The effects of a Severn Barrage on wave conditions in the Bristol Channel

Abstract

The study investigates the impact that construction of a Severn Barrage in the Severn Estuary, on the west coast of the UK, might have on local wave conditions. Implementation of a barrage will impact on tidal currents and water elevations in the wider region. There is strong tidal modulation of wave conditions under the natural regime and therefore barrage-induced changes to tidal conditions could affect wave modulation in the region. This paper uses Swan, an open source 3rd generation spectral wave model, to investigate the possible impacts of construction of a barrage on tidal modulation of the wave conditions. It is found that current variations, rather than water level variations, are the dominant factor in tidal modulation of wave conditions. Barrage implementation does not substantially change the modulation of the wave period or direction. However, barrage implementation does affect the tidal modulation of wave heights in the area of interest. The tidal modulation of the wave heights is generally reduced compared to the natural case; the peaks in the wave heights on an incoming tide are slightly lowered and there is lesser attenuation in wave heights on the outgoing tide. This modulation leads to net changes in the wave heights over one tidal cycle. For all of the tested wave conditions, this net change is small for the majority of the tested domain, namely to within ±5% of the no barrage case. There are some areas of greater change, most notably larger net increases in the wave heights near the North Somerset coast where the post construction net wave height increase over a tidal cycle approach 20% of the pre-construction conditions. These changes do not impact coastal flooding because the wave height increase is not co-incident with high tide. Importantly, the maximum wave height is not increased and thus the likelihood of extreme events is not increased. The area of greatest reduction is between Swansea and Porthcawl. Changes over a neap tidal cycle show similar patterns of net change, but the modulation over the tidal cycle is different; primarily the magnitude of modulation is half that for the spring tide case and the shape is altered in some locations.

The cumulative impact of tidal stream turbine arrays on sediment transport in the Pentland Firth

“…Waves were not included in this contribution given the vast number of permutations of possible wave conditions that would need to be tested, however future work should consider this aspect. Not only would, under certain conditions, wave driven sediment transport alter or mask the tidally driven transport described here, but wave fields would potentially be modulated by changes to hydrodynamic conditions forced by renewable installations [70].…”

A Comparison of Numerical Modelling Techniques for Tidal Stream Turbine Analysis

“…Researchers have also investigated impacts on sediment transport and associated changes to morphology [32][33][34][35]. Wave-current interactions [36] can also be an important process, both in affecting the tidal resource and the changes to currents impacting the wave climate [37][38][39], the water quality [40] or aquatic organisms. More recently, optimal siting for power production over a large area has been considered [41].…”

“…MIKE3 has an inbuilt turbine tool based on actuator disk theory [38]. The drag force FD is calculated as:…”

Flood Hazard Assessment for a Hyper-Tidal Estuary as a Function of Tide-Surge-Morphology Interaction

“…Locally-generated wind waves and propagating swell waves, generated by an offshore storm, which coincide with an extreme water level can increase flood hazard at the coast (Wolf 2009;Pye and Blott 2010). Maximum wave height at time of tidal high water can be significant for coastal flooding (Fairley et al 2014), and runup associated with direct wind setup or breaking offshore waves can influence defence overtopping and breaching (Cheng et al 2015). Future work to consider the influence of swell and wind waves on water levels and uncertainty in wave forcing has the potential to provide improved understanding of the combined effect of tide-surge-river-waves on water levels in a hypertidal estuary.…”