Non-renewable groundwater resources: a ... - unesdoc - Unesco

CHAPTER 1 ■ CONCEPT AND IMPORTANCE OF NON-RENEWABLE RESOURCESThe main occurrences of non-renewable groundwater resources tend to fall into one orother of the following two categories :● unconfined aquifers in areas where contemporary recharge is of small volume and veryinfrequent, and the resource is essentially limited to aquifer storage reserves (Figures 1 A-C);● ‘confined sections’ of some aquifer systems, where groundwater development intercepts (orinduces) little active recharge, as a result of natural geohydraulic impedance to groundwaterFigure 1Hydrogeological settings to illustrate the occurrence of essentially non-renewablegroundwater resources(A) hyper-arid area with average rainfall of less than 100 mm/a and prolonged (up to 30 months) dry periods– occasional storms result in flash floods down otherwise dry valleys (wadi) and lead to small amounts of localisedrecharge, but bulk of aquifer contains fossil groundwater, which infiltrated during a Holocene humid period at least10,000 years or more ago and still has an active residual flow to a perennial discharge area.(B) similar climatic situation to above, but hydrogeological setting includes an aquitard which confines the groundwaterand increases residence times of the freshwater aquifer, but allows limited leakage and discharge via anoverlying shallow saline groundwater system.15