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

U0072Q

nearly five times as much water as the Lower Basin,
it would be consistent to look to the Upper Basin
for most of the extra water. say 500,000 acre-feet
(3.5% increase). and to the Lower Basjn for 250,000
acre-feet (8% increase).
In the Upper Basin, treatments as described
earlier might be considered on the acreages indi-
cated in table4. The average increases projected for
each vegetation type are arithmetic averages of the
ranges in values shown in tables 1 and 2. Averages
of the adjusted values were used for the aspen,
mixed conifer, ponderosa pine, 'and chaparral
types. In the Lower Basin (table 5), a larger per-
centage of the area would have to be treated to get
the increases desired.
From these arbitrary examples of hypothetical
treatments and acreages, it appears that 500,000
acre-feet of extra water could be generated in the
Upper Basin by committing up to 22% of each
vegetation type, except the aspen forests, in which
40% would be treated. The management strategy
for the aspen type is 80-year rotation c1earcut har-
vest in patches covering 20% of the total area plus
25-year rolation of patch cuts on an additional 20%
of the total area.
Treatment on 22% of the subalpine forests in-
cluding Douglas-fir, would produce 50% of the
total increase. Mountain brush and aspen would be
the next largest contributors. The increases attri-
buted to the alpine zone and big sagebrush vegeta-
tion are projected with less certainty than for the
other types because it is uncertain that these
amounts of water can be generated on a watershed
basis.
In the Lower Basin. more extensive treatments
would be required to generate 250,000 acre-feet of
extra water. Only small increases could be ex-
pected from snow management in the mountain
grasslands and from patch cutting in the aspen,
even if these cover types were fully treated. Also,
because of the limited acreage of the mixed co-
nifers. the potential for this type is small. There-
fore. attention is focused on the chaparral and
ponderosa pine forests, where 92% of the expected
increase would be generated by treating about 20%
of the chaparral and 33% of the ponderosa pine.
Again. these acreages may not produce the desired
amount of extra water if the suggested treatment
practices should require modification to better ac-
commodate other resource values.

Whv not treat a larger percentage of chaparral,
since ihe potential is good for increasing yield and
the type is low in commercial value? First. large
portions may not be treatable because cover is too
sparse or slopes loa steep, or because certain areas
are classified for other uses such as wilderness.
Also, the term treatment area as used for the

chaparral refers to the actual area converted to
grass or otherwise modified: it does not include
surrounding or intervening areas left untreated for
wildlife or other purposes. Therefore. treatment of
20% of the chaparral or mountain brush involves a
much larger all-inclusive acreage than one in five.
since untreated intervening areas may equal or ex-
ceed the acreage actually converted to grass.
However, availability of treatable acres is un-
certain in all of the vegetation types. The arbitrary
selection of treatable acreages used in this assess-
ment should not be construed to mean that these
acreages would be available for treatmenL Treat-
able acreages may ultimately prove to be less (or
more) than these, in which case the projected in-
creases in water yield would also be differenL

Cost of Producing Additional Water

Costs of initial treatment vary from a few dollars
per acre to a few hundred dollars per acre, de-
pending on the type of treatment and type of vege-
tation. Initial treatment cost figures are of limited
value. however, in determining cost of increased
water yield. unless tradeoffs are included and
maintenance costs are properly evaluated over a
period of years. Some of the treatment possibilities
in the example given here may not now be
economically feasible, although they might be at
some later date.
Although few good economic evaluations are
available, cost estimates indicate where low- and
high-cost water could most likely be obtained.
Generally, water derived from management of
commercial forests is the least expensive. since
relatively small additional outlays or tradeoffs are
required to get the extra water. Several estimates
made during the mid to late 1960's pegged costs of
additional waterfrom multiple use management of
western forests at $1 to $5 per acre-fool. Esti mates
of costs of increasing water yield by type conver-
sion in the chaparral ranged from $10 to $50 per
acre-foot. the average being near $20. The cost of
producing extra water by snow fences in alpine
and mountain grassland areas has not been deter.
mined. However, some preliminary estimatesB in-
dicate that, on favorable sites, additional \Vater
might be obtained at costs of $10 to $20 per acre-
foot. These costs would be higher tnday, although
the relationship of cost to value of water may not
have changed much.
In an economic analysis of chaparral conversion
in central Arizona, T. Brown et aL (1974) con-
8Maninelli, M. R. Tabler, and R A. Schmidt 1975. An estimate
of snow management potentIal on Straight Canyon barometer
warershed, Utah. 9 p, unpublished repon. USDA For. Serv.,
Rocky Mr. For. and Range Exp Srn., Fon Coffins. Colo.

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