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Section 3 <br />Agricultural Water Use <br />Water conservation has its own set of specific terminology that must be understood <br />when discussing options and linutations. Irrigation water applied to cropland consists <br />of the following nlajor components: <br />1. Total water diverted fronl the river or aquifer to irrigate tlle field <br />Includes crop consunlptive use + water required to conlpensate for systenl <br />inefficiency (nonbeneficial evaporative losses, return flows ulcluding deep <br />percolation, and surface runoff) <br />2. Water taken up froin soil by the crop <br />^ Crop Transpiration + Evaporation = Evapotranspiration (ET) <br />^ Season-long Evapotranspiration - Effective Precipitation = Consunlptive Use <br />(CU) <br />3. Water lost from farm non-crop consumptive use <br />^ Evaporation fronl areas not under crop <br />^ Consuinptive Use fronl plants not under crop land <br />^ Deep percolation not retiirned to streanl <br />When considerulg the entire water budget needed for irrigation, t11e nlajority of the <br />water diverted for irrigation typically is for crop consunlptive use and return flows. <br />The actual anlount of total water lost to non-beneficial consumptive use is site- <br />specific, but has been estinlated at about 10 percent of the crop consunlptive use. <br />Figure 3-2 is a schematic of an irrigation systein illustrating tlle fate of water diverted <br />fronl the river for irrigation. <br />River Flow ~ <br />River <br />Diversion <br />~ <br />Canal Consumptive <br />Losses <br />(Phreatophytes, <br />Evaporation and <br />Deep Percolation <br />not returned to the <br />stream) <br />~ Irrigation Surface <br />and Tributary <br />Groundwater <br />Returns <br />FARMIRANCH <br />1 <br />1 <br />Crop Consumptive Other Farm Non-Crop CU <br />Use (Non-Productive Evaporation) <br />Figure 3-2 <br />Irrigation System Schematic Including Return Flows <br />DRAFT 3-2 <br />