An assessment of potential groundwater recharge zones in Bulgaria

Groundwater resources on the territory of Bulgaria are unevenly distributed in both spatial and temporal aspects. The effective usage of these valuable assets is of paramount importance, since any over-exploitation would eventually lead to their depletion. Remote sensing data and satellite images have increasingly been used in groundwater exploration and management. An integrated approach was applied in the present study in order to delineate potential groundwater recharge zones on the territory of Bulgaria. Data from various sources were used to prepare different thematic layers. These layers were then transformed into raster data of 1×1 km. Lineament and drainage density maps of the research area were made with the help of GIS technology. In addition, a map was made for the annual total precipitation for the period from 1931 to 1985. DEM (Digital Elevation Model) data on a global scale at 90 m horizontal resolution were used for the slope analysis. A groundwater potential map was produced, which integrates several thematic maps, such as annual rainfall, geology, lineament density, land use, slope, soils, and drainage density. The thematic maps were then converted into a raster graphic format in order to be easily integrated into a GIS platform. The raster maps of these factors were then allocated a fixed score and weight-computed. The weights of those factors contributing to the groundwater recharge were derived by using the following components: geological map, lineament-length density map, land cover data base, soil data base, drainage-length density map, and slope gradient map. Subjective weights were assigned to the respective thematic layers, and they were overlaid in a GIS platform for the identification of potential groundwater recharge zones within the study area. These potential recharge zones were then categorized as being very good, good, moderate, poor, and very poor