ReFH Model
The ReFH Model is a rainfall-runoff model based on procedures developed by the Center for Ecology and Hydrology (CEH) to update the FSR/FEH Rainfall Runoff Method, in response to concerns that the FSR/FEH design model tended to overestimate design floods. ReFH2 is the latest version of the model.
In InfoWorks ICM, the main difference between the two versions of the ReFH model is the way in which the Initial Soil Moisture (Cini) and Initial Baseflow (BF0) are calculated in a subcatchment or used to generate a rainfall event.
The ReFH model consists of the same three main components as the original FSR/FEH model: a loss model, a routing model and a baseflow model:
The ReFH Runoff Routing model must be used in conjunction with the ReFH Runoff Volume Type. See the ReFH Unit Hydrograph Model topic for details of the routing model component.
Loss Model Component
The loss model is based on the Probability Distributed Model (PDM). Effective rainfall is evaluated sequentially during a storm and if soil storage is filled, runoff will equal 100%.
The required input parameters are:
- Cini - initial soil moisture content specified in the Rainfall Event initial conditions
- Cmax - maximum soil moisture capacity specified in the Subcatchment Data Fields
Cini and Cmax can be either user defined or estimated from catchment descriptors.
The percentage runoff can be calculated for observed events by:
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where: qt – runoff at time t Pt – rainfall at time t Ct – soil moisture content at time t Cmax - maximum soil moisture capacity
And the soil moisture store is updated by:
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The percentage runoff can be calculated for design events by:
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where a is an adjustment coefficient (specified in the ReFH Rainfall Event) |
A description of the loss model can be found in section 3 of the R&D Technical Report FD1913/TR Revitalisation of the FSR/FEH Rainfall Runoff Method. See the report for more details.
Baseflow Model Component
The baseflow model is based on the linear reservoir concept with a characteristic recession defined as an exponential decay.
The required input parameters are:
- BF0 - initial baseflow specified in the Rainfall Event initial conditions
- BL - baseflow lag specified for the Subcatchment Data Fields
- BR - baseflow recharge specified for the Subcatchment Data Fields
All three baseflow parameters can be user defined or estimated from catchment descriptors.
A description of the baseflow model can be found in section 3 and Appendix B of the R&D Technical Report FD1913/TR Revitalisation of the FSR/FEH Rainfall Runoff Method. See the report for more details.
