Professor Robert Nicholls at the University of Southampton has suggested that one of the best ways to defend against flooding along coastal regions is to, in fact, do nothing.
This comes from a recent study, of which he is the co-author, that has shown that while protecting cliffs along coastal areas from erosion should be continued, in some cases the risks of flooding are reduced if these features are allowed to erode naturally. Due to measures taken to protect coastlines in places like the UK, there has been a negative effect on beach formation (sediments from headlands are washed across harbours in the direction of wave action and settle along adjacent shores, and a disruption of this process will directly affect these coastal features). These beaches can and often do provide a natural flood defense.
Nicholls suggests that in a future where global warming and increased water levels are predicted, we must take action to do what is best to protect settlements along the coast. Sometimes this will mean maintaining beach areas artificially, while at other times natural erosion is the best solution. There are cost factors in the former case that may be prohibitive over time and a full understanding of the issue will allow jurisdictions to properly plan for these scenarios.
Coastal defences put in place over the last century or so have re-shaped the UK coastline, artificially protecting some areas, but at the expense of beaches in adjacent areas.
This man-made situation increases the risk of flooding in low lying coastal settlements where beaches act as a natural flood defence. Beach levels can be artificially recharged, but maintaining this indefinitely along large stretches of coastline is costly and likely to be unsustainable.