Based on the Nigel Pontee’s award winning paper, this lecture will look at the impact of managed realignment design on estuarine water levels. Delegates will explore the factors that influence changes in water levels and learn how to design schemes successfully.
In an estuarine context, the term managed realignment is used to describe the process of deliberately removing flood defences and re-introducing tidal regimes to low lying land previously reclaimed from the sea. In the UK, these schemes have been promoted by both the Environment Agency and private developers in order to replace lost habitats or reduce flood defence costs.
The impacts on estuarine water levels have not been widely documented and it is important to rectify this since managed realignment schemes, which are often promoted as reducing flood risk, can cause increases in water levels in some circumstances.
The lecture will provide a brief introduction to managed realignment, explaining how the location of such schemes determines their impacts on water levels and describe results from hydrodynamic modelling carried out as part of design.
The presentation will describe the various options that were explored in the design process. The results confirm that managed realignments schemes that lead to the significant expansion of intertidal areas near estuary mouths can alter the tidal propagation within estuaries leading to increases in water levels. The results also suggest that the design of such schemes needs to carefully consider the location, number and size of breaches since these elements, which are within the remit of the engineer, are also important in determining the impacts. These effects would be expected to apply to other hyper- and macro-tidal estuaries.
These findings suggest that it is necessary to consider the hydrodynamic impacts of schemes when choosing sites an estuary wide scale (e.g. as part of estuary flood risk management strategies) as well as during the detailed design at specific sites.
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