Sand Motor – Delfland

Lessons Learned

The main lesson learned of the monitoring period 2011-2016 can be found through this link , other lessons learned can be read below.

  • Mega-nourishments are tailor-made; to be successful the relevant site-specific coastal processes, such as hydrodynamics, morphodynamics and ecosystem dynamics, need to be understood.
  • The specific properties of a particular location will also determine the design of a mega-nourishment.
  • Define all (ecosystem) functions and related stakeholders in the area considered. These are crucial to the various project phases, as the selection of alternatives is seldom based on cost-effectiveness alone: socio-economic and political considerations always play a role.
  • When considering a mega-nourishment it is important to discuss the merits, costs and effects of various alternative strategies. Focus on comparing the option of a mega nourishment with more traditional alternatives (periodic small-scale nourishment) and identify plusses and minuses of each alternative.
  • When considering a mega-nourishment it is best to discuss design (location, position and volume), implementation and management as one comprehensive set, including the way in which monitoring and risk management can take place.
  • Mega-nourishments are generally not the most cost-effective in terms of getting sand on the beach, and will only become a preferred strategy if other benefits are taken into account, such as recreational potential and avoiding frequent ecosystem disturbances.
  • The form of a mega-nourishment is a matter of choice, governed by a combination of preferences. A temporary island is less suitable for recreation, since it is difficult to reach, very dynamic and may create conditions that are unsafe for swimmers; on the other hand an island is ideal for birds and sea mammals, as it cannot be reached by terrestric predators like foxes. A peninsula helps forming a lagoon, which is an asset for recreation as well as nature development. Foreshore nourishment is ideal if the existing beach conditions are already optimal. Beach nourishment may be the preferred option if beach sports are to be facilitated that require wide open beaches, but also in situations where tidal currents close to shore make offshore alternatives less cost-effective
  • A logical choice is to nourish as much as possible within the active zone, as sand within this zone is most susceptible to onshore transport. If the costs of foreshore and beach nourishment do not differ much, there is a strong preference for beach nourishment, of which the losses to deeper water are less.
  • Sand properties: using readily available sand is financially often the most attractive. If one may choose between different grain sizes, there is a preference to use the coarser sand below the low water mark, where it will create a steeper stable slope and therefore requires a smaller total volume. The finer fractions then can be kept for dune formation. If wind-blown sand constitutes problems, e.g. because of nearby roads and houses, coarser fractions may be preferable.
  • Most mega-nourishments will be quite dynamic, whence their longer-term development is difficult to predict. Close monitoring, adaptive management, scientific supervision and a well defined communication strategy to the stakeholder community therefore are necessary.
  • In order to take maximum profit from a large-scale experiment like this, monitoring, data management and generic research need to be specified, arranged and funded before construction.
  • Read the results of the first monitoring period 2011-2016 here.
  • NatureCoast (website offline), a scientific research program with 12 PhD students and 3 postdocs will deliver its results in 2017.