Technical: Olympic Water
Scarcity and over-supply of water have both been catered for in the design of the Olympic Park.
Look at images of the happy people sitting on grass watching events on the giant screen in the North Park
during the Olympics and Paralympics, and probably the last thing that comes to mind is ‘flood attenuation’. Yet those lawns were designed to be flooded and hold water during exceptional events. They are just one part of a thorough-going strategy about water which informs the entire design of the Olympic Park.
And, because the landscape is one that works hard, in few places is it obvious what is happening. The park represents green infrastructure at its most integrated and engaging. The one change that is obvious is entirely positive. Where once there were heavily polluted waterways, now there are fish and frogs and, soon, one hopes there will be otters — their holts have been built and they just have to decide to use them. The creating of a waterside environment in the North Park, complete with the planting of wet woodland, was just one aspect of the work that was done to clean up the waterways.
Other aspects included the construction of a new lock, Three Mills Lock on the Prescott Channel south of the Park. Along with dredging, this deepened the channel and allowed larger boats to access the site during construction. Additionally, because it is upstream of the Abbey Mills Sewage Treatment Works, the lock reduced the potential for sewage overflow to move upstream into the park with the tide, and so helped clean the water. River walls in the South Park were repaired and replaced, making it possible to create wider towpaths. The Channelsea River was culverted, and this, along with the additional flood storage in the North Park, decreased the risk of flooding both within the park and to neighbouring areas.
The wet woodland itself required considerable study. In order to create the right environment, the water engineer (Atkins) had to create low embankments that would hold water after they had been overtopped. Coir blocks were used for the planting, both because they created the right conditions, holding enough water, and because they speeded installation.
But managing water is not just about dealing with having too much — scarcity is important as well. Water, particularly potable water, is an increasingly precious resource, and the design of the Olympic Park took this into account with novel approaches to both saving water and treating water.
The first important step was to reduce water demand. The planting has a large role to play, as most of it was deliberately designed not to need permanent irrigation — the only two exceptions are the London 2012 Gardens and the Great British Garden. In contrast, the widely used perennial meadows need irrigation only for the first two years while they are establishing.
Considerable studies were carried out to find the best way to provide the water that was needed for irrigation. Abstraction from the river network was discounted as it was already near the maximum acceptable level. Rainwater storage on site, either in swales or tanks, would have occupied too much space, and in any case most rainwater was being used within the buildings, as part of a process that also reduced their demand.
The solution therefore was the construction of something that is relatively unknown in the UK, and has never been done on this scale — a black water treatment plant adjacent to the site. Known as the Old Ford Water Recycling Plant, it takes sewage from the Great Northern Outfall Sewer and treats it to a non-potable, but high, standard. As well as its use for irrigation, this water is used for toilet flushing in the venues and also used in the Energy Centre for cooling water.
One of the great achievements of the Olympics was that there were not just nice words said about environmental issues. Hard targets were set, and were measured, and as a result, were achieved. The use of water was one of these targets. Potable water use was to be reduced by 40 per cent compared to standard practice. The black water recycling and the choice of planting that did not require constant irrigation played a part. Also important were the measures that were put in place in the buildings, such as low-water-demand appliances and rainwater harvesting. As a result of the combination of all these measures, the target was exceeded comfortably, with a saving of a very impressive 58 per cent.
What is really impressive about the attitude to water on the Olympic Park is that in almost every case moves to improve water quality or the use of water have led to additional benefits. So the cleaning up of the waterways created an environment in which a wide variety of species could thrive. The opening up of the banks of the rivers facilitated this, and also helped with flood prevention. By allowing the water to overflow the banks it was possible not only to alleviate flooding but also to create a wet woodland environment that, while originally indigenous, is rare today. The decision to keep irrigation demand to a minimum was one of the driving factors that resulted in a planting regime that wowed the visitors and will continue to be seen as innovative for some years to come. The need for some irrigation, on the other hand, tipped the balance towards the construction of the black-water treatment plant. Like so much of the work on the site, there is evidence of innovation — but innovation that has been shown to work, and so is reproducible.
The site itself will be a repository of knowledge although it wears its learning lightly. For those who want to delve further, the creation of the Learning Legacy website ensures that the knowledge can be shared as widely as possible — as it deserves to be.