Flash Flood Hazard Assessment in an Ungauged Piedmont Basin in the Sierras Pampeanas Western Region, Province of Córdoba, Argentina

Abstract

In Argentina , in both mountain and piedmont basins , generally with insufficient hydrological data , flash floods are recurrent . The objective of this paper is to evaluate the flash flood hazard of a typical ungauged piedmont basin , the Arroyo (= creek) Chuchiras, province of Cordoba , Argentina , through the analysis of geomorphological , sedimentological , hydrological , and anthropogenic variables that control the behavior of these fluvial systems . The concept of hazard represents the susceptibility and natural fragility of a region exposed to a threat. The susceptibility was evaluated through the following indicators: slope, aspect, valley depth, landscape and landforms, and road networks. Five classes of flash flood susceptibility and hazard were defined. To assess the threat, analysis was made taking into account temporal distribution and intensity of precipitation , field hydrological evidence , and eyewitness reports. The Manning and the paleo-hydraulic methods were used to estimate mean velocity values during the extraordinary event flash flood which occurred on February 4, 2014. The flash flood hazard in the western piedmont of the Sierras Grandes de Cordoba is the result of the combination of variables: low permeability rocks in the upper basin; important topographical contrasts between the fault scarp and piedmont area ; and streams with torrential regime and high energy (velocity, competence, and transport capacity ) that make up distributary systems in the distal-middle piedmont and high intensity rainfalls . A 26% of the study area presents high/moderately high flash flood hazard , associated with the lower reaches and proximal-middle active alluvial fan of Arroyo Chuchiras; 64 and 10% of the investigated sector correspond to low/moderately low and moderate classes of flash flood hazard , respectively.