The FastFlood Method

The FastFlood method uses a series of recent innovations in fast flow routing and flood estimation. The steps of the method are the following:

The a-temporal nature of the model (only predicting peak flood heights) comes from its usage of steady-state principles. This means a flow state is found where for each location, in and outflow are equal. This equates to the flow state on a landscape after a rainfall event of infinite duration. In reality, a steady state is rarely reached, so a correction is applied. This correction works by estimating the catchment properties (length, average travel distance, average velocities, slope etc..) for each location. From these, the actual peak throughflow in a partial steady state is estimated. Because of the a-temporal nature, the model features sensitivity to the usual parameters (elevation model quality, Mannings surface roughness coefficient, infiltration rates) and, just as any other physically-based model, required calibration and validation.

In many of these steps, the fast sweeping algorithm has been adapted for optimal routing and spatial processing of data. The infiltration currently employs a fixed-rate infiltration that is subtracted from the precipitation. In an upcoming version, the Green and Ampt model will be employed in an analytically integrated manner.