Coastal engineering: going multifunctional?
By Ankita Singhvi.
A quarter of the world’s population lives within 100km of a shoreline, with urbanisation on the rise. Coastal space is scarce and valuable, but it is becoming increasingly vulnerable due to climate change. The main hazards that the coast needs to be protected against are erosion (the loss or displacement of land, or the consistent removal of rocks and sediment along a shoreline due to waves, currents, tides or storms) and flooding (when sea height exceeds the elevation of land and covers it, caused by high tides or storms). In order to protect the coast, various interventions are taken on the shoreline: e.g. dikes, dunes, seawalls, beach nourishment. In particular, multifunctional coastal protection has increasingly been receiving attention due to its promise of enhancing adaptation to the threats of climate change, as well as relieving the pressures of increasing urbanisation. Multifunctionality refers to the multiple benefits that an intervention can provide beyond risk reduction. The concept emphasizes the explicit interweaving of ecological, social, and economic functions. What does this look like in practise? Here, I will describe two cases in the Netherlands – one ‘nature-based intervention’ and one ‘grey’ intervention.
Sand Motor, Monster
The coast of Monster has a large, man-made hook-shaped peninsula (see image above) – one of the few interruptions to the otherwise uniform shoreline of the Netherlands. This peninsula is a beach nourishment project called the Sand Motor (also referred to as Sand Engine and Zand Motor). It was constructed by placing 21.5 million m3 of sand on the beach with the aim of reducing the speed of coastal erosion and protecting upland infrastructure from storm surges or high tides. Typical nourishment projects are a repetitive process; a coastline is artificially replenished every five years. In contrast, five times the volume of the average sand nourishment was used at the Sand Motor with the expectation that replenishment would become unnecessary along the Delfland Coast for the next twenty years.
The Sand Motor’s design uses an ecosystem-based conceptualisation of multifunctionality and emphasizes ‘building with nature’ in its design philosophy. In other words, the multiple benefits that the coast provides in addition to protection are dependent on the newly created sandy ecosystem. The hook-shape of the peninsula is crucial for the creation of a shallow lagoon, which supports kitesurfing, recreational swimming, fish habitats and soil organisms. The sediment size and grading of the sand, as well as the presence of shells allows dune formation, which supports an underground fresh water lens and above-ground vegetation and habitats for wildlife. The width of the beach supports recreation, and the entire system is a pilot project that benefits research and education.
Scheveningen Boulevard, The Hague
Scheveningen’s boulevard has a 2km long dike integrated into it for the purpose of flood defence. The boulevard has an undulating course that follows the historical coastline. On the sea side of the boulevard, the beach has been widened to reduce the impact of waves on the flood defence structure during extremely high water. This allows a lower crest height for the dike to suffice. Furthermore, sand supplementation has made the beach ~50 metres wider with the aim of creating a smooth transition from the boulevard to the beach. The core principles that guided the design of the boulevard are: accessibility, vitality, spatial quality and strengthening the identity of Scheveningen.
The boulevard takes a spatial planning conceptualisation of multifunctionality: it uses the dike-in-boulevard to increase the capacity of the shoreline to provide services such as parking spots, hotels, residential buildings and commercial zones – which are all built on top of the dike. The premise of this multifunctional dike is that it is more cost-effective than a conventional dike because it optimises land use by providing multiple real-estate development opportunities. In addition to coastal protection, the dike serves the town with a mixed-use program that should be interesting for both tourist and business visitors, and secure a year-round programme to attract more long-stay visitors. Scheveningen is the most popular seaside resort of the Netherlands, and the dike aims to support this function rather than subtract from it.
To summarise, both coastal protection interventions showcase multifunctionality in different ways: in the Sand Motor, it stems from the ecosystem, and at Scheveningen it stems from the urban system. In the context of increasing scarcity of space in urban areas, it no longer makes sense to build mono-functional infrastructure. The cases show how multiple functions can increase the adaptivity of an intervention to an uncertain future by making it useful even when there are no immediete flood or erosion hazards. Multiple functions help in building public and political support for large investments, and they support the creation of multiple lines of defence – leading to safer, higher quality spatial planning for our cities.