Broad green dike sound alternative to traditional stone dike

Published: 22 May 2014

Broad green dikes are cheaper to build and often provide more protection than traditional dikes with stone or asphalt revetments. Generally, they are also a more harmonious match with the surroundings. This alternative should therefore be considered more often during dike upgrades.

Brede groene dijk goed alternatief voor traditionele stenen dijk

This is the conclusion of a study by Deltares and Alterra Wageningen University and Research Centre for the dike upgrade in the Eems-Dollard area. The study looked at the options for a broad green dike along the Dollard, and compared the construction costs and protection level of a broad green dike with those of a traditional dike.

Alternative often used in the past in the Netherlands

A broad green dike has a very shallow slope and a foreland consisting of marshland. The dike is built entirely from clay and covered with grass. Including natural features in the design generates interest from nature conservation organisations and local residents. This approach to building dikes has been used often in the past in the Netherlands but it is no longer considered as an alternative because there is a preference these days for dikes that take up as little space as possible. A broad green dike admittedly takes up more space and this makes these dikes inappropriate in locations where space is at a premium. However, the Eems-Dollard area is actually very suitable for this type of dike.

More material, but cheaper

The cost per kilometre of a broad green dike is significantly lower because an expensive asphalt or stone revetment is not needed. The researchers were surprised by this result because more material is needed for the dike.

In terms of safety, the broad green dike also comes out better than the traditional dike. This is because the larger base width of the dike, in combination with the marsh, makes it less susceptible to seepage and piping, mechanisms that render dikes unstable. In addition, the crest of the dike does not need to be as high and this also improves stability.

Design testing on a small scale

With the results of the comparison being so favourable, the researchers advise small-scale tests over the next few years for the new dike concept and the extraction of clay from the marshland. This will generate additional information and it may then be possible to consider the option of broad green dikes as a possible alternative during the next round of dike upgrades.

Study in response to rejection of dikes

The ‘Detailed exploration of a green Dollard dike’ study was conducted as part of the national government’s Wadden Area Delta Programme in collaboration with Rijkswaterstaat’s corporate innovation programme, the rich Wadden Sea programme and the Rural Area Department (Dienst Landelijk Gebied). The study was initiated in response to the rejection of a number of dikes in the northern Netherlands because the hard revetments were no longer able to cope with the waves.

Click here for the report ‘Detailed exploration of a green Dollard dike’