basin,in which the plain section of Yongding River is dry without water all year round,and the river in Ziya River Basin has serious seasonal breakage.The ecological water replenishment target is proposed for the Yongding River basin and the Ziya River basin,in which the Daxing section of the Yongding River basin restores water to the river during the year（average annual cross-sectional flow ≥0m~3/s）,the Wuqing section restores water to the river for 150 days（May to September）,the Handan section of the Ziya River basin restores water for 180 days（May to October）,the Xingtai section and the Hengshui section of the river The water is restored for more than 300 days a year,and the water is restored for 120 days（June to September）in the river section of Cangzhou.3.Based on the ecological recharge simulation objectives,the Yongding River basin and the Ziya River basin were selected to simulate the ecological water recharge scenarios using the SWAT model.The results show that:（1）The recharge efficiency of the upper reaches of the Yongding River is higher through the Yang River tributary to the downstream,and the Yang River tributary is suitable for a long time and large volume recharge,while the Sanggan River tributary is more effective in a short time;choosing the Yang River tributary for recharge is more favorable to optimize the ecological recharge efficiency of the Yongding River and increase the volume of water into the Guanting Reservoir.（2）In the plain section of the Yongding River,the recharge effect of the multi-water recharge scenario using water saved from agriculture and industry combined with recycled water is the best,significantly increasing the runoff of the two sections and restoring water to the river for more than 300days;the target of restoring water to the Wuqing section can be achieved by increasing the water transfer of 22.5millionm~3/a based on restoring water to the Daxing section.（3）The Fuyang River basin is located in the upper reaches of the Ziya River has the Handan section and Xingtai section,which is setting the maximum water saving replenishment scenario based on the Handan section through the upstream replenishment of 100 million m~3/a can reach the May-October restoration of annual water days greater than 180 days,the river restoration runoff is greater than the ecological base flow,The Xingtai section through the upstream increase in replenishment of 150 million m~3/a can restore water days greater than 300 days But the restoration of minimum ecological flow requires an annual replenishment of more than 327 million m~3/a,and consider the single-channel concentrated time replenishment method in the upper reaches.（4）The Hengshui section and the Cangzhou section in the lower Ziyang River basin have better water-saving and replenishment effects than water transfer and replenishment effects under the same amount of water replenishment.The Hengshui section needs to replenish0.15 billion m~3/a under the maximum water saving in the basin to achieve the target of restoring water for the whole year,the Cangzhou section can achieve the target of restoring water under the latter four replenishment scenarios,and the Cangzhou section can achieve the target of restoring water due to the water replenishment through two water systems.The maximum restoration runoff at the Cangzhou section can reach 2.03 m~3/s,which is the ecological water requirement of the Ziya River basin,and the best ecological restoration effect of the river.Based on the current situation of water shortage in the watershed of the Beijing-TianjinHebei region and considering the actual situation of ecological recharge in the watershed of the Beijing-Tianjin-Hebei region,this paper uses the SWAT model to simulate the changes in river runoff under different ecological recharge scenarios,analyze the effect of runoff restoration under different scenarios,and make suggestions for optimizing the ecological recharge scheme in Beijing-Tianjin-Hebei region.