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Water-Sensitive Urban Design

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Updated: May 29, 2020

Australia – the world’s hottest, driest continent. How much can a koala bear? Well, sadly, not a lot! It seems that koalas have developed a new response caused by our drying climate. Once upon a time, eucalyptus leaves contained enough water for a koala’s needs. Yet, a changing climate has seen them becoming less succulent, forcing the little fellas to now desperately seek out and drink water.

With some states’ average rainfall dropping by as much as 40 per cent, trendy names like, “Water Sensitive Urban Design” have become just plain common sense. We all need to collect more of what falls on our roofs, use it wisely and improve the quality of any minimised run-off.

From tanks to irrigation, permeable surfaces to bio-diverse planting, there is money to be made in ‘climate adaptation’– yes, another win, win for the customer, the environment and the landscaper!

Collection

Moderate to severe water restrictions in many towns and cities has led to customers becoming increasingly concerned about how they will irrigate any new landscaping. Provisioning for rain water tanks, pumps and irrigation is becoming the new normal on domestic and civil projects.

The National Construction Code, adopted in 2016 sets out a, “six-star standard on energy efficiency and water saving” with a minimum of 2000 litres of storage connected to all toilets in the building. State, territories and local government requirements may vary, but a plumber will be required to install the ‘rain saver’ device, which switches between tank and mains water to ensure there is no back flow.

Where storage is to be used for both toilets and gardens, siting of tanks will depend on a number of considerations such as access to power for pumps, reducing pipe runs, service access and, in hotter climates, placement in the shade to reduce water temperature and possible bacterial growth.

On new builds, there are opportunities to excavate for underground water storage in concrete or poly tanks. Storage could be under the driveway or garage slab or even under the lawn. There are also opportunities for storage under a stump-mounted house or a post-mounted deck using bladder tanks, which consist of a flexible plastic or rubber bladder.

Above ground tanks are made from a number of materials with polyethylene, colorbond aquaplate and galvanised steel being the most popular, other options include, stainless steel, concrete and fibreglass. Poly tanks may be the best solution for rural applications for the storage of corrosive bore water. Colorbond tanks continue to gain market share, relying on aquaplate – a thin sheet steel with a colorbond coating on the outside and a specialised waterproof internal coating.

The most common method of mounting an above-ground tank has been to board up and in-fill with sand making a self levelling base but, beware, sand can be washed away, if the tank overflow can’t keep up during torrential rains for example, so consider a concrete base. Customers often ask, “how much storage do I need?” – well… 1mm of rain on 1m² of roof will provide 1 litre of water.

Irrigation

Having less water to play with has led to rapid advances in irrigation – the days of risers, jets and misters are diminishing replaced by drip flow systems targeted at beds of plants with similar water requirements.

Irrigation controllers have meant that landscapers can create stations that provide just the right amount of water for a particular area. Programs linked to a rain sensor have become an essential option as jets pumping out the good stuff on a rainy day is not a good look! It’s also important to become a bit of a techno-geek utilising all of the micro-computers options, such as water budgeting, which allows water requirements to vary with the seasons or even consider setting up non-watering days for particular stations. Now there are even controllers that allow you to check and program via your smartphone while sipping coffee!

In the past, pop-up lawn sprinklers were either constantly jammed in the ground or stuck above-ground as target practice for the ride-on! Today, people are very aware of water wastage, making it essential to quote for a quality pop-up system – one that can be flushed as well as containing reliable long-life seals and heavy duty retraction springs.

Infiltration

Impervious surfaces can cover up to 94 per cent of the ground in urban areas. This results in low sub-soil moisture impeding the growth of plants, making them dependent on irrigation. In cities like Melbourne, all this concrete and asphalt has led to shallow rooted, unstable street trees.

If impervious surfaces are required, like the driveway or paved patio, consider providing fall to vegetated areas rather than to the street, with the provision of sub-surface slotted drains in case the soil reaches field capacity. Amazing how green roadside verges are, even in a drought!

In droughty times, turf tends to get a bad rap. Sure, even new drought resistant, less-thirsty lawn varieties may need irrigation but that beautiful green swathe has some significant green credentials.

Turf obviously rates as a permeable surface, but, also has the added benefits of acting as a ‘carbon sponge’ while cooling the surrounding environment.

Permeable pavement uses either plastic or concrete grid systems. The gaps in and between the pavers are filled with gravel or alternatively, with a turf mix to establish a green driveway or overflow carpark.

But a word of caution – if the lawn is going to get constant daily parking, it’s difficult to guarantee growth without sunlight!

Storm Water

Ironically in our wide, brown land a changing climate has meant floods from tropical cyclones and extreme storms have become more devastating, quickly overwhelming poorly designed drainage systems.

One of the biggest innovations in storm water products has been the manufacture of drainage pits using glass reinforced concrete (GRC). Pits made from GRC are significantly lighter than cast concrete and can be lifted by one or two labourers – freeing up the backhoe or excavator. Allowances for pipe entries can be done easily on site with a drill and ball pen hammer. Despite their lightness, GRC pits can be engineered for all load ratings and approved to depths of 5m.

Low-profile, zero-step down driveway drainage in marine grade stainless steel has certainly become an alternative to UV stabilised polymer grates, providing both durability and style.

Landscape requirements like WSUD spur product innovation. The slow rise in demand for green roofs, for example, has led to specialised drainage products that will drain and discharge during a storm while allowing water to percolate back out of the channels into the garden during light rain.

Checklist

When quoting, make sure water is in there with retaining, paving and plants. Get your clients to consider:

  • Collection (rain water tanks and pumps)
  • Irrigation (drip systems and controllers)
  • Permeable surfaces (turf and permeable paving)
  • Run-off (grates, sumps and even bio-retention swales, basins or constructed wetlands on larger jobs)

Just like our cuddly koalas, landscapers need to adapt to a changing climate – altering what we do, the services we provide, to guarantee the water needs of our customers and the environment.

The K-Rain Pro-S™ Flush Cap sprinkler range is of contractor quality and suitable for residential and light commercial irrigation installations. Featuring a high-pressure flush cap, which is ideal for flushing the irrigation system at the start of the season or after maintenance. Replace the flush cap with a spray nozzle once the system is flushed.