| Jinan is known as its spring.In recent years,the contradiction from water supply and demand has become increasingly acute,with the rapid development of social economy.Several sources of urban water supply?such as the Yellow River water?have been used to replace karst water in Jinan,which has alleviated the current situation of regional water shortage to a certain extent.However,with the continuous advancement of urbanization,the impervious area has increased sharply in the direct recharge area of karst water.This makes the recharge quantity of karst water reduce suddenly,and causes a serious threat to the continued outflow of spring water in Jinan spring catchment.To alleviate the pressure from spring water protection and urban water supply in Jinan,several groundwater recharge projects have been carried out in Yufu River of western Jinan.It plays an important role in improving the status of spring water protection and urban water supply in Jinan.However,the existing researches are mainly focused on the spring water protection and urban water supply in Jinan,and the?quantity of water resources?is as a focus for researches.These studies are less involved in the multi-water source recharge projects in Jinan and lack of in-depth study on the changes in the?quality of water resources?during the multi-water source recharge.Study area in this paper is from the Zhaiertou to the Nanbeiqiao in the upper reaches of Yufu River.The concept of?controlled groundwater level?during the recharge process is proposed based on the regular monitoring data of pore and karst groundwater level from November 17,2017 to May 5,2018.And then the controlled groundwater level is combined to optimize the effect of multi-water source recharge from the perspective of?water quantity?.Additionally,the improved matter-element model is developed by combining the water quality data of groundwater and recharged water source to analyze quantitatively the evolution trend of groundwater quality during different water sources recharge.We hope that this investigation can comprehensively study the multi-water source recharge project from the two aspects of water quality and quantity,and finally realize the dual control and optimization in the groundwater recharge process.This will provide a basis for further scientific and efficient research on multi-water source recharge projects and risk management plans.The specific research results are as follows:?1?The recharge water quantity is optimized according to the monitoring data of pore and karst groundwater level in the Cuima from November 17,2017 to May 5,2018.We can see that the karst groundwater level is raised from 32.6m to 41.14m?the bottom of Quaternary sand–gravel formation in the Yufu River bed?when the recharge quantity is4.7655×106m3,the average flow rate is 1.986×105m3/d,and the total duration time of groundwater recharge is 24 days.This groundwater level can be used as the controlled groundwater level during the recharge process.When the groundwater level reaches the controlled groundwater level and the groundwater is continuously replenished,the ineffective recharge of groundwater will increase and the effective recharge will decrease.?2?When the recharge water source in turn is Wohushan Reservoir,Yellow River,and South-to-North Water Diversion Project,the changes of water quality in pore and karst water are similar.And the extension index of groundwater quality increases gradually,the water quality in pore and karst all show a decreasing trend during the recharge process.Additionally,if the recharge period and water quantity of recharge water sources are similar,the degree of negative impact of recharge water source on regional groundwater quality are:South-to-North Water Diversion Project>Yellow River>Wohushan Reservoir.Therefore,the long-term use of surface water from the Wohushan Reservoir,the Yellow River and the South-to-North Water Diversion may damage the groundwater system and reduce the groundwater quality in study area.?3?Groundwater quality indexes total hardness?c1?,nitrate nitrogen?c3?,ammonia nitrogen?c4?and dissolved total solids(c12)are the high-risk indexes during Wohushan Reservoir recharge.Total hardness?c1?,nitrate nitrogen?c3?,ammonia nitrogen?c4?,sulfate?c7?,turbidity(c11)and total dissolved solids(c12)are the high-risk indexes during Yellow River recharge process.When the South-to-North Water Diversion Project is used as a recharge source,total hardness?c1?,nitrate nitrogen?c3?,ammonia nitrogen?c4?and dissolved total solids(c12)are the high-risk indexes in groundwater quality.Therefore,the content of high-risk indexes in the recharged water source should be reduced as much as possible,before implementing the groundwater recharge projects with multi-water sources.Meanwhile,the aforementioned high-risk indexes should be strictly monitored in the groundwater.Overall,we can strictly control the content of high-risk indexes in water quality to reduce the adverse effects of surface water on regional groundwater quality during recharge processes.The above research results are of great significance to study the conversion mechanism between surface water and groundwater in Yufu River,optimize the multi-water source recharge schemes and alleviate the pressure of spring water protection and urban water supply in Jinan.We hope that this study can provide a basis for the development of efficient and low-risk multi-water source recharge mode. |
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