EVOLUTION OF GROUNDWATER SEEPAGE FIELD IN HEIJIAYI AREA WITH MULTIPERIODIC ENGINEERING

Southwest China has carried out a lot of engineering activities in recent years. As a typical karst region, in the Heijiayi region of Binchuan, Yunnan, multiperiodic enginnering including "Deverting water from Erhai Lake to Binchuan" (1987), "North Main Canal" (2006), and the Heijiayi section of the Haidong tunnel of Dianzhong Water Diversion Project (2018) affected the groundwater seepage field strongly. Based on the investigation, the geological environment and karst hydrogeological conditions, the groundwater seepage field is analyzed qualitatively. The spatial structure and boundary conditions of Heijiayi aquifer are studied, the parameter values were determined and the three-dimensional seepage flow field numerical model was established, the influence on groundwater environment are forecasted, the main conclusions are as follows:

(1)Before 1987, the Matoushan-Laotai karst water system was in the initial state. The Qingshan Formation was rich in water and karst developed, recharged by rainfall, it enters the karst pipeline system through karst depression, sinkhole and underground river, flow along the fault zone, discharged to the Erhai Lake and the Waxi River.

(2)After 1987, the tunnel passed the Qingshan Formation at 1945 m, groundwater trapped by the tunnel and become the lowest drainage datum on the south side. The water level of groundwater is between 2280 ~ 1940 m. Laotaiqing underground river has cutoff.

(3)After 2006, affected by the "North Main Canal" project, which started from the outlet of " Erhai Lake to Binchuan " and crossed the weakly water-rich and weakly permeable basalt group at 1930m, became the lowest discharge base level on the south side, the Xicun reservoir near the tunnel drops from 1890 m to 1870 m, and dry up lately.

(4)After 2018, the Heijiayi section of the Haidong Tunnel in the Dianzhong Water Diversion Project will cross the Matoushan-Laotaiqing karst water system in the northwest-southeast direction. With the new drainage datum, the impact radius is 500-1100 mand extensive groundwater level decline.

(5) After 2026, the seepage field recovery under the completely blocked condition of the Heijiayi section would completed. Simulation result show that after 1 year, 3 years, 5 years of block, the seepage field basically recovered to different status, 5 years or so it would be fully recovered.