| Due to the development of urbanization,the karst water supply area of Jinan City has been destroyed,and the effective infiltration of the direct supply area of spring water has been reduced,which threatens the normal gushing of spring water.Therefore,Jinan City proposes to reduce the groundwater exploitation in the direct supply area and the indirect supply area,and introduce the water from the Yellow River and the Yangtze River into the East Route Project of South to North Water Diversion(SNWD)and the water diversion project from the Yellow River.Using external water to replace the local groundwater effectively reduces the exploitation of groundwater,but the quality of external water is obviously worse than the local karst groundwater in Jinan.To ensure that the water quantity and quality meet the requirements of economic and ecological benefits in the process of source replenishment,it is proposed to transform surface water into high-quality groundwater through the managed aquifer recharge(MAR)technology,which can not only raise the karst water table of western of Jinan,but also effectively improve the water quality.Yufuhe River Basin,located in the west of Jinan,is a unique place for recharge,with the advantages of sufficient source water and strong permeability.Five automatic monitoring wells were set up in the reach from Dongkema to Cuima village in Yufuhe River strong seepage zone,which can monitor the impact of recharge on water table and water quality in real time.The monitoring results showed that the water table responded quickly and rose greatly,indicating that the aquifer had good permeability.However,the continuous discharge of water makes the water table higher than the quaternary floor,and part of the water was discharged downstream from the quaternary pore water and surface water,resulting in invalid recharge.Moreover,the water quality of the SNWD Project is quite different from that of the local groundwater.Through the investigation of the background value,the sulfate content of SNWD Project water is 344mg/L,and the TDS value is 1100 mg/L,which exceeds the standard value of groundwater.Through the interaction between the recharge water and the local groundwater,the TDS value and sulfate content in the groundwater rises rapidly,and the groundwater quality presents potential risks.Aiming at the problems of water quantity and quality in the long-term recharge of Yufuhe River with SNWD Project water,this paper established a semi-coupled numerical model to simulate and predict the interaction process of water quantity and quality between rivers and groundwater in different situations,and puts forward an efficient water discharge scheme and reasonable water quality improvement measures.(1)To solve the problem of invalid recharge water,a semi-coupling model of river-groundwater was established by using HEC-RAS and HYDRUS-3D.Based on HEC-RAS,the hydraulic model is established,and the water surface lines corresponding to the water discharge volumes of 350000,300000,250000,20000 and 150000 m~3/d are calculated by the hydraulic model;based on HYDRUS-3D,the groundwater model is established,and the water surface profile line are input into the groundwater model with initial water depeth of 40,30 and 25 meters as the constant head boundary,and the effective recharge rates under 15 scenarios are calculated.The results show that the optimal drainage scheme is 200000 m~3/d,and the effective recharge rate is 67.20%,68.28%and 68.69%respectively when the buried depth is 40,30 and 25 meters.Before the water recharge,the groundwater depth can be obtained by monitoring well.Combined with the optimal water discharge volume,the corresponding optimal water discharge amount and time can be selected,and the efficient water discharge scheme can be formulated to reduce the invalid supply.(2)In view of the problem of water quality risk,in order to better reflect the impact of Yufuhe River recharge on the overall karst groundwater quality in Western of Jinan,MODFLOW with scale advantage is selected to establish a three-dimensional groundwater solute transport numerical model of complete hydrogeological unit in Jinan Spring Area.Combined with the advantage of HYDRUS-3D which can simulate the flow movement of unsaturated zone,a three-dimensional solute transport numerical model of saturated-unsaturated zone is constructed to simulate the influence range and degree of concentration field in the process of physical mixing of SNWD water with high TDS concentration and local groundwater with low TDS concentration.The TDS values of six water sources in western of Jinan are predicted after 10 years of continuous water recharge by SNWD with the optimal water release scheme.The simulation results show that except qiaozili,the TDS values of other water sources have increased in varying degrees,with an average increase of 95.52 mg/L.The affected area determined by 510 mg/L isoline with 289.3km~2 accounts for 22%of the total area of Jinan spring area;the excessive value area determined by 1000 mg/L isoline with 20.25 km~2 accounts for 7%of the affected area.The results show that the karst groundwater in western of Jinan will face potential water quality risk if Yufuhe River continues to use the SNWD water recharge and only recharge but not exploits mode.(3)Aiming at the problem of improving water quality,it is proposed to increase the exploitation amount of six water sources in the lower reaches,pump out the high TDS concentration recharge water,replace and renew the groundwater,and reduce the TDS concentration.Four pumping schemes of 0%,50%75%and 90%recovery ratio,are simulated to observe the degree of TDS reduction and the change of water table.The results show that,compared with the zero exploitation,the TDS concentration of 50%75%and 90%recovery ratio decreases successively;the TDS recovery reduction rates are 27.89%,46.83%and 64.10%respectively;the reduction efficiency is 55.80%,62.44%and 71.23%respectively.The results show that the effect of reducing TDS with 90%recovery ratio is better than the other two schemes.Based on the analysis of water table changes in water source areas under three recovery ratios,the results show that compared with zero exploitation in water source areas,the water table of 50%75%and 90%recovery ratios rises in different degrees,and the average rise values are 4.17,2.37,1.47 and 1.05 meter higher than the background value respectively.Comprehensive analysis results show that the TDS reduction efficiency is the highest under the condition of 90%recovery ratio,and the water table remains stable and slightly rises.Therefore,90%recovery ratio can be selected as the pumping scheme of each water source to meet the requirements of economic and ecological benefit. |
PDF Full Text Request