Simple modelling approach for assessing the impacts of a tidal lagoon and tidal barrage on the eutrophic status of the Severn Estuary, UK

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Margaret Kadiri, Junqiang Xia, Roger Falconer, Bettina Bockelmann-Evans

Friday 3 july 2015

13:45 - 14:00h at Europe 1 (level 0)

Themes: (T) Hydro-environment, (ST) Renewable energy resources

Parallel session: 16G. Environment - Renewable

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Tidal renewable energy schemes are designed to extract the energy from tidal energy resource and convert it into electricity using structures such as tidal barrages and tidal lagoons, where low head turbines are encapsulated in impoundment structures. This study uses a simple modelling approach to assess the impacts of a tidal lagoon and a tidal barrage on the eutrophic status of the Severn Estuary, UK. The model predictions are compared against CSTT thresholds for assessing eutrophication in coastal waters. The estuary was found to be potentially eutrophic both without and with the barrage and lagoon as the predicted equilibrium dissolved nutrient concentrations and potential phytoplankton biomass exceeded the CSTT thresholds. Potential primary productivity in the estuary without the structures was found to be significantly lower compared to those with the barrage and lagoon. This is due to a combination of increased residence time of nutrients in the water column and light availability with the structures. However, the conditions for phytoplankton growth are likely to be more favourable in the estuary with a barrage as the potential maximum primary production was found to be about an order of magnitude greater in the estuary with a barrage compared to that with a lagoon.