Under The Conditions Of South-to-North Water Diversion Prediction Study Of Surface Water And Groundwater Exchange In The Liangji Canal Region

The implementation of the South-North Water Transfer Project has effectively alleviated the contradiction between water supply and demand in the northern receiving areas,and has contributed to the economic,environmental and social development of cities and towns along the route.Most of the South-to-North Water Transfer Project uses natural rivers or channels to transfer water,which changes the water level of rivers and canals,thereby affecting the relationship between surface water and groundwater recharge and discharge.The South-North Water Transfer Project uses the unlined Liangji Canal to transfer water to the South-South Lake and Dongping Lake section,which fundamentally changes the water flow conditions of the Liangji Canal from north to south to south to north;during non-transfer periods,high water levels are maintained to meet navigation requirements.The above changes affect the surface watergroundwater exchange in the Liangji Canal area,and the current research on the operation of the South-North Water Transfer mainly focuses on the optimal scheduling of water resources,water quantity and water quality,but there is little research on the impact of different water transfer conditions on the surface water-groundwater exchange.Therefore,this paper takes the Liangji Canal area as the research object and conducts a study on the impact of South-North water transfer on surface watergroundwater exchange,which can provide a reference for the fine scheduling of the water transfer project’s downstream diversions and is of great significance to the operation and management of the Eastern Route Project.The main research contents and conclusions are as follows:(1)Calculation and analysis of seepage losses in the Liangji Canal under water transmission conditions.The results of the traditional Kostiakov empirical formula are fixed values,which cannot fully reflect the dynamic characteristics of water transmission losses along the course of the river when applied in unlined sections with large geological changes along the course.In order to overcome the limitations of the original formula,the Kostiakov empirical formula was improved using the integral science method and the generalised simple gradient method,and the improved formula was used to calculate and analyse the seepage losses under different water transfer conditions.The results show that the improved Kostiakov empirical formula method has effectively improved the calculation accuracy,and the average relative error between the calculation results and the measured data before and after the improvement has been reduced from 19.49%to 7.37%.Under the three water transmission conditions of 80 m3/s,100 m3/s(design flow)and 120 m3/s,the calculated seepage losses are 44,817,700 m3/a,50,773,300 m3/a and 59,634,800 m3/a respectively.(2)SWAT model construction and surface runoff simulation in the Liangji canal area.Different water transfer conditions have an important influence on the seepage losses of the Liangji Canal,but for year-round water transfer,the influence of rainfall needs to be considered.Therefore,the SWAT model was constructed based on the data of DEM digital elevation,land cover,soil type and hydrological information in the study area,and the surface runoff in the Liangji Canal area was simulated,and the measured data from Houying hydrological station were used for rate determination and validation to lay the foundation for the coupled surface water-groundwater simulation.The results show that the constructed model can better simulate the surface runoff in the study area,with determination coefficients R2 of 0.90 and 0.88 for the rate period(2014～2016)and validation period(2017～2018),and Nash coefficients NSE of 0.86 and 0.83,respectively.(3)Coupled surface water-groundwater simulation and analysis under the Liangji Canal regional water transfer conditions.As the groundwater simulation software Visual MODFLOW has the limitation that the infiltration process of rainfall is not finely carved,in order to fully consider the influence of flood rainfall on groundwater,ArcGIS software was used to realize the spatial correspondence between SWAT hydrological response cells and Visual MODFLOW orthogonal grids,and water transfer conditions were set in the source and sink items to realize the construction of the coupled model.The groundwater level data were also used for rate determination and validation,and the surface water-groundwater conversion was simulated under the water transfer conditions.The results show that the coupled model can better simulate the dynamic changes of groundwater in the study area,and the simulated water level errors of monitoring wells in the rate period(2013～2016)are less than 1m,and the R2 and root mean square error RMSE in the validation period(2017～2018)are 0.89 and 0.17 respectively.(4)Prediction and analysis of surface water-groundwater conversion under different water transfer conditions.Based on the NAR neural network to predict rainfall and evaporation from 2019 to 2025,the coupled model has been constructed to predict and analyse the surface water-groundwater exchange under three different water delivery conditions of 80m3/s,100m3/s(design flow)and 120m3/s from 2019 to 2025.The results show that,spatially,surface water and groundwater recharge each other in the Hukou～Changgou and Denglou～Baliwan sections of the Liangji Canal,and the river water in the Changgou～Denglou section recharges groundwater by seepage all year round.In terms of time,the multi-year average surface water-groundwater exchange volumes under the three water transfer conditions are 20,878,900 m3,24,681,400m3 and 25,213,700 m3 respectively;the surface water-groundwater exchange volumes during the flood season are 16,252,000m3,20,929,300m3 and 20,304,900 m3 respectively,accounting for 84%,77%and 80%of the annual surface water-groundwater exchange volumes respectively 77%and 80%respectively.