Coastal Engineering with Tetrapods

Coastal Engineering with Tetrapods

25th October 2016

Earlier this year we published a series of blog posts on bricks – the history of the humble brick, different types of brick and innovative new types of bricks that are changing the way in which we build.  While researching for that series we found some fascinating information on tetrapod blocks which are used in coastal engineering, a practice that is becoming more popular in many parts of the world.  Firstly, we need to explain that coastal engineering is the branch of civil engineering that concerns the very specific demands post by constructing near the coastline as well as developments that are actually off the coast itself.

Coastal engineering is used to alter the shoreline in certain areas which is a pretty powerful activity (think King Canute and the sheer futility of trying to stop the tide).  It’s also used to create artificial islands like the spectacular ones in Dubai Waterfront of the artificial islands built by China recently as part of a land reclamation project.  None of these modern coastal engineering projects would be so successful if it weren’t for the humble tetrapod blocks that form the lynchpin of these artificial islands and restructured coastlines.

The tetrapod is a t tetrahedral concrete structure that’s now used to armour breakwaters instead of boulders or conventional concrete blocks.  These earlier barrier materials, while initially effective, become dislodged over time by the force of the sea constantly crashing against them.  The tetrapod’s unique shape is designed to dissipate the force of the incoming waves by letting the water flow around them, rather than against them.  This serves to reduce displacement, creating a much more stable foundation for any structure built on or shored up by tetrapods.

The tetrapod was developed in 1950 by Laboratoire Dauphinois d’Hydraulique (now ARTELIA) in France – however they are not protected by a patent and are produced by many contractors and used all around the world.  The word tetrapod means “having four legs” and if you look at a concrete tetrapod, you can clearly see four “legs” protruding from the middle of the structure.  When tetrapods are deployed in a random distribution, the legs interlock, forming a porous, but stable barrier that will remain stable under even the most extreme weather and sea conditions.

The tetrapods are often numbered as a method of monitoring their stability.  They are usually monitored using satellite photography so that any changes in structural form or displacement issues can be addressed immediately.

Tetrapods may seem like the best thing to hit the global construction industry since the brick, but they have their opponents.  Some people argue that they are a danger to swimmers, surfers and boaters which others reckon they accelerate the rate of beach erosion but disturbing the natural process that create constantly changing coastlines.  They’ve also been criticised for aesthetic reasons – they don’t improve the shoreline scenery.  However, they are protecting shorelines around the world, a vital requirement in these days of global warming when we’re seeing higher tides than ever before.  In areas where the coastline is eroding at an alarming rate, we often see tetrapods being used to protect the land and, no doubt, we’ll see them being used a lot more in the future.