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Abstract
Floods are frequent hydro-meteorological hazards which cause losses in many parts of the world. In hilly and mountainous environments, floods often contain sediments which are derived from mass movements and soil erosion. The deposited sediments cause significant direct damage, and indirect costs of clean-up and sediment removal. The quantification of these sediment-related costs is still a major challenge and few multi-hazard risk studies take this into account. This research is an attempt to quantify sediment deposition caused by extreme weather events in tropical regions. The research was carried out on the heavily forested volcanic island of Dominica, which was impacted by Hurricane Maria in September 2017. The intense rainfall caused soil erosion, landslides, debris flows, and flash floods resulting in a massive amount of sediments being deposited in the river channels and alluvial fan, where most settlements are located. The overall damages and losses were approximately USD 1.3 billion, USD 92 million of which relates to the cost for removing sediments. The deposition height and extent were determined by calculating the difference in elevation using pre- and post-event Unmanned Aerial Vehicle (UAV) data and additional Light Detection and Raging (LiDAR) data. This provided deposition volumes of approximately 41 and 21 (103 m3) for the two study sites. For verification, the maximum flood level was simulated using trend interpolation of the flood margins and the Digital Terrain Model (DTM) was subtracted from it to obtain flooding depth, which indicates the maximum deposition height. The sediment deposition height was also measured in the field for a number of points for verification. The methods were applied in two sites and the results were compared. We investigated the strengths and weaknesses of direct sediment observations, and analyzed the uncertainty of sediment volume estimates by DTM/DSM differencing. The study concludes that the use of pre- and post-event UAV data in heavily vegetated tropical areas leads to a high level of uncertainty in the estimated volume of sediments.
Highlights
Hydrological disasters such as river floods and flash floods associated with extreme weather events have caused significant damage [1,2]
The sediment deposition height was measured in the field for a number of points for verification
Flood hazard maps are created from hydrodynamic models [3,4,5,6,7], and the flood intensity is linked to the physical vulnerability of elements at risk using damage curves that are related to building of land use types [4,8,9,10,11,12,13]
Summary
Hydrological disasters such as river floods and flash floods associated with extreme weather events have caused significant damage [1,2]. While there are many studies that focus on the erosion process [14,15,16,17,18], relatively few have investigated the relation between erosion and sedimentation and the incurred damages and costs. The research efforts on the quantification of the damage and clean-up costs incurred by sediment deposition are much less than those that model the initiation and transportation processes
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