Irrigation is often managed by simply guessing how long to run the sprinklers, which frequently leads to wasted water and unhealthy turf. Accurately measuring the output of an irrigation system is fundamental for water conservation and promoting deep, resilient root growth. Overwatering causes shallow roots and increased disease susceptibility, while underwatering leads to drought stress. The goal is to determine precisely how much water, expressed in inches of depth, your system delivers over a specific period, allowing for informed adjustments.
The Catch Can Method for Measuring Depth
The most direct way to measure water delivery is by performing a catch can test. Gather between five and nine straight-sided containers, such as tuna cans or specialized rain gauges, which provide a consistent measurement plane. Place these containers randomly across a single irrigation zone, positioning them both near the sprinkler heads and in the areas between them to capture a representative sample of the coverage.
Run the irrigation zone for a fixed, short duration, typically 15 minutes, to collect the water. This duration provides a measurable depth without wasting excessive water. Once the cycle is complete, measure the depth of the water collected in each can accurately, using a ruler to the nearest eighth of an inch. Large variations in collected depths indicate a problem with the system’s distribution.
Calculate the average depth of water collected across the entire zone. Sum the depths from all containers and divide that total by the number of containers used. This average depth is the foundational number needed for all subsequent calculations, representing the amount of water the zone received in that 15-minute interval.
Calculating Your Lawn’s Water Application Rate
The raw data collected must be converted into the water application rate, which is expressed in inches per hour. This rate allows for easy comparison with the lawn’s actual weekly water needs. The calculation extrapolates the average depth measured over a full sixty minutes: (Average depth collected / Test duration in minutes) multiplied by 60 equals the Application Rate in inches per hour.
If the test duration was 15 minutes, the calculation simplifies: the average depth collected is multiplied by four to determine the hourly rate. For example, if the average depth was 0.25 inches, multiplying by four results in an application rate of 1.0 inch per hour. This means the system must run for one hour to deliver a full inch of water.
For alternative irrigation methods, such as drip or soaker hose systems, the application rate focuses on flow rate rather than distribution depth. This involves measuring the system’s flow in gallons per minute (GPM) and dividing that by the total square footage of the area being watered. However, for a typical sprinkler system, the catch can data provides the most practical inches-per-hour rate for scheduling purposes.
Checking for Uniform Water Distribution
The catch can test also checks the uniformity of water delivery across the zone. Uniformity measures how evenly the water is distributed and is assessed by comparing the minimum and maximum water depths recorded in the containers. If one can registers 0.5 inches while another collects only 0.1 inches, the system has a significant non-uniformity issue that must be addressed.
Poor distribution uniformity results in dry patches and over-watered areas, even if the average application rate is correct. Common causes include low water pressure, which prevents proper spray pattern overlap. Wind drift, partially clogged or worn nozzles, and tilted or sunken heads can also skew the results.
Improving uniformity starts with a visual inspection of the system while it is running. Simple solutions include cleaning debris from the nozzles or adjusting the spray angle of the heads to ensure head-to-head coverage. Correcting these issues is necessary before creating an efficient watering schedule, as poor uniformity requires over-watering some areas to keep the driest spots healthy.
Translating Measurements into a Watering Schedule
Once the application rate and uniformity are satisfactory, translate these measurements into a practical watering schedule. Most established lawns require 1 to 1.5 inches of water per week during the peak growing season. This total weekly amount should be delivered in two or three deep watering sessions, rather than many short daily bursts, to encourage deep root growth.
The calculated application rate determines the necessary run time for each watering session. If the goal is to apply 0.5 inches of water, and the system’s application rate is 1.0 inch per hour, the required run time is 30 minutes. This is calculated by dividing the desired depth by the application rate and multiplying by 60 minutes.
For lawns with heavy clay soil or sloped areas, the application rate may exceed the soil’s infiltration rate, leading to wasteful runoff. In these cases, employ cyclic watering, running the system for short bursts (10 to 15 minutes), allowing the water to soak in, and then repeating the cycle after a brief pause. Seasonal adjustments are necessary, as the lawn’s water demand decreases significantly during cooler spring and fall months.