To the Last Drop
Due to competing needs for existing water resources, the amount of water available for irrigation is dwindling. Like it or not, we're going to have to learn to irrigate more efficiently. This is why it is so important to schedule irrigation according to plant needs, not simply according to a clock. The latter is the case with all automatically scheduled irrigation that does not take the weather (sun, wind, temperature), evaporation and transpiration (ET) into consideration.
If you don't know how well your irrigation system is operating, or how much water is being delivered by each sprinkler in a zone, you should perform an assessment and an audit to obtain this valuable information. You can then use this information to make changes to the irrigation system that will increase efficiency.
Assessing your system
Before you can improve your system, you must determine its inefficiencies and then commit to making the changes needed to bring it up to par. Changes might involve respacing sprinklers, reducing pressure, changing nozzles, resizing pipes, repairing or modifying a pumping system, upgrading a controller, adding or recalibrating a weather station, adding flow and metering devices, or other changes that may be needed. Many irrigation systems operate at around 65- to 70-percent water-use efficiency. If you can increase the efficiency by as little as 10 percent, the resulting water savings will be substantial. Water savings at sites we have worked on ranged from 25 percent up to a 72-percent savings for a 24-acre site. The latter has resulted in a substantial saving on their water bill — to date, enough to pay for the audit five times over.
Additional savings can be realized in the form of less electricity for pumping, lower fertilizer needs, fewer system component repairs from reduced operating time and slower plant growth, resulting in less frequent maintenance services.
At one site, we introduced a flow sensor so we could track real flow numbers. This goes a long way in demonstrating the savings that you actually achieve. Another useful device is a dedicated, irrigation water meter. I find that when the actual amount of water used at a specific site (sports field, golf course, commercial site or even a large residential site) is known, the owners or managers are much more ready to adopt conservation practices to reduce the daily, weekly or monthly irrigation volume.
Some metering devices are capable of shutting down the main water supply in case a pipeline ruptures, which is another way to save water.
Auditing your system
One of the main goals of a water audit is to achieve as balanced a system as possible based on economies of scale and return on investment. You would not spend $1,000 to get a $1.00 a year savings. However, you probably would spend $1,000 if that would net you a $500 reduction that year and every year after as long as you operated the irrigation system.
A balanced system applies water as evenly as possible throughout the irrigated zone. An unbalanced system may apply too much in one location, resulting in wet areas, while not applying enough in another location of the same zone, creating dry areas. The result is that you always overwater because you must run the system long enough to meet the requirements of the driest areas.
When considering an audit, it helps initially to actually watch the site's system in operation. Doing so, you should be able to tell if overwatering is occurring and if you will be able to reduce the usage by a lot or just a little. You don't want to spend your time — and your client doesn't want to spend the money — where no substantial reductions will be achievable.
Obtain as much background information as you can. Weather data, historical water use, system layout, components, water source, water meters, controllers, etc. Prearrange with the client permission to operate each zone of the system for about 5 to 10 minutes. On the first visit, run a test program to determine the operational condition of the system prior to the actual audit being performed.
Any significant repairs that affect the performance of the irrigation system must be corrected prior to performing the audit. Otherwise, the increase in efficiency ultimately derived from your audit of the overall system may be overlooked because the savings will be “lost” in the savings from the repairs.
Once repairs are properly completed and the system to be audited is operating to its best level, conduct the actual catch-can test of each zone of the system. If it is windy, reschedule the test: Wind will distort the findings dramatically.
Run the station and flag all sprinklers in that zone.
Record operational pressure at the sprinklers.
Time the rotational speed of rotating sprinklers.
Place graduated-cylinder catchment devices about 2 feet away from each head, and midway between the heads. Make sure to use at least two catch cans per sprinkler by filling in the entire zone watering area as if it were laid out on grid paper, as evenly spaced as possible. Low trajectory sprinklers may require you to dig in the catch device closest to the sprinkler so it does not block the sprinkler trajectory of throw.
Run the test for at least five passes of a rotating sprinkler so that an average of 25 ml (about an ounce) of water is caught in the catch devices. This may take about 5 to 10 minutes per zone, depending on the size of the sprinkler.
Record the data and note any special situations (obstructions, etc.) that may affect the results of the zone's test.
