Graduation of Sietse Weistra

Dynamic Tidal Power in the Voordelta: Assessing the potential of a southwest-oriented DTP dam for renewable energy and coastal resilience

• Professor of graduation: Prof. dr. ir. S.G.J Aarninkhof

• Supervisors: Dr. ir. R. J. Labeur (TU Delft), Ir. Y. H. Attema (Svašek Hydraulics), Dr. J. A. Arriaga Garcia (TU Delft)

A possible way of generating a stable and predictable base load of renewable energy, supplementing
the shortcomings of wind and solar energy, is dynamic tidal power (DTP). DTP is generated by a DTP
dam, which is built in the sea under an angle with the propagating tidal wave. A dam of sufficient
length can create a phase difference in propagating tidal wave on either side of the dam, creating head
differences over the dam, which can be used to generate renewable energy using large turbines in
the dam. Previous studies into the possibilities of DTP all considered a dam built perpendicular to the
coast and the direction of the propagating tidal wave. However, a construction of this size extending
into the North Sea interferes with other area functions. Instead of a perpendicular dam, an oblique dam
off the Dutch delta coast has been proposed to reduce this interference. This design has the additional
benefits that it could increase the coastal safety of the surrounding area and potentially increase the
sediment budget of the Voordelta area in front of the coast.
In this study, a first-order assessment of the impact of a DTP dam with such an orientation has been
carried out. This assessment focuses on two aspects: the expected energy yield and how this compares
to the expected energy yield of a perpendicular dam under the same conditions; the impact this
dam has on the coastal safety of the surrounding area. Furthermore, an analysis of the change in
hydrodynamic and morphological processes in the Voordelta as a result of the construction of such a
dam has been carried out.
The propagation of the tidal wave around an oblique DTP dam in the North Sea has been modelled,
with the use of FINEL2D, a two-dimensional flow model. The reference layout of the DTP dam has been
determined beforehand based on several requirements concerning the location and length. Using a
turbine module integrated into FINEL, the ratio between the water head and discharge through the
turbine at every timestep has been calculated for every grid cell in the dam. Based on this discharge,
the energy output of the DTP dam has been calculated. The same model has been run with a dam
located perpendicular to the Dutch coast, similar to previous studies.
With the model, a DTP dam with a length of 62.5 km and a southwest direction starting at the Maasvlakte
2 was found to have a maximum power output in the order of 800 MW and a yearly generated energy
yield in the order of 2 TWh. Both of these values were approximately a factor three lower than the power
output of the perpendicular dam with a length of 50 km at the same location. This is because, in the
case of the perpendicular dam, a phase difference in the tidal wave over the dam was created, creating
a large head difference over the dam. In the case of the oblique dam, such a phase difference was
very slight, significantly reducing the water head over the dam. Instead,a head difference was created
as a result of reflection of the tidal standing wave within the estuary.
Subsequently, a SWAN wave model has been nested in the flow model. In these two models, a design
storm with a return period of 10000 years has been simulated, of which the wave characteristics and
water level in the area around the dam were compared between the scenarios with and without oblique
dam.
A large decrease in both significant wave height and peak period behind the dam was found across
nearly the whole Voordelta area, with the largest decrease offshore immediately behind the dam. However,
the significant wave height was increased on the outside of the dam and near Westkapelle. The
same result was found for scenarios where 25 cm and 80 cm MSLR were applied. This is because the
incoming waves from a northwestern direction are blocked by the dam, resulting in the wind-generated
waves behind the dam becoming dominant in the area. The maximum water level during the storm is
seen to decrease near in the nearshore area.
As the area behind the dam is transformed into an area resembling an estuary, the dominant hydrodynamic
and, consequently, the morphodynamic processes are changed. As the dam blocks all incoming
waves from the west and northwest, which are the dominant wave directions in the area, the
wave energy within the area decreases significantly under storm conditions. At the same time, the tidal
amplitude is expected to be amplified within the area. These changes cause the area to become more
tide-dominated. As a result, an increase in the cross-shore directed sediment transport into the area
is expected. Dominant sediment transport mechanisms with the estuary are also changed, but for a
more accurate view of the extent to which this happens, a morphological model is necessary, which
has not been applied in this study.
In summary, a DTP dam oblique to the Dutch coast can provide a substantial amount of energy, although
it is significantly less than anticipated in previous studies. A further advantage of this dam is that the
area behind is sheltered against storm wave conditions and extreme water levels. It is foreseen that
the area attracts more sediment by the creation of the dam, but this needs to be confirmed by a future
morphological model assessment.