Alluvial hazard in the department of Pocito, province of San Juan

Abstract

Torrential rains during summer can cause violent floods that are characterized by high speeds, relatively shallow depths and a great sediments and debris loading during a short time. The phenomenon is aggravated when the infiltration index reduce due to previous rains that saturate the area. These torrents are generated in the mountainous zone, with high gradient that erode the existing rocks and carried loose materials from the outcrops. Most of the piedmont is practically barren of vegetation, so superficial runoff is very rapid.The extent of active areas on the Zonda piedmont have been determined from geomorphology study of aerial photographs and topography. The active areas are inset at lower relative elevations in relations to adjacent ancient piedmont surfaces. In the floodplain, where the urban and rural areas are located, historical floods have been confined to number 13 and 15 streets, that are oriented parallel the downslope direction of the piedmont, with a west-east trend. During rainfalls these streets have been transformed in natural riverbeds that flow through the populated areas, influencing the path of the floods and limiting damages to structures. But streets and irrigation channels with a north-south trending are affected and damage. In this work, an evaluation of hydrologic aspects of torrential La Lechuza creek basin is made. This stream cause the largest of damages in the department.The establishment of a prediction and warning system, public education and structural measures are means to minimize alluvial plain flooding at Pocito department.