Chapter 3 : Reservoir models - KU Leuven

Figure 3.29 : Coordinate system used in the reservoir modelling system Remuli.
This piecewise linear approach with a translation of the coordinate system also allows
the incorporation of extra storage during the overflow event.
The overflow can be modelled as one of the outflows, so that the total outflow Q out
becomes :
V
Q Q Q
( )
V Q V
V Q Q Q V
out = through + over = m + mo = m + mo
(3.14)
V
Q
through
m
where Q m and Q mo are the maximum throughflow and maximum overflow respectively.
Consequently both flows can be found as :
Qm
V V Qm
= =
Q + Q Q
m
m
m
mo
out
m
(3.15)
Q
over
Qmo
V V Qmo
= =
Q + Q Q
m
m
mo
out
(3.16)
This approach of modelling different outflows from one reservoir using different linear
relationships can be extended to more than two outflows. This makes it possible to
handle more complex models where one reservoir can have more than one overflow.
In this way it is not necessary to split up every sewer system into different reservoirs
each with one overflow, nor is it necessary to perform the modelling of subcatchments
with more than one overflow in several stages. These reservoirs with more than one
overflow are not implemented yet, but it can be performed easily.
3.32
The influence of rainfall and model simplification on combined sewer system design