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

摘要

Flooding is a natural disaster which affects thousands of riverside, coastal,and urban communities causing severe damage. River flood mapping is theprocess of determining inundation extents and depth by comparing historicalriver water levels with ground surface elevation references. This paper aimsto 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 seriesof maximum annual level records of the Uruguay River, for the years?1942 to?2017,were linked to the Brazilian Geodetic System using geometric leveling andsubmitted for descriptive statistical analysis and probability. The DEM wascalibrated with ground control points?(GCPs) of high vertical accuracy basedon post-processed high-precision Global Navigation Satellite System surveys. Using the temporal seriesstatistical analysis results, the spatialization of flood hazard classes onthe calibrated DEM was assessed and validated. Finally, the modeling of the simulated flood level was visually compared against the flood area on the satelliteimage, which were both registered on the same date. The free DEM calibrationmodel indicated high correspondence with GCPs (R2=0.81; p<0.001). Thecalibrated DEM showed a 68.15% improvement in vertical accuracy(RMSE=1.00m). Five classes of flood hazards were determined:extremely high flood hazard, high flood hazard, moderate flood hazard, lowflood hazard, and non-floodable. The flood episodes, with a return time of100?years, were modeled with a 57.24m altimetric level. Altimetric levelsabove 51.66m have a high potential of causing damage, mainly affecting propertiesand public facilities in the city's northern and western peripheries. Assessment of the areas that can potentially be flooded can help to reducethe negative impact of flood events by supporting the process of land useplanning in areas exposed to flood hazard.