Identifying flow regime in the aquifer of fractured rock system in Germi Chai Basin, Iran

Abstract

Considering the importance of fractured rock aquifers in the hydrogeologic process, this research aimed to analyze the flow regime, internal degree of karstification, and estimate storage volume in fractured rock aquifers of the Germi Chai Basin in northwest Iran, which is attributed to its active tectonics, erosion, and the lithological diversity. Given the geological setting, the hypothesis is that this basin is characterized by a high degree of karstification and diffuse or intermediate flow regime leading to variation in discharge flow rate. The hydrodynamic and hadrochemical analysis was conducted on 9 welldistributed springs across the basin from 2019 to 2020. The maximum flow rate in most of the springs appeared in the early wet season despite their different levels of fluctuations on the monthly discharge time series. Analyzing the spring recession curve form revealed an aquifer containing multiple micro-regimes with α recession coefficients and a degree of karstification ranging between 0.001 to 0.06 and 0.55 to 2.61, respectively. These findings indicated a dominant diffuse and intermediate flow system resulting from the development of a high density of fractures in this area. The electrical conductivity of the spring changes inversely proportional to the change in flow discharge, indicating the reasonable hydrological response of the aquifer to rainfall events. Hydrograph analysis revealed that the delay time of spring discharge after rainfall events mostly varies between 10 to 30 days. The total dynamic storage volume of the spring for a given period (2019-2020) was estimated to be approximately 1324 million cubic meters reflecting the long-term drainage potential and high perdurability of dynamic storage. Estimating the maximum and minimum ratio revealed that the springs recharging system in Germi Chai Basin comes under the slow aquifers category. This finding provides valuable insight into the hydrogeological properties of fractured rock aquifers contributing to effective water management strategy.