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Bringing Dutch tidal defence model to the UK

The Crown Estate is calling on engineers to develop the Dutch “sand engine” coastal defence proposition to protect the UK’s coastlines.

The Crown Estate is the low-profile, part government owned commercial business whose property portfolio would give even the most accumulative property tycoon a distinct feeling of inadequacy. Its total holdings in the UK are estimated to amount to £11.5bn – a figure that includes roughly £8.12bn of urban assets encompassing celebrated diadems like Regent Street in London and £1.65bn of rural land that includes jewels such as Windsor Great Park.

Actually, the “Crown” element of the organisation’s name is slightly misleading. Although Crown Estate properties were historically owned by the British monarch, they are not the private property of the reigning sovereign and income from the Estate goes to the UK Treasury.   

As Ian Selby, the organisation’s head of minerals and infrastructure, explains, a 1961 Act dictates that, far from being an instrument of private enrichment, the organisation is mandated to work for the public good.

Ian Selby, the Crown Estate

Ian Selby, the Crown Estate

“Part of our job is translating these resources to benefit society and the economy,” he says. “We could just sit here and be completely passive and still take some sort of contribution, but part of our duty is to maintain and enhance the value of the estate.”

Selby explains that, as a corollary of this, his job is increasingly about taking a more active approach to asset management.

“[The Crown Estate is] the mineral owner offshore,” he says. “We own the entire seabed out to 12 nautical miles but we have mineral rights that extend out to median lines and also some energy rights.

“We’re actually blessed with the best range of aggregate resources – that’s sand and gravel on the seabed – for a country of our size in the world.”

Crown Estate aggregates

Crown Estate aggregates being used at Hurst Spit - a shingle bank at the easternmost point of Christchurch Bay in the Solent

Since the mid-1950s, the Estate, with the help of its contractor partners, has dredged an estimated 1bn tonnes of this resource for use as construction and marine aggregate, not least for massive land reclamation projects like the London Gateway Port and traditional beach recharge schemes to protect the UK’s coastline. But now Selby says the Estate wants to find more efficient and innovative ways to use the aggregate resource.

Sand engine

Creative engineering approaches that have earned the Estate’s admiration are the “sand engine” – or “sand motor” – coastal protection schemes being pioneered in the Netherlands where the low lying land makes coastal protection and resilience even more of a pressing issue.

As reported previously in NCE the acknowledgment in Holland that investment in tidal defences is the right thing to do, wedded to a more joined-up approach among stakeholders, has created the freedom to experiment and come up with this new model.

“Typically beach recharge schemes involve a sort of repeated deposition of sand on beaches to which you return every year. You spray sand on the beach, you pump sand on the beach and you have your coastal defence through the sand,” says Selby. “That is obviously dredger intensive and every year you have to go back and set up the equipment to make that happen.

“The [Dutch sand engine approach] is about defending a stretch of coast for a decade, two decades, or three decades. You actually deposit a significant volume of sand in one go, in one place and then you let coastal processes distribute that sand, so you’re using natural energy, not carbon,” he adds (see box).

“We own the entire seabed out to 12 nautical miles but we have mineral rights that extend out to median lines and also some energy rights.”

Ian Selby, The Crown Estate

The cynic might ask why the Crown Estate would be interested in an engineering approach which makes more efficient and irregular use of its saleable aggregate resource, but this ignores its institutional obligation to work for the public good, and the fact that the Estate, as a landlord, also stands to benefit from any regeneration of its coastal assets. “Of course there are significant efficiency savings, but we also thought actually it’s more than that,” he says. “We see it as a multi-benefit scheme because there are also benefits around habitat and potential regeneration in such schemes.”

Revitalisation

He points to examples where beach recharge schemes rather than sand engines in Colwyn Bay and Clacton have contributed to the revitalisation of these areas. In the case of Colwyn Bay, a distressed beach was recharged to create a more substantial tidal defence, something which has in turn attracted finance and tourism into the area.

Sandscaping scenario

Artist’s impression of how sandscaping might bring tourist benefits to a coastal region

“There’s a whole positive spin around regeneration and the sand engine in the Netherlands has noticed the same,” says Selby. “It’s become a kite surfing area so then businesses have started to pop up associated with the scheme, so it has this positive focus beyond the coastal defence.”

For more projects to emerge like these, Selby thinks that UK stakeholders will have to move away from an approach where they all operate in separate silos to one where they work together.

“I went to a meeting in the Netherlands and in the meeting there were all sorts of gender diversity, profession diversity – all ages – all talking in the same language about getting things done and being prepared to innovate and engaging across those different sectors,” he says. “I’ve never seen anything like that here.”

Facilitative

Selby thinks that the Crown Estate’s position in the industry can help to bring all of these stakeholders together.  

“If you’re the Department for the Environment Food and Rural Affairs (Defra), you manage your part. If you’re the Environment Agency you manage your part, the local authority manages its part,” he says.  “We see our role as facilitative and positive; we have that overview that a lot of organisations don’t have.”

He adds that from this facilitative position, the Crown Estate would like engineers to work with other stakeholders to develop funding models and to put more flesh on the sand engine proposition.  

“The important thing is, we don’t do this, we don’t operate things, so again, [we are] working in this facilitator role,” he says. “My message to engineers would be to engage because we see a lot of evidence of general political support for the principle.”

The Sand Engine explained

Royal HaskoningDHV was heavily involved in the development of the Sand Engine concept in the Netherlands. The company’s director, water governance & strategy, Jaap Flikweert describes the decision to create a hook-shaped peninsula to protect the Delfland coast near Rotterdam as a “really joined-up initiative” between the public sector, academia and the engineering profession. “What really helped was that the right people at the political level believed in this idea,” he says.

The Sand Engine

The Sand Engine

Suction hopper dredgers claimed sand 10km off the coast and deposited it to form the hook-shaped peninsula. The logic behind the process is that that if the sea is inclined to move sand around, perhaps it could do the human work of replenishing sand-deprived areas.

Describing how the same concept might be applied in the UK, Flikweert says: “It’s about working with sediment at a large scale which is important for two things really. Working at a scale that is up to 20 times larger than the current largest beach nourishments in the UK creates economies of scale. It means the dredgers can use bigger vessels and that reduces their costs.

“The second key bit is working with natural processes, building with nature, so you are really actively trying to make use of how the coast works and even trying to influence that a little bit to your benefit.”

Readers' comments (2)

  • This is an excellent idea not only for using economies of scale, but because it operates over a longer period of time, allowing the natural processes to be better understood. Moving away from a "sticking plaster" solution might also make schemes less vulnerable to political whims.

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  • This approach seems sensible - as long as it does not simply cover for where the Crown Estates are allowing offshore excavation that causes the need for the sand engine. If that is the case it simply means a hidden subsidy and boost to the construction industry.

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