WSP11421

• File Number: 8276.855
• Description: Grand Valley Unit-Colorado River Basin Salinity Control Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1993
• Title: 1993 Report to the USDI-Bureau of Reclamation - Grand Valley Demonstration Project
• Water Supply Pro - Doc Type: Report/Study

,GO

H"

, . C\l
..-i

,-,

At the end of FY93, 243 surge units had been requested by cooperators in the
Grand Valley Unit as part of the cost-share approach of the Colorado River Salinity
Control Program. An additional number of units, not readily quantifiable, have
been purchased by area farmers using their own funds. Nearly all of these units
are in place because of the surge demonstrations in the area made possible
through this grant and other Extension activities.

c.:::

IMPLICATIONS:

The benefit to downstream water users is the 560 acre inches that was not
percolated through the soil profile on the surge irrigated portions of the fields and
the resultant salt loading reductions as shown by the combined data. This is the
measured total from the farms irrigation systems evaluated over the four year
period. See column 12 of the attached data sheets under the heading of acre inch
reduction of deep percolation. This value is different than the projected value
calculated if all farms were measured at all irrigations. Note that 1,000 tons were
measured during the course of the study but that 1,617 tons were projected during
the 1993 irrigation season. This difference is partially due to not having the
equipment available to measure each irrigation event during the season on all farms
and the necessity of averaging salt load reduction values.

Improved irrigation water management by irrigators and/or reduced application
rates due to irrigation equipment hardware changes do not save water on basin-
wide basis. Those who expect to harvest this "saved" water do not understand
the hydrological cycle.

I~
\''\>

i

Water that is deep percolated past the root system in the Grand Valley is
eventually returned to the Colorado River for use downstream. This time period is
variable but based on observations of the various drainages in the valley the
quantity of water deep percolated from irrigations is back in the river by April of
the following year. This water is degraded in quality but the quantity has not been
significantly reduced. The purpose of the Colorado River Salinity Control Program
is to address water Quality, not Quantity. If less water is diverted because of
better irrigation water management the flow will be available downstream at an
earlier date but there will not be more flow available. While the water is
underground in the irrigated areas it is subject to less evaporation than while in the
major reservoirs downstream; this concept is often overlooked.

Deep percolation reduction made possible by surge units purchased with cost-share
and private funds is beyond the scope of this study, but will be included as part of
the total USDA salinity reduction report.

Water crossing over from one irrigated furrow to another prevented accurate flow
measurements on some fields. This implies poor irrigation water management,
More frequent and/or deeper furrowing by the farmer may remedy this problem.

11