Flood susceptibility study based on geomorphological analysis of the hydrographic basin of Arroio Santa Isabel, coastal region of Rio Grande do Sul, Brazil

Abstract

Floods cause damage worldwide, affecting mainly the population who lives in areas near the rivers. Considering the diversity of flood conditions, this study aims to understand the interrelationship between geomorphological, climatological, and anthropic factors to map and classify flood susceptibility in the Arroio Santa Isabel basin, a tributary of the Camaquã River, south of Rio Grande do Sul, a region which is frequently stricken by floods. The analysis of geological, geomorphological, hypsometric, clinographic, vegetation and land use maps was based on historical series of rainfall data (46 years) and on images related to periods of flooding captured by the Landsat 5 sensor, making it possible to identify five levels of susceptibility to flooding in this basin. The determining factors for this classification were: amplitude of the relief, slope of the floodplain and its immediate surroundings, and direct and indirect anthropogenic interventions in this lowland, with emphasis on removal of vegetation and changes in the channels (dam construction). The influence exerted by the Camaquã River on the downstream part of the basin was also considered. In this basin, 75% of the fluvial system has moderate to very high susceptibility to flooding. The methodology uses an integrated approach of easy-access data and was successful in analyzing flooding, providing a foundation for territorial ordering.