News
A drier landscape
21st July 2006
With water shortages predicted to worsen, facilities managers need to find new ways to care for planting schemes, advises Keith Weatherhead.
As water becomes increasingly scarce in the UK facilities managers will have to look for innovative ways to look after the grounds around their premises, advises Keith Weatherhead, senior lecturer at Cranfield University and co-author of the Landscape Institute’s ‘Technical Bulletin on Water’.
Crucially, it is good design and planning which will have the greatest impact on being able to create and maintain attractive public and private communal spaces in the drier conditions. There are a number of methods that can be introduced to allow landscapes to thrive in our evolving climate, with its increasingly common warm and dry summers and less rainfall in the winter months. Options include irrigation, perhaps together with reusing and recycling water; using ground materials that retain water; and considering the use of plants which are suitable for warmer climates.
The use of landscape irrigation is growing rapidly in England, particularly in the south east. But with water predicted to be an increasingly scarce resource, thanks to economic growth and climate change, water availability and efficient use have become key issues. The 2006 drought is already concentrating minds on short-term strategies and longer-term options.
Determining Water Needs
Water needs should be carefully defined during the planning process. Computer modelling can be used for larger areas, but designers should beware of the impact of micro-climates around buildings and near non-irrigated areas, particularly tarmac and concrete areas. Individual pot plants can have extremely high water demands.
It is important to distinguish between short-term needs, when establishing planting, and long-term continuing needs. Care during the specification and establishment stages can greatly reduce or even eliminate long-term irrigation needs – options include drought-resistant plants; concentrating and holding local rainfall; using water retentive soils; and encouraging deep rooting. However, even with such measures in place, access to adequate and reliable water supplies will still be essential.
Direct Water Abstraction
Most larger irrigators abstract water directly from surface or groundwater sources. This is still much cheaper than mains water. All new licences are now time limited and subject to a minimum flow. It is difficult to obtain reliable new summer abstraction licences in much of southern and eastern England. Indeed, many catchments are over-licensed or even over-abstracted, and the Environment Agency is trying to reduce licensed quantities at low flows. Winter water or, more correctly, water during high flows, is often still available, but requires storage until needed.
In the past, smaller users often found direct abstraction too expensive due to the cost and complexity of obtaining a new licence. A welcome change in the licensing regulations, contained in the 2003 Water Act, means that direct abstractions of less than 20m³/day no longer require a licence. Depending on the plants irrigated, that could be sufficient for up to 1ha of irrigated surface at peak demand. Add a storage pond and you could abstract 7,300m³ per year – enough for several hectares.
Mains Water
Many landscape irrigators rely on mains water. It is clean, of good quality and comes ready-pressurised for distribution. To comply with water regulations, however, the irrigation systems cannot be plumbed directly off the mains without protection against backflow. Normally, a break-pressure tank with a class A air-gap is used; unfortunately, the water then has to be pumped up to pressure again.
Mains water is costly - typically 70p per m³ or more – plus there can be the even higher sewerage charge, usually levied on 90 per cent of the water supplied. Large commercial users may be able to negotiate discounts, but the typical irrigator’s pattern of peak summer usage is not really welcome to water suppliers. Recent “intelligent metering” trials may lead to much higher summer prices and lower winter prices – not favourable to irrigators.
Facilities managers should not assume they can simply take mains water for irrigation of commercial sites. Night-time-only or limited-flow restrictions are common, and, in critical areas, supply may even be refused. The mains supply is usually considered highly reliable, although some temporary storage capacity is recommended. But the current hosepipe bans and likely drought orders show that irrigation has a very low priority in a drought.
Alternative sources
Fortunately, other water sources can be used for many landscape areas. Roof and hard-standing areas give good sites for rainwater harvesting, perhaps integrated with sustainable drainage systems; moat buildings produce “grey water” that can be reused once treated; and even partial desalination may be worth considering. Most of these are cheaper if planned from the outset and will save money on water bills in the longer term for the tenants or owners of the premises.
Ultimately, climate change is predicted to bring more dramatic weather conditions such as extremely heavy rainfall, storms and drought conditions. Investing in ways to store the water when it is available and to dispense it during the dry season will be key to maintaining our properties, both commercial and domestic.
Keith Weatherhead is a senior lecturer at Cranfield University and co-author of the Landscape Institute’s “Technical Bulletin on Water”. For more information on the Landscape Institute, visit www.landscapeinstitute.org.
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