Conservation in the landscape depends on intelligent use of water resources. Since many landscape professionals rely on irrigation systems to supplement water that plants receive from rainfall, keeping these systems functioning properly is key to conserving water. One tool to help determine if irrigation systems are working adequately is an irrigation audit.
An irrigation audit is a procedure used to collect and provide information about the uniformity of application, rate of precipitation, and overall condition of an irrigation system (Irrigation Association). It is most often performed on sprinkler-type systems, although methods exist for testing performance of drip irrigation set-ups. Formal audits are conducted by an independent certified landscape irrigation auditor, but landscape managers and clients can readily use audit methodology to perform ongoing system checks. Currently, no consistent procedure exists for irrigation audits; the Irrigation Association (a non-profit organization that supports the irrigation industry and promotes resourceful water management, has drafted guidelines anticipated to standardize the audit process.
A typical irrigation audit will include many of the following procedures:
- Visual inspection of irrigation system
An irrigation auditor observes each zone in a sprinkler system and the landscape surrounding sprinkler heads to identify sources of inefficient water use: broken, damaged, or leaking heads; improperly positioned sprinklers watering streets and sidewalks; sprinkler heads too low or off vertical; sprinkler heads improperly spaced or arranged in pentagon patterns instead of water-conserving triangle or square patterns (Whiting et al, 2003); misting around sprinkler heads (excessive water pressure) or large water droplets falling close to heads (low water pressure); and poor system design features (no automatic or manual shut-off during rainy weather, non-uniform sprinkler heads used).
- Evaluation of distribution uniformity (DU)
While many of the problems described above affect DU, a catch can test is routinely used to quantify whether or not irrigation water is being uniformly applied to the landscape. To perform a catch can test, an auditor places collection containers in a grid pattern on the surface of an irrigated zone, runs the irrigation system through a typical timed cycle, and collects and records the amount of water in each catch container. The data gathered is then used to identify areas of over- and under-irrigation (relative to the targeted application amount); results of a catch can test may also be correlated to observations of plant health in the test area.
- Determination of precipitation rate
Data from a catch can test is also used to determine the rate at which water is applied by the irrigation system. Since individual site conditions, specifically water pressure and sprinkler head spacing, may alter a system's performance, using catch can test results is more accurate than relying on the system manufacturer's performance specifications (TAES, accessed May 2006). Knowing the rate of application is important for developing appropriate irrigation schedules.
- Determination of landscape's watering needs
An evaluation of the landscape features present at a site provides a great deal of information about that site's water requirements. Factors to consider in developing a watering schedule include the types of plants present and the depth of their roots; whether they are growing in sun or shade, on flat areas or slopes; the presence or absence of a thatch layer in turf; whether or not non-turf plantings are mulched; soil texture and structure; and evidence of compaction and drainage problems.
- Review and development of irrigation schedule
An irrigation auditor will review a site's current irrigation schedule (amount of water applied and the interval between watering events), and make recommendations based on catch can test results, soil conditions, and plant water requirements, taking into account local climate and rainfall patterns (TAES, accessed May 2006). Because an irrigation audit is only a tool, audit recommendations must be put into practice for water conservation to be realized.
Landscape professionals who want to become more familiar with irrigation audits, or would like to expose clients to the audit concept, have many resources at hand. Colorado State University offers an excellent series of irrigation publications. The Handbook of Water Use and Conservation by Amy Vickers, a Massachusetts-based engineer, and Dr. William Knoop's The Landscape Management Handbook each dedicate an entire chapter to landscape irrigation and outline what is involved in an audit; the Vickers book can be found in the reference section of many libraries, including the Integrated Sciences and Engineering Library at the University of Massachusetts. Although it is aimed at western U.S practitioners, the handbook for Landscape Irrigation Simplified (LIS) is also worth reading. LIS is a step-by-step irrigation review process, similar to an audit, created by the Bureau of Reclamation; the Bureau claims LIS is appropriate for homeowners and landscape managers with smaller, less complex irrigation systems. For those looking to work with a certified landscape irrigation auditor, the Irrigation Association maintains a list of certified auditors by state.
- Irrigation Association Glossary of Irrigation Terms. Version 5/14/04. Accessed May 2006.
- Texas Agricultural Extension Service (TAES). Landscape Irrigation Audit Procedures. Accessed May 2006.
- Whiting, D., R. Tolan, B. Mecham, and M. Bauer. 2003. Irrigation Management: Irrigation Audit. No. 7.759. Colorado Master Gardener Gardening Series. Colorado State University Cooperative Extension. Accessed May 2006.
Written by: Jennifer Kujawski