The application of GIS for estimating the average long-term shallow groundwater recharge

Ever since its invention, in the early sixties of the 20th century, the geographic information system (GIS) has been one of the most rapidly developing areas of information technologies. The groundwaters in some regions of Bulgaria have been inadequately researched so far, and it is precisely in those areas, that GIS techniques find their most widespread usage. Most of the available methods that are currently used in order to obtain a qualitative evaluation of the shallow groundwater recharge are point estimate. Therefore, in the following paper, a more generalized model has been presented, integrating the water balance into GIS environment. This model can be primarily used in mountainous areas, and presents the long-term average shallow groundwater recharge as a function of the climate, geology, the soil texture, and slope gradient.