Simulations of multipurpose water availability in a semi-arid catchmentunder different management strategies

Abstract

In the semi-arid Brazilian Northeast, the exploitation of alluvial aquifers for irrigation and domesticsupply to rural communities over the last 10 years has upset the traditional mechanisms of waterresources management. In the Forquilha watershed (221 km2;581700S, 3983000W), the two main waterresources are reservoirs (with a capacity exceeding 0.9–6.7 106m3), used for domestic water supplyonly, and an alluvial aquifer (2.3 106m3), used for irrigation and domestic water supply. From 1998 to2006, the irrigated area with alluvial groundwater increased from 0 to 75 ha, and the fraction ofpopulation supplied through domestic water networks, using reservoirs and the aquifer, increased from1% to 70%. Based on physical and socioeconomic issues, three main water territories have been defined(‘‘Aquifer’’, ‘‘Reservoirs’’, and ‘‘Disperse Habitat’’). Considering the next 30 years with a realisticpopulation growth, three hypotheses regarding irrigated area (i.e., 0, 75, or 150 ha), and several possiblewater-management scenarios, hydrological balance models were built and used to simulate the differentimpacts on water resource availability and salinity. Simulation results showed that, in all cases, releasesfrom the upstream main reservoir are necessary to keep reservoir salinity below 0.7 g L 1and forguaranteeing domestic needs in the whole watershed. As a consequence, a management approach thattakes into account the interrelations among the three territories is necessary. Moreover, the simulationsshowed that the area of irrigated fields cannot exceed the current extent (75 ha), or serious restrictionson water availability and salinity will take place. Moreover, important socioeconomic problems areexpected, including a high cost of palliative water supply with tank trucks from external sources.