EVALUATION OF THE POTENTIAL GROUNDWATER RECHARGE. EXAMPLE OF THE OGOSTA RIVER BASIN, NW BULGARIA

The aim of the study is to evaluate the potential recharge to the groundwater for the chosen study area - the Ogosta River basin in Northwestern (NW) Bulgaria. Various techniques are used for quantifying groundwater recharge. Some of them are based on water budget methods. The Budyko-type curves allow partitioning of the long-term precipitation sum between evapotranspiration and potential recharge. In case of well expressed seasonal variability and thick soils, usual for water-limited environments, this relationship is shifted towards higher evapotranspiration on the account of the reduced recharge, as predicted by theoretical model developed by Porporato. According to this model, this partitioning is governed by two parameters: the aridity index and the relation of the soil available water capacity (AWC) to the average rainfall depth. The long-term potential groundwater recharge, defined as the excess of precipitation over evapotranspiration, may be estimated based on this model. This method was applied for evaluation and mapping of the long-term potential recharge in the Ogosta River basin. The described method is applicable for sub-humid areas, and is especially useful for the purposes of mapping of the renewable water resources.