We are all too familiar with uncontrolled runoff in landscape irrigation systems.   Low head drainage is not only common throughout residential and commercial landscapes, it is ubiquitous.  When we consider that turf grass consumes more  irrigated acreage and water than the top five agricultural crops (Diep, 2011)it becomes incumbent upon us to use every drop of irrigated water wisely and efficiently.

One of the tools we use to provide optimal irrigation water to landscapes, that is widely supported by public agencies, is the Weather-based Irrigation Controller (WBIC).  A core feature of all robust WBICs is a ‘run-soak’ cycle that is automatically programmed to reduce runoff.  WBICs take inputs of soil, slope, precipitation rate and crop coefficients to maximize efficiency overall and to mitigate against runoff, particularly in sloped conditions.   For example, under extreme slope conditions, a WBIC may dictate a ‘run’ duration of two minutes and a ‘soak’ duration of ten minutes to be repeated five times to provide ten minutes of irrigation.  This study discusses the effectiveness of the ‘run-soak’ cycle and shows that it isgreatly enhanced if drain checks are installed on the low-head sprinklers .  This research posits that there are two sources of wasted water when runoff is uncontrolled: the amount of water that drains from the system each time the zone is turned off and; the amount of water that is used to re-fill the irrigation line that is not applied to the crop.  That is to say, when the WBIC determines the optimal amount of water required for each zone, the water that is used to fill the line does not reach the crop in the time allotted.  These two water sources are termed “fill water” and “runoff”.

Research Methodology

This research study examines the consequences of uncontrolled irrigation runoff in landscape irrigation under conditions when a ‘run-soak’ cycle has been determined by the WBIC  as necessary to mitigate runoff.

This study simulates uncontrolled runoff during five  run-soak cycles of 2 minutes of run time.  The study examines two sources of wasted water: runoff from low head drainage and; the water that is used to fill up the irrigation lines after drainage of the line occurs.  The research simulates the performance of: PVC lines 1″,2″, 3″, 4″,6″, 8″, 10″ and 12″; water velocities 5, 7 and 10 feet/second and;  a fill-time of each line of 30 seconds.  Rates of flow were calculated in Gallons per Minute and  water capacity was calculated in Gallons per 100′ (Diameter Velocity and Flow Rate)