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How much do you want (for) your saltmarsh?

How do the findings of Phase 2 of the Solent Forum's Beneficial Use of Dredged Sediment project inform how we can pursue more restoration work in the Solent or anywhere else?


All of us working in coastal habitat restoration are now acutely aware of the many environmental and social benefits provided by marine wetlands.

There is also a widespread recognition that we need to place greater emphasis on clarifying, quantifying and communicating these benefits if we are to fund and implement more wetland restoration projects and address declines in marine biodiversity and the need for sustainable coastal management.

Over the last couple of years, the Solent Forum and ABPmer have been collaborating on ‘The Beneficial Use of Dredged sediment in the Solent’ (BUDS) project which seeks to do just this.

About the Solent BUDS project

The aim of the BUDS project is to use more of the Solent’s dredged sediment to protect its disappearing saltmarshes, rather than ‘waste’ this material by depositing it offshore.

If this project is to deliver on its goals, in contrast to other previous, stalled, initiatives, it will be necessary to change the long-established status quo.

To do that, the benefits and beneficiaries are being placed at the forefront of the decision-making process.

So far, there have been two phases of the BUDS work.

Phase 1 involved a strategic review of possible restoration sites across the Solent to identify locations where the largest benefits could be achieved.

Phase 2 examined the feasibility, costs and benefits of restoring marshes in a prime candidate area in the West Solent (between Hurst Spit and Lymington).

As the Solent Forum moves to the critical Phase 3 ‘delivery’ stage, the findings and implications of Phase 2 are summarised here to illustrate how we can think about, and actively pursue, more restoration work, whether in the Solent or anywhere else.

What’s it worth to you?

The many societal benefits of saltmarshes include: coastal protection, carbon storage and sequestration, marine biodiversity, fish nursery areas, improved human health and wellbeing.

Many of these are intuitively understood and many have been demonstrated through extensive practical restoration measures (OMReg website) and research work (e.g. Coast Web) over the last quarter century.

As part of this research, a lot of thought has been directed towards assigning a monetary (or ‘Natural Capital’) value to the benefits (or ‘Ecosystem Services’) which ‘flow’ from marine wetlands (UK Government 2020; Natural Capital Committee 2019).

While a lot has been learned on this subject there are still major gaps in understanding about valuations. This is because of the complexity of the processes involved and the large variation in benefits that exist between different locations.

As an example of complexity, we know saltmarshes trap vast quantities of carbon (Chmura, 2003) and that the rate is especially high in accreting managed realignment sites (ABPmer, 2014). However, there are still gaps in our understanding about the processes (Macreadie et al., 2019) and we are a long way from being able to calculate all the bio-geochemical processes with sufficient accuracy to meet verified carbon standards.

Local conditions also have a major influence on marsh value. For instance, their role in providing coastal flood protection varies greatly between locations as does the value that communities in different parts of the country assign to the coastal habitats on their doorstep.

Despite the importance of site-specificity, cost:benefit studies still end up relying on historic and generically-derived cost estimates for sea wall maintenance or making massive approximations of the ‘Willingness to Pay’ (WtP) values by transferring estimates from one site to entirely different locations elsewhere in the country.

While there is still much to be learned on this subject it is also still possible to make reasoned, reasonable and relatively simple first-stage valuations while we wait for the science and for site-specific studies to further inform discussions.

Indeed, it is more than possible it is necessary. This is because we can’t wait too much longer. The valuable Macreadie et al., 2019 study, for example, identified a “road map for the coming decades of future research” into Blue Carbon. However, we don’t have decades to wait for a pragmatic way to embed Blue Carbon valuations into real-world decision making.

The Phase 2 BUDS work is an illustration of what is possible now. For this work, the following considerations and valuations were used to determine the costs of doing nothing and the benefits of actively protecting the Hurst Spit to Lymington marshes:

  • Currently, 2% of the marshes (whether measured as vegetation cover or as sediment volume) are disappearing annually;
  • This rate will increase over time as the marshes decline and fracture so that the vegetated marshes will probably be gone by around 2045-2050;
  • This rate of marsh loss is currently costing society at least £50,000 yr-1 in lost carbon and reduced saltmarsh habitat value alone;
  • There are also likely to be substantial benefits from deferring of capital investment in flood defences works and harbour protection and from a high a level of local appreciation (and WtP) in the habitats. These values will need to be calculated on a site-specific basis.

There IS more to it than money!

There are those who recoil at the use of monetary valuations to underpin decisions about nature conservation (King 2019; Monbiot, 2018).

Such concerns, and requests that we instead accept the intrinsic value habitats and species, are completely understandable. And, it is agreed that we should not rely solely on ‘pound sterling equivalence’ as a decision-making tool.

However, it is also clear that the ‘business as usual’ approach needs to change somehow, and that if we don’t seek to value habitats, we risk them being ignored in decision-making altogether.

We also need to be much better at agreeing what success looks like when it comes to wetland restoration if we are to understand, agree and communicate why we must do so much more.

For example, unhelpful and erroneous judgments are often being made now about whether restored marshes are as good as ‘natural’ habitats.

We also remain uncertain about whether compensatory coastal restoration measures have achieved desired impact-offsetting goals (ABPmer Habitat Creation Conference 2013).

We do still seem confused about the effectiveness of what we do (this is a subject we will return to in another article).

If done well then, the use of habitat valuation can help with clearly communicating success because it fundamentally recognises the functionality and social role of the restored habitats.

It can therefore be used to provide a common and objective language to facilitate conversations between different people and organisations with different priorities and perspectives.

And, as ABPmer and many others have regularly argued, we really do need to better understand, and argue the case for, all the benefits of restoration if we are to genuinely reverse habitat declines, achieve Net Gain and not just continue as we are.

