Proposta metodológica para análise espaço - temporal de inundações: aplicação na área urbana de Alegrete - RS

Abstract

The municipality of Alegrete, located in the west of the State of Rio Grande do Sul, presents a great recurrence of floods. Positioned near the middle course of the hydrographic basin and located on the banks of the Ibirapuitã River, the urban area of Alegrete is frequently affected by floods during periods of overflowing the river and its tributaries, Regalado, Jararaca and Caverá streams, affecting its population . The research problem of this doctoral thesis is structured from the floods in the urban area of Alegrete and in the understanding of its dynamics. A spatiotemporal analysis of flood risk areas in the urban area of Alegrete is presented from different flood scenarios. It was characterized the behavior of the Ibirapuitã river basin and its relationship with the temporal and probabilistic dynamics of the occurrence of flood events. Special attention was given to the danger of flooding to urban areas from the digital terrain modeling, in perspective of different times of return and analyzed the use and occupation of urban space and vulnerability by determining the number of affected buildings and their characteristics, from primary and secondary data. From this routine was performed the hierarchy of risk areas associated with floods, based on the hazard and exposed elements. The descriptive and inferential statistical analysis allowed us to establish how the Ibirapuitã river basins behave throughout the 74-year series or during specific periods, such as during floods, and it is possible to establish the mean water level throughout the series, maximum and minimum recorded, in addition to the data analysis also considering the monthly and seasonal variations. The limnimetric measurement of 840 mm was considered as reference for flooding. This value was established considering the field survey conducted at the linymetric station and also information from the Civil Defense Coordination of the Municipality of Alegrete. Empirical and statistical relationships between recurrence, exposure and risk were identified for areas below the 82 meter elevation in the urban area, considering affected buildings and population. By means of geotechnologies and techniques of digital terrain modeling, the following scenarios were proposed for the occurrence of floods: Scenario of susceptible areas; Scenario of flood hazard areas; Flood scenario according to typologies of urban land use; Flood vulnerability cenario; Flood risk scenario; Contingent hit by floods