Lawn Irrigation Systems
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.