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If it is assumed that, during recession periods, the gradient of the slowflow dB/dt is very much smaller than the quickflow gradient dQ/dt, then the slowflow B(t) may be estimated from
formula
6
where q(t) is the observed streamflow, and dq/dt the gradient of the observed streamflow. In practice, some small oscillations are found in these resulting slowflow estimates, and a constant value is fitted through them. For example, for event No. 18, which took place on 28 September 1967, Table 1 shows pre-event and post-event slowflow estimates of 0.061 mm.h−1 and 0.175 mm.h−1, respectively, occurring during the periods of recession.
Table 1

Significant flow values for event No. 18 on catchment No. 61001

DescriptionUnitsValue
Catchment No.  61001 
River name  Western Cleddau 
Station name  Prendergast Mill 
Catchment area km2 197.6 
Event No.  18 
Date of occurrence  28 Sep 1967 
Pre-event slowflow mm.h−1 0.061 
Quickflow at end of pre-event recession mm.h−1 0.083 
Time ordinate at end of pre-event recession 
Minimum observed flow mm.h−1 0.128 
Maximum observed flow mm.h−1 0.795 
Post-event slowflow mm.h−1 0.175 
Quickflow at start of post-event recession mm.h−1 0.281 
Time ordinate at start of post-event recession 23 
Quickflow at end of post-event recession mm.h−1 0.051 
Time ordinate at end of post-event recession 41 
DescriptionUnitsValue
Catchment No.  61001 
River name  Western Cleddau 
Station name  Prendergast Mill 
Catchment area km2 197.6 
Event No.  18 
Date of occurrence  28 Sep 1967 
Pre-event slowflow mm.h−1 0.061 
Quickflow at end of pre-event recession mm.h−1 0.083 
Time ordinate at end of pre-event recession 
Minimum observed flow mm.h−1 0.128 
Maximum observed flow mm.h−1 0.795 
Post-event slowflow mm.h−1 0.175 
Quickflow at start of post-event recession mm.h−1 0.281 
Time ordinate at start of post-event recession 23 
Quickflow at end of post-event recession mm.h−1 0.051 
Time ordinate at end of post-event recession 41 
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