LIT194-Handbook of TII.pdf - Diamond Head Sprinkler Supply

Example:A zone in your system is irrigating established warm season turf which is growing in a sandyloam on a slight slope with an available water holding capacity of 1" per foot of soil. The rootdepth of the turf is 9". The average precipitation rate is 0.49 inches/hour. The system is locatedin San Marcos, CA where the daily moisture loss (ET o ) to be replenished is 0.20 inches. The cropcoefficient (K c ) is set at 70%. The allowable water depletion will be 50%.F = 1.0" x 0.75' x 50% = 1.0 x 0.75 x 0.50 = 2.68 = 2 days0.20" x 0.70 0.20 x 0.70Sprinkler Run TimeThe sprinkler run time formula calculates the number of minutes required to apply enoughwater to replace the water lost by evapotranspiration for a specific crop irrigated with a system at aparticular precipitation rate and efficiency.The "run time" is calculated using the following formula.T = 60 x D x Et o x K cPR x IEWhere:T = sprinkler run time in minutes60 = constant for conversion of area, flow, inches per hour and inches per day intocommon unitsD = watering frequency in daysEt o = reference evapotranspiration rate, in inches per dayK c = crop coefficient, decimalPR = precipitation rate of the area, in inches per hourIE = application efficiency of the system, percentExample:Determine the sprinkler run time for an athletic field with a daily Et o of 0.15 inches and a cropcoefficient for the warm season turf of 0.70. The watering schedule is set for every three days. Thesprinkler precipitation rate is 0.50 in./hr. with an application efficiency of 75%.T = 60 x 3 x 0.15" x .70 = 60 x 3 x 0.15 x .700.50" x 75% 0.50 x 0.75T = 50 minutes every 3 days®Handbook of Technical Irrigation Information29