In most cases, dikes are primarily strengthened by using extra soil to make them higher or wider. But the researchers believe that this could also be done more efficiently. Allowing more flowers and forb to grow on our dikes would have quite a beneficial effect. The dikes would not only become sturdier due to deeper rooting, but insects would also benefit from the broader plant diversity.
The Dutch dikes of today are dominated by green turf with relatively few herbs. Grassroots do not usually penetrate the soil as deeply, which means that the soil is not as well bound, while herbs often tend to have deeper roots. In addition, these grassy surfaces are not very resistant to increasingly prolonged periods of drought and, as a consequence, this also leads to less sturdy dikes. This calls for new and different types of vegetation for our future dikes.
Re-enacting a flood
“Over the past year, our ‘Future Dikes’ research project has primarily focused on the current state of affairs,” says Nils van Rooijen, who is a researcher at Wageningen University. “Where are most of these species-rich types of vegetation found on dikes, how is the soil structured in these dikes and how strong are the dikes themselves?”
In the forthcoming weeks, Van Rooijen and his colleagues will be investigating how flood-resistant different types of floral dikes in the Nijmegen area are. For this purpose, vast amounts of water will be poured over the crest of the dike until a hole forms in the topsoil. “We’ll be looking at the differences between the vegetation, soil composition and root growth in order to find out how erosion-resistant our biologically diverse dikes are,” says Van Rooijen.