Chapter 3 : Reservoir models - KU Leuven

When a resulting subcatchment after separation still contains more than one overflow,
the modelling can be performed in several stages. For instance, for a subcatchment
with two overflows two stages are necessary. In the first stage the different overflows
are modelled as one overflow. In the second stage the overflow which starts spilling
first, is modelled together with the throughflow so that only the overflow events of the
second overflow are obtained. The overflow events of the first overflow can then be
obtained by subtracting both overflow series from each other. In figure 3.10
the storage/throughflow-relationship is presented for a catchment with two overflows
and a single pump as throughflow, where the two overflows are modelled together.
In figure 3.25 for the same catchment the storage/throughflow-relationship is given
where the first spilling overflow is modelled as throughflow in order to obtain
the overflow events from the second overflow. This kind of methodology can be
extended to more than two overflows per subcatchment. However, this is a labourious
methodology. It would be easier if these different stages would be implemented
in the reservoir modelling system itself for which a methodology is proposed in
paragraph 3.3.2.
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11
10
9
8
7
6
5
4
3
2
1
0
throughflow (mm/h)
f = 1 f = 2
f = 3 f = 4
f = 5 f = 6
f = 7 f = 8
0 1 2 3 4 5 6 7 8 9 10 11 12 13
storage (mm)
Figure 3.25 : Storage/throughflow-relationship for the second spilling overflow
in a small sewer system with one pump for the throughflow
for a range of composite storms with different frequencies f
(the discharges of the first spilling overflow are modelled as throughflow).
3.26
The influence of rainfall and model simplification on combined sewer system design