Project by: Jo Groven & Ian Officer, Netherlands
Location: Terneuzen/Province of Zeeland, NL
Client: Wageningen University MSc thesis
Link: Thesis report PDF
Landscape Infrastructure for Coastal Safety: From single coastline towards a landscape zone of size
A design strategy is proposed that simultaneously cures the ecological problems in the coast’s natural system and secures the coastal zone for the future by eco-engineering the coastline into a broad coast, a ‘coastal landscape zone of size’.
After centuries of man-to-nature interventions, the Dutch coast has been turned into a single defence line by use of dikes and dams, and is commonly considered to be ‘safer than ever’. But dikes and dams divide an aquarelle into a mosaic: the once rich coastal ecosystem has suffered intensely due to the loss of gradual transition areas that are under influence of both land and sea. This ecosystem degradation returns to be a problem for coastal safety, since these transition areas provide a buffer for both ecological soundness and coastal safety, such as by countering erosion and foreshore instability. The fact that large parts of the Dutch coastal defence need an update due to global climate change, provides the point-of-departure for a different strategy handling coastal defence.
The solution is found not in height but in width; a broad coast instead of a coastline. The proposed broad coast can be designed by three minimal interventions, afterwards natural processes can take over the construction. They are: 1. providing sand, 2. allowing and guiding dynamics and change, and 3. providing space between a dual defence system. This strategy is tested with a design for a 860 ha. pilot project near Terneuzen, since due to the 2005 Schelde Verdrag border treaty between Belgium and the Netherlands (Vlaams Gewest & Koninkrijk der Nederlanden, 2005: 3), six hundred hectares of land has to be developed into intertidal nature in this region, in order to compensate for the dredging of the shipping lane to the port of Antwerp. After the three minimal interventions have been set to a start, a situation is created in which the natural processes can take over the ‘construction’ of the broad coast. Tides and currents, sedimentation and ecological succession now become the generating motor of this living landscape machine. Over time it transforms to a living landscape that defends, regulates and provides diversity and multi-functional use.
How it works
We will focus on the working of the pilot project. The project starts with making clear that the current technical approach falls short and a new ‘landscape’ approach is needed; from single coastline defence towards a broad coastal landscape zone of size. The pilot project is intended not to show a finalized, detailed design, but instead to show the site as part of a nation wide coastal defence landscape zone. The focus for this site is mainly on inter-tidal ecology, since the area is mandatory to compensate habitat loss due to the dredging of the Antwerp shipping lane.
The concept is very simple. It starts by preparing the site. First, space is provided between a dual defence system; the site’s existing primary dikes are made overtopping proof, secondary dikes are made ready for use and built on plots are surrounded by small ring dikes. Second, the right conditions are set. Fresh water discharge pumps that are currently in the primary dike are moved inland along the discharge creeks to a location in the secondary dikes. The locations along the primary dikes are replaced with inlet-sluices. The basic conditions for fresh-saline transitions now exist; brackish nutrient-rich agricultural water can be discharged in the landscape zone and will be automatically mixed with saline seawater arriving through the inlet-sluices due to tide, turbulence and natural run-off. The conditions are improved for a higher performance by introducing dikes and dams. Dikes and brushwood dams are strategically placed perpendicular to the run-off direction, between the outer ring and the built-on plots. These both secure access to buildings and direct the water flow, hereby lengthening its course and increasing water mixture and nutrient uptake by vegetation. Also, several dikes partition the area into six different regimes by in- or decreasing water intake, levels and dynamics. Differences in preliminary conditions (fresh, brackish or saline water, high or low dynamics, frequent or infrequent inundation, local saline seepage differences) will create possibilities for maximum habitat diversity ranging from tidal marshland and saline meadows to brackish forest.
Third, with the conditions set for maximum performance, the landscape is now opened up for the water. Natural generative processes and time can from now on do their creative task. Tidal exchange and dynamics are allowed on-site and—guided by the framework of dikes and dams—will create a new morphology. The daily import of sediment-rich sea water allows the site to grow along with sea level rise over time. Within the first year, tidal dynamics, together with erosion and accretion have changed the morphology and mud flats are growing, increasing dike stability. Within 5 years several salt marshlands with creek systems have developed and after 30 years, parts of the dryer regimes have developed forest. Nutrients are converted to biomass. Successive processes will diversify the site. During storm surges, inlets are closed and waves are pushed far up the primary dikes slopes causing overtopping, the site will function as a inundated landscape to store overwash water and create back pressure on the primary dike, hereby countering dike slides.
Fourth, with the landscape machine initialized, several ‘light’ functions will be added besides nature compensation for experiencing the site. Education and extensive recreation is made possible; hiking trails and boardwalks, information panels and back-to-basic camp locations are set up, as well as a visitor centre, bike routes and picknick spots. Seasonal colours range from the purple of sea aster in summer to the bright red of salicorn in autumn.
Fifth, over time functions can be added or removed, depending on market demand. Possibilities for flood-proof housing (especially in the proximity of Terneuzen), (experiments with) saline agriculture or aquaculture are all an option. When the pilot project’s strategy is followed by national application, this broad coastal zone can grow into a nation-wide landscape infrastructure of size, a safe, resilient and diverse defence and natural zone, allowing mulitple-day hikes, learning, recreation, housing, food production and more.