Irrigation Efficiency Study in Belmar


According to the United States Environmental Protection Agency, nationwide, landscape irrigation is estimated to account for almost one-third of all residential water use.  Experts estimate that fifty (50%) of that water is wasted.  In August 2009, New Jersey Water Savers, in partnership with the Middletown Sprinkler Company, conducted an irrigation audit of the Magical Garden Greenhouse and Community Garden in Belmar.  The irrigation audit consisted of three main components: site inspection, performance testing, and irrigation scheduling. 

This study presented an opportunity to educate homeowners about the importance of operating an efficient irrigation system and when water supplies are limited how to maximizing water use efficiency on home lawns and gardens, commercial properties, and sports fields. Even the most efficiently designed irrigation systems are susceptible to excess water waste and performance problems.  To compensate for poor uniformity, people tend to set a system to operate longer, which in turn overwaters the landscape.  The key to efficiency is uniformity, which starts with the proper selection of the sprinkler head.  In addition, to saving money, a reduction in the stormwater generated at residences ultimately reduces nonpoint source pollution travelling to surface water bodies.

Irrigation Audit Procedure

  • Turn on the irrigation system to locate and mark the sprinkler heads.  The sprinkler heads could be marked using a catch device.  To save money, consider using a coffee can for a catch device.

  • The catch devices should be placed in a pattern throughout the garden to get an accurate representation of the irrigation system performance.  Try not to place devices too close to sprinkler heads to avoid altering spray patterns.

  • Turn the irrigation system on and allow the water to fill the catch devices, and the time recorded.  Record the data by zones.  Zones should be selected based upon the plant’s irrigation water requirement and sized according to available water supply.  

    Zone irrigation systems should consider the following:

    • Plants from deep rooted zones & low water use plants should be separate from high water use areas; separate and distinct watering requirements are needed for turf, drought tolerant vs. non drought tolerant landscape plants and herbaceous garden plants (vegetables and flowers)

    • Exposure to sun and wind

    • Different soil types

    • Different depths of rooting and thus different depths of wetting for trees (18-36 in.), shrubs (12-24 in.), herbaceous plants and turf (6 -12 in.)

  • After a measurable amount of water has fallen, measure the depth of water (in inches) contained in each device using a ruler.  Record these values on a data sheet.  Also, record how long in minutes the zone was operated.

  • Using the data from testing, you may be able to determine the precipitation rates for each individual zone on the irrigation system.  The simple equation for calculating precipitation rate is given as follows : Precipitation rate (in./hr.) = (average can depth (inches)/ test run time (minutes)) x 60; Where precipitation rate is in inches per hour and average catch can depth is in inches.

  • Make notes on any broken heads resulting from vandalism or mower damage; misaligned heads that may throw water onto hardscapes such as streets or sidewalks; sunken heads (do not “pop-up properly”); insufficient or excessive operating pressure (high or low pressure); and mixed head types.

Measures of Irrigation Performance

There are two measures of irrigation performance, distribution uniformity (DU) and irrigation efficiency (IE).

  • Distribution Uniformity - Distribution uniformity is a measure of how evenly water soaks into the ground across a field during the irrigation. If eight inches of water soaks into the ground in one part of the field and only four inches into another part of the field, that is poor distribution uniformity. Distribution uniformity is expressed as a percentage between 0 and 100%.

  • Irrigation Efficiency - Irrigation efficiency is defined by the American Society of Civil Engineer's On-Farm Irrigation Committee as the ratio of the volume of water which is beneficially used to the volume of irrigation water applied.

Magical Garden Case Study

The audit revealed that the existing irrigation system was inefficient with a DU of 38.31%.  By replacing the sprinkler heads with new MP Rotator nozzles, the Magical Garden now properly irrigates the garden on forty-two percent (42%) of the water that was required with the old nozzles.  The Magical Garden Greenhouse and Community Garden in Belmar is used by dozens of school children and community residents.  Teachers use the Magical Garden as a living laboratory where science and other subjects come to life through horticulture projects.  The Magical Garden is featured in an 11-mile walk-bike-drive tour that has seventeen (17) “points of interest.” A link to the tour is listed below in the Resources Section.  



The Partners