Corresponding author Raimundo Almir Costa da ConceiçãoFlood modeling is one of the layers that compose the preliminary susceptibility map, which after the field investigation step is part of the Mass Movement and Flood Susceptibility Map. These maps are produced by the Geological Survey of Brazil, through the National Plan for Risk Management and Response to Natural Disasters (Programa Nacional de Gestão de Riscos e Respostas a Desastres Naturais, PNGRRDN). Initially, the flood modeling methodology consisted of applying the HAND model based on the following variables, hydrographic basin, and soil susceptibility. However, several inconsistencies were observed during fieldwork, especially regarding the model capacity to describe regions with specific hydrological regimes. A methodological improvement using other variables became necessary. Among the proposed variables, the relief susceptibility to floods yielded the most satisfactory results, especially since it could be applied to the entire national territory and was, therefore, introduced to replace the hydrographic basin susceptibility. Furthermore, the methodology used for defining the thresholds of the three flooding susceptibility classes (high, average and low) has also been modified by using the quartile deviation, which provides a less subjective class distribution. Using relief susceptibility and quartile deviation in flood modeling was tested in the Conceição do Castelo and Presidente Kennedy municipalities (Espírito Santo, Brazil), where the morphological configuration covers a wide variety of environments, which is fundamental for the validation of the new variable. The results of the new model were satisfactory. The various types of plains continue to be well represented while a substantial improvement has been observed in the representation of flood-susceptible areas such as marine terraces and colluvium ramps.
In the Amazon region, there are more than 26.000 people living in areas at risk of fluvial erosion processes. In addition to the large number of people impacted, studies have shown that the erosion patterns identified on the margins of mega rivers in the Amazon region are distinct due to the fact they are related the mass movement leading to great soil displacement known as ‘Terras Caidas’. In this context, this study aims to evaluate quantitatively the degrees of risk in areas subject to fluvial erosion in three communities: Itanduba, São Braz, and Fátima de Urucurituba. The methods include hazard attributes, as well as vulnerability aspects, through the Analytic Hierarchy Process (AHP). A multitemporal analysis were made to validated the marginal erosion at the studied areas. The results indicated a high risk of fluvial erosion on these areas. The local families lives under high and very high social vulnerability in conditions with little infrastructure and very close to the susceptible erosive riverbank. The riverbank is composed of poorly consolidated sediments, show instability indicators, and are usually associated to drainages with flow rates above 100.000m3/s. The results and methodology brings an important contribuition to territorial planning of the region.
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