- Growing municipal and industrial water use adds another dimension to the drought risk situation.  While urban water demands are small compared with irrigation demands, they have a year-round character that is less variable than irrigation demands—certain levels of urban water service must be sustained for public health and sanitation despite temporal reductions in precipitation and stream flows.  Also, urban water supplies have higher water-quality standards to meet, and droughts negatively affect water quality.

Taking all the above into account, and adding in flow requirements for hydroelectric facilities, the water management challenge in the Guadalquivir basin is substantial and complex. Maintaining adequate river flows to sustain irrigation demands and hydropower requirements in the central and eastern portions of the basin, urban water demands at various locations but especially in and around Sevilla, and agricultural water needs in the lower portion of the basin, proves particularly difficult. Water shortages appear to create zero-sum situations where meeting one sector’s needs means failing to meet another’s.<sup>4</sup> Water users and water managers have described the basin’s overall situation as one of “water deficit.” The Andalusian Department of Public Works and Transport estimated the available water resources within the basin to be 3,357 Mm<sup>3</sup> /yr, and total water demands to be 3,578 Mm<sup>3</sup> /yr, yielding a balance of negative 241 Mm<sup>3</sup> /yr. (COPyT 1997) Thus, even in an average year, water demands in the Guadalquivir basin exceed available supplies. In a drought, conditions are only worse.

Water quality problems in the basin are substantial. As agriculture has expanded in the basin, agricultural runoff (including irrigation tailwater) has contributed to water quality degradation tributaries and the main river stem. Industrial sites—manufacturing plants, food-processing facilities, etc.—have discharged chemical and other wastes to the river system. The growing urban population generates sewage and wastewater that is discharged to the river system as well.

Municipal and industrial pollution sources are now covered by national regulations and EU directives requiring pre-discharge treatment, but the construction and 4 A striking illustration of those tradeoffs involves the water supply and water quality requirements of upper-basin and lower-basin irrigators. As mentioned earlier, one of the main irrigation water uses in the basin is for rice cultivation in the area of the lower Guadalquivir river and estuary, which has experienced an important increase in the past 15 years. With its low slope and coastal terminus, the Baja Guadalquivir area is influenced by tides all the way up to the Alcala del Rio dam, approximately 90 km inland. When flows across the dam fall below 40 m<sup>3</sup> /sec, seawater (20 gr/l) penetrates the estuary between 9 and 15 km. Upstream of this point, in the interface between seawater and freshwater, a marked salinity gradient called _tapón salino_ is established. The length, salinity concentrations, and movements of this _tapón salino_ depend on the Guadalquivir river freshwater flow and the height of the tide.

The CH Guadalquivir has calculated that in order to maintain a salinity of about 0.8 gr./l in the area of estuary where water is diverted for irrigation (between 50 and 75 Km inland), flows of 25-30 m<sup>3</sup> /sec should pass the Alcala del Rio dam. During the rice irrigation period, large amounts of water that were stored in upstream reservoirs during the winter must be released in order to maintain salinity requirements in the lower basin. These releases for the rice farmers, however, have consequences elsewhere in the basin where other irrigators wish to have priority given to permanent plantings such as the fruit orchards prior to annual herbaceous cultivation. Satisfying the upstream orchards, on the other hand, aggravates the “rice water shortage.” Rice farmers have been pressing for the construction of a sluice on the estuary to avoid the entry of tidal water during the irrigation season of the rice cultivation areas.

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