Study on the boundaries and properties of the underground river system in Nandong, Yunnan Province

With a fixed source of recharge and resource elements, underground river system forms an independent unit in karst groundwater circulation, controlling karst water movement and enrichment, hydrochemical evolution, composition of water resources and environmental geological problems. In order to carry out karst groundwater system research, the primary task is to determine the location of the system boundaries and its hydrogeological properties. In this paper, taking Nandong underground river system as the research object, based on field investigation, exploration, test data, a multi-disciplinary method including modern karstology, geology and hydrogeology are applied. It is conclude that the Nandong underground river system is composed of two subsystems, namely No.1 and No.2 underground river subsystems, and the No.2 underground river system has two full-row type underground subsystems of Pingshiban and Heilongtan.The aquifer is mainly limestone, calcite dolomite and dolomitic limestone of Triassic system. According to the hydrogeological properties of the boundaries, it can be divided into surface watershed boundary, underground watershed boundary, confining boundaries, karst aquifers deep stagnant boundary and other types.