Abstract: Qilu karst basin is a closed catchment-flow and faulted lacustrine basin.After inflooding the Qilu lake in the flow area,surface water and groundwater concentrating in the basin replenish the Gaozhai underground river system from the Yuejiaying sinkhole.Through a karst conduit the water flows to the eastern Huaning basin and drains as an underground river.Because of clogging of the underground river conduit with sand and mud,the maximum runoff of the sinkhole decreases continuously,weakening the...