Update and Optimize Your Landscape's Irrigation System

Sprinklers watering trees and shrubberyThe function of an irrigation system is to provide the desired amount of water for each individual plant on a consistent basis. A system that is malfunctioning or mismanaged can lead to health and safety issues, property damage, plant death and excessive water costs. In this article we will cover two main topics: the system itself and operating the system. The system includes irrigation system maintenance, repairs and design improvements, while operation covers information on efficient operation of the system using current weather data to program time controllers based on reference evapotranspiration rates.

Prior to spring time start up, the irrigation system should be “tuned-up” to assure all components are in good operating condition. The system should also be assessed for design flaws and outdated hardware that are reducing the efficiency of water delivery. Here are three areas of irrigation systems that you should look at:

Tune-Up the System

The following is a tune-up check list:

Water Supply

Check the water supply. It should have been shut off for the winter. Turn it on. If the system is fed by a well, check the pump operation, pressure settings and filtration systems. If the system is fed by a municipal water supply, inspect the meter, backflow device and pressure regulators, if any.  There should not be any leaks. Backflow devices should have a current certification. And an operating pressure range of 40 – 50 psi is ideal for most sprinkler heads. If pressure is too low or too high, proper sprinkler head coverage will be impaired.

Main Lines

Check the main lines. The main pressure lines are the water pipes that connect the water supply to the various control valves located throughout the system. Look for leaks. Major leaks will be obvious with water flowing over the surface. Minor leaks may be detected by observing the water meter when the system is not operating. Look inside valve boxes, standing water is an indication of leaking fittings. If you cannot find a suspected leak, professional leak detection services are available.

Time Controllers and Control Valves

Check the time controllers. Batteries should be replaced annually. Operate the controller in the manual mode to assure each remote control valve activates and also shuts off. Note: There is often a delay before a valve shuts off. If a valve does not shut off within 30 seconds it should be adjusted or repaired.

Lateral Lines

Check the lateral lines and sprinkler heads on each station. The lateral lines are the water pipes that connect the control valves to the sprinkler heads. Each station is called a watering zone. Look for any breaks, leaks, clogs or constrictions in the pipes, swing joints, sprinkler heads and nozzles.

Sprinkler Heads

Take a closer look at the sprinkler heads to make sure they are set perpendicular to grade and at the correct height. Check the spray patterns for the correct radius and arc. Water spraying in the street is wasted; water spraying on the building can cause property damage. Check for obstructions; often plant material grows up to block coverage. While performing the tune-up, assess the system for design deficiencies and/or outdated hardware.

Check for Design Flaws

Hydro Zones

A good irrigation system design will have the landscape broken up into watering zones based on plants with similar watering requirements. Plants are usually broken up into hydro-zones according to species and climatic exposure. Other factors to consider are grades and sprinkler hardware.

Here are some examples of each zone grouping:

  • Species–If thirsty turf plantings are being watered along with arid ground covers, separate them into individual zones.
  • Climatic Exposure–If hot southern exposures are tied together with shaded northern exposures, separate them into individual zones.
  • Grade–If steep slopes prone to run-off are connected with flat basins that collect water, separate them into individual zones.
  • Sprinkler Hardware–If high flow spray heads are running with low flow drip systems, separate them into individual zones.

Hydraulics

Is the water supply and plumbing sufficient to supply the water demand of each of the watering zones? For example, a 1-inch remote control valve out-letting into 1-inch diameter lateral line piping will supply 15 – 18 gallons of water per minute. One full circle pop-up spray head can consume up to 4 gallons per minute, 2 gallons a minute for a half circle, and 1 gallon for a quarter. At these rates, the 1-inch diameter pipe can supply 2 full circle sprinkler heads, 2 half circle and 4 quarters. Any more and the demand exceeds the supply, causing the system to operate below the optimum pressure and affecting spray patterns to reduce the distribution uniformity (DU).

The most common solution to an inadequate water supply is to reduce the zone’s demand. This can be accomplished by either changing the sprinkler heads or nozzles to lower flow products, or by breaking an oversize zone into two smaller zones by adding another valve.

Sprinkler Head Placement

Sprinkler heads and nozzles are designed to operate with “head to head” coverage, resulting in 100% overlap. When sprinkler heads are spaced further apart, the spray pattern no longer applies water evenly and the DU is adversely affected.

In some cases, over spacing may be corrected by upgrading the existing head or nozzle to increase the radius of the spray pattern. If this is not possible then existing sprinklers will have to be repositioned and additional heads added, being careful that you don’t increase the zone’s water demand to exceed the capacity of the water supply.

Matched Precipitation Rates

In order to achieve a uniform distribution of water, all sprinkler heads operated by any given valve must have matched precipitation rates. If sprinkler heads have different precipitation rates, the DU is reduced. Re-nozzling the sprinkler heads may correct the problem. In other cases, you may need to install upgraded sprinkler heads.

Update Your Hardware

Time Controller

The time controllers are the key to efficient programming. Make sure that the time controllers at the minimum have the following two features:

  1. Multiple Programs–Stations with similar watering requirements should be grouped together and programmed separately from other stations with different watering requirements. For example, turf stations may need watered 4 days per week where as a groundcover station may only require water 2 days a week. With multiple programs the turf and the groundcovers can be separated into groups and programmed individually.
  2. Multiple Cycle Starts–Most sprinkler heads will apply water faster than most soils can absorb water. If the entire water requirement is applied in one cycle, the result is excessive water runoff. By utilizing multiple cycle starts of shorter duration, water is allowed to soak in between applications.

For the high-tech consumer, there are several new time controller products that have the ability to link up with weather data sources and automatically adjust their programming to meet changes in weather conditions. The ability to have a controller reprogrammed on a daily basis to meet changing weather conditions has the potential to produce significant water savings.

