South Africa is in the midst of a drought, with water restrictions that have been in place since November 2015. Recently new restrictions have been imposed along with tariff increases as Johannesburg Water tries to curb water usage by residents. One of these is that home owners must water their gardens with hand-held hosepipes rather than irrigation systems, but whilst this is likely to have the desired effect – because home owners may be too busy or too tired after work to manually water their gardens – it should also be noted that manual watering can lead to water wastage, and that correct use of an irrigation system is a more efficient solution.
Before we look at the facts and figures regarding water usage in our gardens, take a look first at this series of pictures of manual watering:
These photos were taken since the new restrictions and tariff increases came into effect, so although it’s possible that manual watering had always taken place here, the pictures show what can go wrong when manually watering a garden. It doesn’t take much to realise that a significant amount of water is wasted on the street, but there are other problems too that are not as clear in these pictures, problems related to precipitation rate and equal application.
To illustrate these, consider first, a heavy highveld thunderstorm. Most of us would agree that such storms are one of the true pleasures of living on the highveld. But what effect do these storms have on our gardens? When thunderstorms put down more water than our soils can absorb, saturation and run-off occurs, which is why one of the most frequent requests we get when the rainy season starts is: “please come and fix my drainage!” Soil can only hold so much water before further application results in wastage. Ironically though, we often unwittingly replicate this process when we manually water our gardens. How often do we as homeowners or gardeners forget to move a sprinkler or turn off the tap? And if we’re holding a hosepipe, how do we know how much water is enough, or that we’ve reached all areas of the garden equally? Much of our hosepipe use relies on guess work and intuition, so it’s little wonder that inefficient watering can so easily occur. Over-watering is a common problem in gardens, and has a detrimental effect on our plants: nutrients can be leached from the soil, and fungi and disease can proliferate. Poor plant growth or plant loss results, and our trees, which require strong and sturdy roots, develop shallow root systems which compromise their stability.
This is where precipitation rate comes in. Rate of precipitation (ROP) is the rate at which water is applied to a given area of your garden. It’s usually measured in millimetres per hour (mm/h), and is calculated by dividing the litres per hour by the area. So, for example, if you have a garden that is 5 metres by 5 metres, and you apply 17 litres of water per minute to that particular area, then your rate of precipitation would be:
17 x 60min = 1020 litres per hour
5m x 5m = 25 square meters
= 41mm/h (Rounded)
This, incidentally, is roughly the same precipitation rate of the high-radius nozzles that one sees on green risers in office parks and gardens.
But let’s adjust the above figures: what happens if we reduce the size of the area to only cover 1 meter by 1 meter? In this case the calculation would be:
17 x 60min = 1020 litres per hour
1m x 1m = 1 square meter
To say this is a high precipitation rate would be an understatement. Most soils can only absorb water at a rate of 25mm/h, so it far exceeds the ideal rate of application, and would quickly result in saturation and run-off. It is equivalent to pouring 8.5 x 2 litre bottles of water onto one shrub every minute. And yet, this is what can happen when we use a hosepipe to water our gardens. If the flow rate from our hoses is 17 litres per minute, and we water one plant for one minute, then this is the type of precipitation rate we would have. Looking back at the figures, it doesn’t take much to realise that we could have watered 25 square meters of garden in the same amount of time, with the same amount of water, and at a rate that is far more favourable to our soil and plants.
As a nation, we should embrace the fact that a well installed irrigation system is more efficient and healthy for our plants than manual watering. Unfortunately though, poor irrigation practices have become common in gardens, resulting in poor application rates and inefficient systems. In our daily visits to gardens we frequently encounter systems that have not been designed correctly, do not employ head-to-head principles, have mixed sprinklers with differing precipitation rates on the same station (resulting in flooding of certain areas or dry spots in others), and, perhaps the bugbear of most home-owners, poorly trenched piping resulting is frequently punctured pipes (you can’t blame your gardener for a burst pipe when the pipes have been trenched only a few centimetres below the surface). Practices such as these give the industry a bad name, and only perpetuate the myth that manual watering is more efficient than a well installed irrigation system.
So what are good irrigation practices? Here are a few points to consider:
– Correct scheduling is important. Many systems are scheduled to run everyday, sometimes twice a day, which is over-watering your garden. Plants and trees need ‘days off’ in order to develop strong root systems and healthy growth. In summer we should not be watering more than once every two days, and in winter, perhaps only once a week. Watering in the mornings or evenings is more efficient too, as it allows our plants to take up water before it is lost to evaporation in the heat of the day.
– Precipitation rates per station should be taken into account. If the stations that feed your beds have nozzles with high precipitation rates (e.g 100mm/h – 40mm/h), then those stations should only be run for 5-10 minutes. (which results in roughly 7mm per day or 24mm/week if watering every second day) Likewise if your lawn stations have precipitation rates of 10mm/h, they can be run for longer in order to achieve the same desired precipitation.
– Areas of your garden that have their own microclimates or plant types can be zoned accordingly. For example, a shaded south facing corner of your home is likely to remain moist for longer than a sunny north facing side, so these areas could have their own stations and be watered accordingly. Similarly, zones that encorporate water-wise plants such as succulents can be watered for less time
– Designs should employ head-to-head principles, so that all areas of our gardens receive an equal amount of water, and dry-spots can be avoided.
– Trenching should be done correctly, to avoid the risk of puncturing pipes in day-to-day gardening activities.
There are also newer techniques and technologies available that we can employ in our gardens:
– New rotary nozzles have a much lower precipitation rate than conventional nozzles, and are less affected by wind. They can be used on our lawns and in our beds to provide more efficient use of water.
– Automated systems have budget facilities, allowing us to reduce the watering cycle by percentage in order to cater for seasonal changes or water restrictions.
– Rain sensors can be used to switch off your system if its raining, and soil probes can be used to measure the moisture content of your soil and pause the system until the soil requires it. You can even add a fully fledged weather station to your system if you have the budget.
And then of course, there is rain water harvesting: storing our rain water in tanks and using a booster pump to feed our irrigation systems. All of these systems and technologies are available, and if we are going to become a water conscious nation, then all of them should be explored and implemented.
Technology is a great asset when it comes to water usage in our homes. If we do want to water our gardens, let’s make the most of it and help to play our part in conserving this precious natural resource.