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Simulations of multipurpose water availability in a semi-arid catchment under different management strategies.

IWRA World Water Congress 2008 Montpellier France
1. Water availability, use and management
Author(s): Julien Burte
Jean-Yves Jamin
Anne Coudrain
Horst Frischkorn
Eduardo Savio Martins
a) FUNCEME, Av. Rui Barbosa, 1246 60115-221 Fortaleza-CE BRAZIL Fone: +55 85 3101.1088 - Fax: +55 85 3101.1093 e-mail: julienburte@yahoo.fr b) CIRAD, UMR G-EAU (CIRAD, IRD, CEMAGREF, ENGREF) BP 5095, 34196 Montpellier, France c) IRD, Great Ice (UR IR

Keyword(s): Water management, Scenarios, Alluvial aquifer, Semi-arid, Modeling

AbstractIn the semi-arid Northeast of Brazil, the alluvial aquifers exploitation for irrigation and domestic supply of rural communities over the last decade has upset the traditional mechanisms of water resources management. This paper looks into this problem using as case of study the Forquilha watershed (221 km²; 5°17’ S, 39°30’ W). In the Forquilha watershed, main water resources are reservoirs (1 to 7 hm3), used for water supply only, and an alluvial aquifer (2,3 hm3), used for both irrigation and domestic water supply as well. From 1998 to 2006, the irrigated area by use of alluvial groundwater has increased from 0 to 75 ha and the percentage of population supplied with domestic water from both sources (reservoirs and alluvial aquifers) has increased from 1 to 70%. As one could expect, pressure on water resources is increasing and water availability for all the categories of uses and users is an open question. In this paper, an approach based on both physical and socio-economic issues was used in future availability simulations. Three main water territories (‘aquifer’, ‘reservoirs’ and ‘disperse habitat’) were identified, within which water related issues guide stakeholders actions. Different scenarios of water resources exploitation strategies were built for the next 30 years, considering a realistic population growth and multiple use hypotheses. Hydrological balance models were built and used to simulate the different impacts of different possible water management scenarios on water resources availability and salinity. The results of the simulations show that if the irrigated area remains the same (i.e. 75 ha), seasonal releases from the main reservoir higher than 50 l/s are necessary in order to sustain activities such as breeding and irrigation. This guarantees the recharge of the alluvial aquifer during dry season in 9 out of 10 years, keeping water salinity of the reservoir below 0,7 g/l. In the case of doubling irrigated areas to 150 ha, the use of water resources would lead to restrictions on irrigation, breeding and domestic water during 80% of time in the territory ‘aquifer’ and during 25% of time for the territory ‘reservoirs’. As a consequence, the cost of palliative water supplying through bowsers would then increase 100% relative to the hypothesis of no increase of irrigated areas.
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