The expectation is that costs will decrease as more experience is gained in implementing natural solutions. At the same time however, an adaptive approach to implementation, management and monitoring will continue to be necessary due to the dynamic nature of such projects. Additionally, the differences in costs are difficult to interpret, primarily because it is hard to determine how the costs for various parts of these Building with Nature projects are distributed. On the one hand, this is a result of the integrated nature of such projects, which makes it impossible to connect a specific part of the costs to a function, and on the other, it is due to the absence of an accurate inventory of the costs for different projects. For example, information on how much of the contract value was spent on construction and how much on maintenance is not always available, which makes it difficult to fine-tune the above-mentioned indicators and to gain new insights. Therefore, one recommendation is to create a database to record the breakdown of costs for existing and future Building with Nature projects.
Key factors in decision-making and planning
For the projects under review, interviews were also conducted with project owners to investigate the decision-making process. How did they actually end up choosing a Building with Nature solution? There are several similarities between the motives for selecting natural solutions and the planning and implementation phases.
The decision to implement a natural solution for dyke reinforcement is often taken early on in the planning phase. It is often made by a small group of people from different organisational units who endorse a Building with Nature solution and its advantages. A crucial factor here is the early conclusion of an ambition agreement that combines objectives for flood protection, nature and recreation. This is exemplified by the Houtribdijk project, where an early decision was taken to reinforce half of the defence with rock revetment and the other half with sand. The ambition agreement for the Sand Motor, in which shared goals are laid down, also formed the basis for selecting a Building with Nature project. The interviewees mentioned the following key reasons for favouring Building with Nature projects.
Building with Nature measures utilise space in a different way than traditional reinforcements, which often require space inside the dykes. This can make natural solutions a more attractive option for increasing flood protection. Reinforcing the Prins Hendrikdijk using traditional methods would be at the expense of agricultural land, buildings and nature areas located within the dyke. Consequently, the local community had a strong preference for a reinforcement outside the dyke that combines flood protection with nature development. Similar arguments were also put forward in the Hondsbossche Dunes project; here, a Building with Nature solution makes it possible to increase flood protection whilst using as little space as possible in the area protected by the dyke.
Co-financing by nature organisations can be a decisive factor in selecting natural solutions. With additional funding, it is possible to broaden the scope of the project rather than opt for a monofunctional solution. The sand-based solution for the Prins Hendrikzanddijk was awarded a EUR 12 million grant from the Wadden Fund. Without this contribution, and the additional funding from other parties, it would have been impossible to implement a natural solution. The depositing of 5 million m3 of sand has created a varied sandy area with dynamic character in front of the sea dyke. This project also includes the creation of a new 200-hectare estuarine nature area and a breeding island. The initiative for the realisation of the Marker Wadden came from the Dutch Society for Nature Conservation (Natuurmonumenten). Thanks in part to a contribution of EUR 15 million from the Dutch Postcode Lottery, they were able to undertake the planning and part of the construction of the project.
Additionally, knowledge development is a powerful incentive for implementing Building with Nature projects. Long-term knowledge programmes such as NatureCoast at the Sand Motor and the Marker Wadden Knowledge and Innovation Programme (KIMA) also attract additional funding from organisations such as the Dutch Research Council (NWO). EcoShape, a foundation under Dutch law that facilitates the Building with Nature network, develops and shares knowledge on pilot projects in which Building with Nature is applied. More parties are involved in the planning and implementation of natural solutions than in traditional dyke reinforcement projects, such as government bodies, research institutes, the business community, social organisations, nature organisations and knowledge partners.
Since these projects have multiple objectives, it can often be beneficial to put them out to tender in a different way. Collaborating with the market at an early stage opens up opportunities for creating added value from the outset. This way, the contractor also has more freedom when it comes to shaping the project. For the reinforcement of the Hondsbossche and Pettemer sea defences, this led to the construction of a lagoon that had not been included in the original plan. For the Marker Wadden project, a conscious decision was made not to use a detailed design in the tender but to focus on building using natural processes as much as possible.
However, innovative tendering is not always possible. In the case of the Hertogin Hedwigepolder, an agreement was reached with the Flemish Region setting a lower limit of 600 hectares of estuarine nature. In the Netherlands, tender specifications are usually based on functional requirements; however, Belgian clients often prefer to work with a strict framework of what has to be delivered. This once again underlines the fact that not all positive findings from this exploratory study are directly applicable to other projects. They do however, provide useful pointers for future initiatives.
Building with Nature projects are generally effective in combining flood protection, nature development and recreation. The projects reviewed in this study are regarded as success stories that will inspire future initiatives. Besides the impact on flood protection, nature development and recreation, there are several other factors that also increase the appeal of Building with Nature projects, such as not taking up space in the area protected by the dykes.
The costs of natural solutions are typically higher than for projects solely aimed at reinforcing flood defences. The additional costs of Building with Nature projects as part of flood protection projects are similar to the costs of nature development projects. The additional costs per hectare of developed nature are on average EUR 120,000 per hectare, with considerable differences between the projects. The differences in costs are partly due to the varying flood protection challenges, the characteristics of the working environment and the possibilities for cost-neutral nature development by using the resources released during one project in another. The findings of this study can be used to inform the planning and decision-making process for future projects, including cost figures and drivers for successful decision-making.
To obtain a more complete information base, further research into the benefits of Building with Nature solutions is required. The impact on flood protection, nature development and recreation is monitored through monitoring and research programmes and, where possible, quantified. This exploratory study also demonstrates the value of investigating the actual costs of Building with Nature projects, hence the recommendation to compile a database in which the costs, broken down by project component, are recorded. This database can also be used to compare the costs of hydraulic engineering Building with Nature projects with the costs of nature development at other locations throughout the Netherlands. Reliable insights into the costs could further reduce the barriers to implementing Building with Nature projects, which will ultimately ensure that such projects move beyond the pilot stage and are applied more widely in hydraulic engineering.