WSP06888

• File Number: 8270.100
• Description: Colorado River Basin Water Quality/Salinity -- Misc Water Quality
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 4/1/1982
• Author: USDA
• Title: Colorado River Water Quality Improvement Program - Final Environmental Impact Statement for Lower Gunnison Basin Unit - Montrose and Delta Counties CO and Uintah Basin Unit
• Water Supply Pro - Doc Type: EIS

and supports valuable wetland habitat. Water seeps from earthern canals and
ditches, often saturating the soil and supporting such hydrophytic and phrea-
tophytic plants as cattails, rushes, willows and cottonwoods. Open drains
often support dense stands of reed canarygrass, willows and tamarisk. Return
flows from irrigated areas contribute water to natural drainages, supporting
native wetlands or creating new ones. Irrigation induced or increased wetlands,
including single and multiple water source wetlands, constitute almost 38
percent of the total wetland habitat in the study area.

The small mammal and bird populations are important components of the food
chain for larger animals. Many raptors have been observed feeding along ditch
banks and in seepage areas. In addition, small birds and mammals are important
not only as raptor and mammalian carnivore food, but also for the color, diversity
and interest they add to rural and urban life styles.

Some irrigation induced wetlands may prove to be important native plant habitats.
Frequently disturbed areas, such as ditch banks and open drains, are usually
vegetated by early successional plant species. Seepage induced wetlands along
the major canals, often undisturbed for nearly 100 years, have more diversified,
stable plant populations. Due to their age and stability, they may prove
important as reservoirs of native wetland vegetation and as "relict" areas. for
vegetation studies.

There are an estimated 39,600 acres of wetland within the irrigated area of
the Lower Gunnison Basin Unit including 37,400 acres interspersed throughout
the irrigated portion of the study area. Table IV-6 shows probable water
sources supplying these wetlands. Soils with gley characteristics (both red
and grey which develop in permanently wet soils) make up about 6,000 acres of
the natural wetlands. These soils with gley characteristics are not expected
to be affected by the salinity control program. Irrigation management (method
of irrigation and level of management) contributes a significant portion of
the water supply to about 14,800 acres (37.4 percent) of the wetlands. Table
IV-7 identifies those wetlands influenced by irrigation, either separately or
in combination with other water sources.

TABLE IV-6
WETLANDS AS CLASSIFIED BY WATER SOURCES, _1/
LOWER GUNNISON SALINITY CONTROL STUDY

Water Sources

Percent of
Total Wetlands

Acres

Natural
Irrigation Management (onfarm)
Canal
Natural & Irrigation Management (onfarm)
Natural & Canal
Natural & Irrigation Management (onfarm)
& Canal
Irrigation Management (onfarm) & Canal
Total

60.1%
15.3
1.7
19.2
0.8

23,810
6,050
620
7,610
320

0.1
2.8
100.0%

40
1,100
39,600

l/ After Lower Gunnison River Basin Wetland Inventory and Evaluation,
Rector, Mustard and Windell, 1978. p. 16. (Numeric values extrapolated to
be representative of the larger irrigated area studed by SCS.)

IV-34

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