| The recharge of karst groundwater is being seriously affected along with the continuously southward expansion of Jinan city, and the infiltration volume tends to reduce greatly which causes the springs in urban area to stop gushing intermittently. In this context, the transformation of surface water to groundwater is a practical way as well as an important measure to solve the problems of spring protection and water supply security. The Yufu River in the west of Jinan plays a key role in the transformation process. Currently, three groundwater recharge projects have been built in Yufu River: one is Wohushan Reservoir drainage project, whose source is surface water from Wohushan Reservoir. The other one is the transformation project of surface water to groundwater which pumps the Yellow River water in Yuqing Lake Reservoir to the upstream of Yufu River for groundwater recharge. The remaining one is south-to-north water diversion in Jinan city which transfer water to Wohushan Reservoir by pipelines, and the source is Yellow River water or Yangtze River water. The determination of reasonable recharge volume and recharge time is the main problem we face currently.In this paper, the study area was selected from Zhaiertou to South-North Bridge in the upstream of Yufu River. Through the methods of field surveys, field monitoring, field test and numerical simulation etc., and combining with the hydrogeology conditions of the strong seepage area and the existing recharge engineering, the maximum infiltration volume was calculated in the study area. The recharge scheme was proposed to make the maximum volume of surface water recharge into the karst aquifer effectively in three scenarios, which are the maximum groundwater depth, the minimum groundwater depth and groundwater depth between the two so as to mainly facilitate the limestone karst water recharge and reduce the invalid quaternary pore water recharge and the discharge of surface water.The reasonable hydrogeology parameters were selected to study the recharge volume by analyzing the field investigation data, the field test and monitoring data and the existing datum, the results are shown as follows:(1) According to the collected data, the recharge water sources are the surface water of Wohushan Reservoir and the Yellow River water. The permeability coefficient is respectively 4.75m/d?20.3m/d and 1.45m/d according to the field double-ring permeability test conducted in the riverbed of Dongkema, Cuima and South-North Bridge, which lays a foundation for the numerical simulation.(2) The variation of groundwater level was summarized through the analysis of the groundwater level monitoring data and the formation lithology data. The results show that there are close hydraulic connection among surface water, quaternary pore water and karst water in the study area, and the recharge was obviously affected by the formation lithology, geological structure, etc. The groundwater level from Dongkema to Cuima had the largest increase which was up to 13 m.(3) Combining the hydrogeology condition with the existing formation lithology data, the study area was divided into 4 reaches, which are Zhaiertou to Dongkema, Dongkema to Cuima, Cuima to Tientsin-Pukou Railway Bridge and Tientsin-Pukou Railway Bridge to South-North Bridge. According to the drainage conditions of Wohushan Reservoir, the flow measurement was implemented in March, July and December in the four reaches of the study area. The infiltration of every reach was simulated by Hydrus-2D which required the input of the actual data and some empirical parameters for verification. The results show that the fitting effect is good. Therefore, the model can simulate the recharge process accurately in study area.(4) With the purpose of understanding the maximum infiltration ability of study area, three scenarios were simulated by Hydrus-2D which were the maximum groundwater depth, the minimum groundwater depth and groundwater depth between the two. By analyzing the changes of groundwater level, the maximum recharge amount and the time were calculated on the premise of no surface runoff. The regression equation was established between recharge amount and recharge time which provide a basis for water drainage of Yufu River. Aiming at the infiltration ability and formation lithology of the study area, the Yufu River recharge scheme was proposed for the reference of different periods.The above results have not only an important theoretical and practical significance for the karst groundwater recharge in the study area but also a reference value for water drainage of Yufu River. |
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