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The Coon Creek Water Yield Augnlentation
Pilot Project
G.
s. Bevenger and C. A. Troendle1
Abstract--Research in the Rocky Mountain subalpine zone has demonstrated that vegetative manipulation (primarily clearcuttlng) causes a
net reduction In evapotransplratlonallosses, changes the laerodynamlcs
and energy balance of the timber stand, and results In Increased
streamflow. Because the results of research on small watersheds has
shown that water yield can be Increased, and because forest management
represents one of several options for manipulating water yield, the Coon
Creek Water Yield Augmentation Pilot Project was initiated. The objective
of the project is to apply state-of-the-art technology in water yield management on an operational timber sale. The project also will make possible
large-scale testing and field verification of hydrologic prediction tools so
commonly used in planning.
Watershed Description
]\fore than 70 years of watershed researc.h throughout the
United States, and specifically in the Vt.Test, has provided the
technology to substantially increase usable water from forested lands. The long-term intent of the Coon Creek project
is to produce increased quantities of usable water in harmony
with sound multiresource management of National Forest
land. The Fore.st Service, Rocky Mountajn Region, responded
to a 1980 national initiative to augment water yield by proposing the Coon Creek !'ilot Project to apply te.chnology developed primarily at the. Fraser Experimental Forest and elsewhere in the Rocky ]\fountain Region. A second objective is
to eva.1uate, on a large scale, the reliability of state-of-the-art
hydrologic predictive tools currently being used, such as the
Subalpine Water Balance Model (Leaf and Brink 1973a,
1973b), Vt.'RENSS (Troendle and Leaf 1980a), and other
locally developed models.
Coon Creek was selected as the project area primarily
because the watershed in which it is located, the East Fork of
the Encampment River, is a large, uncut and unroade.d watershed of the. size nec.e.ssary for evaluating a commercially viable
timber sale. The basin consists of two watersheds of c.omparable size, aspect, and timber type.s, which allows for a paired
watershed study. The drainages are uniformly cove.red wi.th
commercially operable timber, and the drainage selected for
treatment (Coon Creek) can be logged by conventional harvesting methods using standard silvicultural practices (patch
clearcutting) .
Coon Creek, the treatment watershed, is a 3,987-ac.re
drainage loc.ated on the Hayden District of the Medicine Bow
National Forest in Wyoming. It drains to the west at elevations
ranging from 8,800 to 10,980 feet. Adjacent to Coon Creek is
the Upper East Fork, the 2,252-acre control watershed. The
Upper East Fork drains to the southwest at elevations ranging
from 8,800 to 10,090 feet. Soils in both drainages are deve.Ioping from alluvium and colluvium by weathering of igne.ous and
metamorphic mate.rial. Soils ge.nerally vary between 20 and 60
inches in depth and are well drained. The soils are capable of
absorbing water at rates in excess of snowmelt and normal
rainfall intensities, so surface erosion is minimal.
The dimate of the area is generally influenced by frontal
systems and orographic storms during winter months, and by
orographic and convectional storms during summer months.
Mean yearly precipitation and mean yearly temperatures are
estimated to be 40 inches and 34° F, respectively. Approximately 70% of the precipitation comes in the form of snow.
Streamflow from May to Septembe.r is directly and indirectly
the result of snowmelt, and flow generation is mostly subsurfac.e in nature. Estimated average annual water yield is 1.8
acre-feet per acre, with water quality generally good to
excellent.
Forest cover consi.sts of spruce-fir stands along stream
courses, on north slopes, and at upper slope positions. Lodgepole pine. grows on all low- and mid-elevation southerly or
high-ene.rgy exposures. i\.l.pine. tundra is above timberline.
Part of the area was extensive.ly harvested for railroad ties in
the early 1900s, but regrowth now completely occupies the site
hydrologically.
1Bevenger was Hydrologic Technician, Hayden District, Medicine
Bow National Forest, Encampment, Wyo. Troendle is Research Hydrologist, Rocky Mountain Forest and Range Experiment Station. Station
headquarters is in Fort Collins, in cooperation with Colorado State
University.
145
To date, 4 to 5 years of record have been colle.cted,
depending on the parameter: 4 years of flow record (1987 is the
fifth year), 5 years of snowcourse record, and 4 years of
temp~rat~re, f;recipitation, radiation, and humidity ·data. So
far, the correlations between the watersheds appear quite
good for all parameters.
