Study on hydrologic regime of underground river in typical karst valley— a case study on the Qingmuguan subterranean stream in Chongqing

In order to grasp the hydrologic regime of underground river, a case study on the Qingmuguan subterranean stream in Chongqing is carried out. During May 2007 to June 2008, a water table gauge (WGZ-1 photoelectric figure fluviograph monitor) and water quality monitoring site were set up to record the water level, temperature, pH and conductivity. Hydrology dynamic method is adopted to analyze the response of hydrologic dynamic of the subterranean stream to the rainfall in this paper. The result showed during the rainfall, water table and discharge increased with the rain, especially on July 17, 2007, some peaks appeared in the large storm, the highest water level was 1.175m, and the response lagged for 6h10min after the largest rainfall intensity with the highest discharge being 2.578 1m3/s but the smallest only 0.0189 m3/s. It was found that there is a significant correlation between the water table regime and rainfall event, which indicates the Qingmuguan subterranean stream is strongly developed with single conduit and weak water-storing ability. Conductivity, pH and water temperature also responded to the rainstorm rapidly, conductivity fell down from 602.7 to 462.09μs/cm, pH fell down from 7.24 to 7.01, and water temperature risen from 18.9℃ to 19.5℃, all these indexes lagged shorter than 15 hours.