Chapter 3 : Reservoir models - KU Leuven

In figure 3.7 the storage in the system at the beginning and at the end of the storm are
shown as well as the maximum storage that occurred. If these storage values are ranked
as a function of the maximum overflow discharge (i.e. approximately the maximum
outflow minus a constant throughflow when the overflow starts spilling), a clear trend
is observed. The storage at the end of the overflow event is an almost constant value.
At this moment the rainfall input into the system is most often nil or very small. In that
case the system behaves as a static reservoir with a fixed volume that is completely full.
The maximum storage in the system appears to be linearly varying with the maximum
discharge. The difference between the maximum storage and the storage at the end of
the event can be assigned to the dynamic storage, which seems to be highly correlated
with the maximum discharge. The fluctuation of the storage at the beginning of the
overflow event is due to the shape of the hyetograph. For peaked storms and (high)
constant rainfall input over short durations the storage at the beginning of the overflow
event will be near to the maximum storage, while for constant rainfall input over longer
durations the storage at the beginning of the overflow event will be more
an intermediate value. This indicates that the dynamic storage is highly dependent on
the instantaneous inflow.
3.2.3.2 Static storage
The maximum static storage is the storage in a sewer system when the system is
filled up to the crest of the weir, when there is no throughflow and the water is
stagnant (figure 3.8).
Figure 3.8 : Longitudinal profile of a sewer system
on which the static storage is indicated (hatched area).
Chapter 3 : Reservoir models 3.9