Overview

As discussed in this guidance document, research has shown that FEH methods are more accurate than methods such as IH124 for estimating peak flows within small catchments and for conducting plot scale greenfield runoff calculations. ReFH2 is a recommended method within the CIRIA SuDS Manual for undertaking the estimation of greenfield runoff rates and volumes using the rural model. It is also a recommended method for undertaking the estimation of post development runoff rates and volumes for simple developments using the urban modelling capabilities.

This section describes the direct use of ReFH2 for undertaking these analyses and should be read in conjunction with the SuDS manual.

ReFH2 has been integrated within Autodesk InfoDrainage drainage design software and Causeway Flow software. For this category of use please refer to the software documentation for these drainage software packages.

ReFH2 can use both catchment and point exports of design rainfall and catchment descriptors from the FEH Web Service. For assessing the runoff from development sites, it is anticipated that the usual route would be to use a point export from the FEH Web Service for your development site.

The software automatically selects the plot scale equations for Time to Peak ($Tp$) and Baseflow Lag ($BL$) (see Model parameter estimation) if you import a point export. If you are using a catchment export then you will need to select the use of the plot scale equations on the Catchment Details tab to apply the ReFH2 model at plot scale. This is achieved via a tick box at the import of catchment descriptors and will result in the plot scale equations being utilised for the analysis.