WSP05944

• File Number: 8276.300
• Description: Lower Gunnison Basin Unit - Colorado River Basin Salinity Control Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 4
• Date: 9/1/1981
• Title: Final Report of the Lower Gunnison Salinity Control Study
• Water Supply Pro - Doc Type: Publication

potential for reducing the river's salt load by as much as 500,000 tons,
reducing salinity concentration of the Colorado River at Imperial Dam by 52
milligrams per liter. However, the practical limit of reduction is about
420,000 tons or 44 milligrams per liter.

TABLE I-I SUMMARY OF SALT LOADING AND POTENTIAL REDUCTION
ATTRIBUTED TO IRRIGATED AGRICULTURE IN .THE LOWER GUNNISON UNIT 1/
LOWER GUNNISON SALINITY CONTROL STUDY, COLORADO

Source

Length of
Lateral
(miles)

Sal t Loading
Quantity Potential Reduction
(-----------tons/year----------)

Onfarm.
Head Ditch Seepage
Deep Percolation
Tailwater Ditch Seepage
Subtotal Onfarm

210,000
135,000
95,000
440,000

160,000
115,000
60,000
335,000

Off-Farm 11
Small Laterals 21
Large Laterals 31
Main Canals 41
Subtotal Off-Farm

135
210
140
485

25,000
110,000
65,000
200,000

20,000
90,000
55,000
165,000 51

Total 485 640,000 II 500,000
11 Does not include data for laterals within the Uncompahgre Project Area
being studied by the Bureau of Reclamation which contribute about
200,000 tons annually.
2/ Small laterals carry flow rate less than 20 cubic feet per second (cfs).
31 Large laterals carry flow rates between 20 and 100 cfs.
41 Main canals carry flow rate greater than 100 cfs.
II Reduction of this magnitude is not cost effective.

Local benefits resulting from these improvements will be reflected in
reduced costs of production, improved irrigation systems and increased crop
yields. However, these improvements also will adversely impact up to 13,200
acres of the 14,800 acres of irrigation-induced wetland that have developed
as a result of introducing irrigation into the valley. There are an addi-
tional 24,800 acres of riparian wetlands that will not be adversely
impacted. The loss of irrigation induced wetlands can be mitigated by up-
grading the habitat value on as much as 18,300 acres of wetlands otherwise
undisturbed by proposed program actions and by developing 3,700 acres of new
wetland habitat if Alternative 8 is implemented.

This report describes eight candidate plans that address four concepts
for reducing the river's salt load. These concepts are: a continuation of
ongoing programs (no accelerated action alternative), onfarm irrigation
water management (non-structural alternative), onfarm ditch lining only, and
combining improved onfarm irrigation water management with ditch lining at
two levels of development. Lining of off-farm laterals is displayed as a
supplemental action to six of these alternatives.

2

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