Map regions that are likely to be below water during an extreme rain event using SCALGO Flash Flood Mapping

A consequence of extreme rain events where the sewage system is exhausted and the ground is saturated with water is that water gathers in depressions of the terrain. This can have catastrophic effects on housing and other assets within the depressions. Therefore, analyzing how water gathers in depressions of detailed terrain models is an important part of flood risk analysis.

SCALGO Flash Flood Mapping shows how much rain has to fall before any given cell of a raster terrain is below water. Consequently, the mapping can be easily used to compute what part of each depression is below water after a given amount of rain, and thus effectively shows how water collects in depressions for all possible amounts of rain.

SCALGO Flash Flood Mapping considers all potential rain amounts and analyzes how depressions within other depressions are filled with water; it takes the volume and watershed of each depression into account, as well as the changes to watersheds that occur when other upstream depressions are filled with water. The mapping can be produced for “non-uniform” rain, simulating real extreme rain events. It is also possible to fill depressions that are completely flooded after a certain amount of rain and thus compute a realistic flow network. This makes it possible to analyze how critical situations can occur when depressions fill with water resulting in dramatically increased watersheds for other downstream depressions.

Figure showing parts of the terrain below water for 50mm (red), 100mm (yellow) and 150mm (blue) of rain, respectively.

Map data ©2011 Google Imagery ©2011 COWI A/S, DDO, DigitalGlobe, GeoEye, Scankort