The handbook of Technical irrigaTion informaTion - Hunter Industries

Handbook of Technical Irrigation InformationSprinkler Run TimeThe sprinkler run time formula calculates the number of minutes required to apply enough water to replacethe water lost by evapotranspiration for a specific crop irrigated with a system at a particular precipitation rate andefficiency.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 into common 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 crop coefficient for thewarm season turf of 0.70. The watering schedule is set for every three days. The sprinkler precipitation rate is 0.50inches per hour 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 days26