Modelling the influence of a tidal barrage on the eutrophication potential and the estuarine ecosystems using a system dynamics approach

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Eva Fenrich, Reza Ahmadian, Bettina Bockelmann-Evans, Silke Wieprecht, Roger Falconer

Tuesday 30 june 2015

9:30 - 9:45h at Antarctica (level 0)

Themes: (T) Special session, (ST) Marine renewable energy

Parallel session: 4D. Special session: Marine Renewable Energy

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With a growing need for carbon neutral electricity, the Severn Estuary with its high tidal currents tidal range could play an important role by providing tidal renewable energy. However, the operation of tidal renewable energy schemes across an estuary can have significant implications on the unique aquatic environment. The Severn Estuary together with its tributaries, e.g. rivers Severn, Wye and Usk has been recognised as internationally and nationally important and it has been designated under the Habitats and Birds Directives and Ramsar Convention as well as being “Sites of Special Scientific Interest” (SSSIs). The intertidal areas are important feeding habitats for birds. Primary production in the estuary is currently mainly limited by light conditions due to the high turbidity of the estuarine water. Therefore suspended sediment concentrations play an important role in assessing the risk of eutrophication and the system’s overall productivity. With the introduction of a tidal barrage a decrease of suspended sediment as well as a loss of intertidal areas have been predicted. A systems dynamics approach was used to model the effects of tidal energy devices on the whole estuarine system. A qualitative input-output graph was used as a base description of the structure of the system. Transfer functions and parameters were derived from DIVAST and other modeling result as well as from empirical data. Linkages between tidal energy usage, the eutrophication potential and the estuarine foodweb were integrated into the systems dynamics model for different tidal barrage scenarios including ebb-only and two-way generation. With this approach it was possible to study connections between more localized effects in the estuary and global effects of tidal energy along a timeline taking requirements from different stakeholders into consideration. This can help to reduce negative effects, optimize mitigation measures and improve operation schemes for different tidal power devices.