Where we are in the UK today is that marine wetland restoration projects are dominated by the need to compensate for losses under the Habitats Regulations. This has been the driver for delivering some 70% of the 3,000 ha of intertidal marsh and mudflat habitat created since the early 1990s (OMReg database ABPmer unpublished calculations 2019).

While these regulations are vital for nature conservation and offsetting developmental impacts, their intense gaze remains focused on certain habitats and species rather than the bigger picture and wider restoration needs and opportunities.

So, while it is definitely not all about the money, deriving valuations and pursuing cost:benefit analyses helps to lift the debate and should be used to drive a change in the status quo.

Having a better understanding about valuations and using them more often in discussions really should help to inform discussion, clarify motives, identify beneficiaries and seek funders in order to do more.

This is also especially important for the BUDS work, because unrealistic expectations have historically been placed on those carrying out the dredging to pursue often costly beneficial use projects.

Instead, there is a need to focus more on who benefits to drive action. The BUDS project therefore seeks to re-frame the way we think about beneficial use, and restoration more generally, by changing perspectives and adopting a more benefits-led approach.

What does it cost?

Beyond our incomplete knowledge about the benefits, the other major challenge with making decisions about restoration is that we have an incomplete understanding about the costs of intervention. This is especially true when discussing beneficial use.

We do know a lot about the fees incurred for managed realignment after nearly 30 years of actively doing such projects. This has been helped by cost reviews that ABPmer carries out as part of our ongoing work and independent research (ABPmer 2015).

By comparison though, our understanding about the costs of beneficially using dredge sediment for habitat restoration has, until recently, been really very poor. This is in part because costs in the dredging sector can be very variable as well as somewhat opaque.

It is also because we have simply not done enough restoration projects and there has been a fundamental lack of curiosity and communication about this subject.

There is still a great deal to be done to understand this subject better, but the BUDS project, and ABPmer’s own independent research into the costs of previous beneficial use projects (ABPmer, 2017) is now starting to redress this situation.

As is to be expected the cost is very variable and new projects can range anywhere from around £3 m-3 to atypically levels of £122 m-3 when expressed as the differential costs (i.e. the extra fee above the usual costs for standard disposal). But, there are also good examples of projects being cost-neutral or providing net savings where they are carried out in a regular and sustained manner with reduced transport distances.

For the Phase 2 BUDS project, four different potential beneficial use projects were reviewed which could be undertaken in the West Solent. These ranged from small to large scale and their costs ranged from several £1,000s to £10,000s, to £100,000s up to more than £million. As the scale and costs of these four different project examples increased, then so did the size of the change they brought about and the societal benefits they could achieve.

The really encouraging finding here was that, based on the assumptions used, all but the most expensive of the approaches had lower net costs for the beneficial use intervention than the ‘No Intervention’ scenario. It was concluded that:

  • Relatively low-cost interventions which defer capital expenditure on flood risk management or harbour protection works are likely to be cost effective;
  • Where interventions significantly reduce rates of erosion of existing marshes or create new saltmarsh, this can also provide substantial benefits;
  • The assessments are particularly sensitive to assumptions on the extent to which beneficial use projects might delay the need for capital investment in flood protection and harbour protection works, but these assumptions are reasonably well supported by the emerging evidence on the effectiveness of beneficial use projects; and
  • While there are uncertainties concerning the monetary values of some of the ecosystem service benefits associated with West Solent saltmarshes (the ‘Brander bundle’ benefits), these uncertainties don’t appear to be material to overall decision-making which is more influenced by assumptions on the timing of capital investment and the loss of sequestered carbon.

Learning by doing more and communicating effectively!

With the completion of BUDS Phase 2, we now have an improved understanding of the benefits of doing something, and the costs of doing nothing, in the West Solent.

It is hoped that this can now be a springboard for active intervention in Phase 3, where the recommended plan is to start with smaller scale work and then build rapidly to more ambitious projects as confidence in the techniques, cost and benefits grows. 

As this work progresses, it will be helpful to fill the outstanding gaps in understanding about the technical delivery and value of recharge projects.

However, it will also be vital to clearly communicate the most relevant lessons whilst increasing efforts to fill knowledge gaps. We could, for example, start placing conditions onto licences that require the dissemination of accurate costs and technical details to wider audiences.

This strategy of “starting small, communicating the lessons clearly, and doing more” makes logical sense. But history warns us that there is a need for ongoing pro-active support if this is to happen. In the absence of leadership in the past, we have tended to follow the model of “start small, fail to communicate effectively, forget and start again as if it’s all new.”

It is important therefore that the Solent Forum has stepped into a leadership role in this case, and it is also extremely helpful that we have witnessed some small-scale practical restorations in the West Solent in recent years (by the Lymington Harbour Commission and Wightlink Ltd.). These have acted as valuable, local, real-world, proofs of concept.

However, to realise Phase 3 and beyond, and to achieve larger and more ambitious projects, the Solent Forum will clearly need substantial ongoing support from a range of beneficiaries, including: the Environment Agency, Natural England, the local community and many other specialists and interested parties (including the MMO and Defra).

It will also draw upon advice from Beneficial Use Working Group (BUWG) that was founded on the back of the RSPB SEABUDS project (RSPB, 2017). The BUWG is now overseeing this sector and will be providing guidance and assistance on aspects such as the licensing process.

Ultimately, the work in the Solent should be viewed as an exemplar of how to deal with biodiversity loss and meet ambitions for nature-based coastal management. If, though, we cannot do a lot more in the Solent or elsewhere in the UK using this benefits-led ‘BUDS approach’, then this will pose questions about the seriousness with which we are taking these subjects.

Prepared by Colin Scott, Habitat Creation and Restoration Specialist