Surface Local Flood Flow in Very Low Relief Areas - Case Study: Tres Arroyos, Argentina (PAP014893)

Código

PAP014893

Autores

Adolfo Villanueva, CARLOS SCIOLI, GEORGINA CAZENAVE

Tema

Land use and Floods, landslides and erosion

Resumo

In this paper, the expression local flood flow" refers to floods covering from several hundred to a few thousand square kilometers. In areas with very low relief, as the Argentina pampas (the agricultural heart of the country), classic hydrological models often have little or no applicability, because the concept of watershed and of convergence of flow towards a hierarchical drainage network frequently is not valid. Moreover, multidirectional sheet flow over areas several hundred or thousands of square kilometers is more frequent than channel flow, and overland flow can take different directions, depending on relative water levels. The characteristics of this type of systems (non-typical hydrological systems) also mean that model calibration cannot follow conventional procedures. In this kind of area, floods are usually caused by local or nearby rainfall, not by flow from an upstream basin and river overflow. Because of that, a raster grid distributed model was used to simulate superficial runoff and it was calibrated analyzing the spatial evolution of flood water on the area. This analysis was carried on comparing model results with satellite images. Model results were then used to analyze the multidirectional movement of water. With this analysis the variation in size and form of the contributing areas to several "basin exit points", and the local runoff directions were evaluated. As flooding does not follow the usual pattern of river overflow, usual methods for flood risk zoning and mapping cannot be used, flooding is not related to a river water level. In this work, the modeling procedure commented in the precedent paragraph was used to analyze sheet flow and water ponding distribution, levels and durations over the study area. This flood mapping was then combined with agriculture vulnerability factors, such as crop phenology, soil type, road network, etc. to produce flood exposure, vulnerability and hazard maps."