Radboud University Finds Flowery Dikes Are Equally Strong and Better for Biodiversity
New combinations of grass and herb species on dikes can help restore biodiversity. Such a ‘species-rich dike revetment’ is also at least as strong as traditional grass revetment. This is the conclusion of the HWPB innovation project Future Dikes. The results from the research will be presented on June 4 and may help with dike reinforcements in the future.
Over the next 30 years, 1,500 kilometers of Dutch dikes must be reinforced to meet new safety standards. On more than 95% of the Dutch dikes just grass grows. On 3 to 5% of the dikes there is species-rich dike revetment: a mix of grasses and herbs, also known as a flower-rich dike. Species-rich dike revetment can contribute to the recovery of biodiversity: there is room for special plant and insect species. Moreover, dikes meander through the Dutch landscape and can thus connect different ecosystems.
More species-rich dikes strengthen biodiversity. Within the Future Dikes project, researchers from Radboud University and their partners have investigated whether these biodiverse, species-rich dikes are just as strong as dikes containing mainly grass. They also looked at the preconditions for the construction and maintenance of species-rich dikes.
Vegetation, soil and tensile strength
The researchers compared vegetation, soil and erosion susceptibility of sod from existing species-rich dikes with that of traditional grass dikes. This included tensile strength tests and large skip tests (with a lot of water) on existing species-rich grass revetments. The various tests showed that the species-rich dike revetment is at least as strong as the conventional grass revetment and also much more biodiverse.
Ecologist Hans de Kroon: “The species-rich dike revetment is at least as safe as grass-dominated dike revetment. Since species-rich dike revetment includes many more plant species and attracts more different insects, this dike revetment also contributes to maintaining biodiversity in the river landscape.”
Guide
To ensure that species-rich dike revetment can be applied on a larger scale in the future, the research team put together a guide. The guide contains recommendations for the preconditions for the construction and development of flower-rich dikes. Important are soil composition, management and the right seed mix for these dikes. This knowledge is available at www.handreikinggrasbekleding.nl and www.ru.nl/futuredikes .
Ambition
The Hoogwaterbeschermingsprogramma and the water boards have expressed the ambition to achieve “Strong species-rich dikes as standard.” In phase 2 of Future Dikes, the researchers want to realize this ambition by conducting a number of practical experiments on new and existing dikes. This will give managers all the tools they need to start working on species-rich dikes with confidence.