The sand is running out

Apart from a small amount used to make concrete, Baptist says there are two main reasons why the Netherlands mines sand from the North Sea: "Firstly, we use a lot of sand for the subsoil of roads and residential areas. A solid layer of fill sand is particularly important on soft peat soils. Secondly, we need a lot of sand to reinforce our coast. Without that reinforcement, the sea will erode the dunes and flood the hinterland."

In the 1980s and 1990s, this was a real threat, he recalls: "Back then, we experienced progressive coastal erosion, with beach pavilions disappearing into the sea and a lot of dune erosion. Now we have a pretty good idea of how much sand we need from the North Sea to keep the coast strong. But climate change is causing sea levels to rise faster. That means we need more sand for our coastal protection.”

The Netherlands is lucky to have a shallow sandpit on its doorstep. “But the stock in the North Sea is limited,” Baptist warns. "And other users are also claiming parts of the North Sea. The further ships have to sail to mine sand, the more expensive sand mining becomes. Moreover, there are ecological consequences: digging deep pits and trenches everywhere changes the habitat of flora and fauna in the North Sea."

The public-private partnership programme OR ELSE is developing an approach to 'ecosystem-based' sand mining. "The bottom line is that we want to maintain the use of natural resources for sand mining as well as the ecological status of those resources. The aim is for the programme to produce recommendations that policy makers and implementers can start working on immediately. That’s not just about technology and nature. It is also about how all the agencies dealing with the North Sea do it together. How do you combine all those interests, how do you make agreements?"

Because the North Sea is a busy place, he emphasises: "Shipping has big interests, there are extensive wind farms, partly under construction, which require cables to be laid. There is an important fishing industry. There is nature that deserves protection. And there are pipelines from the old oil and gas industry. These things often get in each other's way."

OR ELSE connects hydraulic engineering, ecology and policy with universities, research institutes, nature organisations, government and industry as partners. Key to Wageningen Marine Research's contribution is exploring the extent to which large-scale sand mining impacts soil life and fish stocks, and how to manage that impact through design and planning. Baptist adds: "Can you choose a depth for sand mining that has fewer undesirable effects or even desirable effects? How does the gradient of a sandpit affect tidal flow? That gradient determines how water and sediment move and therefore how soil life and fish communities are affected."

The Marine Strategy Framework Directive is crystal clear: "According to that directive, soil conditions must not structurally deteriorate. We are therefore looking for design principles that slow down the flow less abruptly. For example, the orientation relative to tidal movement or more gentle slopes of sandpits. And a less steep slope is also important for fishermen: they don't want their fishing gear to suddenly sink much deeper."

In OR ELSE, models of water movement and sediment transport are coupled with habitat and population models. For fish stocks in the North Sea, Wageningen Marine Research uses so-called Dynamic Energy Budget models. "With these models, we calculate how temperature and food affect the energy budget of fish. In other words, how much energy does a fish need to survive, grow and become sexually mature? When food conditions deteriorate due to sand mining, fish are less able to meet their energy needs. The warming of seawater due to climate change is also affecting fish stocks."

A factor in this is that the Dutch North Sea coast is an important nursery area for juvenile fish: "We don't call it the nursery for nothing. Plaice, sole, turbot, brill: they all grow up in the shallow waters off our coast. If those species grow smaller due to sand mining, it will also affect the commercial fishing industry."

Part of the North Sea has been designated for sand mining. "This area is relatively close to the coast, but not so close that you are digging up your own beach," Baptist explains. "The idea is to extract as much sand from it as possible. So: the deepest possible pits."

One of the aspects that Baptist and his colleagues are studying is the supply of fish larvae. He explains: "The fish that grow up off our coast swim further into the North Sea to spawn. The larvae swim back to shore, crossing the sand mining zone. To do so, they make very clever use of the corkscrew flow. This is caused by fresh Rhine water at the top and salt water at the bottom circling around each other. The larvae flow towards the coast via the deeper water layers."

That corkscrew flow is vital for larvae, which are not yet accomplished swimmers. But what happens to that flow if sandpits 6 to 12 metres deep are dug everywhere? The answer hasn’t yet been found, but Baptist says it is crucial to find out.

The social dimension is also important in OR ELSE. Because more sand mining clashes with existing interests. The challenge is to resolve these issues together. To help achieve this, Wageningen University & Research and Breda University of Applied Sciences have developed a serious game. This is a simulation in which government agencies, the fishing industry, wind sector, dredging industry and nature organisations together plot sand mining on the map, visualise conflicts and explore options. "With the serious game, we spark a conversation between stakeholders."

Initial experiences have been positive: "The nice thing is that you can say to someone from the Department of Public Works: you are now the fisherman. It helps people understand each other better and start looking for joint solutions."

To calculate in detail the effects of design choices around location, depth and slope angles, the Digital Twin North Sea is under development at Deltares. This connects data of hydrodynamics, habitats and populations. Baptist adds that the first version is now running: it models the effects of a sand mining pit on water movement. Ecological modules are now being incorporated.

The programme has reached the halfway stage. What insights has it provided so far? "The study confirms the tension that exists between deeper mining and ecology. You don’t really want to dig pits 6 to 12 metres deep, which increases the chances of sediment catchment and permanent habitat change. Shallow mining restores soil life in say six years, but requires a much more extensive area. Pits with more gentle gradients might be a solution."

What seems certain is that the Netherlands must expect substantially higher costs for sand mining in the long term: "Further out to sea there is more sand, but that area is becoming increasingly crowded with wind farm expansion. And because of the greater distance, transport costs will increase. Unless technology makes significant advances and autonomous, electric-powered vessels start helping us. That will take some time."

Meanwhile, policy makers are much more aware of sand mining thanks to OR ELSE, says Baptist: “The North Sea Agreement included detailed agreements on nature, energy, fisheries and use of space, everything except sand mining. This has indeed changed. Everyone realises the importance of developing strategies for long-term policies."

His inner ecologist is not happy at the prospect of having to dig deep pits in the North Sea. But he is also hopeful: “Any area can be managed in a way that is good for productivity as well as biodiversity.” The North Sea, for example, is home to many shellfish. And those shellfish, in turn, are food for other animals. We need to preserve these kinds of elements. Perhaps by reinforcing them in other places in the North Sea. If sand mining continues to be essential, perhaps we can make the underwater landscape more diverse. And maybe we can use sandpits to improve the habitat for many different species."

"We simply cannot escape more sand mining off our coast," he concludes. “It is therefore up to policy makers to ensure a good balance between coastal reinforcement, economics and ecology. With OR ELSE, we are laying the foundation for that."

'OR ELSE: Operational Recommendations for Ecosystem-based Large-scale Sand Extraction' is financed by the Dutch Research Council (NWO) with project number NWA.1389.20.097.

• Boskalis
• Breda University of Applied Sciences
• Deltares
• Digishape
• TNO - Geological Survey of the Netherlands
• Van Hall Larenstein University of Applied Sciences
• ICES
• KIMO
• Ministry of LVVN
• NIOZ
• Dutch Fishermen's Union
• NSAC
• Dutch Research Council (NWO)
• PO Wieringen
• Rijkswaterstaat
• Stichting De Noordzee
• Delft University of Technology
• University of Twente
• Van Oord
• Wageningen University & Research