During the MV2 sand extraction project, many new insights were gained concerning technical and ecological aspects of the design and the organisation of large scale, deep sand extraction projects and ecosystem-based landscaping. The project also generated a broad discussion amongst the various stakeholders on how changing physical conditions can trigger the development of new ecological habitats.
An important lesson learned is that ecosystem-based landscaping in sand extraction sites only make sense if:
- the sand extraction volume and area are large enough for ecosystem-based landscaping to have maximum added value;
- Ecosystem-based landscaping can be used to increase ecological value (de Jong et al., 2015; De Jong et al., 2016, 2014);
- Ecosystem-based landscaping can be carried out during the extraction process without additional equipment mobilisation and with minimal interference to the overall sand extraction production process.
Overall, it became clear that it is still too early to prescribe landscaping to other sand extraction projects, even if they meet the above conditions. The present pilot experiment is still on-going and its added ecological value remains scientifically to be proven.
Lessons on project development
The most important lessons learned are:
- Take a joint approach involving all stakeholders, from initiator, consultant (technical) experts and contractor to permitting authority.
- Make sure the decision to include landscaping in the design is taken early in the process.
- Involve the contractor in the design process.
- Base the design on a mix of ecological, morphological and practical expertise and include this expertise in the design team.
- Clearly specify the aim of the landscaping on beforehand, keeping in mind that there will always be a certain degree of uncertainty because of natural variability.
- Make sure all stakeholders are continuously informed in a clear and transparent way (minutes of meetings, technical documentation, overall process guidelines, etc.); inform them on progress, new insights and ideas, etc. (permanent liaison).
Lessons on physical and technical aspects
Several lessons were learned concerning physical parameters and the technical realization:
- Determine physical parameters in close cooperation between physicists, morphologists and (marine) ecologists to determine effectiveness, and with contractors to determine workability (realistic / pragmatic approach).
- Use expert knowledge and numerical models to predict the behaviour of the bedforms in the sand extraction site to make sure that they are relatively stable and allow sufficient time for the ecosystems to develop.
- The size of the sand extraction site determines the type and number of ecosystem-based bedforms that can be situated in the site. Appropriate modelling techniques can identify any side effects of the landscaped bedforms (e.g. large flow contraction or sedimentation-erosion patterns).
- Make sure that there is enough space around the bed forms to manoeuvre the dredging equipment. Too little space directly influences the extra costs of creating bed forms.
- It is advisable to check whether the existing seabed composition (spatial distribution of grain sizes after dredging) already provides sufficient gradients. If so, bed form creation may not be necessary.
- Small bed forms are more difficult to create, as the dredging ships need to manoeuvre more. This will result in a loss of productivity and increase in costs.
- Bed forms that have an orientation more than 20-30 degrees off the main current direction are much more difficult to create, so these are also more expensive.
Lessons on the ecological response
- Pioneer species (white furrow shell, Abra alba) settle very quickly in the deep sand extraction site followed by plaice (Pleuronectes platessa).
- The occurrence of distinct species observed in the deep sand extraction site site and ecosystem-based landscaped sand bars seems to be related to differences in sediment characteristics.
- A ‘new’ macrozoobenthic species assemblage was observed, characterised by Abra alba (deposit-feeding bivalves).
- The fish assemblage at the crests of the sand bars differed significantly from the troughs with tub gurnard (Chelidonichthys lucerna) as a specific species of the crests. This is a first indication of the applicability of landscaping techniques to induce heterogeneity of the seabed although it remains difficult to draw a strong conclusion due the lack of replication in the experiment. it remains difficult to draw strong conclusions due the lack of replication in the experiment, furthermore, an ecological equilibrium is not reached after 2 years since biotic and abiotic variables are still adapting.
Lessons on governance
The project team worked closely together with the stakeholders, thus learning several lessons concerning governance issues:
- Make sure all relevant stakeholders are identified and contacted beforehand. Determine who will be politically and administratively responsible for approving the permit and make sure they are involved or regularly updated on the process. This may seem obvious, but appears in practice to be more complicated.
- Discuss and investigate the potential of landscaping an sand extraction site within the prevailing permit limitations before the design is made (input for design);
- Use technical documentation and workshops to inform the permitting authorities, explain the rationale underlying the ecosystem-based landscaping and indicate its expected effects;
- Approach the permit application procedure in an opportunity-driven manner, searching for possibilities rather than restrictions.
- The stakeholders acknowledged that the project offered a great opportunity to study in practice the potential of landscaping in terms of development, design and ecological outcome. Based on the gathered ecological data, 4 scientific articles are published in peer-reviewed journals.
Lessons on realization
Several important lessons were learned during the execution of the dredging works, concerning the workability of the design and the consequences of creating a specific landscape as compared with a case without predefined bedforms:
- Make sure that there is sufficient data on bathymetry, sediment properties, local currents and tidal windows. This is essential information for contractors to determine their dredging strategy.
- Involve the contractors early in the design phase, so that the final design fits easily into the dredging plans and methods and can therefore be created cost-effectively, i.e. with a minimum loss of productivity. Use their knowledge on sediment properties, ship types, planning and general dredging expertise when designing and planning the location.
- Make the decision on landscaping as early as possible and provide data on requirements and/or locations so that the contractors can fit the bedform creation into their dredging plans and therefore also in the permits.
- Maintain an open communication with contractors / dredger captains to determine the actual workability of the design and to discuss the need for any optimisations;
- If the scope of the project and /or available fleet of TSHDs changes, confer with contractor to determine if the design needs to be adapted (e.g. concerning dredging depths).
Lessons on monitoring
- Ensure frequent updates of the bathymetry of the landscaped bedforms, to be able to monitor their development and steer expectations among stakeholders. Morphological monitoring will enable to evaluate the design, predict is longevity and assess its effectiveness in reaching the goals of the concept.
- Apply adaptive processes to the ecological monitoring strategy: tune monitoring to developments found at previous efforts, while still maintaining consistency in data collection for good comparison objectives.
- As an ecological equilibrium is not yet reached, monitoring the medium and long-term effects is recommended (not every year but for example every 10 year).