SURFACE AND SUBSURFACE KARSTIFICATION OF AQUIFERS IN ARID REGIONS: THE CASE STUDY OF CHESHME-ALI SPRING, NE IRAN.

Objective karstification assessment is a key component of hydrogeological studies of aquifers. In this research, surface and subsurface karst development have been assessed, based on different methods, to get insights into karstification processes in the area of the Cheshme-Ali karstic aquifer, located in northeast Iran. GIS information, remote sensing, and field measurements of fracture density and frequency have been used to determine surface karst development. The monthly spring discharge rate and physicochemical parameters of the Cheshmeh-Ali Spring in 2003-2004 were used to determine subsurface karstification rate. Additional monthly measurements of discharge rate and chemical parameters were carried out in 2010-2011. The evaluation of surface karstification (Sk) illustrates moderate karstification of 51.47 percent. The response of the aquifer to precipitation shows the impact of one or more conduits in the water level fluctuation zone that generate a rapid response of the spring to large precipitation events. The spring hydrograph analysis indicates a pseudo-diffuse flow system in the region. The hydrograph and chemograph analyses demonstrate average subsurface karstification index of 1.7 m. Finally, it is concluded that although both methods demonstrate karstification processes in an aquifer, these kind of reservoirs still require more intelligible approaches, as well as comparable methods for their description. [ABSTRACT FROM AUTHOR]