With your soil probe, take several samples in each zone to determine root-zone depth and soil composition. Note types of plant material within this zone. Also note exposure to sun, shade, wind, and hilly or flat ground, low lying areas, etc.
Computer software is available with which you can analyze the data you collect. A schedule, which is used for determining all other schedules, is created from this data. This is known as a Base Schedule and it usually reflects your average watering month. It can then be adjusted up or down for less or more water, depending on the weather.
Even without the benefit of computer analysis, it's usually easy to see where large differences in application are occurring. From the readings of each catch device within a zone, you will note which catching device caught the most (wet area) and which one caught the least (dry area). You need to investigate why the variation exists. Start by running the sprinklers again. Are the nozzles different, plugged or damaged? Measure the sprinkler spacings. Are they equal to the others, or are they randomly placed or out of place? Test the pressure. If it varies by more than 10 percent, pipe size could be the problem. Check the as-built to see if pipe sizes were changed from the design.
Once you pinpoint the problem, you need to figure out how to correct it. If you don't know, then call in experts to assist you in your findings. After your modifications have been completed, you need to retest your system to see if you have achieved the required efficiency changes.
When the system is operating at peak performance, which varies for each system and type of sprinkler, you can then begin fine-tuning your operating schedule to achieve your water savings. But be careful! Fine-tuning involves cutting back on water that your plant material has become accustomed to receiving. The weakest sections of your irrigation system distribution will show up as you cut back on the water. You must slowly reduce the water as your plants increase rooting depth. For some plants, this can take a couple of seasons. As these weak areas show up, study them to see what can be done to improve the coverage within the area without increasing the amount of water applied.
Various types of sensors are available that provide valuable feedback about environmental conditions that could affect irrigation scheduling.
- Rain sensor
There are several types of rain sensors on the market. Although they may use various mechanisms, they all do one basic thing: they interrupt irrigation when it rains. In my experience, using rain sensors alone will save about 12 percent of the water that would have been used without a rain sensor. All automatic irrigation systems should have some sort of a rain sensor incorporated during installation or as a retrofit.
- Freeze sensor
In northern climates, this device could save you from a nasty legal battle. If an automatic irrigation system still is scheduled to water in the late fall, and you get caught by an early cold spell, a real potential exists for icing up a site. Remember, the only difference between an irrigation system and a snow-making system is the air temperature. At fall shutdown, we may even create snow when we blow the lines out if it is late and cold enough. I suggest at least offering the freeze sensor to your clients so that you have covered your bases in case of bad weather (literally and figuratively).
- Wind sensor
A wind sensor shuts down irrigation when the wind exceeds a certain velocity, depending on how you have set it. Wind sensors automatically rest and allow irrigation to start or continue once the wind speed drops. This device helps to ensure that the water you or your client is paying for is going to be of benefit to their landscape and not their neighbor's.
- Portable soil moisture sensor
This device allows you to take actual soil moisture measurements, as a percentage by volume. Plant-water relations is a topic for another article, but suffice it to say that it's difficult to accurately match irrigation with plant needs if you don't a have a method of evaluating soil moisture. These sensors make this a much easier task. Being portable, you can make multiple readings in each zone to get a good feel for how wet or dry your soil really is. This can even be helpful in diagnosing specific symptoms, telling you whether too-wet or too-dry soil is a factor.
- Automatic soil moisture sensor
Now you can go to sleep knowing someone is paying attention. Or, I should say, something. Soil moisture sensors are available that will shut off the irrigation once the soil is damp enough. Depending on how you have programmed the controller, they can start up the irrigation again once the soil is on the drier side.
As you can see, upgrading an irrigation system to be an effective water management tool can initially involve extensive time and labor and, therefore, can be expensive. My company has performed over 100 audits in the past 7 years with varied results. Golf courses and commercial sites usually have a fairly short payback period. The residential sector is the only market segment where the cost is not easily recovered. The more water a site uses, the bigger the return on investment from an audit. An important point to remember (and make clear to potential clients) when selling audits is that after this efficiency work has been performed, every year thereafter generates savings as long as the system continues to be maintained and operated efficiently.
Lorne Haveruk is president of Diamond Head Water Management Services. He has been actively saving water throughout North America since 1991. You can contact the author at firstname.lastname@example.org or 877-H2O-WISE (420-9473).
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