3. Pier Pressure: Man-Made Reefs as Scour Protection

Infrastructure Protection at Lillebælt
Lillebæt, Danish for Little Belt, is a strait between the island of Funen and the Jutland Peninsula. The area has two large bridges, the first being a truss bridge (pictured on the left) which opened in May 1935, and the much newer, larger bridge (pictured on the right) that opened in June 1998. 

To help stabilise and mitigate erosion of the bridge’s pillars/piers, scour protection is implemented on the riverbed. In this case, it is in the form of rock armour. These are large, heavy, angular rocks that can withstand the rivers force and dissipate the energy of the flow, which helps protect the underlying soil from being eroded further and swept away. 

The diagram above presents a pier foundation and its associated scour protection, illustrating the internal arrangement and relative densities of the materials beneath the seabed. 

Lack of secure foundations for bridge pillars can lead to collapses, which may result in the loss of life, and cause temporary disruptions to transport, trade, and local economies. The Schoharie Creek Bridge in New York, collapsed in 1987 after heavy rainfall eroded its foundations, claiming the lives of ten people. Closer to home, Ireland's Malahide Viaduct collapsed in 2009, due to seabed erosion beneath one of the piers. Fortunately, there were no fatalities as no trains were passing at the time. These incidents underscore the vital importance of scour protection and regular maintenance of bridges, especially as climate change brings increased rainfall and flood risks, potentially endangering more bridges. 


The picture above shows an aerial view of the Schoharie Creek Bridge, New York, USA, after it had collapsed due to the piers eroding after heavy flooding. One car and tractor were on the bridge at the time of collapse but before the bridge could be closed off, three more cars plummeted off the bridge. As a result, there were a total of ten deaths. 


Hydrophone Collection
I went to the Lillebæt bridges to collect hydrophones - microphones that detect sound waves underwater. There were six hydrophones in total (four hanging from the old bridge and two from the new bridge). These hydrophones pick up "pings" sent out from fish that have been been tagged with an acoustic tag (a transmitter). By collecting this data, researchers can piece together the journey of individual fish and may even forecast their future movements. This knowledge is necessary for effective conservation and sustainable management of fish populations. It enables researchers to better predict how they'll respond to environmental changes and guides them in protecting habitats to increase long-term viability of both the fish stocks and the wider ecosystems they support.


The picture above shows the weight used to keep the hydrophones in place. Over time marine species attach themselves to them, like mussels, starfish, and seaweed (also known as biofouling). This adds further weight which could cause the chain holding the hydrophone to snap, losing valuable equipment.

Location: Little Belt, Denmark

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