ABSTRACT
Groundwater and surface water commonly form a linked system. The ow can be in any direction, and the rate of ow varies geographically and seasonally. The interchange is not signicant for some aquifers. However, groundwater supplies an estimated 30% of the total ow in surface streams, and seepage from streams is a principal source of ow to some aquifers. Water drawn from wells situated along a bank of an alluvial stream can affect an appreciable reduction in the surface ow and the diversion of surface ow can reduce groundwater recharge. The supply for groundwater and surface water cannot be evaluated independently unless the interchange is minimal. There are two distinct types of circumstances concerning the development and management of groundwater supplies. Groundwater is considered a renewable source, with optimal use restricted to the average rate of recharge; mining of groundwater, however, is sometimes carried out with xed-term objectives. Average annual recharge can, in extreme cases, be relatively insignicant, as in the major regional Nubian aquifers in northeast Africa.
