Assessment of current and potential yield of hand-dug wells in a semi-arid zone in south-central Chile using an analytical methodology

摘要

The semi-arid interior dryland region in south-central Chile is characterized by shrink-swell granitic soils and a semi-arid Mediterranean climate, which together cause scarce dry-season surface water supplies. Historically, the lack of easily accessible water has limited the region's economic development. In most of the region's rural communities, the only local water supplies for drinking and small-scale irrigation are shallow, hand-dug wells. The objectives of this study, conducted in the San José catchment in the Biobío Region (36°24' S, 72°30' W), were to demonstrate the usefulness of a simple aquifer characterization methodology to assess the likelihood of additional extraction of groundwater in this area with existing wells, estimate potential increases in productivity through increases in well depth, and present the spatial distribution of aquifer properties in this area. Hydraulic conductivity values (Ks) were measured from analyses of recovery rates of hand-dug wells. Values of Ks ranged between 0.04 and 5.1 m d-1 (mean = 1.07 m d-1; standard deviation = 1.36 m d-1), which resulted in a low yield from the shallow wells. These Ks values were used to estimate the potential groundwater yield which could be extracted from hand-dug wells in the region in their current condition with increased pumping and, where feasible, if wells were deepened by 0.5 m. Results suggested that existing wells could produce up to 0.008 m yr-1 and up to 0.02 m yr-1 by deepening them. Since current water usage has been estimated as 0.002 m yr-1, these results suggest that additional groundwater supplies could be exploited.