WSP02037

• File Number: 8200.700
• Description: Colorado River Basin - General Publications
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 11/1/1979
• Author: US Forest Service
• Title: Managing Vegetation to Increase Flow in the Colorado River Basin - US Forest Service
• Water Supply Pro - Doc Type: Report/Study

00071 ?

Table t .-Polential and adjusted water Yield Increases (inches) and total area of each vegetation lype, Upper
Colorado River Basin

Millions
of acres

Potential
Increase

Adjusted1
increase

Alpine
Mountain grasslands
Subalpine
Aspen
Ponderosa pine
Mountain brush
Big sagebrush
Pinyon-juniper
Upstream riparian

1.3
unknown
6.8
3.2
1.5
3.3
17.6
12.6
unknown

2.5
1.5-3
1 - 3
3.5
, -3
1.3
0- 1
0-0.5
6-24

21 -3
0.3. ,
.1-1

lAdJustmenrs reflect multiple use and other considerations.
2ND reduction was indicated for subalpine forests because patch cuttil'Jg, which tends to be most water
productive, was also considered to De acceptable from multiple use and 5//vicultural standpoints. Under shelter-
wood. individual free selectIon. or group selection harvest methods. warer yield Increases probably would be less
than one-hall these values.

Table 2.-Potenlial and adjusted water Yield Increases (Inches) and total area 01 each vegetation type, Lower
Colorado River Basin

Millions Potential Adjusted1
of acres increase increase
Mountain grasslands 0.1 1.5.2
Mixed conifer .4 3-4 '.2
Aspen .1 3-5 0.3.1
Pondersoa pine 6.0 '.3 ,-,
Chaparral 3.5 1 - 5 2.4
Pinyon-juniper 19.9 0-0.5
Upstream riparian .1 6- 24

'Adjusfments reflect multiple use and other considerations.

(water uniformly distributed over the treatment
area) expected from manipulation of vegetation
and snow. In commercial conifer forests-
subalpine, mixed conifer, and ponderosa pine-
treatment area refers to the entire working area
where timber harvesting or other management
practices are applied, including intervening trees,
shrubs, or open areas which may receive some type
of silviculturaltreatment, or are left undisturbed.
However, in the aspen, brush lands, pinyon-
juniper. and upstream riparian zones. treatment
area refers only to area cleared, converted, or
otherwise modified: it does not include sur-
rounding or intervening areas left untreated for
wildlife, esthetics, or other purposes. A somewhat
different interpretation of treatment area is applied
to alpine, mountain grasslands. and high elevation
sagebrush lands, where snow management is the
water yield improvement method. Under these
situations. treatment area refers to the snow source
area (fetch) upwind of snow fences or other bar-
riers, plus the downwind accumulation area where
the snowdrift forms.

Variations in site capability, climate, and treat-
ment methods determine the range of response in
each of the vegetation types. The grealest response
in streamflow can be expected on sites where large
reductions can be made in evapotranspiration,
whether this is done by trapping snow or by re-
ducing vegetation. Clearcutting and type conver-
sion are the methods that usually increase
streamflow the most. except in the subalpine zone.
where patch cutting is considered most water pro-
ductive.
The vegetation type that offers the best oppor-
tunity for improving water yield in Ihe Upper
Basin is the subalpine, followed by aspen. moun-
tain brush. and ponderosa pine. In the Lower
Basin, the opporluni ty to improve the water supply
is best in chaparral and ponderosa pine. Oppor-
tunities in mixed conifer and aspen are limited by
the small acreage of these forosts.
The potential for increasing water yield per L1nit
area of treatment is greatest in upstream riparian
vegetation. and is least in pinyon-juniper and
sagebrush lands. However, the upstream riparian

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