Morphometry of a Central Andean basin, San Juan, Argentina: assessment of conditional factors to the occurrence of flash floods.

Abstract

The present work aims to determine flash flood occurrence prone areas, in the Jáchal river basin, San Juan Province, Argentina. The Jáchal river basin covers ~29,000 km2 and has a perimeter of ~2,400 km, while the eponymous river extends for nearly 570 km. It is a 7th order basin according to Strahler’s classification, subdivided into four 6th order sub-basins. Various morphometric basin characteristics are analysed and some basic and derived parameters are calculated. These calculations allow predicting the basin behaviour due to heavy rainfall, which translates into large volumes of water with peak f lows capable of generating significant f lash f loods. The basin has a torrential character, so in case of intense rainfall the terrain conditions would contribute to increasing the f low of the main rivers. An inventory of alluvial deposits was carried out and their relationship with the conditioning variables of the terrain was evaluated. At the conf luence zones, the river tributaries show more intense overf lows than the main collector. This promotes the generation of f lash f loods. The areas most likely to be affected by f lash f lood events correspond to low-humidity, east-facing slightly rough terrains, with slopes of up to 15° as well as low-lying f lood plain sectors, and at the conf luence of tributaries with the main rivers. Populated centres and provincial and national routes are prone to be affected by alluvial events in the study area.