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Coastal protection: a job for nature itself
Research

Coastal protection: a job for nature itself

The answer to climate change is not necessarily pouring more concrete.

5 minutes
03 March 2021

Sea levels are steadily rising, and climate change appears to have heavier storms in store for us. How can we prevent finding ourselves literally up to our necks in water? By cleverly moulding local nature, we can make the coast much more resilient. Among other things, researchers are investigating how marram grass can prevent beaches from eroding.

Will the ice cream parlours, seafood restaurants, and toy shops at the seaside soon have to leave because we will be forced to raise the dikes? It need not come to that: the answer to climate change is not necessarily pouring more concrete. “There is a trend to move towards more natural methods of coastal protection”, says Professor Pieter Rauwoens of the Coastal Engineering and Soil Mechanics Research Group on the Bruges Campus. “This is called the ‘dune-in-front-of-a-dike’ principle: you build a targeted sand buffer that decreases the energy of the waves.”

The research of Professor Rauwoens and his colleagues specifically emphasizes nature-inspired solutions to protect the coastline from the impact of the sea. “Compared to man-made seawalls, they have the advantage of allowing a more flexible deployment in response to climate change. Predictions vary considerably: some models suggest that by 2100, we will face a sea level rise of sixty centimetres, while others even predict rises of up to three metres.”

“There is a trend to move towards more natural forms of coastal protection”, says Professor Pieter Rauwoens.
“There is a trend to move towards more natural forms of coastal protection”, says Professor Pieter Rauwoens.

Furthermore, dunes have numerous ecological advantages. “They provide a habitat for a variety of fauna and flora. Dunes also retain fresh water from precipitation and thus form a buffer against saltwater intrusion into the polders, another consequence of rising sea levels.”

Drones over the dunes

If you want to build a smart sand buffer, knowing how the sand will ‘behave’ is key. And that is by no means easy. Sand shifts around both underwater (due to wave action) and above water (due to the wind). Storms induce cliffs at beaches and dunes, and in calmer periods, the sand gradually returns into place. The researchers use simulation software to predict these processes. But field measurements are essential to validate these complex computer models against the reality on the ground.

“Twice per year, the Flemish Government’s Coastal Division flies an aeroplane over the beach to conduct altimetry, and every three years, they do the same thing for the dune areas”, Professor Rauwoens says. “The elevation maps of the beaches and dunes provide a helpful picture of what occurs over the longer term: where has sand been deposited, where has erosion occurred? But we sometimes also want to analyse processes over the short term. We therefore occasionally commission additional measurements from companies that use drones to conduct altimetry in a certain region.”

To resupply sand shortages, so-called ‘sand nourishments’ occur regularly. “Dredgers deposit sand on the beach by means of a long pipe”, Professor Rauwoens explains. “But sand can also be supplied on the foreshore. The ship then simply opens up and dumps the sand on the deeper seabed. The sand is then carried to the beach via natural processes. This method has the additional advantage of reducing the impact on the environment.”

Sand catcher

Replenishing sand shortages is essential, but it is not the only weapon in a sustainable coastal protection strategy. You also need to keep as much of the sand as possible on the beach. The researchers therefore also investigate the optimal use of vegetation as a sand catcher.

In an experiment on the beach in Ostend, the researchers investigate which pattern of beach grass works best to keep the sand on the beach.
In an experiment on the beach in Ostend, the researchers investigate which pattern of beach grass works best to keep the sand on the beach.
© KU Leuven – Glenn Strypsteen

In cooperation with Coastal Division, the research group launched an experiment on a beach in Ostend. They planted a kind of puzzle of marram grass, with six large patches of four hundred square metres each. “We are experimenting with different patterns and plant densities”, Professor Rauwoens explains. “Our aim is to discover which pattern and density works best to capture shifting sands on the beach and thus optimally stimulates the spontaneous formation of dunes.”

Using the results of this research, Professor Rauwoens and his team aim to provide advice to coastal municipalities and governments to pursue a scientifically underpinned and natural approach to coastal protection. “We sometimes receive questions of a more practical nature, about wind-blown sand nuisance in the streets, squares and beach promenades for example. Then we analyse where brushwood fences or sand screens can be installed to limit the inconvenience of drift sand.”

Wavemaker

In addition to coastal protection, the research group also has extensive expertise concerning the impact of waves and currents on ships and constructions in the sea, such as windfarms and artificial islands. “For example, in an ongoing doctoral project, we analyse the limit states of wave height and currents within which a vessel can still operate safely in the vicinity of a wind turbine. This research specifically concerns crew transfer vessels: ships that transport workers to turbines to carry out maintenance.”

There are also computer models for this type of research, and ways to test them in practice. For example, the researchers are currently completing what might be described as a scientific ‘luxury wave pool’. “In cooperation with Ghent University and Flanders Hydraulics Research, we are building a new wave basin in Ostend”, Professor Rauwoens says. “It is a large, 30 by 30 metre basin that is 1.4 metres deep and which enables us to investigate the influence of waves, tides, and wind on ships and structures in the sea.”

The research group itself has smaller variants of the wave basin, so-called current and wave flumes. “These demo installations enable us to showcase practical solutions for waves to break before they reach the seawall.” This is just one example of how students are familiarized with the work of a coastal engineer. Students are in frequent contact with the industry. “We conduct collaborative projects with the large companies in our sector. This close relationship was recently formalized by establishing the chair in coastal engineering. Don’t forget that some of the largest dredging companies in the world were founded in Belgium.”