Qp 22 AT

Total rainfall

Initial soil moisture

Cjni

Initial baseflow BF0

Total rainfall

Initial soil moisture

Cjni

Net rainfall

Routing

model

(Tp)

Baseflow model (BR, BL)

Fig. 13.7 Structure of the FEH 'revitalised' flood hydrograph method (ReFH) design event model (after Kjeldsen, 2007, Copyright NERC (CEH)).

13.5.5 The FEH 'revitalised' flood hydrograph method

The FEH 'revitalised' flood hydrograph method (ReFH) method was developed to make improvements to the main components of the FEH design event approach in order to address problems identified with the original method in large-scale comparison studies (Webster and Ashfaq, 2003), in particular a widely held view that the design flows it produced were too high and that it produced overly symmetrical hydrographs. The ReFH method is described in FEH Supplementary Report No. 1 (Kjeldsen, 2007). The basic structure of ReFH (Fig. 13.7) retains the fundamental form of the FEH design event model, that is, a loss module combined with a unit hydrograph 'routing' module, superimposed on a baseflow hydrograph.

The loss model in the ReFH method uses the concept of the probability distributed soil moisture model or PDM (which is described in Section 12.8.1). Soil moisture is continually updated throughout the event, which in effect allows for an increase in percentage runoff throughout the storm, answering one criticism of earlier event-based rainfall models. The parameter Cini is the soil moisture content at the start of the storm. The parameter Cmax represents the maximum localised soil moisture storage capacity in the catchment. For gauged catchments it is best estimated from flow and rainfall data using an optimisation method that simultaneously estimates the time to peak. Otherwise, it can be estimated from catchment descriptors:

0 0

Post a comment