Skip to Main Content

The four component hydrograph separation technique facilitates the definition of various important flows in terms of suitable combinations of the various subcomponents (Table 2). The terminology ‘underlying flow’ is adopted directly from the analysis presented in Reed et al. (1975), while that of ‘nonseparated flow’ is based more loosely on the term mentioned in NERC (1975). These suggested definitions may be more exact than those presented previously in the standard event-based models described earlier. For example, historically the use of the word ‘baseflow’ is sometimes ambivalent. More often than not it is used to represent the nonseparated flow, but occasionally it is used to suggest the underlying flow (see, for example, Figure 2.5 in Beven (2001)).

Table 2

Suggested revised definitions of the most important flows arising from hydrograph separation

TermDefinitionFour component interpretation
Underlying flow The flow that would have occurred if the current storm event had not taken place SFP + QFP 
Slowflow hydrograph The slowflow response resulting from a combination of the preceding storms and the current storm event SFP + SFS 
Nonseparated flow The quickflow response to the preceding storms, added to the slowflow hydrograph OR SFP + SFS + QFP 
 The slowflow response to the current storm event, added to the underlying flow OR SFP + QFP +SFS 
 The quickflow response to the current storm event, subtracted from the overall observed streamflow hydrograph (SFP + SFS + QFP + QFS) − QFS 
Quickflow hydrograph The quickflow response resulting from a combination of the preceding storms and the current storm event QFP + QFS 
TermDefinitionFour component interpretation
Underlying flow The flow that would have occurred if the current storm event had not taken place SFP + QFP 
Slowflow hydrograph The slowflow response resulting from a combination of the preceding storms and the current storm event SFP + SFS 
Nonseparated flow The quickflow response to the preceding storms, added to the slowflow hydrograph OR SFP + SFS + QFP 
 The slowflow response to the current storm event, added to the underlying flow OR SFP + QFP +SFS 
 The quickflow response to the current storm event, subtracted from the overall observed streamflow hydrograph (SFP + SFS + QFP + QFS) − QFS 
Quickflow hydrograph The quickflow response resulting from a combination of the preceding storms and the current storm event QFP + QFS 

Close Modal

or Create an Account

Close Modal
Close Modal