Rain Sensor

Most time controllers can be retrofitted with rain sensor devices that will shut down watering during periods of rain fall. Not as complex as the self-programming controllers described above, rain sensors can produce a water savings during the transitional months in the spring and fall.

Remote Testing

Most time controllers can be retrofitted with a wiring harness that will allow for a service technician to plug in a receiver for a remote transmitter that will activate watering stations while traversing the property. The cost of this upgrade is nominal, easily outweighed by the labor savings realized during testing and repairs.

Sprinkler Heads

Sprinkler heads and nozzles are one of the key components responsible for water delivery. The irrigation industry is under pressure to develop products that deliver water with increased efficiency. New features like pressure compensating nozzles and built in check valves are water saving devices. Replacing older and worn sprinkler heads is another opportunity to increase system efficiency.

Operating the System 

A state of the art efficient irrigation system is only the first step to irrigation efficiency. The next step is efficient operation. This requires constant monitoring of soil moisture, plant health and system hardware. The time controller programs need to be adjusted frequently, following changes in weather conditions.

Before getting started, there are some important terms you should know about.

Important Terms for Irrigation

Evapotranspiration: The combined process from which water is transferred from the soil surface and from the plant surface to the atmosphere.

Reference Evapotranspiration (ETo): The rate of evapotranspiration from tall, cool-season green-grass of uniform height (4-6 inches), completely shading the ground, and not short of water. We use ETo because the water requirements are very similar to that of ornamental turf grass.

To obtain a current ETo, we turn to the California Irrigation Management Information System (CIMIS). CIMIS is a program operated by the California Department of Water Resources that manages over 120 automated weather stations throughout the state. A CIMIS weather station factors soil & air temperatures, solar radiation, humidity, precipitation and winds to calculate an ETo rate. ETo is provided on a daily or weekly basis and is expressed in inches. In a hot week in July ETo in the North Bay area can exceed 2 inches. Check out the CIMIS website to obtain current ETo rates and additional CIMIS information.

Precipitation Rate (PR): The rate at which water is applied expressed in inches per hour. In general terms, most spray systems range from 1 ½ to 2 inches per hour. Rotor and impact head systems range from ½ to ¾ inches per hour.

Distribution Uniformity (DU): The ratio of the average low-quarter depth of irrigation to average depth of irrigation to the whole field, expressed as a percent. Distribution uniformity is a measurement of how evenly water is applied throughout the watering zone. A poor rate would be 50%, a good rate would be 75%.

Precipitation rates and distribution uniformity rates can be developed by having an irrigation system audit performed. During an audit, a series of catch cans are placed throughout a watering zone, the system is run for a specified time period after which the water levels in the catch cans are recorded and precipitation and distribution uniformity rates are calculated.

Now we can discuss the time controller program that utilizes the information above.

Time Controller Programming

The following method is called evapotranspiration (ET) based time controller programming. The goals for this type of irrigation programming are:

  • Apply only the amount of water necessary this week to replace the water that was consumed last week.
  • Apply only the amount of water that will remain in the root zone of the target planting. Excess water will percolate beyond the root zone and not be available for use.
  • Allow for consumption of 50% of the available water in the root zone before applying additional water. Forcing the plant to reach for water will encourage deeper rooting.
  • Apply the water in increments (cycles) that allows the water to soak in between cycles to minimize runoff.

To determine the amount of water necessary to replace last week’s usage, track the reference evapotranspiration rates. In order to use the Eto data to create an time controller program we also need the precipitation rate and the distribution uniformity rate for each watering zone in the irrigation system.

Calculate Actual Water Needed

By using last week’s reference evapotranspiration rate and the irrigation system’s distribution uniformity and precipitation rates we can calculate the water we need to apply this week. We need the following variables:

  • Reference Evapotranspiration Rate (ETo)
  • Distribution Uniformity Rate (DU)
  • Precipitation Rate (PR)

To calculate the weekly water requirement, divide the reference evapotranspiration rate by the distribution uniformity rate:

ETo ÷ DU = Weekly Water Requirement

Next, we use the weekly water requirement (WR) and divide it by the precipitation rate to calculate the station run time:

WR ÷ PR = Station Run Time

For example if: ETo = 1.4 inches per week     DU = 70%     PR = 1.5 inches per hour

  1. Plug in the data to the first formula: 1.4 inches per week ÷ 70% = 2.0 inches per week
  2. Now plug in the data to the second formula: 2.0 inches per week ÷ 1.5 inches per hour = 1.33 hours per week
  3. We have calculated a total station run time of 1.33 hours, or 80 minutes per week.

To meet our remaining programming goals—only apply water to the root zone, encourage deeper rooting and minimize runoff, the total weekly requirement of 80 minutes run time needs to be broken up into several applications spaced a couple days apart applied in multiple cycles of short duration. Variables in soil type, rooting depth, soil compaction and slope are among some of the variables that will affect both the rate at which water can infiltrate into the soil and the water holding capacity of the root zone. Once you put a program in place, observe the results and make adjustments.

Note: While the use of reference Eto is good for developing turf programs, other crops containing ornamental shrubs and groundcovers can survive on substantially less water. Depending on the drought hardiness of the target planting, a crop coefficient between 60% - 80% may be applied to further reduce water applied.

Conclusion

Now that you’ve reviewed, assessed, and updated your current irrigation system, and you’ve optimized your operating practices, your landscape should be looking better than ever. And you’ll be saving money by reducing run-off or overwatering, making it a great investment in more ways than one.  


Adapted from an article by Darryl Orr of Pacific Landscaping. Image courtesy of Toa55 at FreeDigitalPhotos.net.

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