Determination of karst aquifer characteristics using physicochemical parameters (A case study from west of Iran)

The karstic Rijab Spring with an average discharge of 3290 l/s is located in the Alvand River basin in the northwest of the Zagros, Iran, which drains Asmari formation. To investigate groundwater flow in the catchment area of the Spring, the physicochemical parameters include major cations and anions, discharge, EC, pH, and temperature were studied from September 2000-2002. The results indicate that the karst aquifer has a diffuse-conduit flow system since the diffuse condition supplies mostly base flow whereas the conduit system, providing quick flow, activates mostly during snowmelt period at late-winter and early-spring. The spring hydrograph shows two recession coefficients in both 2000-01 and 2001-02 water years. In both years, the steep recession coefficient (α1=0.0225 on average) which occurs in the wet season is related to the conduit flow system whereas the gentle recession coefficient (α2=0.00685 on average) corresponds with the dry period and related to the diffuse flow. Moreover, the temporal variations of EC, major ions concentrations and saturation indices of the calcite and dolomite also suggest diffuse-conduit flow system. Furthermore, investigation of both the hydrograph and chemographs of the Rijab Spring indicates that about half of the spring catchment area is distributed out of surface catchment boundary.