Mention the word audit at a party and a deafening hush blankets the room. That is, unless you're in a room full of irrigation contractors. To them the term audit represents security, reliability, and professionalism.

Irrigation audits have become increasingly simple and effective in servicing clientele. They can save valuable plant material, hardscapes and equipment, while enhancing the aesthetics and resources used to maintain the landscape. Any client is impressed when, by performing some basic tests and calculations, you can save them money and headaches with measured, quantifiable data.

Perhaps the easiest way to land a new client, or to hold an existing one, is simply by walking the site with them and inspecting the irrigation system and the landscape. If there are problems with hot spots in the turf, drooping shrubbery, swamping, eroded hardscapes and other eyesores, chances are the situation can be reconciled with a few changes in the irrigation design, installation or operation.

While touring the site, ask about the frequency and duration of irrigation schedules. How often are schedules adjusted, how old is the system, and how often are repairs necessary? Oftentimes, simple scheduling adjustments can result in significant water savings and healthier plant material, and ultimately might increase the life of many irrigation components.

 

Initiating an Audit

The best way to begin an audit is to do catch-can tests to establish the irrigation system's current performance. Catch-can tests assess distribution uniformity and quantify precipitation rates. They should be conducted under typical operating conditions.

Briefly run the stations you intend to test and flag the heads in each zone using different color flags for each zone. Take sample pressure readings from sprinkler nozzles to detect any differences between heads near the beginning, middle and end of the zone.

The most practical method of laying out the catch-cans is in a grid. Place the identical, straight-sided containers within ten feet of each other. Place containers at problem locations, such as dry or soupy areas, whether or not they fit the grid.

After you've positioned the containers, draw the grid on a sheet of graph paper. Mark the location of all containers and assign each a number. Run the station long enough to capture about 1/2-inch of water from sprayheads or ten revolutions from rotors. Runtimes should be similar for each zone with similar emission devices.

Measure the water in one container at a time by pouring it into a graduated cylinder. Record the amount in the container on the paper grid. When you have measured the water in all the catchments in the zone, add all the amounts together to calculate the total amount of water collected. Divide the total collected by the number of containers to find the average amount of water per container.

Divide the total number of containers by four. This represents 25 percent of all containers. Starting with the container with the least amount of water, identify the 25 percent of the catchments with the lowest amount of water. Find the average amount of water in this group of containers. This calculation will provide the low-quarter distribution uniformity, which is used to determine the correct amount of water to apply in order to insure the minimum required precipitation for the poorest performing sprinkler in each zone.

 

Multiply the low-quarter calculation by 100 to convert it to a percentage. Your goal is to get this percentage at 85 percent or above. DUs in the 60 to 70 percent range are common. don't be surprised if you find some DUs below 40 percent.

 

Factors Affecting Distribution Uniformity

After completing the first catch-can test, it's time to get to work. Walk each zone and measure the spacing between heads and the rotation time of rotor and impact heads. Record the make and model of each head and note the size of its nozzle. you'll need this information to determine if the spacing is appropriate by comparing it to manufacturer specifications.

The first step to achieving matched precipitation rates in a zone is to make sure all heads are the correct model and have the right nozzle. It's tough to match precipitation rates for sprinklers made by different manufacturers. Increasing runtimes to compensate for mismatched sprinklers is the biggest threat to irrigation efficiency.

Check the tilt of each head with a small level or T-square for sloped areas. Each head should pop-up to be perpendicular to the ground. Inspect each nozzle for wear and clogs. You might also discover deficiencies such as cracked or broken risers, a mixed bag of risers or swing joints, heads that don't extend fully, and plugged strainers. Water flow is affected by many different things, including resistance, pressure, pipe size, and elevation. These conditions should be the same for each head in a particular zone.

Check that sprinkler heads are properly set to grade. Plant material can block the stream of water and debris can collect on heads that retract below the surface. Heads that sit too high are subject to traffic and equipment damage.

