Challenges: The need for cost effective coastal protection

The coastal area is an essential region for humanity. Around 40% of the world population is living within 100 km of the coast and around 600 million people live in coastal areas that are less than 10 meters above sea level. Parts of the vulnerable coastal areas are protected by coastal structures like breakwaters and revetments.

The call for cost effective coastal structures is growing because:

  • The investments protected by coastal structures are increasing.
  • The demand for coastal developments pushes these further into the sea
  • Due to global warming the sea level is rising, (tropical) storms and cyclones become more intense and storm tracks are changing.

Coastal engineers are therefore even more challenged to come up with reliable yet cost effective coastal protections.

Figure 1: The revetment protecting Panama City

The design process

Historically, the design process of coastal structures is based on guidelines, expert judgement and physical model tests. Each method has its own pros and cons. The design guidelines are easy to apply but tend to include large safety margins. Expert judgement is often required to extrapolate the design rules outside their range of validity which incorporates implicit risks. To cope with these uncertainties, physical model tests are frequently used.

The physical wave flume

To check if the designed coastal structure is indeed safe, often a scale model of the design is tested in a hydraulic laboratory. The scale model is placed in a physical wave flume and subjected to the design wave conditions. When the design shows to be safe (i.e. is not collapsing and showing not too much overtopping), generally the designer (and client) are happy as the tests confirm the design. Not seldom optimisations (cost savings) are discarded and included as “extra safety”. When the design is not safe, like due to the limitations of the design guidelines, the design is adapted and re-tested in the flume. This may lead to a quick increase in model testing costs.

Figure 2: A physical test of a breakwater.

The numerical wave flume

Being aware of the limitations of conventional design approaches and the costs for physical model tests, Royal HaskoningDHV embraced the possibilities of advanced computer modelling (through the CFD packages OpenFOAM and Waves2Foam) to strengthen our capabilities to design coastal structures. By us in short referred to as “CoastalFOAM”, this software package provides us with a numerical wave flume to test our designs.  The numerical wave flume is currently being used to optimize breakwater designs before physical scale tests are executed. Additionally, it aims to reduce the required physical scale tests.

For more information please contact Stef Boersen or Cock van der Lem.