Characteristics of groundwater circulation in typical karst trough areas：A case study of Longtan trough valley in Youyang, Chongqing

Although the southwest karst valley region of China has an abundance of groundwater resources, little is known about the variations in the karst trough valley’s groundwater types and their cycle features. Using the Chongqing Youyang Longtan trough valley as a case study, this research systematically analyzed the flow attenuation process, water source composition, recharge characteristics, and storage role of karst springs on the downstream and reverse slopes of the valley by the methods of hydrological impulse function simulation, water balance principle, and flow attenuation. The results show that the attenuation process of single spring flow in the study area can be divided into two stages, with the attenuation coefficient of the first stage being at least one order of magnitude higher than that of the second stage. The characteristics of different water-bearing media are clearly distinct, with the primary source of karst water being the fissure water stored within the aquifer. The theoretical recharge area of the downslope karst spring is 66.15 km2, while that of the inverse-slope seasonal karst spring is only 0.99 km2. The recharge coefficients of the two springs in the seasonal changes are large in winter and spring and small in summer. There are significant fluctuations in the flow rate of downslope normal-flow springs throughout the year, but these springs have a strong capacity to store water, and the inverse-slope seasonal spring can also store water. From May to September, the system of downslope and inverse karst springs is mainly dominated by groundwater storage, while groundwater release occurs predominantly in the other months. During the summer drought, the downslope seasonal springs ma experience broken flow. This study offers a scientific foundation for the development and utilization of groundwater resources in the area by highlighting the variations in the features of the water cycle processes of recharge, storage, and discharge of karst springs with various properties on the downslope and reverse slope of the trough area.