FLOODING THE FIELDS

Allowing fertile farmland around the Humber estuary to flood will save 400,000 homes. Ed Owen reports.

The Humber estuary has been fertile agricultural land for generations, but that could soon change thanks to a new flood management strategy that will see the area flooded in favour of saving people's homes.

Echoing controversial moves to fl ood vast swathes of fertile farmland in Norfolk (NCE 3 April), the Environment Agency's £323M Humber Strategy will protect the majority of properties living around the estuary – save for a few isolated homes.

According to Humber Strategy manager Philip Winn, much of what will now be flooded was originally land reclaimed from the estuary.

Farmers built banks to channel the chocolate-coloured river water inland, allowing it to dump silt, in a process known as "warping", to gain fertile soil. Heaven for farmers, but hellish during floods since the area is low-lying and flat. With sea levels rising as much as 1m in the next 100 years, this land is under severe threat.

"The Humber is rising about 1.8mm per year – a modest amount," says Winn. "But we also have to allow for up to 6mm per year due to the additional eff ects of land settlement."

Existing flood defences are dotted about the coast and will define the coastline as the Humber rises to meet them. One consequence of this is that bird habitats occupying the areas between high and low tides will be lost. This is significant because these habitats are protected by EU law.

This so-called "coastal squeeze" must be replaced. "As sea levels rise you lose designated areas and the Agency has to pick up the losses," says Winn.

Solutions have to be planned so as to strike the right balance between preservation and artificially forcing the coastline to adapt. The Agency's solution is to allow controlled flooding at strategic places using the ancient idea of warping.

Some areas to be flooded have already been purchased from farmers and will be deliberately flooded via channels during high tides. This will help attract bird colonies.

Other much larger areas will act as safety-valves or channels that will dissipate flood water over much bigger areas.

Some new flood defences will be built where sacrificial fl ooding is not an option. For example, the BAE Systems facility near Brough and the extensive petrochemical works near Immingham Port will be protected by hard defences.

"In some places a second line of defence can be built, but there has to be a good economic case. Isolated properties across the estuary, which may add up to 2,000, will fall between the two," says Winn.

The strategy is already under way, with small plots of land purchased just inside the existing flood defences. A 160ha area near the village of Paull Holme to the east of Hull was deliberately breeched in 2003 to replace "coastal squeeze".

The next step will be to secure the safety-valve channels to reduce flooding along the Humber.

A site at Alkborough is up and running, using the same idea of deliberately flooding areas, but on a much grander scale. Here, 400ha of farmland will be flooded when river levels are high. During this period, the Agency will lease the land from the farmers to compensate for the damage caused to crops.

Channels will draw water inland, turning the area into massive holding-ponds. "In high flood, a 1km section of specially lowered embankment will breech, allowing the entire area to fill. This will allow water levels to lower in the estuary by about 100mm," says Winn.

Further large-scale schemes are planned near Goole on the River Ouse and Flixborough on the Trent.