Evaluation of geologic risk in the El Salado stream basin, within the framework of sustainable development of the Iglesia department, San Juan

Abstract

 The sub-basin of the El Salado stream is part of the surface drainage network of the Blanco River, in the north of the province of San Juan. Its head is developed in the Colangüil mountain range, where sandstones from the Cerro Agua Negra formation, upper Paleozoic age, outcrop. These have been intruded by the granite rocks of the Los Puentes pluton, upper Permian– lower Triassic in age.  

The water system is supported by snow and rainfall, less than 100 mm annually.  Approximately half of the longitude of its main axis is extended on modern alluvial material. The area exceeds 400 km², allowing an extraordinary water runoff greater than 150 m³/sec. The addition of solid material, before an immediate runoff, would be incorporated in the lower segment of the basin, where both terraces and river channel materials, and shrubby species predominate. Another important risk is seismic, as it presents high-intensity events in the historical distribution of earthquakes in northwest Argentina.

 The vegetation cover, in a section of the alluvial valley, exhibits a characteristic distribution of patches, constituted predominantly by Larrea divaricata, Bulnesia retama, and another, of lesser coverage, of scrub of Proustia cuneifolia or mendocina. The wet surface of the channel for much of the year or, failing that, the shallow depth of the groundwater and the type of soil with high permeability characterize the balanced ecosystem for the latter species, and constitute a hydrogeological exploration guide.