Regenerating the saltmarsh
Work on the north-west side of the island has involved a different management technique. Here we have reused sediment that had been previously dredged to maintain the navigation for boats and barges to Maldon. Carefully placing the sediment avoids new channels being formed through the saltmarsh east to west and reduces the higher flows that have been causing further erosion and vegetation loss.
This technique modifies the flows within the saltmarsh itself. It takes some of the energy out of the tide so that sediment can naturally be deposited there. This in turn allows the health of the saltmarsh to improve, which then helps reduce the effects of wave action over the saltmarsh surface. To date we have regenerated a hectare of saltmarsh vegetation on what had been eroding, bare clay.
The new area created sits higher than the existing saltmarsh and regenerates naturally with saltmarsh plants. This improves the diversity of the saltmarsh and provides a niche area for some of the rarer saltmarsh species that are under immediate threat from coastal squeeze.
Reprofiling the embankments
We don’t need to remove all the flood defences that exist. It's also not desirable for nature conservation. But where we do decide to keep embankments in place, we need to make sure they can cope with the higher tidal levels predicted over the next century to avoid any sudden and catastrophic failures and further loss of saltmarsh. To do this, we can use a technique known as reprofiling.
A shallower profile
On the north-east embankment at Northey Island, we have reduced the risk of the embankments breaching when flood waters come over the top. Breaching often happens from the landward side as the water floods over the bank and rushes down the relatively steep slope on the back face of the bank.
Once breached in this unmanaged way, deep scour holes form at the site of the breach and the surrounding saltmarsh is rapidly eroded. By making the back slope of the remaining north-east embankment shallower in profile, we have reduced the risk of this happening.
Releasing the flood water
The flood water can then be released back to the estuary in a controlled way through sluice pipes, avoiding loss of habitat there. In this way, the freshwater and slightly salty (brackish) habitats that exist in ditches, ponds and areas of terrestrial grazing marsh on the land can recover and survive into the future.