Delimitation of flood areas based on a calibrated a DEM and geoprocessing: case study on the Uruguay River, Itaqui, southern Brazil

Paulo Victor N Araújo,Alexandre B Lopes,Robert M Silva,Venerando E Amaro

doi:10.5194/nhess-19-237-2019

Abstract

Abstract. Flooding is a natural disaster which affects thousands of riverside, coastal, and urban communities causing severe damage. River flood mapping is the process of determining inundation extents and depth by comparing historical river water levels with ground surface elevation references. This paper aims to map flood hazard areas under the influence of the Uruguay River, Itaqui (southern Brazil), using a calibration digital elevation model (DEM), historic river level data and geoprocessing techniques. The temporal series of maximum annual level records of the Uruguay River, for the years 1942 to 2017, were linked to the Brazilian Geodetic System using geometric leveling and submitted for descriptive statistical analysis and probability. The DEM was calibrated with ground control points (GCPs) of high vertical accuracy based on post-processed high-precision Global Navigation Satellite System surveys. Using the temporal series statistical analysis results, the spatialization of flood hazard classes on the calibrated DEM was assessed and validated. Finally, the modeling of the simulated flood level was visually compared against the flood area on the satellite image, which were both registered on the same date. The free DEM calibration model indicated high correspondence with GCPs (R2=0.81; p<0.001). The calibrated DEM showed a 68.15 % improvement in vertical accuracy (RMSE = 1.00 m). Five classes of flood hazards were determined: extremely high flood hazard, high flood hazard, moderate flood hazard, low flood hazard, and non-floodable. The flood episodes, with a return time of 100 years, were modeled with a 57.24 m altimetric level. Altimetric levels above 51.66 m have a high potential of causing damage, mainly affecting properties and public facilities in the city's northern and western peripheries. Assessment of the areas that can potentially be flooded can help to reduce the negative impact of flood events by supporting the process of land use planning in areas exposed to flood hazard.

Highlights

Flooding, as a major natural disaster, affects many parts of the world including developed countries, and has severe impacts on populations and causes socioeconomic damage
This study aims to conduct a robust mapping of flood hazard delimitation areas influenced by the Uruguay River, using the case study of Itaqui in the state of Rio Grande do Sul, southern Brazil, through a calibration of digital elevation model (DEM) from Shuttle Radar Topography Mission (SRTM) images, historical fluviometric level data collected at Itaqui station, and geoprocessing techniques
– Digital image processing (DIP) was the technique applied to improve the visualization of the historical flooding from the CBERS-4 MUX satellite images

Summary

Introduction

As a major natural disaster, affects many parts of the world including developed countries, and has severe impacts on populations and causes socioeconomic damage. Due to this kind of natural disaster, billions of dollars in infrastructure and property damage, as well as hundreds of human lives, are lost each year (Demir and Kisi, 2016; Elnazer et al, 2017). It is understood that flood risks and hazards will not subside in the future and, with the onset of climate change, flood intensity and frequency will threaten many regions of the world (IPCC, 2014). Araújo et al.: Delimitation of flood areas based on a calibrated DEM and geoprocessing: Uruguay River

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