Auditing drip irrigation systems can be challenging, especially on systems due to tubing and emitters buried under mulch, weed barrier, plant roots, plants, and turf. The best time to conduct and audit is during original installation. It's easier and the information can be used in maintenance and scheduling of the drip irrigation system.

A catchment device and pressure gauge are the primary tools necessary to conduct a simple – but accurate -- drip system audit. Photo courtesy: Joseph Fortier.

The auditor should check if there is an appropriate amount of emitters installed around the plant to meet the plant water needs and to develop a sound root system. When installing a new sub-surface drip irrigation system or evaluating an existing system, should check the volume of output, as well as the spacing of the emission points and between the tubing. When evaluating new and existing drip irrigation systems, verify that the system was installed per plans.

The following are the recommended steps to conduct a proper drip irrigation audit. First, locate the irrigation control valve, filter, and pressure regulator (make sure to record the manufacture and model). Check the filter for debris and note flow and pressure information of pressure regulator if marked.

Second, determine the area the control valve covers and the plant types. Keep in mind that control valves can water shrubs, ground covers, trees, or a mixture of the three.

Third, document the type of plant material, plant condition, size, age and micro-climates. Photo documentation and good notes help develop efficient watering schedules—as plants mature, the water requirement increases.

Fourth, locate all valves, filters, pressure regulators, drip emitters, tubing, piping, type of emitters, sub-surface tubing, flush plugs, and any other equipment. Next, if you have a map, document where all the irrigation equipment is located.

Then conduct pressure tests at the beginning, middle, and end of end of the longest tubing run and document all the gathered data. Next, measure the emitter performance using catch devices. And finally, calculate the emission uniformity.

In the course of conducting the review, some common problems need to be noted during the evaluation process. Look for misplaced and clogged emitters, emitters installed incorrectly (near trunks of plants, too far from a plant to establish a sound root system, or not enough emitters to promote healthy plant growth). Additionally, tubing issues such as damaged or kinked tubing, broken fittings, and buried flush plugs need to be documented.

Irrigation systems with drip emitters operate at low pressures between 5 psi to 60 psi and have a flow range of 0.5 gph to 30 gph. The most common emitters have a flow rate of 0.5, 1.0, or 2.0 gph. Higher flow rate emitters will require larger catchment devices. Inline emitter tubing has flow rates ranging from 0.25 gph to 1.0 gph. Emitter spacings for inline emitter tubing are usually 12-, 18-, or 24-inches on center. Emitter and row spacings are used when calculating precipitation rates.

When reviewing the drip irrigation system, the control valves and pressure regulators need to be inspected for proper equipment that works well together. Control valves have a minimum flow requirement for proper closure of the valve. The manufacturer, size, and model of the control valve should be noted. A review of the manufacturer’s specifications is necessary in order to ensure the valve is correct for the flow of the zone.

Fixed pressure regulators will have minimum and maximum flow ratings and preset pressure outputs. Like the control valves, one should inspect them to ensure they will operate within the requirements of the zone.

CONDUCTING THE AUDIT

Pressure readings can provide some of the most important information on the performance of a drip irrigation system. Sam Tobey, formerly of Salco Products, taught me over 30 years ago that pressure readings can indicate major problems with a drip system better than anything else.

The first step is to turn on a designated control valve and allow the zone to fully pressurize (this can take several minutes, depending on the size of the zone). Next, perform pressure readings at the beginning of the zone near the valve, in the middle of the run, and the end of the longest run. If there are multiple runs, check the pressure at the end of each run.

For pressure compensating emitters, there should be no more than a 20 percent pressure difference from the beginning to the end of the zone. For non-pressure compensating emitters, there should be no more than a 10 to 15 percent pressure difference from the beginning to the end of the zone.

In large drip irrigation zones with multiple pressure regulators, pressure readings need to be conducted on the piping immediately following each individual pressure regulator. Extreme pressure loss in a zone can be the result of too many emitters on the lateral line, incorrect pipe sizing, blockage in a lateral line, too long of lateral line for the size of piping, among other complications.

Measuring emission uniformity in drip systems can be difficult to conduct, especially in existing systems with mature plants. The challenges are finding and exposing the emission device outlets. The tubing and emitters are frequently buried, or can be hidden by weed barriers, mulches, plants, root systems, and turf. The optimum emission uniformity for pressure compensating devices should be 0.90, and should be 0.80 for non-pressure compensation devices.

There are different methods to conduct a field test. However, I find one method the least challenging. The test should be conducted on a minimum of 20 different emitters within a zone with the same flow rate. The emitters will need to have enough tubing exposed to pick up the tubing to place over a catchment device. If necessary, add micro-tubing in order to conduct test properly.

The following procedure uses a single catchment device. First, locate a minimum of 20 emitters of the same flow rate with the zone. Second, activate the drip system so that it is running fully and the air has been expelled. Third, place the catch device under the first emitter outlet, time the water flow for 30 seconds, then measure and record the volume in the catch device. Fourth, repeat the third step for the balance of emitters in the zone. From the data recorded, an emission uniformity can be calculated and utilized to develop irrigation schedules. \