The handbook of Technical irrigaTion informaTion - Hunter Industries

Formulas – SchedulingPrecipitation Rate – Minimum Rate RequiredThis formula is used to determine the minimum precipitation rate than can be used to deliver the required waterduring the peak period of water usage.Minimum PR =ET x Total AcresHours Avail. x Acre per Section x Valves x EfficiencyWhere:Minimum PRETTotal AcresHours Avail.Acres per SectionValvesEfficiency= minimum required precipitation rate in inches per hour= amount of water to be applied in inches per day, including crop coefficient= the area to be irrigated in acres= hours available for irrigation each day= average area covered by one control valve in acres= number of valves operating at one time= system operating efficiency in decimal equivalent of percentExample:What is the minimum precipitation rate that will deliver 0.28 inches of water to 15 acres under the followingconditions:• during a 12 hour period• the average section is 0.40 acres (17,424 square feet)• there will be two valves operating at one time• the system efficiency is 75%0.28 x 1512 x 0.40 x 2 x .75= 0.58 inches per hour minimum precipitation rate required23