Central Yunnan The Yangzonghai Basin Karst Groundwater System And Its Vulnerability Assessment

Yangzonghai is one of nine large lakes dispersely distributed in Yangzonghai basin in central Yunnan province. The main characteristic of Yangzonghai's subterranean drainage system is to produce Karst groundwater, whose aquifer system and circulating system are very complex.It is an imperative topic to investigate the hydrogeological conditions of the Yangzonghai's subterranean drainage system, and its distribution situation and dynamic evolution process, and the vulnerability evaluation of the subterranean drainage system, then to provide some suggestions to protect the water environment in the area.The paper investigates and analyses the hydrogeological conditions of the Karst groundwater in the Yangzonghai basin in detail,and assess the vulnerability of the subterranean drainage system. The main results and contributions of the paper are as follows.First,the paper finds out there are fourteen Karst spring groundwater sub systems in the Yangzonghai basin.According to its own characteristic,the paper concludes five Karst subterranean drainage system structure modes.They are fracture zone mode,layered structure mode, syncline mode,bedding strike mode and rock through mode.The paper analyses the differential expressions of the enrichment characteristic of the Karst groundwater, the controlling factor,the water circulating regular pattern and the environmental geological issues of each mode.Second,With MapGIS platform and DRASTIC method,the paper assesses the vulnerability of the groundwater in the Yangzonghai basin by different areas.The results indicates that vulnerability index is high in the Yangzonghai basin, which is susceptible to be polluted,and may affect the surface water.The paper divides the Yangzonghai basin into extreme high,high,moderate and low four levels and thirteen areas.Third,the paper divides the Yangzonghai basin to four key protective areas,which total area is 27.2 square kilometers according to the human's construction activity, Karst geological environmental conditions and vulnerability partitions,combined with the economic and social development planning factors of the area.At last,the paper suggest to take the measure of "prevention first,combining prevention with abatement",which is the key measure to protect the water environment in the Yangzonghai basin.