Guide to Estimating Irrigation Water Needs of Landscape Plantings

Worksheet Example
A landscape manager in San Bernardino is interested
in estimating water requirements for a large
planting of African daisy (Osteospermum
fruticosum) for the month of July. The planting is
in an open area and is not exposed to extraordinary
winds for the area. The manager estimates that irrigation
efficiency is 70% and, using the work-sheet,
follows the three steps (see below).
Step 1.
KL = ks x kd x kmc
ks = 0.2 (from WUCOLS list)
kd = 1.0 (complete canopy cover and one vegetation type)
kmc = 1.0 (open area, no extraordinary winds)
KL = 0.2 x 1.0 x 1.0 = 0.2
Step 2.
ETL = KL x ETo
KL = 0.2 (from Step 1)
ETo = 7.4 inches (for July in San Bernardino) (see Appendix A)
ETL = 0.2 x 7.4 = 1.48 inches
Step 3.
TWA = ETL
IE
ETL = 1.48 inches (from Step 2)
IE = 0.7 (70% irrigation efficiency estimated by landscape manager)
TWA = 1.48 inches = 2.11 inches
0.7
(To convert 2.11 inches of water to gallons, see "Inches to Gallons".)
The landscape manager has estimated that the
groundcover will need 2.11 inches of water for the
month of July. Using this estimate, the manager
can develop an irrigation schedule. Other factors
may need to be considered before deciding if this
estimate is appropriate for the planting. Chapter 7
addresses these considerations.
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