The precipitation rate, expressed in inches per hour, is the amount of water a sprinkler system delivers. Understanding this rate is fundamental to efficient watering, as it allows for the creation of an accurate irrigation schedule. Without knowing the precipitation rate, it is common to either overwater, leading to wasted resources and runoff, or underwater, which can stress plants. Calibrating your system helps prevent these issues by ensuring that the landscape receives the precise amount of water it needs to thrive.
Essential Supplies for Testing
The most reliable method for determining a system’s output is a physical measurement test. This test requires a few simple items:
- Containers with straight sides, such as catch cups or small food cans, to collect the water.
- A ruler that can measure depth precisely, ideally to the nearest millimeter or tenth of an inch.
- A stopwatch or timer to accurately record the sprinkler run time.
- A calculator for the final computation.
Executing the Catch Can Test
The catch can test begins by placing the containers randomly throughout the area covered by a single sprinkler zone. It is important to use a minimum of six cans, but using more will increase the accuracy of the final measurement. The cans should be scattered to cover various spots, including areas near the sprinkler heads and those halfway between them. This random placement ensures that the test captures the variations in water distribution, which is rarely perfectly uniform.
Once the containers are in place, the specific sprinkler zone should be run for a set duration, often 10 or 15 minutes. Running the system for a shorter, fixed time reduces the total water used during the test. After the run time is complete, the water depth in each can must be measured and recorded. Observing the difference in water levels between the cans can also immediately highlight areas of poor water distribution, indicating a potential issue with a specific sprinkler head or pressure.
Calculating the Precipitation Rate
To find the average water depth collected across all the cans, add the measured depths from every container and then divide that total by the number of containers used. This average depth represents the amount of water applied during the test run time. To convert this measurement into the industry-standard rate of inches per hour (in/hr), a simple mathematical extrapolation is necessary.
The formula takes the average depth, divides it by the test time in minutes, and then multiplies that result by 60 to scale the measurement up to a full hour. For example, if the average collected depth was 0.25 inches over a 15-minute test, the calculation would be (0.25 inches / 15 minutes) multiplied by 60, resulting in a precipitation rate of 1.0 in/hr. This hourly rate provides a standardized figure that can be directly applied to determine the necessary run time for any desired water amount. This process should be repeated for every separate irrigation zone, as different sprinkler types and water pressures will yield distinct precipitation rates.
Using Results to Optimize Watering
The calculated precipitation rate is the foundation for establishing an efficient watering schedule. Turfgrass, for instance, typically requires a weekly total of about 1 to 1.5 inches of water to remain healthy and resist drought stress. By knowing your system’s output rate, you can precisely calculate the run time needed to apply a specific depth of water, such as 0.5 inches per watering cycle. For a system with a 0.5 in/hr rate, applying 0.5 inches of water would require a 60-minute run time.
The precipitation rate may exceed the soil’s infiltration rate, especially on heavier clay soils or sloped areas. If the application rate is too high, water will run off the surface before it can soak in. To prevent this runoff, the total run time can be broken up into shorter, repeated intervals, a technique known as cycle soaking. This method allows the water to soak deeply into the soil before the next irrigation cycle begins, maximizing absorption and ensuring the target water depth is reached without waste.