3.4. aquifer exploitation

3.4. Aquifer exploitation

In semi-arid or water scarcity regions, the aquifers play a vital role in meeting water demands, not only as regards quality and quantity, but also in space and time.

Aquifers usually prove to be a natural solution to water scarcity, and they are used to overcome a wide range of situations: for supplying in some particular situations, controlling on account of their abundant reserves and the extensive areas they cover and, for the same reason, for transporting and distributing. They are also employed as water quality protection elements, by providing quality reserves in zones where the surface runoff in summer proves insufficient to maintain acceptable quality standards, and even when the runoff is too low to maintain minimum or ecological discharges.

However the use of the potential of aquifers in semi-arid areas brings with it the problem of average annual recharge and the difficulties involved in its management.

Some southern EEA areas have very little aquifer recharge. It becomes worse taking into account the great amount of tourism in those areas, particularly in summer months, making demands to rise to very high values compared to the rest of the year. In addition, the climate in those areas allow the cultivation of high value crops, which also require a great deal of water for irrigation in spring and summer.

The management problems, understood as a set of operational rules that determine the handling of aquifers in particular and water resource systems in general, prove particularly difficult and costly to manage and maintain.

Intensive exploitation of aquifers can give rise to over-exploitation problems. Aquifer over-exploitation depends on the balance between demand and renewable resources. In the semi-arid Mediterranean regions of Europe the absence of high rainfall and the existence of ephemeral rivers make an increasing development of groundwater resources. This leads to over-exploitation, which commonly arises from excessive abstraction for irrigation. The resulting increase in productivity and change in land use can establish a cycle of unsustainable socio-economic development within an irrigated region. Additional resources are exploited to satisfy the increased demand from the population and agriculture, exacerbating the already fragile environment by reducing groundwater levels and, in some circumstances, accelerating the desertification processes (EEC, 1994). Wetlands or wet ecosystems are also damaged when the water table drops. In contrast, over-exploitation in Northern Europe is mainly a consequence of the fact that groundwater resources have historically provided a low-cost, high-quality source for public water supply. Current issues are the cost of alternative water sources, the associated infrastructure and the environmental impact of over-exploitation.

In 1991 the EC DG XI commissioned a report into the sustainable use of groundwater in Europe (RIVM/RIZA, 1991). It was based on the earlier work of Fried (1983) in which a preliminary inventory of known European cases was prepared. Over-exploitation turned out to be the major threat to the sustainable use of groundwater in Europe. The development of guidelines for environmental impact analysis, management tools, standardised data management and abstraction licensing were cited as key requirements for improving management of groundwater resources.

Contamination problems also affect numerous aquifers, either because of point-source pollution or as a result of a widespread pollution caused by agricultural and livestock activities. Any potential decrease in water quality depends on the activities affecting the underlying or adjacent aquifers.

3.4.1. Spain

In Spain, the systematic study of aquifers has been carried out in the "Estudio de Delimitación de Unidades Hidrogeológicas del Territorio Peninsular e Islas Baleares y Síntesis de Sus Características (DGOH-ITGE, 1988)" (Definition of Hydrogeological Units on the Spanish Mainland and the Balearics Study and Synthesis of Their Characteristics). 442 hydrogeological units have been defined up to date, covering 174,745 km², which amounts to approximately one third of the national territory. The total annual recharge for these units is roughly 20,000*10⁶ m³/year, which is equivalent to approximately 18% of the total national runoff. This volume of groundwater resource is slightly greater if the small aquifers of local interest are included, (MOPTMA-MINER, 1994).

Direct use of groundwater in Spain, is currently estimated at 5,000*10⁶ m³/year, of which 4,000*10⁶ m³/year are destined to irrigation and the remaining 1,000*10⁶ m³/year are for water supply. On a national level, this means that 18 % of the total water is used for irrigation and 22% of the total is used for water supply. Such figures could give rise to confusion given that, for example, although Spanish irrigation activity using groundwater only accounts for about 900,000 ha, the economic benefits obtained in these zones are the same as or greater than those obtained in the remaining 2.300,000 ha. that receive surface water. Furthermore, the efficiency with which groundwater is used, is almost double than that of the use of surface water (Llamas, 1995).

A total of 51 hydrogeological units have a pumping/recharge ratio greater than 1.0, and the deficit, obtained by calculating the mean annual difference between pumping and recharge is 710*10⁶ m³/year. However, one third of this deficit corresponds to La Mancha Occidental, and an almost identical proportion corresponds to the Province of Murcia (Valle del Guadalentin), the rest being distributed throughout the Provinces of Alicante (River Vinalopo Basin) and Almeria (Campo de Dalias and Campo de Nijar). To date, the Spanish government has declared 18 overexploited hydrogeological units, covering a total surface area of 13,032 km² and having a deficit of 468*10⁶ m³/year (MOPTMA-MINER, 1994). The figures corresponding to each of these units are shown in Figure 3.4-1