Water Werx

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Updated: October 4, 2019

Australians live on the driest continent on earth so it’s no surprise that water restrictions currently exist for all Australian states except Tasmania and the Northern Territory. Some states have even imposed permanent restrictions on how and when water is used by its residents. We use water in different ways and it is sourced from different means, which will impact on how we manage it in the landscape.

Water can be sourced from a mains water tap, water tank, a combination of both and/or multiples of both. Water storage tanks can be located underground or aboveground and come in all different colours, shapes and sizes and are made from materials like plastic and metal.

Irrigation is all about the useful things we do with water in the landscape and drainage is all about dealing with that water to result in our desired outcomes.

Underground tanks free up space for landscaping, living spaces and driveways. An inflatable tank is particularly useful when aesthetics, tight spaces and budget are priority in a landscape project. Isn’t this the case most of the time?

The various commercial underground water storage tank manufacturers nowadays have extremely efficient filters fitted so we can use collected water from rooftops, roads, car parking lots and sport field runoff. In order to choose a tank type and size you need to know what uses the collected water will be put to and therefore how much water you will need; how much of it can potentially be collected by good design and how you deal with any runoff and therefore any subsequent possible drainage problems.

What are the water collection points for water in the landscape?

Besides coming off the roof of a building when it rains or after seeping through soil profiles, we can also use what’s been termed ‘grey water’. Grey water is the waste water a site produces such as bathroom and laundry waste water. Grey water systems can be retro fitted to existing facilities – a licensed plumber must install these systems.

TIP: The client should be advised to start using low phosphate washing powders and detergents if using a grey water system at home because otherwise there will be a detrimental effect on their gardens. It is not to be used for any fruit and vegetable growing.

Once the water storage question is sorted you need to consider what type of irrigation system to install for your client or recommend a licensed plumber and drainer, if your project meets certain criteria, which differs from state to state. This will depend on aesthetics, the client’s budget, the runoff area, garden size and the desired outcomes from managing all this water.

What are the types of irrigation systems? There are two main types of irrigation systems: sprinkler systems and drip irrigation. Misting is another less common option.

Firstly, sprinkler systems: the dimension and size of lawns and gardens will determine the size and number of sprinklers that will need to be used. Consider local authority water restrictions – if large lawn areas need to be maintained, then this is the type of system to install. Try to link the sprinklers into different zones if possible because some areas of the garden will need to be watered more often than others. For example, vegetable gardens will need more water than a bed of native plants. It may also be that you need a lawn to be watered at different times and rates than the garden. Some irrigation suppliers sell smart controllers, providing daily automatic adjustments to a controller’s watering schedules based upon changing weather conditions.

TIP: It’s important to determine minimum pressure so your sprinklers work properly. Once you know this you can design the system and the type of sprinkler heads to be used.

The simplest method I know to test the flow rate in litres per minute from a mains water source is: time in seconds how long it takes to fill a standard bucket (9 litres) with water from the tap you will connect the system to. For example, if it takes 10 seconds, then divide that into 60 (seconds in a minute), which is 6 and multiply 6 by 9 (bucket size in litres) = 54 litres per minute flow rate. The usable water available to you is always 80 per cent of that total.

Specialist irrigation shops can work it all out for you or go online and provide the total square metres to be watered, the shape of that area and any zone needs, and you are almost there.

Line lengths and the number of sprinkler heads from the source also work against water pressure. Another way to combat water pressure – or lack of it – is to install a pump. Different pumps are used for different situations, for example to pump water long distances, up steep slopes and in big volumes. There are: floating pumps, submersible or turbine pumps, booster pumps, end suction centrifugal pumps, and displacement pumps.

The second main type of irrigation system is drip irrigation, which is extremely water efficient. It uses much less water, minimises evaporation, eliminates wind drift and overspray, reduces run off and delivers water directly to the roots of the plants, which is the healthiest way to deliver nutrients to a plant.

There are three main types of drip systems: water weeping hose, in-line drip tube, and plug-in drippers. Water weeping hoses weep water at a rate of approximately 2 litres per 15m per minute along their entire length. They are designed to run at a low pressure and each hose can be up to 30m long.

TIP: On a slope they tend to weep more from the lower end of the hose and so do not give an even amount of water to plants along the hose length. They should not be used with muddy or hard water because it will block up over time.

In-line drip tubes are poly pipes that have drip emitters built in at regular spacings. Netafim has been the global leader in smart drip and micro-irrigation solutions since 1965 for greenhouses, large gardens, acreages and irrigating crops. Visit: www.netafim.com.au

Plug-in drippers can be fixed or adjustable. Fixed drippers can be set at a rate of 2, 4, and 8 litres per hour while adjustable drippers can be set anywhere from 2 to 45 litres per hour. The drippers may be plugged directly into low density poly pipe or connected via 4mm spaghetti tube cut at different lengths to suit.

TIP: These can be tedious to install over great distances because you have to ensure all drippers are upright and continue working every time you move the hose. However, it can be a great system for watering lots of potted plants because you can alter the flow rate for each pot.

Hand in hand with irrigating a landscape is drainage. What type of drainage system needs to be installed? Remember, all drainage systems work because water always flows to the lowest point, which means that you need to design the system so the drainage water will drain to the lowest point in the area in question – into a ditch, swale, dry river bed, underground storage unit, or a soak away using groundcover plants that readily take up the water. To achieve this all the drainage pipes must have a fall on them of no less than 1 in 200 in the direction you wish the water to flow.

The most common type of subsoil drainage is in the form of a special pipe, which is covered with geotextile material. The pipe itself has a number of perforations through it to let the water escape and drain away.

TIP: Some landscapers surround the pipes in coarse washed river sand as a more economical alternative to using geotextile materials.

A French drain is an efficient and easy-to-construct pipe drain with no pipe. The idea is that when the drain is working the water runs into a soak away and over a few hours soaks into the surrounding ground soil. For this reason it is best to pick an area of land that drains freely. The water collects in a recycled concrete aggregate channel, which starts just below ground level. First you dig a trench behind a wall that is about 150mm wide and as deep as required with a fall of 1 in 200 so the water flows. Next, the trench should be lined with geotextile material. Backfill with recycled concrete aggregate (20mm), wrap the sheeting over it and backfill this time with the topsoil previously excavated. The drain will need to end in a soak away, which is a large cube-shaped hole lined with geotextile material and filled with clean rubble or recycled concrete aggregate. The next time you quote for paving, think about using pavers that help with drainage. Porous paving is an economical paving system designed to filter water through to the underlying media, which is usually specified for a landscape that is trying to contain water as opposed to allowing runoff into stormwater drains. Porous paving is ideal for use around tree trunks, as footpaths in parks and gardens, beneath outdoor showers or tap outlets, and along wheelchair access routes.