Unconfined aquifer permeability near hand-dug wells in the coastal and interior dryland of the Libertador General Bernardo O&rsquo|Higgins region, Chile

David E. Rupp1*, Oscar Reckmann2, Jorge Vergara3, Hamil Uribe4, and John S. Selker5

In the dryland of the Libertador General Bernardo O’Higgins Region in Chile, most farmers rely on wide and shallow hand-dug wells as their primary source of water during the dry summer. Few of these wells have sufficient yield for more than domestic use (human consumption, livestock, and irrigation of a subsistence garden). To more accurately assess available groundwater resources, saturated hydraulic conductivity (K) of aquifers in the eight counties that comprise this region’s dryland was estimated using evacuation and recovery tests in 353 hand-dug wells. K followed a log-normal distribution and ranged over nearly five orders of magnitude. County median K varied by a factor of 5 and a slight increasing K trend in the southward direction. In one northern county, less than 4% of the sites had K > 4 m d-1. In the t two southernmost counties, approximately one-quarter of the K values exceeded 4 m d-1. This is approximately the minimum K required for a typical well (1 m diameter and 3 m depth below the water table) to yield 1 L s-1 of water, which is roughly the yield required to irrigate 1 ha. Aquifers located where parent material was predominantly intrusive granite had slightly higher and statistically significant K than those formed predominantly of metamorphic and sedimentary rock. A semi-variogram of K provided weak evidence of a characteristic length scale of approximately 4 km.

Keywords: Groundwater, well recovery, slug-test.
1Oregon State University, Cooperative Institute for Marine Resources Studies, Newport, Oregon, 97365, USA. *Corresponding author (david.rupp@oregonstate.edu).
2Instituto de Investigaciones Agropecuarias INIA, Carrera s/n, Marchigüe, Chile.
3Universidad de Chile, Facultad de Ciencias Agronómicas, Av. Santa Rosa 11.315, La Pintana, Santiago, Chile. Instituto de 4Investigaciones Agropecuarias INIA, Casilla 426, Chillán, Chile.
5Oregon State University, Department of Biological and Ecological Engineering, Corvallis, Oregon, 97331, USA.