There is a growing interest in tidal energy, owing to its predictable nature in
comparison to other renewable sources. In the case of the UK, its importance
also lies on the availability of exploitable areas as well as their total capacity,
which is estimated to cover more than 20% of the country demand. However,
the level of development of this kind of technology is still far behind other types
of renewable energy. However, several studies focused on a variety of individual
devices, followed by more recent research on the deployment of large arrays or
tidal farms.
Potential sites for energy extraction can be found in narrows between
islands and the coast or estuaries. The latter present some advantages for the
installation and the connection to the grid but estuaries are often prone to flood
risk from tides and surges. Therefore, the objective of this thesis is to evaluate
the effect that very large groups of turbines could have on peak water levels
during flooding events in the case of being deployed in estuarine areas. For
that purpose, a new methodology has been developed, which implies the use of
a numerical model (MIKE 21 by DHI), and it has been demonstrated against a
real case study in the UK: the Solway Firth estuary. Another objective has
consisted of integrating in this thesis the results from detailed CFD modelling
and optimisation techniques involved in the project. A literature review has
been carried out in order to identify the current state of the art for the different
subjects considered in the thesis. Different aspects of the numerical model
used for this study (MIKE 21) have been presented and the modelling of the
turbines within the code has been validated against experimental and CFD data.
The procedure to include large numbers of turbines in the code is also
developed. An analysis has been done of the different estuaries existing in the
UK suitable for tidal energy extraction, identifying their main geometrical
features. Based on this, idealised models of estuaries have been used to
assess the influence that the channel geometry could have on the impact of
tidal farms under extreme water levels. The effect has been measured by
comparing the results of the numerical model between the case with and
without turbines under different flooding scenarios. Finally, the same
methodology has been applied to a real case study selected from the previous
group of estuaries namely the Solway Firth. An initial model has been created,
according to the available data at the start of the research, which contained
some errors related to the water depth at the intertidal areas in the upper
estuary. Therefore, when a more realistic dataset became available, an
improved model was created. The improved model has been used to assess
the effects of tidal farms in the estuary under a coastal flooding event.
It is concluded that there is significant influence of the channel geometry over
the locations where the maximum changes in water levels due to the tidal farms
will happen. Nevertheless, the effects seem to be more relevant in terms of the
decrease rather than the increase of peak water levels for all geometries and
the maximum changes seem to be in the order of dm. This is in agreement with
the results of the Solway Firth models and can be summarised as a positive net
effect over flood risk. On the other hand, a concern has been raised about the
impact on intertidal areas, which could be the subject of future research.University of Exeter - College of Mathematics, Engineering and Physical Sciences
EPSR