Finding Innovative Solutions to Runoff Control Problems

Can surface water runoff be controlled by The ET Water systems? ETwater tackled that challenging question in developing its highly efficient irrigation system.

First, ETwater reviewed research on the subject from California State Polytechnic University (Pomona), the Center for Irrigation Technology at California State University (Fresno) and the Irvine Ranch Water District. All three institutions recognized the need for runoff control and had conducted numerous studies to determine the effects of various landscape conditions on irrigation runoff. The studies showed that there are numerous factors affecting runoff conditions, including:

• The relationship between slope angles and sprinkler precipitation rate
• The rate of soil absorbency
• Location of sprinklers and spacing of sprinklers on the landscape
• Runoff leads to many problems. Plants do not get their needed water requirements.
• Runoff damages asphalt and concrete over time and creates annoying puddles.
• Most importantly, studies show that surface water pollution rates are increasing, primarily from pesticides and fertilizers contained in irrigation runoff.

ETwater has designed its ETwater Manager Web-based user interface and the supporting software algorithms with runoff control in mind. When a user initially configures a landscape setting, specific questions are asked about sprinkler system type, slope percentages and soil conditions.

The ET Water software analyzes the user inputs and calculates the total amount of water required for an irrigation event. It then breaks down the total amount of required water into maximum cycle times and minimum soak periods to ensure that runoff doesn't occur. Water is never applied at a rate that is faster than the landscape soil's ability to absorb it.

How ETwater Runoff Control Works
The chart illustrates how ETwater effectively controls runoff. On the flat surface, sprinklers can only run for 10.5 minutes before the soil is fully saturated and water accumulates on the surface. A soak period of 30 minutes is required between run time cycles to ensure that water is fully absorbed before the next cycle is applied.

On the sloped surface, the ET Water algorithm calculates a much different schedule. Sprinklers can only run for 3 minutes before the soil is unable to absorb water and runoff occurs. A longer soak period of 45 minutes is also required between run time cycles due to the combined effects of the less absorbent clay soil and the steeper slope.

	Scenario 1	Scenario 2
Slope	Flat	20% (Steep Slope)
Soil Type	Loamy	Clay
Plant Type	Cool season grass	Cool season grass
Sprinkler Type	Spray heads	Spray heads
Soil Intake Rate	.35 inches per hour	.1 inches per hour
Sprinkler Precipitation Rate	1.5 inches per hour	1.5 inches per hour
Maximum Cycle Time	10.5 minutes	3 minutes
Minimum Soak Time	30 minutes	45 minutes
Recommended Schedule to Minimize Runoff	2 cycles 10.5 minutes per cycle 30 minute soak	7 cycles 3 minutes per cycle 45 minute soak

In addition to the soak and cycle calculations, the watering schedule for both flat and sloped surfaces is further adjusted automatically for weather changes. The schedule is downloaded daily to the ETwater Smart Controller at the landscape site, producing a precise schedule that is both efficient for plant needs and controlling runoff.

In fact, in a recently completed study of the ET Water system at the Center for Irrigation Technology, ETwater received an unprecedented rating of 98.5% for efficiency - defined as the ability to irrigate without overwatering or creating runoff.