Hydrologically sensitive areas: theory and application to Barigui river watershed, PR, Brazil

Abstract

The concept of hydrologically sensitive area (HSA) is discussed and applied to Barigui river watershed (58.5 km²), located in Almirante Tamandaré city, Parana State, Brazil. The HSA is considered as the area of the watershed with a higher probability of reaching a soil saturation condition, and is, therefore, defined as the area that remains saturated for more than 30% of the time. The Topmodel was used to simulate the saturated zone dynamics in the watershed. The model assumes that the saturated zone dynamics can be obtained by hydrological similarity given by the spatial distribution of topographic index, based on the construction of the soil saturation probability in the watershed. The Topmodel showed good results in observed flow data, confirming a high performance in the meso-scale watersheds, with humid climate and smooth relief. The HSA's in the watershed totaling 17.1 km² or 27% of the total area. Considering the HSAs as those of interest for environmental preservation, an increase of 13.2 km² of the permanent preservation areas in the watershed was found according to the Forest Code (Law n° 4.771 / 69). It makes a total of 44% of the whole watershed environmentally important.