THE EFFICIENCY OF A SPRINKLER SYSTEM
DISTRIBUTION UNIFORMITY (DU)
Simply put, DU is how even water is applied over a certain area, expressed in a percent.
DU values of different irrigation systems vary a lot. It’s common to see DUs of <40%, most are 30-50%, and we are 60-80%.
This is important because the area with the least amount of water is what determines how long you run the zone for.
Imagine a bunch of measuring cups placed throughout an area, which is then watered for a set amount of time. With a DU of 100%, every cup would have the same amount of water in it. The lower the DU, the larger the difference between the amount of water in each cup.
Every cup which has more water than that is called over-watering and is wasted water.
LET’S TAKE A CLOSER LOOK AT THE THREE MOST COMMON CLAIMS EVERY IRRIGATION COMPANY MAKES CONCERNING THEIR SYSTEMS.
SAVES TIME (AND MONEY)
On the surface, this looks quite straightforward.
Every irrigation system saves the client time by not having to water manually, but it doesn’t end there.
The higher the overall quality of an irrigation system, the less it takes of both time and money to maintain. An obvious example would be the quality of the installation and parts used, and how often they need to be repaired, or simply the time you need to devote to be home during a repair. The lower the quality, the more you need of both.
There are many more which are quite often overlooked, here are a few examples.
RUNNING OUT OF TIME
The higher the DU, the less time it actually takes to water the entire property.
If you live in a municipality which has strict watering restrictions, the value of your systems DU could mean the difference between being able to adequately water your entire property in the time allowed, or not.
Higher quality systems are more flexible to landscaping changes, making them cheaper to reconfigure when necessary.
Simply put, the more sprinklers and zones you have, the less important each individual one is towards the overall performance.
Consider two irrigation systems watering the same area of grass. One uses “head-to-head” spacing (the proper method) and ends up using 4 sprinklers. The other system in order to save money uses 2 sprinklers to water the same area. The loss of 1 sprinkler in each system will have radically different results. With 4 sprinklers there will be a 25% reduction in performance, but with only 2 sprinklers it results in a 50% reduction. This often is the difference between having to pay to modify your irrigation system after a small landscaping change, or not.
In order to compensate for deficiencies in coverage, some irrigation systems will end up spraying water onto areas which it should not.
A few examples would be a wood deck, accelerating rot, or onto unistone decks, facilitating the growth of weeds in between the stones. The worst and most common example is directly onto a house, whether it’s the foundation or a window. Most people won’t make the connection between the cost of everyday repairs around the house, and the operating costs of their irrigation system, but the two are often related.
A poor quality installation often times doesn’t show up until after the warranty is over.
With the majority of an irrigation system underground, this can be easy to hide. The two most common examples are pipes not being deep enough, possibly being susceptible to damage during aeration, and sprinklers becoming crooked over time.
Poorly designed systems will often have sections of pipe which are too small.
Incorrect pipe size can cause excessive pressure each cycle, which slowly wears down valves and pipe, causing them to fail prematurely.
Most reports estimate that 30% of all residential water use is used for watering, and close to 50% of that is wasted water. Mainly due to improper system design and scheduling.
it was found that Quebec’s per capita residential water use was 386 liters/day, whereas, in Ontario, it was 225 liters/day
This statistic is important because it highlights just how apathetic we are in Quebec when it comes to saving water at home. For those of you who consider water conservation as important as we do, we applaud you. This section is for everyone else.
Most municipalities around Montreal use a flat tax for water use, rather than on a volume basis. Because of this, there is a perception that an irrigation system with a high DU has no monetary value. While this may be true for the actual cost of water, the savings come from other sources.
Consider two irrigation systems, identical in every regard except that System A has a DU of 70%, and System B has a DU of 50%.
System B has to run 39.7% longer every time versus System A, and therefore all of its components will wear down 39.7% faster.
This can be applied to virtually anything which saves water in an irrigation system. Every time a rain sensor stops an irrigation system from running, it not only saves water, it also saves unnecessary wear and tear on all of its components. All of the water that a “Smart” controller saves, also extends the life of the system.
