7 minute read
Water resilience in housing around the world
SuDS system at Arizona State University Campus, using dry stream beds as water attenuation features. © Tom Young
Water is a precious resource and vital to functioning landscapes. But how can we design water resilience into future housing developments?
Landscapes universally require water if anything is to grow.
Historically we have been blessed with a mild temperate climate in the UK, with predictable rainfall and plentiful water supplies. However, due to much greater demand in particular areas, unpredictable weather patterns and historic over abstraction, water use is now much more carefully monitored, with available water likely to decrease in the future.
New developments are having to demonstrate water efficiencies as part of planning conditions.
Over the last 18 months, I have been lucky enough to participate in a Nuffield Farming Scholarship. This gave me the chance to travel the world visiting different practitioners involved in water security. I was able to see many examples of how water is used in other countries which experience severe water stress and to learn from them.
I didn’t have to travel far to see the water security challenge faced by the landscape sector. I live in Cambridge which has a similar annual rainfall to Tel Aviv, Israel. A fellow Nuffield Scholar who farms in the area has measured annual rainfall between Sept 2021 and Aug 2022 of 539mm and between Sept 2022 and Aug 2023 of just 280mm.
Cambridge is one the UK’s fastest growing UK cities, partly due to central government’s commitment to turn the area into a world leading scientific hub. The city’s population is expected to increase by 6% by 2043, with an extra 250,000 homes needed in the region by 2040. At a regional level, the population of East Anglia is forecast to increase by nearly 1 million by 2040. Several large developments in the area are currently being blocked by the Environment Agency over long-term water supply issues. These will need to be resolved before certain developments can be built.
This issue is also affecting other water users such as sports pitches, parks and agriculture – all likely to face reductions in water allowances in the future. Other users such as Cambridge University Botanic Garden also face water-sourcing issues, having lost valuable specimens in the 2022 heat wave due to an inability to irrigate sufficiently.
So how can landscapes be designed to improve their water resilience?
Landscapes can and should be fully integrated into the water cycle. Sustainable Drainage System (SuDS) design principles can be employed to direct water into vegetated areas. These can be constructed so that they store water for later reuse, rather than just holding it for a short period of time. Such systems can also be combined with subsurface irrigation systems which use water more efficiently, in some cases saving up to 60% over conventional arrangements.
Providing sufficient water can be a challenge on many projects and requires close collaboration between the engineer, architect, ecology, and landscape teams, with a clear client vision from the outset. Plant and soil selection must be closely aligned with this vision, with plants specified that tolerate both drought periods and sudden inundations with water.
Landscape standards and best practice guidance has a huge role to play in promoting water-efficient design. For example, the latest 2022 GRO (Green Roof Organisation) Code⁵ has minimum substrate depths and design parameters to reduce need for supplementary water. Other best practice guidance, such as from Building with Nature, actively promotes the reuse of water onsite, and climate resilient design. These strategies should become more commonplace as more local authorities adopt them as standard design principles and when the new SuDS legislation comes into force in England in 2024.
National planning policy goes a step further, with mandated water use reduction offsets required for some local authorities (Water Neutrality). This requires new developments to help finance water efficiency measures in the same catchment. The developments’ use is offset, resulting in no net gain in water demand. This mainly focuses on domestic water use, but irrigation requirements may form part of any assessment if it has a significant demand in that situation.
The Enabling Water Smart Communities project managed by Anglian Water won Ofwat funding in 2022 and is looking at how water demand can be decreased in new developments. The project is looking at innovative methods, such as dual pipe supply to new developments with one pipe supplying potable and other non-potable for uses such as toilet flushing. In other areas some developments already use rainwater harvesting for this purpose.
Existing landscapes can benefit from long-term water security masterplans. These look at the long-term use of water within a landscape, potential new sustainable sources (rainwater capture, seasonal abstraction and non-potable sources), and an integrated plan and long-term vision. The Environment Partnership is currently working with Cambridge University Botanic Garden to produce a 50-year water infrastructure masterplan, with extensive irrigation efficiency upgrades and large-scale rainwater harvesting opportunities identified across the site.
However, many solutions I observed on my travels are not routinely carried out in the UK. The reuse of treated wastewater is extremely common abroad, whereas it is extremely uncommon in the UK, with legislation currently not able to support its use.
Israel treats water availability as a national security issue and is constantly developing new water efficiency technology. Drip and sub-surface irrigation is standard, with treated wastewater used to irrigate over 90% of all crops. I was amazed to see the use of treated wastewater in many public parks, with warning signs about the potential dangers of swimming in the water. This constantly educates park users about water security and highlights that this type of landscape is only possible due to use of wastewater.
In Spain I visited a high-end golf course that only had access to treated wastewater. Surfaces are still immaculate, despite having to manage variable salt levels in the water, which have just become part of the normal management regime.
Singapore takes this one step further and has made the island a giant water harvesting system with over 60% of all surface water draining into a series of 17 reservoirs. All wastewater is treated and reused, with some of it to such high quality it can be drunk.
In Arizona I saw many examples of very large SuDS systems draining into public landscape areas. These systems dwarfed any I have seen in the UK, and must cope with extreme desert drought, in addition to intense inundation. The philosophy was to let water infiltrate into the landscape, even if it means some areas are temporarily saturated.
There are many ways for landscapes to become more water resilient. The key requirement is that it must be a primary feature of any landscape design, with long-term water demand factored into the design and management strategy at the outset. With a changing climate, and overall reduction in available water resource, we have no option but to change the way we design and manage landscapes. Therefore, landscape architecture has the ability to lead the way in integrated water management, acting as a pioneering industry for others to follow.
Dr Tom Young is an integrated water management and landscape specialist working for TEP, a board member for the UK Green Roof Organisation (GRO) and a 2022 Nuffield Scholar.
