Independent thesis Advanced level (professional degree), 20 credits / 30 HE credits
This thesis is a study of model predictive control of water levels and flows in a water
system. The water system studied includes five lakes and six dams that are regulated
manually by sluice-gates. The water is used in the papermaking process at Holmen
Paper Mill in Hallstavik. The aim of this thesis is to find out how to control the
water system when all dams are automated and to minimize the discharge of water
from the system without risking production stops due to water shortage. To fulfil
the aim, a simulation is made during a dry period with low amount of rain. The
simulation is then compared to the same period but when the system was manually
In this thesis two models of the water system are constructed, a simple linear model
and a more complex non-linear model. In the linear model the channels between
the lakes are assumed to be delays of water flow. In the non-linear model the same
channels are described by Saint Venant equations of changes of flow and Manning’s
equation on how water flow and the cross-section of a channel are related. In both
models, the lakes are modelled as the change in volume with respect to time due to
inflow to and outflow from the lake.
The non-linear model is verified against measured water levels, flows, sluice-gate
heights and precipitation to ensure that the model describes the water system well
The linear model is used in the model predictive controller to calculate the optimal
outflow from the dams. The optimal outflows are then converted into optimum gate
heights in the dams, which in turn are used as input to the non-linear model. The
non-linear model is used to simulate the water system.
The results from the simulation show that the control of the water system can
significantly be improved. The conclusion of this thesis is that a lot more water can
be saved when the system is automated and that the water levels in the lakes can
be kept more stable with respect to a set reference level. The recommendation if
only one dam is to be controlled initially is to start with the dam at Närdingen.
2012. , 98 p.