Faster, deeper, cheaper

Taking the long view on design

While sea level rise is an important issue in costal engineering, including sea walls, promenades and dykes, overall its effect is not very large on existing breakwaters, according to Professor Jentsje van der Meer, principal of Van der Meer Consulting.

The wave height attacking the breakwater may be a little larger, leading to a little more wave overtopping and more severe wave attack, possibly resulting in damage to the breakwater, he says.

However, a breakwater is often designed for a functional life of about 50 years. “In 50 years, a lot may happen to a harbour, like expansion for example. Look back 50 years and compare our harbours with the existing situation. Some breakwaters have already been removed or do not function any more as expansion brought larger and bigger breakwaters and harbour areas. For this reason, there are no actual plans to improve breakwaters for expected sea level rise only.”

However, he says, sea level rise is taken into account in the design of new breakwaters or improvement of existing ones, leading to higher and stronger structures. Prof van der Meer says new technology is the main driver in terms of innovations in breakwater projects, “technology to look under water at what you are doing, even if the visibility is zero”.

“Divers were used before but more and more techniques show the driver of a crane or excavator what and where he or she is placing under water in real time. This leads to faster and more accurate construction of large rock and concrete units.”

For an example of improved technology, he points to the use of the Blockbuster crane for the construction of the low-crested breakwater at the Maasvlakte II extension. “This crane was able to place 40-tonne concrete cubes within 30 cm accuracy and in a pre-defined pattern which saved on the number of blocks.