Study of the spatial distribution pattern and water quality characteristics of karst water resources in a typical anticlinal trough valley：A case study of Yiju river basin

Karst springs are the mainly water sources of domestic water supply in karst mountainous areas, where anticlinal trough valley is an important part in the areas. To study the spatial distribution pattern and water quality characteristics in Chongqing karst anticline region, through the hydrogeology survey in the Yiju river basin, and combined with different hydrogeological units within the basin,of which is mainly composed of Permian and Triassic and Cambrian Ordovician aquifer, we analyzed the water quality and studied the distribution of the karst springs in different hydrogeological units. The results show that,(1) The pH value of karst spring in this basin is between 7.27 and 8.07, with the average value of 7.84 and most of them are neutral and weak alkaline. The total salinity of the samples falls in the range of 129-310 mg·L-1. The Permian and Triassic aquifer water chemistry type spring survey all belong to HCO3-Ca type water, while the Cambrian and Ordovician aquifer part spring belongs to HCO3- SO4-Ca type water, which may be related to lithology and human activities in the area; 93.8% karst spring water is of excellent and good quality, which can be used as drinking water resources. (2) The average flow rate of these karst spring is 0.84 L·s-1 and 78% of them have a flow of less than 10 L·s-1 . The average flow of large karst springs with more than 10 L·s-1 is 76.56 L·s-1. There are differences in quantity and flow of karst springs in different lithologic stratums, which shows the extreme nonuniformity of karst spring development. (3) In the basin with different hydrogeologic units, there are five preferential localities where the karst springs often occur, namely, the karst and non-karst contact zones, fault fractured zones, steep cliff, the low lying discharge areas with low confined , deep valleys and both sides of cutting canyons.