Treatment and Measurement Methods
In 1982, 8-foot Cipoletti weirs were built on both East Fork
and Coon Creek, and they are operated from April to October
each year. To further assist the calibration process and to
evaluate treatment effects, an extensive network of climatic.
instrumentation also was installed across the two watersheds
in 1982 and 1983 (fig. 1). Climatic parameters being monitored
include solar radiation, air temperature, relative humidity, and
precipitation. Precipitati.on measureme·nts include both rain
and snow c.omponents. Include.d in the snow component
measurement Is a 600"point, random-walk snowcourse, which
is surveye.d around April 1 of each year. Survey data are used
to estimate mean water equivalent in the snowpack for each
watershed (all instrumentation imd snowcourse locations are
shown in fig. 1).
Watershed Calibration
Average monthly precipitation is fairly well distributed
throughout the yea.r on both watersheds (fig. 2). Rain falls
during the months of June through August, while snowfall
dominates from September to May. There is a strong orographic effect between elevation and precipitation on Coon
Creek, as is indexed by the relationship shown in figure 3. The
orographic effect holds year round.
Pilot Demonstration
- - - Watershed boundary
Snow survey lines
===
Existing roads
1 mile
1 km
Figure 1.--Map of the Coon Creek and East Fork watersheds showing snow course, climatic
station, and streamgage locations.
146
In addition to the climatic installations, permanently
marked random walk snowcourses also are located jn each
watershed. Approximately 200 stations are located in the East
Fork drainage and 400 in the Coon Creek drainage (fig. 1).
Although the 5 years of existing data demonstrate considerable variability among stations, snowpack accumulation increases significantly with elevation on all snowcourse
transects. Figure 4 presents the relationship of mean peak
water equivalent on the East Fork and Coon Creek watersheds. The agreement is quite strong: an r2 of 0.99 with a
standard error of 0.38 inch. "'ater equivalent on Coon Cre.ek
ranged from 15 to :W inches during the 5 years of record, or
from two-thirds of normal to a one in 4O-year extreme.
The average annual hydrographs for Upper East Fork and
Coon Creek for the years 1983 to 1986 show a strong c.orrelation (fig. 5). The majority of flow occurs in l\fay and June, and
is the result of melting snowpack. Analysis of the first 4 ye.ars
of record indicates that 83% of the variation in flow from Coon
Cre.ek and 95% of the va.riation on East Fork can be explained
by mean peak water equivalent (P"'E) in the snowpack on
April 1 (fig. 4). Although the correlations are higher than
usually observed elsewhere, the relationship is typical of that
for the subalpine forest (Troendle and Leaf 1980; Troendle
and Kjng 1985,1987).
The correlation between annual flows from Upper East
Fork and Coon Creek, like peak wate·r e.quivalent, also is quite
good (fig. 6). The first 4 years of record were very wet years,
with flow level very high and having very little. variation from
year to year. However, 1987 appears to be a dryye.ar (60% of
normal), and the estimated flow level is quite. low (estimate. is
measured flow for A pril, May, and June for both watersheds).
This low value provides the range needed in order to have
confidence in the application of the calibration relationship.
The. range in return jntervals for the calibration period (5
years) goes from one in 0.60 year to one in 40 years.
Coon Creek
Average monthly precipitation
Jan
Month
Figure 2.--Average monthly precipitation for the Coon Creek watershed.
Coon Creek
140
PreCipitati0njelevation
120
Q)
Ol
<1l
Qi
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<1l
'0
100
c
Q)
u
Qj
c..
80
60~
__________
~
8500
_______
~
____
9000
~
_______
9500
~
____________
10000
~
__________
10500
~
11000
Elevation (feet)
Figure 3.--AdJustment factor to be used to adJust average monthly
watershed Ineclpltatlon (fig. 2) for elevatlonal effect.
Water Equivalent by Water Year
,....,
(/)
30
Q)
£
In addition to annual flow, we also evaluated the character
and relationship of storm discharge from the two watersheds.
Thirty-one storms (rain only) occurred during the months of
July through September of 1983 and 1984. Only a minimal
portion of the precipitation was returned as stormflow or
quickflow (using definition of Hewlett and Hibbert 1967). The
individual rainfall events ranged from 0.01 to 0.78 inch, while
storm flow response varied from 0.001 to 0.019 inch. The
average storm size was 0.31 inch, while. the average response
was 0.01 inch, or 3t;t, of the precipitation returned as flow.
