Initiation
An analysis of the planned works and the ambient ecosystem is needed in the first step of the design process. On the basis of a set of conceptual designs, a feasible technical design has been realized and budgeted. A scan has been performed with the Project Agency to identify dike transects suitable for ecobasins.
Pre-feasibility
In the pre-feasibility assessment, the following activities have been undertaken:
- Discussion with the Agency on details of the engineering design and the specification of ecological and recreational potential.
- Discussion with the Agency on the selection of suitable dike sections, taking planning aspects into account.
- Analysis of local communities of hard substrate species as a reference situation.
- Analysis of physical forcing factors and design criteria which may be relevant to the ecologically enhanced design. In this case wave exposure and siltation risk are critical design factors.
- Analysis of the ambient ecosystem and identification of possible interactions and reinforcements. In this case a valuable diverse hard substrate community is already present. Maintaining, and where possible enhancing, this community is a requirement for dike reconstruction in the Eastern Scheldt.
- Pre-design, valuation and costing of ecologically enhanced structures and presentation to the Agency.
- Selection of the most promising eco-structure. In this case one focused on keeping the water at the dike toe and providing a suitable substrate for attachment of macro-algae.
- Analysis of the physical aspects of the water system and the dike section (foreshore and intertidal morphology, wave conditions, dike stability, shape of the dike and the toe)
- Inventory of stakeholders whose interests might be affected by the project (recreational activities such as scuba diving, commercial fishing, etc.)
Feasibility
During the feasibility study, the Rich Revetment plan was further developed via:
- Technical design of the most promising eco-structure within the overall requirements and planning of the engineering works, including aspects such as:
- Slopes and orientations
- Choice of materials
- Size distribution, porosity
- Application method
- Seeding method (if required)
- Detailed costing and phasing within the overall project planning
- Small-scale field trial
- Set-up of monitoring and maintenance plans (clearly a necessity in the case of a pilot experiment). Duration of monitoring should be suitable to follow transition to a fully grown situation. This could take three to five years.
- General observations made are:
- The technical design team should include biological expertise in order to ensure an optimal design.
- As the proposed approach is of a mainly empirical nature, field trials are an important way to establish the feasibility, site constraints and availability of biological recruits for colonization at any new location. Ecobasin field trials concerning the effectiveness of type and sorting of the material are executed by HZ University of Applied Sciences in cooperation with Project Agency “Sea defenses” (Zeeweringen).
- Habitat enhancement measures such as the ones described herein will be designed not to interfere with the primary objectives of coastal defense system.
- Habitat enhancement measures should not lead to undesired proliferation of nuisance or invasive species that related to hard substrate.