Natural water filtration through sand dunes system
Amsterdam, Netherlands, Netherlands
To address water quantity and environmental challenges linked to overabstraction, artificial recharge has been in operation in the dune area to the west of Amsterdam for more than 55 years and has constantly been improved and fine-tuned over the decades. This system is managed by Waternet, a water company that provides water services to 1.3 million people in the municipality of Amsterdam and surrounding region. The company is a non-profit organization, jointly owned by the City of Amsterdam and the Regional Public Water Authority, Amstel, Gooi en Vecht. Waternet covers the entire water cycle, including drainage, drinking water supply, treatment and transport of waste water, keeping surface water clean, and flood control.
One of its main tasks is the management of the Amsterdam Water Supply Dunes (AWD) system, the primary drinking water source for Amsterdam. Waternet produces 90 million cubic metres of drinking water per year on average and pre-treats almost two-thirds of Amsterdam’s tap water in the dune area of Harlem.
Challenges
In the municipality of Amsterdam and its surroundings, water has been sourced through pipes from the dune area of Haarlem since 1847. However, starting in the 1930s, over-abstraction led to saltwater intrusion in the dune area, which also caused severe ecological impacts. Large-scale artificial recharge was initiated in the 1950s to address these issues. Today, the sand dune filtering system and artificial groundwater recharge is a fundamental piece of green infrastructure that the city relies upon for its drinking water. Over eight decades, several conservation and restoration projects have been carried out to ensure adequate management of this nature-based solution.
Financing
The land (36 square kilometres of dune area) was acquired by the city of Amsterdam piece by piece over the second half of the 19th century and the first quarter of the 20th century. These initial investment costs are now considered to be a sunk cost. The natural system delivers both large-scale storage and chlorine-free, natural removal of pathogens. Additional ozone treatment has been added to break down organic compounds but is not essential. As a result, the costs to operate and maintain the systems are low, and total costs of water production are below EUR 1 per square metre. There are no external subsidies, and all costs are paid by water users.
Actions and impacts
The Amsterdam Water Supply Dunes system covers an area of around 3,500 hectares in the Noord-Holland province. It is part of the Natura 2000 network of protected sites. Though supplemented by natural dune water, the main source of water is river water from the Lek Canal, situated 55 kilometres away and originating in the Rhine river. This surface water is pretreated close to the intake in Nieuwegein and then transported to the Amsterdam Water Supply Dunes at Vogelenzang. Once the water has percolated through the shallow groundwater system in the dunes, post-treatment takes place in the Leiduin water treatment plant. High-quality drinking water is produced through a 14-step process, with the dune sand acting as a natural filter for suspended particles and as an environment rich in bacteria that facilitates the decomposition of certain substances, such as pesticides and pathogens. The sand works as a natural barrier against some bacteria and viruses. Sand filtration also breaks down organic micro-compounds. The aquifer recharge system is based on the principle of using groundwater only for storage, removal of pathogens, and attenuating pollution peaks. The recharge system is combined with nature restoration goals and pollution prevention of the water source, which implies quality control in the upper catchment.
Since 1990, Waternet has carried out conservation measures and further large-scale projects to restore the natural dune systems and wetland habitat types. The overall aim of the Amsterdam dunes project was to restore and improve the characteristics and habitat types of the Natura 2000 site. Large-scale restoration was required to reverse the effects of long-term dehydration, eutrophication and the impact of invasive alien species. Specific actions have included removing the nitrogen-rich top layer of soil and invasive species, restoring ponds, mowing, grazing, and other nature management measures.
References
Unesco-IHE, Waternet, Eijkelkamp, Meta Meta, Partners voor Water. (2014). The Amsterdam Dune Water Machine.
EU Commission Life Programme. (2017). Amsterdam Dune project - ‘Amsterdam Dunes - source for nature’, dune habitat restoration project.
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