How an experiment in the Netherlands could change the way we tackle coastal erosion
Coastal erosion threatens homes, livelihoods and animal habitats. Replenishing lost coastlines in a way that does not cause more environmental damage is a challenge facing many low-lying countries. In 2011, a team in the Netherlands came up with an innovative solution.
The problem of coastal erosion
< a href=”https://www.sciencedirect.com/topics/earth-and-planetary-sciences/coastal-erosion”>Coastal erosion is the loss of sand, rock, and other sediment from coastlines which is not replenished by new sediment. Sediment is removed by natural environmental changes – wind and rain, waves and currents – and by human actives, such as sand mining. Coastal erosion can be further affected by rising sea levels which enables water to reach further inland. This also results in a very deep sand bed, so waves and tides cannot sweep as much sand up off the bed and onto the shore.
Coastal erosion impacts negatively on human lives by threatening homes and livelihoods, and also affects nature, with sea birds, plants, and other animals losing important habitats.
An experiment to reduce coastal erosion was born in the Netherlands
Until 2011, the Netherlands tackled coastal erosion along the Delfland coast – the southern part of the country’s coastline – through sand ‘nourishment’. This meant repeatedly collecting replacement sand inland and transporting it to the coast. The process resulted in regular disruption of wildlife and impacted on the enjoyment of visitors to the seaside. It was decided that a longer-term intervention was needed.
The challenge, and the proposal
Any new method would need to deposit at least 12 million cubic metres – enough to fill 5000 Olympic swimming pools – to the coast, while remaining sustainable and environmentally friendly. After a lot of research, the idea of the Sand Motor was born. It would be a new process called ‘mega-nourishment’ – an ambitious and experimental concept. The idea was to create one huge deposit of sand and let nature, rather than humans, redistribute it along the Delfland coast.
The Sand Motor was designed in the shape of a hook curling out into the sea. The sand that makes up the hook would, the developers hoped, be picked up by waves, wind, and tides, and distributed naturally along the coastline over many years.
Construction required months of work
Construction began in 2011. It took four months and cost 70 million euros. It was a huge effort necessitating, in the end, the transfer of 12.5 million cubic metres of sand. This transfer was done by dredging vessels, huge ships that hauled up sand ten kilometres offshore and pumped it into the project area at a rate of three cubic metres per second.
After all the work, the project team had to wait, observe, and hope their models and predictions would come to fruition.
Progress five years on
After five years the project team reviewed the experiment by looking for any new animals and plants that had emerged on the sand motor, checking on swimmer safety, and measuring currents and dune development.
Their findings were mostly positive. Firstly, they found that the sand was indeed being redistributed onto existing sand dunes as hoped. In its first five years, the Sand Motor had supplied sand to a five kilometre stretch of coast: nearly a million cubic metres to the south of the Sand Motor, and 1.5. million cubic metres to the north. And, while they had planned the Sand Motor as a twenty-year project, they realised it would likely last much longer.
The team also learned that sea grasses had settled on the new peninsular and sea holly, a protected species, was flourishing.
There were new currents in the water around the Sand Motor, but lifeboat and lifeguard teams were well supported in adapting to the changes. They created a new current tracking app which helped lifeguards ensure swimmer safety.
It has been too early to assess whether the sand motor has helped maintenance of the seabed, but this will be reviewed at the ten-year stage, in 2021. The team also expect to see the sand redistribution increase in speed, but the ten-year review will measure whether this is the case.
The experiment will have a lasting legacy
The Sand Motor has, so far, proved a success. Other countries have taken note and work on a sand motor in Kent, in south east England, began in 2019.
It has also provided more than ten doctorate research projects which means that not only will the Sand Motor itself bring benefits for many years to come, the lessons learned from its implementation will help us understand coastal erosion and nourishment for even longer.
The ideas presented in this article aim to inspire adaptation action – they are the views of the author and do not necessarily reflect those of the Global Center on Adaptation.
