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Building with Nature Guideline > Building Solutions > Green-grey solutions > Foreshores in freshwater environments 

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Foreshores in freshwater environments


Foreshores in freshwater environments can consist of freshwater wetlands or floodplains. A shallow foreshore or floodplain can contribute in different ways to the strength, the stability and the flood protection capacity of a dike. The foreshore can reinforce the macro stability of the dike and can strengthen the dike by increasing the seepage length. Under certain conditions the dike’s crest can even be designed lower than in a traditional design due to the wave-attenuating effect of the foreshore. This may be enhanced by introducing vegetation such as reeds, shrubs or trees. In the absence of a natural foreshore, a gradually sloping foreshore can be constructed in front of the dike.

Main characteristics of this foreshore dike are the gradual slope, in comparison with the steep slopes of traditional dikes, and the different vegetation zones on this slope that play a role in reducing flood risk. The habitats that can develop on the slope of this dike provide services to the adjacent ecosystem and opportunities for recreation and landscaping. If the adjacent water contains enough sediment to be trapped by the vegetation, the combination of sediment trapping and vegetation-induced soil formation enables the foreshore to adapt to a slowly increasing water level (relative sea level rise).


Foreshore in freshwater environment

A freshwater foreshore in combination with a green dike


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How to use


Shallow foreshores or floodplains take space, so they can only be applied where enough space is available. In the case of lakes this is usually not a problem, but in rivers this point requires special attention. Depriving a river from its storage space has implications for the height and propagation speed of flood waves. Since flood storage in a river is determined by the width at the water surface, this means that the foreshore level should preferably stay below the design water level. On the other hand, the level should be high enough to be effective in attenuating waves under design conditions. 

Water retention along the Scheldt river

Water retention area and natural foreshore in the river Scheldt, Belgium 


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Practical Applications

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Lessons Learned


  • Depending on the situation, dike raising and strengthening can be avoided by creating a shallow wave-attenuating foreshore.
  • Such foreshores also create room for multi-functional use, thus to enhance the system’s benefits.
  • There is no generally applicable design, the solution to be chosen depends on the local physical, ecological and societal situation.
  • Until this has become proven technology, many decision makers are reluctant to adopt this type of solution, because of the perceived risks involved (project delay, uncertainty of the nature component). For the time being, implementation of these concepts in practice depends on ‘champions’ at high political and administrative levels. They can help to get a number of pilot projects off the ground in order to show that the concept works in practice and can be cost-effective.
  • Cost-benefit analyses should take a long-term perspective, with a time horizon exceeding the lifetime of the present project. In that case, the adaptation capacity of shallow foreshores becomes part of the equation.
  • Discounting, as usual in cost-benefit analyses, does not apply to nature components in hydraulic engineering projects, as these cannot be purchased at an arbitrary point in time, but need time to develop.





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