ABSTRACT
Groundwater constitutes an important source of water supply for domestic, industrial, and irrigation uses in different countries due to its availability, which is not subject to multiannual and seasonal fluctuations. At present it is the main source of domestic water supply in most European countries, the United States, Australia, and some countries of Asia and Africa both in large and small towns and in rural areas.[1,2]
Groundwater is used for irrigation in about one-third of all irrigated lands.[3]
Natural groundwater resources are understood to be the total amount of recharge (replenishment) of groundwater under natural conditions as a result of infiltration of precipitation, seepage from rivers and lakes, leakage from overlying and underlying aquifers, and inflow from adjacent areas. In some cases, the average annual recharge of aquifers, evaluated from average annual precipitation, equals groundwater runoff. Natural groundwater resources may be equated to groundwater discharge (runoff) when the evaporation from the water table may be ignored or estimated separately.[4] Under this assumption, groundwater runoff data are widely used to characterize regional groundwater resources and are an important component of the hydrologic cycle and environment.[5-7]
The role of groundwater in the water balance and water resources of regions is quantitatively characterized by the groundwater runoff/precipitation ratio or groundwater recharge. The runoff/precipitation ratio is extremely variable depending on meteorological factors, composition of rocks, etc. Distribution of groundwater recharge to river/total river runoff ratios shows the effect of geographical and altitudinal zonality. The quantity of recharge ranges widely. Analysis of conditions of generation of groundwater resources within continents shows that this global process depends on a complex combination of various natural factors. Principal amongst these are precipitation, vegetation, soil type and geology, and the hydrogeological features of the area.
