Urbanization and exposure to flood hazard: a study in the watershed of Henrique River, Erechim, RS

The spatial clipping of a watershed becomes the appropriate analysis scale for environmental studies, since in its area different alterations can be observed, therefore, their reflexes and impacts. With the urbanization process, interferences in the land surface are visualized, as a result of these disturbances, different components are created that expose the population to the hazard of flooding. The objective of the research is to identify households with different levels of hazard in the Henrique river basin, in the urban area of Erechim, due to the poorly planned urbanization process over 40 years. To make the work feasible, a photogrammetry process was used to elaborate the digital terrain model, thus elaborating a hypsometric map and slope. To analyze the transformations over the years, aerial photographs from the years 1975 and 1989, and satellite images 2010 and 2015 were processed, thus obtaining a 40-year temporal analysis. In order to verify the hazard, secondary data sources were analyzed and primary data were created from the field analysis; all tabulated information presented three danger levels for flood-affected households. The results show that allotments were built on the canals and river terraces, and over 40 years the watershed uses changed from rural to urban, resulting in 68 households being exposed to the hazard. Therefore, it can be stated that urbanization without proper planning exposes the population to the hazard of flooding due to the interference made in the watershed.