© Irrigation Association Analyze the Resource Inventory

© Irrigation Association Calculate Flow Requirements System capacity formula

© Irrigation Association Basic form QT=AD – Q = flow rate (cfs) – T = time (hrs) – A = area (ac) – D = depth (in)

Let’s look at the manual for calculation of GIR

© Irrigation Association Et c is the average daily ET For shallow rooted crops use 5 day period For medium rooted crops use 10 day period For deep rooted crops use 20 day period For sandy soils these values are halved – Example: beans are medium rooted crop 10 days /2 = 5 days period

© Irrigation Association ET During Growing Season Wheat Corn Soybean

© Irrigation Association Daily ET graph

© Irrigation Association Average daily ET

Adjustment Factor for frequency of wetting k f © Irrigation Association

Calculate Irrigation Frequency Maximum is related to MAD x AW x RZ Precipitation reservoir Safety buffer for downtime Balancing frequent irrigations, intake rates and reserve storage

© Irrigation Association Suggested starting intervals 2.5 days for sandier soils 3.5 to 4.5 days for medium textured soils See Appendix G for more information

Let’s look at the manual for calculation of Q s

Fraction of time operated t =the fraction of time that the system is turned on for a typical day during the peak period. Often in design, t = 0.9 is used to account for some down time. © Irrigation Association

Limited water supply Limits on water – Insufficient water rights – Inadequate well or pump capacity – Limited seasonal water supply

Deficit Irrigation What is the responsibility of the designer? © Irrigation Association

Yield vs Evapotranspiration

© Irrigation Association Practice Session #1 - Calculating the design flow rate

© Irrigation Association Practice Session #2 - Design project flow rate