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

Section 4
Agricultural Conservation Measures
Tahle 4-1 Estimated Efficiencies and Casts far Irriaation Methods

T pe of Irri ation Range of
Efficienc Average Capital
CostlAcre Average Annual
CostlAcre
Flood 30-50% - -
Furrow 40-60% $37 $30
Gated Pipe ~60% $178 $51
Center Pivot Circle ~85% $433 $64
Center Pivot with Corner ~85% $568 $80
Subsurface Drip Irrigation ~90% $1,000 $120
Reducing Consumptive Use
Upgrading irrigation systems inmost instances increases water use eff iciency but
does not necessarily reduce consumptive use. A concept that has been discussed can
be termed conserved CU water. This is water that results from the reduction in
productive ET, which can occur when one or more of the f ollowing occurs:
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1. Irrigated acres are decreased.
2. Crop selection is changed from a summer crop
to a cool season crop.
3. Crop selection is changed to one with a shorter
growing season.
4. Deficit irrigation is practiced, applying some
amount less than full ET over the growing season.
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5. Evaporative losses f rom the f field surf ace are
reduced as a result of conservation tillage,
mulching, and or drip irrigation.
If irrigated acres are decreased, it is relatively
simple to calculate the water conserved f rom
reduced ET. This type of conserved water has been
recognized in water court transf ers of agricultural
water rights and is usually accomplished through
the requirement of recording adry-up covenant on
the land that will no longer be irrigated. In this case,
the amount of water that is available f or other uses
is the total consumptive use of the irrigation water
that can be shown to be reduced.
Most of the difference in consumptive use between crops can be explained by season
of active growth and length of growing season. Crops grown during the cool season
such as winter wheat are subject to lower atmospheric demand and thus lower ET
rates. Reducing the length of crop growing days also can reduce irrigation demands.
These differences inseason-long consumptive use as a result of growing day length or
growing period can be seen in Table 4-2 below.
DRAFT 4-2