Abstract
Water from small alluvial aquifers constitutes an attractive and low-cost option for irrigation and rural development in Northeastern Brazil. Based on piezometric measurements, geochemical analyses and electrical conductivity estimates, the present case study identified the main processes determining the hydrosaline dynamics of an alluvial aquifer in a small watershed inserted in the crystalline bedrock of a semi-arid region in Ceará and evaluated the availability of water for irrigation. Accumulation of salts in soil are related to evaporative flux from the aquifer and is increased by irrigation from the groundwater of the alluvial aquifer. The water in these aquifers may be used for irrigation, but represents a risk of soil salinization and alkalinization. Integrated management of surface and underground water resources in the Forquilha watershed may help control irrigation water quality (salinity and residual alkalinity), thereby rationalizing the use of local reservoirs and minimizing losses from evaporation. It has to take into account the complex dynamic of salts and water between the reservoirs, release of water into the river, floods and irrigations.
Highlights
Small alluvial aquifers represent an alternative water resource for irrigation and development of semi-arid regions in Northeastern Brazil
Hydrosaline dynamics of the alluvial aquifer - Whereas the hydrological dynamics of the alluvial aquifer are clearly determined by seasonal runoff patterns, the saline dynamics are less evident (FIG. 3), suggesting the contribution of other factors, including local permeability, as demonstrated in other studies (MONTENEGRO; MONTENEGRO, 2006), and external structures
Beginning in 1998, the development of the use of groundwater for irrigation led to an increase in social pressure on local political leaders, demanding the recharge of downstream aquifers
Summary
Small alluvial aquifers represent an alternative water resource for irrigation and development of semi-arid regions in Northeastern Brazil. The adequate use of all available water resources for agricultural purposes is a prerequisite for sustainable rural development (MONTENEGRO et al, 2010). The low evaporation flux in these small aquifers a few millimeters per year (COUDRAIN-RIBSTEIN et al, 1998) is a interesting feature for water supply in regions with high rainfall deficit (annual rainfall is approximately 700 mm, compared to over 2000 mm in evapotranspiration). The use of alluvial aquifers for irrigation (BASTOS, 2009; MONTENEGRO et al, 2010) and domestic water supply is often compromised by excessive salinity. The main source of aquifer recharge (BURTE et al, 2005), is generally of low salinity (total dissolved solids ~ 0.1 g L-1), in most of the semi-arid Northeast the water salinity of alluvial aquifers (~ 0.7 g L-1) lies between that of reservoir water (~ 0.2 g L-1) and groundwater in the crystalline bedrock (~ 2 g L-1) (AUDRY ; SUASSUNA, 1995; SALES NETO, 2002)
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