WSP06290

• File Number: 8277.600.10
• Description: Big Sandy River Unit - Colorado River Salinity Control Program
• State: WY
• Basin: Colorado Mainstem
• Date: 5/1/1986
• Title: U.S.D.A. Selected Plan - Big Sandy River
• Water Supply Pro - Doc Type: Definite Plan Report

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CHAPTER 1

PROBLEMS AND NEEDS

Salinity Problems

Prior to the introduction of irrigation, small springs along the
Big Sandy River were observed by early ranchers. These springs produced
minimal amounts of water and salt from the underground aquifer.
However, due to irrigation and resulting deep percolation, additional
water is being transported through the underground aquifer and out of
newly developed and enlarged existing springs into the Big Sandy River.
Table 1-2 shows the 18-year (1960 through 1977) water budget tabulation.
Figure 1-1 shows a schematic flow diagram of the water budget as
averaged for the 18-year evaluation period.

The additional water from the irrigated project area is dissolving
large quantities of salt from the aquifer bedrock which is made up of
the Bridger and Green River Rock Formations.

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Annual
table 1-3.
(1960-1977)

salt contributions to the Big Sandy River are shown in
The average annual salt loading for the 18-year period
is estimated at 149,180 tons (at Gasson Bridge).

Irrigation Systems Analysis and Management Improvement Needs

In making the irrigation system analysis, it soon became evident
that the irrigated acreage in the project area was continually changing.
The following Table 1-1 defines the values and definitions of time
periods and relationships used in this report.

A canal and lateral system analysis was conducted for the historic
water record (1960 through 1977 irrigation seasons) on the Eden Valley
Irrigation Project, This analysis indicated that 82 percent of the
water diverted from the reservoirs is being delivered to the farms.

The average consumptive use required by crops grown in Eden Valley
was estimated to be 1.17 acre-feet per acre for the 1960-1977 evaluation
period, The average irrigated acreage for this period was 14,320 acres.
Dividing the consumptive use of water by crops by the total water
delivered to the farm, an average on-farm irrigation efficiency of
3S percent was derived. This indicates the overall project efficiency
to be approximately 29 percent, using an 82 percent conveyance
efficiency (see Table 1-4).

The water not used by the irrigated crops (71 percent) can be
accounted for by (1) phreatophyte use, including essentially all
nonirrigated plants in the project area and along the river to Gasson
Bridge, (2) evaporation from reservoirs and ponds, and (3) drainage
ditch and deep percolation return flows to the Big Sandy River.

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