Water quantity optimal schemes of the karst aquifer recharge with multi-source water at the Yufuhe river, Ji’nan

With steady expansion of the urban area of Ji’nan City, the supply of karst groundwater has been seriously affected. Under the current background, it is a practical way and important measure to transform surface water into groundwater for solving the contradiction between the protection of springs and the security of water supply, in which the Yufuhe river basin in the west of Ji’nan plays a key role. On the basis of three groundwater recharge projects built on the Yufuhe river, it is vital to determine the reasonable recharge volume and recharge time to ensure the limestone karst water recharge and reducing the invalid quaternary pore water recharge and the discharge of surface water. This work selected the section from Zhai’ertou to South-North Bridge upstream of the Yufuhe river as the target. Combining the hydrogeological conditions and other data of strata and lithology, this section was divided into 4 sub-reaches. Using Hydrus-2D to this work numerically simulated the vertical and lateral seepages of each sub-reach, yielding good results. Then we made further simulations on three scenarios with the maximum, medium and minimum groundwater depth, respectively. The modeling permitted to establish the optimal schemes of water quantity for recharge, which suggest that when the flow is about 280，000 m3·d-1, a continuous discharge should be for 19.5 days, 10.5 days and 12.7 days in the cases of maximum, medium and minimum groundwater depth, respectively.