Conserving the salt marsh

Statistically the River Deben has the highest amount of saltmarsh of any Suffolk River. The reason for this is not so much that it is an unspoiled estuary with a great deal of intertidal habitat, but more due to the loss of historically reclaimed areas during the 20th century through natural disasters such as the 1953 floods, failure of walls through flawed management and even in one case as the casualty of a wartime bomb. The outcome of this was that between 1942 and 1965 a substantial amount of land was lost to the tide and quickly reverted to a saltmarsh state.

However, as with many natural systems that have been interfered with or have inadvertently returned to nature, our saltmarshes struggle to achieve equilibrium:

Those saltmarshes that fringe the river walls and form their first line of defence, are under constant stress from tidal action. Their ability to adapt and renew is constrained by the very walls that they serve to protect. A healthy saltmarsh is one that has sufficient complexity to act as an energy dissipater plus the capacity to renew and adapt. Once the channel system is truncated by reclamation work, tidal energy is not so efficiently absorbed the balance between deposition of sediment and erosion is upset and there is no longer the space to adapt and change. Therefore, with a little help from factors such as incremental sea level rise, increase in nutrients, herbicides and pesticides in the system, the saltmarsh becomes degraded.

For those areas that are the result of tidal incursion through accidental failure of river defence walls, if left to establish their own morphology may in the first instance, whilst sheltered from dynamic tidal action, develop healthy saltmarsh. However, over time a breach can only become wider and the channel that feeds through it deeper. On every tide, as the channel systems become established within the new marsh, more water flows through it on a daily basis. Sooner or later there is a strong likelihood that further sections of the defence works, attacked by the tide from the inside, will fail, enabling the tide to flow through the site, washing out the newly established saltmarsh. This is what happened to the saltmarsh at Sutton Hoo and prompted the project undertaken by DEP in 2011 to stabilise it. It is also taking place on Hemley Saltmarsh downstream of Waldringfield.

From 1997, the discussion over an Estuarine Strategy for the River Deben incorporated the question over the viability of some defence walls and the value of the land that they protect. Managed Realignment to create new intertidal habitat was introduced as a potential action. Understandably this did not find favour with the landowning community, leading to a counter-proposal to explore the degree that saltmarsh communities might be restored and managed.

Following the initiative of the River Deben Association in 2009 to introduce a tidal barrier to protect a fringing saltmarsh at Sutton from erosion, the Deben Estuary Partnership has energetically undertaken further projects on an experimental basis to trial a range of solutions customised for the characteristics of particular sites and to use this as a basis for further research into the drivers for saltmarsh loss. Click the link for more detail Sutton saltmarsh defence

The existing projects at Sutton and at Sutton Hoo are quite different solutions for very different sites. A third project for the saltmarsh at Falkenham between Felixstowe Ferry and the outfall for Kings Fleet will be different again where the main emphasis will be upon impeding tidal flow through the site and mitigating the destructive effects of the pumped outfall at Kings Fleet upon the adjacent area. This work will be carried out in collaboration with the landowner and will be a soft engineering solution of brushwood, coir and straw bales.

All three projects are community initiatives set  up in partnership with Suffolk Coast and Heaths AONB Unit, Environment Agency and local and regional authorities. The emphasis has been upon fostering an enhanced awareness of estuarine systems and a heightened sense of community ownership of the estuary and its management.

An RDA Saltmarsh Research Group was set up in September 2016 to try and determine why and how saltmarshes on the river Deben erode and regenerate. Details of it’s meetings can be found <here>.

Saltmarsh Restoration Report – Sep 17