We see a direct consequence of inefficient irrigation systems every year, even though most people don’t realize it. Almost every single watering ban can be attributed to insufficient infrastructure, rather than the common perception that it’s due to insufficient supply. During the summer months, most municipalities simply can’t treat enough water to meet the demand. It’s no coincidence that watering is the first thing that gets banned. Most irrigation systems use the total capacity of a house, and since most people water at the same time, this puts incredible stress on the infrastructure. If everyone had efficient irrigation systems, the spikes in water demand would greatly decrease, decreasing the likelihood of watering bans, and by extension cost the city less maintaining and upgrading their water infrastructure.
CONSIDER ONE MORE EXAMPLE TO ILLUSTRATE JUST HOW MUCH WATER A HIGHER DU CAN SAVE.
We will use the same two systems as above, and calculate the water savings over 10 years.
In order to not appear biased, we will be conservative in our figures.
Let’s assume that both systems use 10 gallons/min, and run twice a week from May 1-Oct 1 for 10 years.
- System A runs for 3 hours each time, giving us a total run time of 82,800 minutes, and a total water consumption of 828,000 gallons.
- System B has to run for 4.17 hours each time because of it’s lower DU, giving us a total run time of 115,670 minutes, for a total water consumption of 1,156,700 gallons.
That’s a difference of 328,700 gallons over 10 years!
1,244,265 liters or 2,488,530 500ml bottles of water!
While water has a significant impact on the health of any landscape, it is only one variable in an elaborate system of interdependence.
Soil type and quality, sunlight, climate, and many other factors determine the overall health of any landscape. For the sake of this article, we will focus on how proper watering, and by extension, a quality irrigation system, can help maintain a healthy landscape. The most common myth is that more water is always better. To debunk this myth we must first understand how and why plants need water.
Water helps a plant by transporting important nutrients through the plant. Nutrients are drawn from the soil and used by the plant. Without enough water in the cells, the plants droop. The water a plant needs enters through the root system and helps the plant maintain the proper temperature as water evaporates, similar to how we sweat to stay cool. When the moisture evaporates from the surface area, it causes the plant to draw more water up through the roots, to replace what was lost, helping to provide a circulatory system. A simple test to see if your grass needs to be watered is to step on a section of grass if it bounces back up it does not need to be watered. This is true for all plants but we don’t suggest stepping on your tulips to see if they need to be watered. If a plant’s soil constantly has too much water, the roots can rot, are more prone to disease, and the plant can’t get enough oxygen from the soil, effectively suffocating the plant.
NOW THAT WE KNOW HOW A PLANT USES WATER, LET’S TAKE A CLOSER LOOK AT THE PROPER WAY OF PROVIDING IT THE WATER THAT IT NEEDS.
We will use grass with 4″ roots as an example, however, everything in this section can be applied to any plant. Ideally, we would water until the soil is saturated to a depth of 4″. Any more watering at that point is wasted because it will penetrate deeper than the roots can reach. Watering beyond this point not only wastes water but is actually detrimental, as it will bring with it important nutrients deeper into the soil and out of reach of the roots.
An easy way to reproduce this phenomenon is with a sponge. Take a relatively dry sponge and put some liquid dish detergent into it. Now slowly pour water on the top of the sponge. Water will travel further down the sponge only when it is saturated with water above. If you stop just before the sponge is fully saturated, all the water and soap will remain in the sponge. As soon as you continue pouring water onto the sponge, soapy water will start dripping out of the sponge. Just like the nutrients in the soil.
Watering would not resume until there is a minimum amount of water left in the 4″ of soil, called “Managed Allowed Depletion”, or MAD. It is usually about 50% the depth of the root system.
Once reached, watering resumes and the cycle repeats.This process of watering is what we call deep, infrequent watering.
Letting the soil dry up to the MAD level achieves two significant benefits.
The first was already mentioned above, giving roots the oxygen that they need, and the second is that it promotes root growth. As portions of the soil dry, roots will grow, in effect looking for water. If the soil is constantly wet there is no reason for the roots to grow.
This is important since any plants overall health, resistance to stress, and resistance to disease comes from its root system. Deep infrequent watering will also make it more difficult for weeds to germinate. New seeds trying to germinate will only have access to water the day which you water, the larger the watering interval, the less chance a new seed will receive the water needed to develop into a weed.