The Polysemic and Increasingly Useless Concept of Overexploitation Overview

This section will consider first the concept of overexploitation from a general perspective, and then the failure of its application in Spain. The term overexploitation has been frequently used during the last three decades. Nevertheless, most authors agree in considering that the concept of aquifer overexploitation is one that resists a useful and practical definition (Llamas, 1992; Collin and Margat, 1993). Custodio (2000, 2002) and Sophocleous (2000, 2003) have most recently dealt with this topic in detail.

A number of conceptual approaches can be found in the water resources literature: safe yield, sustained yield, perennial yield, overdraft, groundwater mining, exploitation of fossil groundwater, optimal yield and others (see glossaries in Fetter, 1994, and Acreman, 1999). In general, these terms have in common the idea of avoiding undesirab/e effects as a result of groundwater development. However, this undesirabi/ity is not free of value judgements. In addition, its perception is more related to the legal, cultural and economic background than to hydrogeological facts.

For example, in a research study on groundwater-fed catchments, called Groundwater and River Resources Action Programme at the European Scale (GRAPES) (Acreman, 1999), three pilot catchments were analysed: the Pang in the UK, the Upper Guadiana in Spain and the Messara in Greece. The main social value in the Pang has been to preserve the amenity of the river, related to the conservation of its natural low flows. In the Messara, the development of irrigation is the main objective and the disappearance of relevant wetlands has not been a social issue. In the Upper Guadiana the degradation of some important wetlands caused by groundwater abstraction for irrigation has stirred an ongoing conflict between farmers and conservationists (Bromley et a/., 2001).

The Spanish Water Act of 1985 does not mention specifically the concept of sustainability in water resources development but indicates that use rates should be in balance with nature. It basically considers an aquifer as overexploited when the pumpage is close to, or larger than, the natural recharge.

The Regulation for the Public Water Domain enacted in pursuant to the 1985 Water Act says that 'an aquifer is overexploited or in risk of being overexploited, when the continuation of existing uses is in immediate threat as a consequence of abstraction being greater or very close to the mean annual volume of renewable resources, or when it may produce a serious water quality deterioration'. According to the law, 14 aquifers have been declared either provisionally or definitively over-exploited, for which strict regulatory measures have been designed. However, to a large extent, these measures have not been successfully implemented and a situation of legal chaos still persists in many of these aquifers (MIMAM, 2000).

The misconception of considering that safe yield is practically equal to natural recharge, already shown by the late well-known American hydrologist Theiss in 1940, has been voiced by many other hydrogeologists (see Custodio, 2000; Sophocleous, 2000; Hernández-Mora et al., 2001).

Several national and international conferences have been organized by Spanish hydrogeologists over the last two decades to discuss and help dispel the misconceptions related to aquifer overexploitation (see Custodio and Dijon, 1991; Simmers et al., 1992). Nevertheless, the success of these activities was rather limited in Spain and abroad.

It was suggested that a possible definition is to consider an aquifer as overex-ploited when the economic, social and environmental costs that derive from a certain level of groundwater abstraction are greater than its benefits. Given the multifaceted character of water, this comparative analysis should include hydrologic, ecological, socio-economic and institutional variables. While some of these variables may be difficult to measure and compare, they must be explicitly included in the analysis so that they can inform decision-making processes. Following Hernández-Mora et al. (2001), the basic categories of extractive services and in situ services are taken into account in the description of costs and benefits of groundwater development. The National Research Council (1997) recognizes that the monetary value of groundwater's in situ services (avoiding subsidence, conservation of wetlands or maintaining the base flow of rivers, among others) is a rather complex and difficult task for which there is only limited information. Yet the WFD foresees that Member states must evaluate the environmental and resource costs, providing motivation to environmental economics to build on new applicable methods. Recently Llamas and Custodio (2003) have tried to present 'intensive groundwater use' as a more practical concept. According to the editors of that book 'groundwater use is considered intensive when the natural functioning of the corresponding aquifer is substantially modified by groundwater abstraction'. This concept only describes the physical changes but does not qualify its advantages or disadvantages from the many dimensions of the sustain-ability concept, including ecological, hydrological, economical, social, intragenera-tional and intergenerational. On the contrary, other terms such as overexploitation, overdraft and stressed aquifers have a derogatory meaning for most people.

Fortunately, the scientific literature on intensive use of groundwater is increasing rapidly. In the book previously mentioned 20 chapters written by more than 30 well-known authors are included. A second book dealing with intensive use has also been recently published (Sahuquillo et al., 2005).

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