FastFlood Technical

FastFlood Technical is the advanced version of FastFlood, designed for experienced modellers who require detailed control over flood simulations. At its core, the tool is built on the Super Fast Flood Simulation (SFFS) framework, enabling rapid, high-resolution flood modelling.

Getting Started

You can access FastFlood Technical at www.fastflood.org. Upon opening the website, you are greeted with the main interface and a global map, showing areas that can be modelled. Closing the welcome message reveals helpful tooltips to guide initial setup. The menu button on the left provides access to all input options and simulation settings, while the Simulate button at the bottom runs the model.

Elevation and Domain Setup

For a simple rainfall-driven simulation

  1. Click the auto-download elevation button and select a rectangle on the map.

  2. The menu will allow you to define the resolution of the model domain (pixel size) according to your needs.

  3. For initial experiments, it is recommended to start with a smaller, coarser domain (e.g., 600 × 600 px at 20 m resolution), which runs instantly on most devices. Larger domains will increase computation time.

Once the simulation runs, the progress dialogue displays its status. Upon completion, a flood map overlays the model domain. Using the Shift button, you can inspect elevation and flood heights.

Precipitation Scenarios

FastFlood Technical allows defining precipitation as the source of flooding:

  • You can specify intensity (possibly spatially varying) and duration for the rainfall event.

  • Both lower intensity and shorter duration reduce flood heights, while the relationship between rainfall and flooding depends on flow velocities, path lengths, and topography.

Spatial precipitation data can also be uploaded as GeoTIFFs, or automatically downloaded for testing purposes.

Model Settings

By default, the model assumes:

  • Homogeneous surface roughness

  • Ignores reservoirs and depressions (faster computation)

  • No non-linear correction in stage-discharge relationships

  • No pressure-driven flow path correction

These default settings can be adjusted in the Settings menu for different flood types:

  • Flash floods: Fastest and accurate with all optional corrections off.

  • Fluvial floods: Enable non-linear correction and flat terrain adjustment for rivers.

  • Urban floods: Flat terrain correction enabled for accurate urban inundation.

The accuracy of simulations depends heavily on the quality of elevation data, while precipitation and surface roughness parameters can be manually adjusted to improve results.

Analysis

FastFlood Technical includes simple analysis tools:

  • Flood depth histogram – visualise the distribution of flood heights across the domain.

  • Average flood depth per land cover class – useful for assessing impact by land use.