Groundwater recharge: an overview of processes and challenges |
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Authors: | Jacobus J de Vries Ian Simmers |
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Institution: | (1) Faculty of Earth Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands, |
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Abstract: | Since the mid-1980s, a relative explosion of groundwater-recharge studies has been reported in the literature. It is therefore
relevant to assess what is now known and to offer further guidance to practitioners involved in water-resource development.
The paper summarizes current understanding of recharge processes, identifies recurring recharge-evaluation problems, and reports
on some recent advances in estimation techniques. Emphasis is accorded to (semi-)arid regions because the need for information
is greatest in those areas – groundwater is often the only water source, is vulnerable to contamination, and is prone to depletion.
Few studies deal explicitly with groundwater recharge in temperate and humid zones, because recharge is normally included
in regional groundwater investigations as one component of the water balance. The resolution of regional water-balance studies
in (semi-)arid areas is, in contrast, often too low to quantify the limited recharge component with sufficient precision.
Despite the numerous studies, determination of recharge fluxes in (semi-)arid regions remains fraught with uncertainty. Multiple
tracer approaches probably offer the best potential for reliable results in local studies that require 'at-point' information.
However, many investigations indicate that these approaches are not straightforward, because in some cases preferential flow
contributes as much as 90% of the estimated total recharge. Tracer results (e.g. Cl–, 3H) must therefore be interpreted with care in areas with multi-modal flow in the vadose zone. Moreover, accurate estimation
of total chloride deposition is essential, and tritium may be influenced by vapour transport at low flux rates. In addition,
paleoclimatic and paleohydrological conditions may cause discrepancies between measured actual processes and calculated long-term
averages.
The frequently studied issues of localized recharge and spatial variability need not be a problem if concern is with regional estimates. The key for practitioners is
the project objective, which dictates whether 'at-point' or area-/groundwater-based estimation methods are appropriate. Many
indirect (wadi) recharge studies reported in the literature are site specific; the relationship between 'at point' hydraulic properties
and channel-reach losses demands further investigation.
Electronic Publication |
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Keywords: | Groundwater recharge Tracer studies Groundwater development Arid regions |
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