4 minute read
Rich Revetments: Enhancing Hard Substrates for Ecology
Zierikzee/Sint Annaland, the Eastern Scheldt, the Netherlands
Many dikes and other hard coastal defense structures around the world are in need of reinforcement in order to meet the changing safety standards associated with sea-level rise. During the dike design and construction phases, increased attention is being given to sustaining the biodiversity attached to these artificial substrates. Ecologically friendly designs were implemented at various locations in the Eastern Scheldt as a part of dike reinforcement projects. For this Projectbureau Zeeweringen effort, which lasted from 2013 to 2017, designs were created from different materials to enhance the natural richness of the dike revetment, the dike foot, and the lower foreshore. For example, concrete dike revetment was designed with small holes to increase both moisture content and attachment opportunities for wildlife. This project showcased how Building with Nature techniques for enhancing species habitat during a reinforcement project can be implemented without significantly increasing the project’s costs.
Article cover: Channeled wrack is a rare species in the Netherlands. It grows well on blocks with basalt fragments. (Photo by Tim van Oijen)
Producing Efficiencies
The design with diamond-shaped pits embedded in the standard concrete blocks is a cost-effective way to enhance biodiversity on dikes. Fabrication requires only a minor adaptation of the standard molds used in the production process. This is less costly than other successful approaches, such as the use of a lava stone topping, which is typically glued to the top of the revetment blocks. The design of the diamond-shaped pits was based on the size of marine invertebrate bodies present on the dike’s hard substrate; the pit design was also based on the settlement requirements of seaweed—both considerations provided project designers with information about the specifications necessary for optimizing the development of a natural rock community.
Using Natural Processes
Creating a substrate with more opportunities for enhancing seaweed growth and for providing bird and marine organism habitat involved utilizing ongoing natural biological processes. These biological processes tend to create a complex network of mutually dependent species, in which one species creates new opportunities for other species. The experiment demonstrates that new modified concrete block revetments can lead to significant differences in short-term biodiversity. Alternative surface adaptations of the concrete block revetments could increase the pace at which the ideal conditions are reached.
Broadening Benefits
The innovations are providing an environmental benefit manifested in species richness and biomass. The social benefit is that the very concept of “green dikes” tends to hold tremendous appeal for local citizens. Economic benefits can be realized by the CO2 fixation resulting from the seaweed and algae growth. Creating species habitats and natural values within a dike reinforcement project will likely contribute additional economic benefits, since the activity should eliminate the necessity to compensate for environmental value in another location.
Promoting Collaboration
Deltares, the Dutch Ministry of Transport, Public Works and Water Management Water INNovations Programme (WINN), the Ministry of Infrastructure and the Environment (Rijkswaterstaat), Projectbureau Zeeweringen, Waterschap Scheldestromen all contributed to this effort in some capacity. The workshops that were conducted from the project’s inception were an important part of its success. Construction companies, suppliers, government personnel, and employees and scientists from various fields took part in these workshops in order to learn from each other and discuss mutual interests. Dike construction, by necessity, has as its primary focus water safety, but this project managed to broaden this one-dimensional approach to incorporate other easily attainable goals, such as creation of ecological habitats.
