Abstract:

The accumulation dam structure at the northern exit of Tianchi Lake in Tianshan Mountains is controlled by its origin and evolution, which affects its groundwater hosting and seepage characteristics. The bedrock burial depth and water diversion structure are crucial to the dam stability, which remains unresolved for many years. Based on geological survey, we used electrical resistivity tomography, optical luminescence dating and hydrochemical analysis to detect the structure of Tianchi Lake accumulation dam, and to determine the age of material formation and the hydrogeological features of the dam. The results show that the Tianchi accumulates are over 100 meter-thick, and the upper shallow massive boulder layer and lower aquifer is 30-40 meter and 30-50 meter thick, respectively, which was underlain by igneous rock complex. Groundwater in the middle part of the dam infiltrates intensively and replenishes the western Xiaotianchi Lake. There are many overflow points and discharge channels on the left bank of the Feilong Stream in the east, which control the seasonal occurrence of shallow spring there. An EW-striking fault (inclining to the upstream) is present beneath the hill of the meteorological station, which forms an aquitard in the Tianchi Lake and rises the phreatic water level. The major water diversion structure model (composed of fault and stratigraphic structure) in the accumulation body is preliminarily constructed. We calculated that the groundwater discharge of the Tianchi dam is 1200 m³/d, whilst the total water discharge is 52×10⁴-113×10⁴ m³/d (from winter to summer).

Key words: Tianchi Lake, accumulation dam structure, electrical resistivity tomography, electrical structure, impervious function