When the summer irrigation season is here, it means valuable water resources are applied to to the landscape. It is the responsibility of all Texans to ensure that water is used wisely. Irrigation audits are the most effective tool for maximizing water use efficiency in the landscape.
Irrigation audits consist of three main activities:
- Site inspection
- Performance testing
- Irrigation scheduling
Each activity in itself can result in significant water and cost savings. Audits 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 is 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. Commonly, 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.”
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, “how long and when to run the irrigation system,” is mostly 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, 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. Due to 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.
Water 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.