The handbook of Technical irrigaTion informaTion - Hunter Industries

Handbook of Technical Irrigation InformationUsing the “Water Supply Requirements” TableThe “Water Supply Requirements” table (page 53) provides a quick estimate of the gallons per minute (GPM)required to irrigate one acre at 70% efficiency for a variety of potential evapotranspiration (PET) rates for varying hoursof operation. This can be used to estimate the water needs of large areas for water service meter size or pump stationrequirement.How to Use the Table1) Determine the approximate PET for the project. This should be the peak ET o and should include a crop coefficient.For example if the peak ET o were 0.34 in./day and the irrigated area was a warm season turf grass with acrop coefficient of 60% (0.60) the PET would be 0.20 in./day (0.34 x 0.60 = 0.20).Find the PET Average in in./day in the second column from the left.Example: 0.20 inches/day2) Read across to the column under the “Average Hours of Operation/Day”Example: 123) Under the column for 12 Average Hours of Operation/Day, the “Minimum GPM per Acre” represents theminimum number of gallons per minute required to deliver 0.20 inches of water per day for one acre using anirrigation system with 70% efficiency.Example: 0.8 GPM minimum per acre required at peak demand.4) Multiply the minimum GPM per acre times the number of acres in the project, if the project being designed hada total of 20 acres.Example: 20 x 10.8 = 216 GPM48