Be on the alert for symptoms of pressure problems. Sprinkler head locations are based on the application pattern of the heads at a certain pressure range. Higher than specified pressures will cause misting and drift. Lower pressures reduce the area of the application pattern. Manufacturers publish specs for a very good reason, proper performance.

High pressure problems can be remedied by adjusting the valve or by installing a pressure or flow regulator. Low pressure problems might be the result of too many heads on a single zone. Remember, everything water flows through causes a certain amount of friction loss. That includes valves, risers, fittings, swing joints, strainers, pipe, and sprinkler heads.

 

Calculating Schedules

After identifying and correcting uniformity problems, retest the zones to check increased performance. The next goal is to adjust the runtimes to meet the needs of the plant material without wasting water.

To determine the precipitation rate (PR) of a zone in inches per hour, add up the water collected in all cylinders in the zone and divide by the number of catch cans. This gives the average amount of water per catch can in inches. Multiply this number by 60, then divide the result by the test time in minutes.

Knowing the precipitation rate of each zone on the system is invaluable when scheduling irrigation sets. Almost anybody can keep turf and plant material green, but the skilled water manager does so with minimal resource consumption. The larger the site, the greater potential for savings.

Combining precipitation rates with other site specific data (weather conditions, soil type, plant requirements, your watering window) will maximize your irrigation efforts. Good scheduling also should consider the frequency and duration of each irrigation event, and the number of irrigation cycles per event.

Weather conditions not only affect distribution uniformity, but also the rate that available water is removed from the soil and the plant material through evaporation and transpiration (ET). Obvious meteorological factors of rain and wind will change irrigation water requirements instantly. Direct solar radiation and humidity also influence plant water needs.

Real-time ET (sun, wind speed and velocity, precipitation and humidity) can be measured by an on-site weather station or might be available from a nearby golf course using a weather station. Reference or historical ET (ETo) should be readily available from state and regional weather networks on your local university extension office.

Landscape coefficients (KL ) are used with ETo in calculating irrigation water requirements. While coefficients are available for most turf species, you might have to hunt for them for ornamental trees and other landscape plants. Your county extension agent can offer direction in obtaining landscape coefficients, or suggest a substitute plant for which an KL is available.

Different soils hold different amounts of water. Heavier or tighter clay soils hold more water and hold it longer than loose, sandy soils. However, it takes clay soils longer to absorb this water than lighter soils. Plant health is greatly influenced by the moisture content of the soil. Irrigation and drainage characteristics of soils are important factors in integrated plant health care.

Take sample pressure readings from sprinkler nozzles near the beginning, middle and end of the zone.

Take a core sample and squeeze it in your hand. Tight soils will form a solid ball. Sandy soils will fall apart when formed into a ball. Tight soils will require short, repeated irrigation cycles to get water to the proper soil depth without creating runoff. Once the profile of a tight soil is wet, however, it holds this moisture longer. Sandy soils wet quickly but require more frequent irrigation events.

As a guideline, allow about a 50 percent depletion of the soil moisture profile before initiating another irrigation event, based on soil texture and root depth of the plant material. The idea is to irrigate when half the water stored in the rootzone is gone and to replace just that amount. Water percolating below the rootzone or running off does the plant no good. Wetting only part of the rootzone is also wasteful.

Each type of plant has its own unique water requirement. Factors such as age, location in the landscape, soil type, rootzone depth, season of the year, and maintenance practices can alter this requirement. Plant-soil-water relationships must be understood and factored into any successful irrigation management program.

By having an idea about plant water use and the level of moisture in the root zone, you estimate the amount of water it will take to replace that used between irrigation events. Based on this estimate, you calculate the length of time it will take to apply this amount of water at the precipitation rate of the particular zone. Then, you or the client must adjust this amount according to the season and weather conditions.

As urban irrigation equipment and techniques continue to advance, so must your knowledge and practices. Progressive irrigation management goes beyond the appearance of the landscape -- it must include water conservation, integrated plant health and managing maintenance costs. Technical skill must be combined with business considerations in order for you to best serve your clients today and in the future.

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