Important new research into coastal marshes suggests that flood-prone land will tend to rise in line with any increase in sea levels caused by global warming.
Dr John French, of University College, London, compared the rate at which sediment was deposited in the Mississippi delta, the Netherlands and Norfolk. His findings on the implications for Norfolk were presented to the conference just before the 40th anniversary of the devastating floods of 1953 when storm tides killed 1,400 people in the Netherlands and more than 300 in East Anglia and the Thames Estuary, after sea walls were breached or submerged.
He said the rate of sediment deposit in the Louisiana marshlands was not enough to keep up with the rise in sea levels. But in Norfolk, the more vigorous tidal action led to a higher rate of deposition and ensured the marshes would continue to keep pace with the best forecasts of sea level rises associated with global warming.
At present, the sea level around East Anglia is rising by about 3mm per year, although Dr French said it was difficult to say to what extent this was due to the ongoing process by which southern England generally was subsiding, or to a newer effect associated with global changes.
But there is, however, a down side: while the marshes may maintain their height relative to sea level, areas will be lost to the sea at the margins. Dr French said this meant some flood defences would have to be moved perhaps 100 yards inland, sacrificing previously protected land. 'Sacrificing such land to make a new buffer zone is perhaps more politically acceptable now than it used to be before the days of set- aside,' Dr French said.