The UK’s first flood barrier spanning a passenger rail track will form a key part of the £18M Newhaven flood alleviation scheme when it is completed next year.
Newhaven, on the East Sussex coast, is an important cross-Channel ferry port on the estuary of the River Ouse. In 2013 a tidal surge flooded almost 60 properties and closed the twin track railway line between Lewes and Seaford.
In response, the Environment Agency and Lewes District Council have developed a scheme to reduce the risks of flooding to approximately 430 homes and 390 businesses in and around the town. It will also protect key infrastructure such as the road network, the railway line, the commercial area near the port, and Newhaven Town station.
There is a perceived risk of “backdoor flooding” from the upstream flood plain north of the town that could be triggered by the breaching of the embankments along the River Ouse during an extreme tidal surge. This would hit the Newhaven Enterprise Zone on the east bank particularly hard.
To protect this area, two clay-cored bunds up to 2.7m high and totalling 600m long have already been constructed. They will eventually be linked by the new floodgate and its flanking concrete walls, which will be situated close to a level crossing 1km north of Newhaven Town station.
A twin leaf hydraulically operated design was chosen by the scheme’s JV design and build contractor Jackson Hyder. Each steel leaf will be approximately 6m wide and 1.2m high and will weigh in at around 3000kg. When there is no risk of flooding the leaves will be parked on each side of the tracks. Should a tidal surge threaten, the leaves can be swung out into position in a matter of moments.
Detailed design continues, but the current estimated cost of the gates and the necessary changes to the railway infrastructure is expected to be in the region of £1.5M. Installation of the gates should take place next year.
Five areas on both banks of the estuary make up the entire scheme, with the floodgates being in Area 1. Construction began in January 2017, and overall completion is scheduled for autumn next year.
Much of the project involves the construction of bunds and walls on both sides of the estuary, but there is another floodgate over the promenade on the west bank. Of the five areas, three are already complete, two, including Area 1, are still under construction. Work on the west bank is substantially complete, reducing the flood risk to 244 homes, almost 90 commercial properties and vital infrastructure.
Overall, the scheme once completed should provide the town with a 1-in-200- year standard of protection, even after making allowances for sea level rises as a result of climate change. This equates to a 0.5% chance of flooding from the sea in any one year. Funding comes primarily from the Environment Agency courtesy of the government’s Flood and Coastal Risk Management Grant in Aid, with two local enterprise partnerships contributing £1.5M each.
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