Subsequent analysis indicated no corre.lation (r2 = 0.00002)
between storm size and storm response. The lack of response
is not surprising, since summer precipitation does not appe·ar
to be well corre.lated with flow in the subalpine environment
(Troendle and Leaf 1980; Troendle and King 1985, 1987).
"'hat storm response that did occur probably was the result of
direct channel interception of the precipitation.
()
C
c
~
25
ro
>
·s
cr
o
Q)
n=5
20
r2=0.99
~
ro
y=1.19+0.98x
Q)
Q.
I
~
Q)
Q)
15
'-
()
c
o
o
()
10
15
20
25
30
Upper East Fork- peak water 'equivalent (inches)
The 5 years of record currently available indicate that
precipitation, snowpack accumulation, and flow all are well
correlated between the wate.rsheds, and the proposed harvest
Figure 4.--The relationship between peak water equivalent on the
Coon Creek and East Fork watersheds.
147
Discharge by Water Year
30
14
12
rf)
OJ
..c
25
()
c
10
~
:<
rf)
~
Average flow 1983-86
~
t
-- - - -
8
20
C\l
Coon Creek
::J
C
- - Upper East Fork
n= 5
c
-0
C\l
~
6
I
-"
OJ
r2= 0.9932
15
y:::4.83+0.905x
~
U
\
\
c
a
a
\
'\
\
U
............. . .
10
''--\
\..-'1..
20
Apr
-"'~".._ ... _ r-~'~ ... _,, __ " ......... "
20
5
May
Aug
Jun
5
20
Sep
5
Oct
5
Tim~
10
15
20
25
30
Upper East Fork-annual flow (inches)
Figure 5.--Average annual hydr~graphs (1983 to 1986) for Coon
Creek and UPI)er East Fork drainages.
Figure 6.--The relatlonshll) between flow on Coon Creek and Upper
East Fork for the first 5 years of calibration.
can proceed as planned, beginning in 1989. V\Te anticipate a
several-inch increase in flow, but a change as small as 1 inch
will be detectable.
Approximately 270/0 of the Coon Creek watershed will. be
harvested in small irregular clear cuts ranging in size from a few
acres to 13 acres (fig. 7). No riparian areas will be harvested,
and the proposed practice wi.ll meet all requi.rements of the
existing forest plan. Current plans are to monitor the watershed for several years following harvest to determine the
response, a.nd how accurately we were able to predict it.
Pilot Demonstration
___ Watershed boundary
6
~~~~~I.~I~~~III'lill~
m
Clear cuts
1 mile
lkm
Figure 7.--Proposed sale layout, Coon Creek watershed.
148
Literature Cited
Pap. RM-99. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and
Range Experiment Station. 22 p.
Leaf, C. F.; Brink, O. E.1973b. Hydrologic simulation model
of Colorado subalpine forest. Rep. Pap. RM-I07. Fort
Collins, co: U.S. Depa.rtme.nt of Agriculture, Forest
Service, Rocky ]\.fountain Forest and Range Experiment
Station. 23 p.
Troendle, C. A.; King, R. ]\.1.1985. The effect of timber harvest
on the Fool Creek watershed, 30 years later. Water
Resources Research 21(12): 1915- 1922.
Troendle, C. A.; KiQg, R. ]\,1. 1987. The effect of partial and
clear cutting on streamflow at Deadhorse Creek, Colorado. Journal of Hydrology 90: 145- 157.
Bevenger, O. S.; Troendle, C. A. 1984. The Coon Creek water
yield a.ugmentation project. In: Water for the twenty-fir!,t
century: will it be there'!: proceedings of the symposium;
1984 April 3-5; Dallas, TX. Dallas, TX: Southern]\1ethod··
ist University: 240-251.
Hewlett, J. D.; Hibbert, A. R. 1967. Factors affecting the
response of small watersheds to precipitation in humid
areas. In: Sopper, W. E.; Lull, H. ,"T. (eds). Forest Hydrology. Oxford, England: Pergamon Press. 275-290.
Leaf, C. F.; Brink, G. E. 1973a. Computer simulation of
snowmelt within a Colorado subalpine watershed. Res.
149