Auditing Your Irrigation System

As the summer heat and drought continue, we are doing what we can to keep our landscapes around our homes and businesses alive.

Temperatures in the high 90s and above take a toll on all plants (except may be cacti), and the tendency is to water to compensate for the heat. In the absence of significant rainfall, we do need to apply water to high-value plants in our landscapes to prevent wilting, stress and possibly death.

However, we also need to make sure we apply that water wisely and efficiently. Applying too little may not meet the needs of the plants. Applying too much is not only wasteful, but may also cause problems with saturated root zones. You may be running your sprinklers just right to apply the proper amounts of water to your lawns and plants. But, do you know how much you are applying? How long should you run the system? Are you getting uniform coverage from your sprinklers so all plants are getting the same amount of water? Do you know how long your irrigation system must run to apply 1 inch of water? The only way to answer these questions is perform an audit of your irrigation system, whether it is a professionally installed system, or a hose-end sprinkler that you drag to various parts of your yard.

An audit will not only help you correct deficiencies in your irrigation system, but also help conserve this most valuable natural resource.

Irrigation audits consist of three main activities: 1) site inspection, 2) performance testing, and 3) irrigation scheduling.

Each activity in itself can result in significant water and cost savings. Together, these activities provide valuable information based on site specific conditions and irrigation system performance.

Site Inspection:

Over time, even the most efficiently designed irrigation system will begin to break down. In the absence of a regular maintenance program, minor operation and performance problems can continue for months resulting in excessive water use, reduced efficiency and decreased plant performance.

Sunken sprinkler heads that do not “pop-up” properly, misaligned spray patterns that throw water onto streets, sidewalks or hardscapes, and broken or missing sprinkler heads resulting from mower damage can result in significant water waste.

Performance problems are often inherent in an irrigation system. A sprinkler system where the heads are spaced too far apart will result in poor water distribution and/or dry spots in the landscape. In order to compensate for this poor uniformity, the system is often set to operate longer, which in turn over-waters most of the landscape.

Insufficient or excessive operating pressure can also lead to water loss through wind drift or poor coverage. Low water pressure is generally caused by insufficient static pressure and/or high pressure losses through valves, meters, piping, too many heads or other components of the irrigation system. Visual indications of low water pressure include large water droplets and short sprinkler throw. High water pressure, on the other hand, indicates an absence of a proper pressure regulation device. High pressure is generally characterized by excessive misting of water that easily evaporates or blown by the wind.

Performance Testing:

Sprinkler application devices, including pop-up spray heads, rotors, micro-sprays and bubblers are designed to operate within specific operating pressures and head spacing. Manufacturer’s specification catalogs rate the performance (mainly flow rate) in gallons per minute and precipitation rate in inches per hour.

Often, the rated performance listed in the catalogs do not accurately represent actual performance.

For example, insufficient or excessive operating pressure and improper head spacing will significantly increase or decrease precipitation rate.

For irrigation scheduling purposes, the most accurate determination of precipitation rate is achieved by conducting a “catch can” test.

Catch can tests measure the amount of water that actually hits the ground at various points within the landscape, and also serves to measure application uniformity.

Since irrigation systems commonly use different types and brands of sprinklers, it is important to conduct catch can tests for each individual zone or “station” on an irrigation system.

Following is the general approach to conducting a catch can test:

  1. Turn on the irrigation system, one zone at a time, to locate and mark sprinkler heads.
  2. Starting with zone 1, layout catch devices only on the part of the landscape covered by zone 1. Catch devices should be placed in a grid-like pattern throughout the zone to achieve an accurate representation of sprinkler performance. Small (5″x8″) plastic containers (typically used for “leftovers”) make excellent catch cans. Try not to place catch devices too close to sprinkler heads to avoid altering spray patterns.
  3. Turn on zone 1, allowing water to fill the catch devices. Keep track of the number of minutes that the zone is allowed to operate.
  4. After a measurable amount of water has fallen, measure the depth of water (in inches) contained in each device using a ruler. (It is recommended that the ruler measure in “tenths” of inches). Record these values on a data sheet. Also record how long (in minutes) the zone was operated.
  5. Repeat steps 1-5 above for each remaining zone on the system.

Using the data from catch can testing, the precipitation rates for each individual zone on the irrigation system can be determined. The simple equation for calculating precipitation rate is given below:

  • Precipitation rate (average catch can depth / test run time) x 60
  • Where: Precipitation rate inches per hour
  • Average catch can depth inches

Irrigation Scheduling:

When water supplies are limited, it becomes even more important that every drop of water is utilized to the fullest. The answer to the question, “when and how long to run the irrigation system,” has been based on assumptions and generalizations about sprinkler system performance and plant water requirements.

An audit can replace many of these assumptions made in irrigation scheduling. With an irrigation audit, it is possible to customize irrigation schedules based upon on catch can results, site-specific soil conditions and plant water requirements. Rather than using the long time recommendation of “fifteen minutes, three times per week”, it is now possible to adjust run times for individual zones based on a measured precipitation rate.

Determining when to irrigate should be based upon the depth of the plant’s root zone and soil-type. Together, root depth and soil type define the amount of water that is available for plant use.

A six-inch clay soil, for example, will hold more water than a six-inch sand. Thus, the number of irrigations per week will be less in clay, though the amount of water the plant needs will remain the same. Root depth also influences irrigation frequency. Shallow rooted turfgrass, for example, will require more frequent irrigations than will a turfgrass with a deeper root zone.

The first step in determining how long to irrigate is to calculate how much water should be applied at each irrigation event. Plant water requirements vary significantly in urban landscapes due to the variety of plant species, maintenance practices and microclimates.

Water requirements also vary with climate trends and rainfall patterns. Turfgrass, which is generally assumed to be the highest water user in the landscape, requires up to 1-inch per week during the summer with less in the spring and fall.

Because of limited water storage capacity in the plant’s root zone, two or three irrigations per week may be required. Once it is determined how much water (in inches) is needed at each irrigation, the conversion to zone run time is simple. The following equation is used to determine zone run times:

  • Run Time Per Irrigation (Targeted irrigation depth / Zone precipitation rate) x 60
  • Where: Run Time Per Irrigation minutes
  • Targeted irrigation depth inches
  • Zone precipitation rate inches per hourWater conservation involves numerous Earth Kind principals and practices.

However, an irrigation system audit is the most effective tool available for reducing water consumption and creating a sustainable landscape environment.