The Revitalised Rainfall-runoff model in ReFH 2 enables you to generate flood peak flows and hydrographs from given rainfall events for both catchments and development sites.

Design flood events in the model are estimated using the corresponding design rainfall hyetographs. These hyetographs are derived from the recommended FEH22 or FEH13 Depth Duration Frequency (DDF) rainfall model (or from the legacy FEH99 DDF model).

Observed rainfall events can also be used to model the flood hydrograph and hence peak flow for that event. The initial catchment conditions prior to the start of the observed rainfall event are estimated using antecedent rainfall and a daily soil moisture accounting procedure.

There are two sets of catchment model equations for estimating catchment parameters, one for England, Wales and Northern Ireland and one for Scotland. These are used in conjunction with initial conditions specified on the basis of the country and rainfall model in use.

ReFH 2 is a recommended method in the 2015 CIRIA SuDS Manual (C753) for estimating greenfield runoff rates and volumes. The model includes parameter equations to facilitate application at the development site as well as the catchment scale.

ReFH 2 models the influence of urbanisation on catchment flood regimes using an explicit model to represent the impacts of urbanisation. Able to partition catchments into greenfield and impervious surface components, ReFH 2 is also recommended in the SuDS guidance for estimating brownfield and simple-site post-development runoff rates and volumes.

When ReFH 2 is used with the FEH22 or FEH13 DDF model, there is no requirement for the legacy FEH99 alpha parameter adjustment procedure. This means these estimates are entirely independent of the FEH statistical-method estimates obtained using WINFAP. Having two independent FEH methods for estimating flood risk in ungauged catchments is a significant advance and reflects the value of the recommended FEH22 or FEH13 rainfall models.

Comparisons have shown that the ReFH 2 estimates and the pooled statistical estimates are comparable, providing an alternative method for the estimation of peak flows in an ungauged catchment.

For further information, see our openly published online technical guide and supporting science reports.