Borth sea defence - multi purpose reefs

Waves are a mixed blessing for the small village of Borth in West Wales. While those waves bring surfers to the area, a much-needed boost for the local economy, they also threaten its very existence.

Positioning the sea defence at Borth
Positioning the sea defence at Borth

In the 1960s sea defences were built to protect the village, but they have not stood the test of time. By the turn of the millennium, on big-weather days, water was breaching the defences and damaging buildings. With the defences compromised the shingle beach in front of the village was disappearing once again and the water was reaching the buildings more and more often.

Community involvement

The local community became heavily involved in shaping Borth's future. They were clear that they did not want traditional high, concrete walls along the sea front. It would have closed the village off from the beach and killed the tourism that bought such a boost to local businesses. Conventional off-shore reefs would not have worked either, because although they would have kept the beach open, they would kill the waves that surfers travelled the length of the country to ride.

Instead they opted for a new idea: multi-purpose reefs. Using more complex structures they could achieve three things. First and foremost they would break the largest of the waves before they reached the shore, they would be shaped to encourage the kind of waves that surfers love and they would provide a nesting ground for sea birds. This would then be accompanied by three other elements. The shingle beach was to be extended with 200,000 tonnes of new material being shipped in, to literally push the ocean back from the village. This was then supported by two groynes and two breakwaters to hold the shingle in position and stop it being eroded or displaced by the tide.

Extending the beach with shingle
Extending the shingle beach

Multi-purpose reef

Initially there were going to be two multi-purpose reefs for the defences, but after modelling the tidal conditions it was found that a second one in the area would interfere with the creation of waves suitable for surfers. So the decision was made to create one multi-purpose reef supported by another, more conventional, reef.

Unlike other artificial reefs built in this country, this is the first reef which could potentially provide a surfing amenity that has been constructed entirely of rock. Matt Richards section engineer for principal contractor BAM Nuttall, says "In the past we could not have made structures like the ones we are building here. The problem is the setting out and surveying: you cannot use traditional survey techniques in the ocean. We are working in water up to four metres deep with relatively small windows of operation that are dictated by the tide. Even if you set out the pegs for the inshore structures, there would be little or no time to work with them and when the tide came back in, it would wash it all away and you would have to start all over again the next day. As for the offshore reefs, it would just not be possible without GPS machine control."

Aerial view of the beach at Borth
The reef begins to take shape

Project approach and outcomes

Accurate excavators

Shaun Price, Topcon's machine control technician describes how the system: "work starts with a design of the required area using a digitally-designed terrain model that is then converted into a format for the site using a GNSS grid, which is an internationally used positioning system and then is calibrated to the local grid system. That means you have two sets of co-ordinates, one local and one wider that are being continuously compared against each other so you can be sure of the accuracy and position of what you are doing with the machines. The wider location is using the WGS84 standard satellite system and then the local grid is surveyed and calibrated to positions around the site. Even working underwater, in the often-rough conditions off the coast of West Wales, the system will give you an accuracy of +/-15mm."

For Matt, that kind of accuracy is crucial to him, "the success of the multi-purpose reef depends entirely on building it to a specific shape to create the right kind of waves. Because the system is more or less instant, the crews can survey the work as they go so we always know we are working accurately. For example, they can place a rock, press the button, check the position there and then and if it isn't right move it. That also means there is no downtime for separate surveys of the structure."

As a part of the site management team this immediacy has other big benefits for Matt. "When the crews get back in, they can pass me a USB stick of the day's work from the excavators. This means I am never more than a few hours away from having a precise, up-to-date picture of what is happening out on site. In terms of assuring the quality of the work and tracking our progress, this is a real advantage for me."


Work on the Borth sea defences is well in progress to finish on target. Once they are complete the village will have a permanent, effective defence from the ravages of the Atlantic Ocean, but without losing their community's economic lifeblood. Something that, as Matt is unequivocal about, "it would not have been possible without GPS machine control."

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