Assessing recharge of Karst aquifer in Dorfak region using KARSTLOP method

Throughout history, the issue of providing safe water has always been one of the main concerns of humanity. Nowadays, according to population growth and increasing consumption and also due to the limited available freshwater resources particularly in the arid and semiarid areas, the importance of paying special attention to available water resources has been announced. Among freshwater resources in the world, the Karst groundwater resources have gathered the attention of the managers and researchers that are aware of the reality of water scarcity during the last decade. These resources require the identification of their quantity and spatial distribution depending on various natural factors such as climate, topography, vegetation, soil, and geology. Different methods for groundwater recharge estimation have been developed in the last 20 years. These methods (direct measurement, water balance methods, Darcian approaches, tracer techniques, hydrochemical or isotopic models) and many of the problems encountered with each have been described by Gee and Hillel (1988), Sharma (1989), Lerner et al. (1990), Allison et al. (1994), Simmers (1997), Scanlon et al. (2002) among others. Recent advances on distributed methods of groundwater recharge calculations have been done by Udluft and Kuells (2000), Udluft et al. (2003), Heathcote et al. (2004), Hughes et al. (2006), Brito et al. (2006) and Zagana et al (2007). Most of the above mentioned methods have been developed in porous aquifers and are then used in carbonate aquifers. However, in karst aquifers, recharge computing is more complex, due to the specific characteristics of these aquifers and the duality of the recharge. In this sense the concentrate and the diffuse type of recharge are defined; these types have been also as allogenic and autogenic differentiated. The aim of this study was potential mapping of the aquifer recharge areas using the KARSTLOP method for Dorfak Karst aquifer, located in the northern highlands of Iran, as the most important supplier for domestic and agricultural water which are characterized by high precipitation rate, and really high infiltration capacity of karst. KARSTLOP method has been developed, applied and calibrated at catchments of several large karst springs of Montenegro by Radulovic et.al. This method is based on Geographic information system (GIS) and its tools. An aim of the new GIS multilayer method is to provide the most accurate categorization based on selected parameters.The acronym KARSTLOP is derived from the initial letters of selected factors: Karstification—K, Atmospheric conditions—A, Runoff—R, Slope—S, Tectonics— T, Lithology—L, Overlying layers—O, and Plants—P. It simultaneously enables the synthesis of available data and complements findings of the studied karst aquifer. Available historical data and remote sensing combined with field survey and measurements (topographic maps, DEM, geological maps, pedological maps, vegetation maps, aerial and satellite images, speleological data, discharge regime, tracer tests results, hydrochemical data) are sufficient for the application of this method. final recharge map showing the spatial distribution of mean annual recharge (Rch) expressed in percentages (%) is created from overlapping the maps of selected factors (layers) according to the established and hereunder presented algorithm. It is clear that the algorithm is created by giving advantage to karstification, runoff and lithology as the most influenced factors. Application of the KARSTLOP method allows the spatial distribution of groundwater recharge to be obtained, which is not possible using conventional methods such as direct measuring on experimental sites, estimation of evapotranspiration by empirical equations, Darcy’s law-based methods, and isotopic and chemical techniques. Results showed that recharge rate of about 30% and 60% of the total area of the aquifer are more than 70% and 50%, respectively. This is indicative of the high permeability of the Dorfak aquifer. Areas with over 70% recharge rate often are in accordance with the developed regions of highly karstified terrains.