Cost and benefits
For an overview of the costs and benefits of ecobasins, the following indicators should be quantified:
- Costs: Investment costs (stones, asphalt etc.); Maintenance costs (inspection for leakage, repair costs); Project management costs (permits, process, contracts etc.).
- Benefits: Increased biodiversity; Education/raising awareness; Creating opportunities for nature mitigation and compensation.
Note that the Government makes no savings for rehabilitation or renewal at the end of the life cycle of a structure. In the Netherlands, for traditional projects in which the dike toe has to be replaced, costs of a standard dike toe of 5 m width are about € 100 the linear meter. The costs of constructing the first prototype ecobasins in the dike toe were about € 400 the linear meter. The total cost of the revetment works of which the toe is a part, are estimated at about €1000 per linear meter. The total length of ecobasins constructed per kilometer was about 60m. Less expensive ecobasins are possible, however, by optimizing planning and construction methods. Ecobasins sealed with foil instead of asphalt or prefab concrete, for instance, are expected to be cheaper. Furthermore, optimization between cost and basin-area is expected to be possible.
Other costs were not monitored in this case. The project has the character of an experiment, since the cost-benefit picture of mainstream application has not yet been completed. Therefore, it is difficult to give an estimate of the project management costs. Estimating these project management costs for a traditional dike toe project gives some insight into the magnitude. Based on pre-calculations by Rijkswaterstaat, the costs for project management are about 18% of total cost. Costs for constructing ecobasins were part of total cost of a complete revetment reconstruction scheme. On-site availability of equipment for stone placement and working with asphalt made construction of the ecobasins more cost-effective. The design requirement of the reconstruction works as a whole is to provide long-term (50 yr) protection against flooding. Maintenance costs are minimized for all aspects of the design, including the basins. It is concluded that additional construction cost of this type and this amount f small ecobasins are marginal compared to total costs of the revetment reconstruction. It is expected that larger-scale basins are cheaper per unit area, because a certain volume of stone is replaced by the basin.
In this case, quantifying the benefits is a lot more complicated than estimating the costs. Benefit quantification is the result of monitoring which was ongoing until the end of 2012. Results indicate increased biodiversity (factor 3-5) in the basins as compared with the surrounding intertidal toe area. Regular foraging of birds on organisms in the basins is observed. Therefore, effects on surrounding ecosystem can be expected. An inventory of species that utilize the basins could reveal that the basins provide benefits to ecosystem quality relevant for the Framework Directive or for species relevant for Natura 2000. This positive effect could be realistic for some red list bird species of the Netherlands (for instance Steenloper species, Turnstone).