Floodable parks as a tool for local flood resilience

As the likelihood of both coastal and rainwater flooding increases with climate change and rapid urbanisation, floodable parks and other innovative sustainable urban drainage solutions provide one answer for local resilience.

A combination of sea level rise and increased frequency of heavy rainstorms across Europe could see flood damages rise to over £1 trillion per year by 2100 – with the UK being the worst hit. Already, heavy rain and coastal flooding have increased noticeably across both the UK and Ireland, and indeed globally. The impacts of climate change, alongside our rapid urbanisation laying down ever more concrete, leave drainage systems struggling to cope.

Copenhagen is a city where both coastal and extreme rainfall flooding are already problematic, and set to worsen. After increased flooding culminated in a 1000-year rainfall event that left the city under a metre of water in 2011 ($1.04 billion of damage), the weather changes prompted the creation of an adaptation plan – Copenhagen’s Cloudburst Management plan.

Actions included ranking areas of the city by threat, calculating the cost of doing nothing (€55-80 million a year from now to 2110), and setting to work on a plan that incorporated both blue and green infrastructure projects alongside the usual ‘grey’ infrastructure, to combine water management with amenity improvements. These Cloudburst solutions were implemented through local plans in synergy projects between municipalities, water utilities, philanthropists, and the public through extensive citizen engagement and workshops. Due to the cost of flooding for local businesses creating a shared incentive, private funding and public-private partnerships were easier to come by for local government.

Enter floodable parks: a type of sustainable urban drainage system and blue-green infrastructure project as featured in Copenhagen’s plan. Sustainable urban drainage systems (SuDS) are designed to not only manage runoff and reduce the impacts of urbanisation on flooding, but also contribute to biodiversity preservation, water quality, and the needs of local communities. These parks are part of a toolkit to help communities adapt to climate change by redesigning existing public spaces to provide resilience. Parks designed to flood – and similar infrastructure such as rain gardens, retention ponds, constructed wetlands, or swales – can prove invaluable in retaining or slowly releasing water to prevent runoff or storm surges from causing catastrophic flooding.

Enghaveparken in Copenhagen was originally built in the 1920s, but the park was recently redesigned to retain the original character while contributing significant flooding resilience to the area. Existing features such as a hockey court and path through a rose garden were lowered to become reservoirs during rainstorms. As the park slopes slightly, at one end a small levee was built around three sides of the park to collect water from the surrounding neighbourhood; the gates can slowly release water when the system is ready for it. Eventually, if needed, the entire park can fill up. 300 similar projects are planned for throughout the city as part of the Cloudburst plan.

In the Netherlands – a country familiar with flood risks – flood parks have also been designed with water storage in mind. at Benthemplein in Rotterdam, a lowered court for playing games surrounded by steps for seating represents one of the basins, but there are three in total and many fun design features to accompany them. Two are shallower, flowing into an underground filtration device before seeping into the groundwater to keep it topped up and keep city plants in shape. The deep basin collects water from a larger area around the square, and this water flows back into the city’s main water system. Stormwater dealt with by the park never flows into the sewage system, reducing both pressure on the system and the risk of dirty water overflowing.

When it comes to coastal and river flooding, parks and other blue-green infrastructure can play just the same role. Given the threats climate change poses to infrastructure in New York, resiliency to flooding from sea-level rise and storms is high on the agenda of city planners. New York is currently considering designs for a 10-mile barrier of flood resilient urban landscaping to stop a repeat of the damage Hurricane Sandy’s tidal surges did to lower Manhattan. However, the pilot park that started it all and proved successful at withstanding Hurricane Sandy’s 4-foot storm surge in 2012 was Hunter’s Point South Park, on the edge of New York’s East River.

Built on an 11-acre former industrial area, Hunter’s Point South Park has been heralded as a new type of urban waterfront development, for not just including anti-flooding defences and resilient planting, but being entirely centred around the idea – without sacrificing design and sociality. The paving areas use a porous type of concrete to resist flooding damage, and planted border areas have hidden channels for draining stormwater quickly. Avoiding overloading the urban sewer system, the park instead takes a “catch and release” approach, purposefully collecting water in certain areas and using a planned run-off system to drain it at a steady pace. The system increases flood storage capacity by 557,800 gallons, or a 6-ft storm-surge flood event. Twice a day, the high tide rolls in and large parts of the park become a marsh, and are planted with resilient, appropriate plants to reflect this. Wooden ‘rafts’ for relaxing, a kayak launch site, a viewing platform across the city and a large oval-shaped open space for relaxing and games (synthetic turf, to withstand regular flooding) are among the many amenities that attract crowds from near and far. Downstream, the park has already inspired a similar project in the much-smaller city of Wilmington, Delaware.

While many of the parks and flood infrastructure projects globally gaining attention are in larger cities – China is experimenting with creating entire ‘sponge cities‘ to embed systems that store and purify excess rainwater – there is no reason why local authorities in smaller towns or rural areas can’t equally apply the principles on a smaller scale. In fact, many such projects have already been carried out all over the UK, and sometimes on microbudgets. For rainfall, pockets of public land such as schools, verges, and smaller green or brownfield sites can be retrofitted to provide sustainable urban drainage. For coastal and river flooding, taking aspects such as saltwater marshes or natural rock walls with walkways instead of traditional grey infrastructure (think sea walls) can protect ecosystems, provide carbon storage, and create visual amenity – in addition to the same or even greater level of flood protection.

With the likelihood and cost of flooding set to soar in the UK and Ireland, now will always be the best time to think about including blue-green infrastructure into the development of areas to harness the multitude of benefits it can offer to both people and the environment, where traditional drainage doesn’t quite cut it.