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The proposed Severn barrage is a controversial but widely discussed proposal to generate clean and renewable energy. A key concern with this technology is that such structures may cause other environmental problems. However, such structures might also have beneficial environmental effects in some areas, such as mitigating coastal flooding from storm surges. In this paper we model the hydrodynamics of the Severn barrage and surrounding area using a depth-averaged numerical model. We simulate a storm surge event based on realistic meteorological conditions coinciding with a spring tide. We find that to the east of the barrage the peak water level is significantly reduced by the barrage. To the west of the barrage, on the ocean side, the presence of the barrage leads to a small increase in the water levels during a surge event despite the reduction in the tidal amplitude. We examine different operational strategies for the barrage during a storm event – these make a small but perhaps significant difference. Overall a barrage can help to mitigate the impact of storm surges on coastal flooding.

The proposed Swansea Bay tidal energy lagoon is an example of a relatively small-scale tidal barrage demonstrator project. A key concern with this technology is that such structures may exacerbate other environmental problems. However, such structures might also create beneficial environmental effects in some areas, such as mitigating the impact of storm surges. In this paper we model the hydrodynamics of the Swansea lagoon and surrounding area using a depth-averaged numerical model. We simulate a number of storm surge events from the past 40 years and analyse how the presence of the Swansea Lagoon (under various operating strategies) modifies the resulting water levels.

There are two approaches to extracting power from tides — either turbines are placed in areas of strong flows or turbines are placed in barrages enabling the two sides of the barrage to be closed off and a head to build up across the barrage. Both of these energy extraction approaches will have a significant back effect on the flow, and it is vital that this is correctly modelled in any numerical simulation of tidal hydrodynamics. This paper presents the inclusion of both tidal stream turbines and tidal barrages in the depth-averaged shallow water equation model DG-SWEM. We represent the head loss due to tidal stream turbines as a line discontinuity — thus we consider the turbines, and the energy lost in local wake-mixing behind the turbines, to be a sub-grid scale processes. Our code allows the inclusion of turbine power and thrust coefficients which are dependent on Froude number, turbine blockage, and velocity, but can be obtained from analytical or numerical models as well as experimental data. The barrage model modifies the existing culvert model within the code, replacing the original cross-barrier pipe equations. At the location of this boundary, velocities through sluice gates are calculated according to the orifice equation. For simulating the turbines, a Hill Chart for low head bulb turbines provided by Andritz Hydro is used. We demonstrate the implementations on both idealised geometries where it is straightforward to compare against other models and numerical simulations of real candidate sites for tidal energy in Malaysia and the Bristol Channel.