AN INTERPRETATION OF SOME OBSERVATIONS ON KARST SPRING REGIMES AND THEIR IMPLICATION FOR THE UNDERGROUND DRAINAGE SYSTEMS IN THE LHASA AREA, TIBET

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Abstract
Tibet is an arid and cold plateau and the springs which occur there have rarely been studied. The chemical concentration, hydrograph and other physical behavior of the karst springs around the Lhasa area have been analysed in order to understand the underground karst development in this area. The springs on Mt. West located to the West of Lhasa have a unified water table and their discharge, lag-time and chemical concentration changes depend on the hydrological zones in which they are located and their regimes mainly respond to rainfall. The aquifer of the Jiala warm spring has the same hydrogeological structure, but its water source comes from the meltwater and its discharge changes are controlled by surface temperature variations, with a stagnant period ranging from 3 months to 10 days. The Quesang hot spring is also supplied by meltwater but with a half year lag-time because of long distance from the source. A cold spring located at the same point as the hot spring reflects the fact that they individually have their independent drainage systems in the same limestone mass, just like some other karst springs in the world. The occurrence of conduit flows is not corespondent with the present-day karst development. Thus such conduits in limestone terrain might be the inherited development of old karst.