Meratyn

Manual/Tutorials

Flood Exposure Risk Assessment

This tutorial maps flood-prone land and joins it with exposed assets and incident clusters: hydrology from a DEM, a buffer around the streams, and two analysis layers on top. It uses the Hydrology tools, the Vector tools, and the Processing toolbox.

1. Load your layers

  • a DEM covering the area (GeoTIFF or COG),
  • asset points you want to check for exposure (facilities, customers),
  • optional: incident or claim points for the hot spot step.

The hydrology tools take a file path in and write a file path out, so a local raster works best (desktop app).

2. Prepare the DEM

  1. Run Processing → Whitebox Toolbox → Hydrology → Fill Depressions (or Breach Depressions Least Cost) so water can flow across the surface.
  2. Run Processing → Whitebox Toolbox → Hydrology → D8 Flow Accum on the filled DEM.

The flow-accumulation grid highlights where water converges; the cells with the largest accumulations are your drainage network.

3. Extract the streams

Run Processing → Whitebox Toolbox → Hydrology → Extract Streams on the flow-accumulation grid and set a threshold appropriate to your area. Start with the default and adjust until the extracted lines match the real channels.

4. Buffer the streams

Run Processing → Whitebox Toolbox → Vector → Buffer Vector on the extracted streams — 200 m is a common first pass for a screening study. The buffer is your flood-prone zone.

5. Join the exposed assets

Run Processing → Vector → Spatial Join with the asset points as input and the buffer as the join layer, keeping only features that intersect. The output is the subset of assets inside the flood-prone zone, with the buffer’s attributes attached.

6. Cluster the incidents

If you loaded incident points, run Processing → Spatial Statistics → Getis-Ord Gi Hot Spot Analysis* on them. Statistically significant hot spots near the buffer are your strongest risk candidates.

7. Style the map

Give the buffer a translucent blue fill, style the exposed assets with a categorized style, and put the hot spot raster under everything at reduced opacity.

Next steps

  • Run Processing → Whitebox Toolbox → Hydrology → Basins to add watershed context.
  • Export a print layout of the assessment for stakeholders.