30 ‎(3)‎

• Board Meeting Date: 5/21/2008
• Description: IWMD Section - Presentation of Agricultural Water Conservation Paper
• Board Meetings - Doc Type: Memo

Section 3
Agricultural Water Use
Water conservation has its own set of specific terminology that must be understood
when discussing options and limitations. Irrigation water applied to cropland consists
of the following major components:
1. Total water diverted from the river or aquifer to irrigate the f field
^ Includes crop consumptive use + water required to compensate for system
inefficiency (nonbeneficial evaporative losses, return flows including deep
percolation, and surface runoff)
2. Water taken up from soil by the crop
^ Crop Transpiration + Evaporation =Evapotranspiration (ET)
^ Season-long Evapotranspiration -Effective Precipitation =Consumptive Use
(CU)
3. Water lost f rom f arm non-crop consumptive use
^ Evaporation f rom areas not under crop
^ Consumptive Use f rom plants not under crop land
^ Deep percolation not returned to stream
When considering the entire water budget needed for irrigation, the majority of the
water diverted f or irrigation typically is f or crop consumptive use and return flows.
The actual amount of total water lost to non-beneficial consumptive use is site-
specific, but has been estimated at about 10 percent of the crop consumptive use.
Figure 3-2 is a schematic of an irrigation system illustrating the fate of water diverted
from the river f or irrigation.
River
Diversion
River Flow
t 1
Canal Seepage Returns ^
Canal Surface Returns I
r
Canal Consumptive
Losses
(Phreatophytes,
Evaporation and
Deep Percolation
not returned to the
stream)
Irrigation Surface
and Tributary
Groundwater
Ret rns
FARMIRANCH
Crop Consumptive Other Farm Non-Crop CU
Use (Non-Productive Evaporation)
Figure 3-2
Irrigation System Schematic Including Return Flows
DRAFT 3-2