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TIMBER FALLS AVALANCHE
vAlL, C0L0RAD0
REPORT PREPARED
FOR
TIHBER FALLS CORPORATION
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CONTENTS
TEXT:
Loca t i on
Area Description
Timber Falls Avalanche
T1 East Ridge
T2 Aspen Sl ide
T3 East Side
T4 Upper lJest Fork
T5 Lower lJest Fork
T5, Main Chute
Analysis of Slides
D iscusS ion
Concl us i ons and Recommendations
FIGURES AND PHOTOS:
Figure | - Gore Creek Avalanche Zone
Figure 2 - Timber Falls Slide
Figure J - Timb.r' Fal ls Subdivision
Figure 4 - Maximum Snow DePth
Photo I - Gore Creck Avalanches
Photo 2 - Timber Falls Avalanche
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MEMORANDUH I
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IT0: Tfimber Falls Corporation t
. Vail, Colorado
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IFR0M: UJtr i tney M, Bor l and
SUBJECT: Avalanche hazard to Timber Falls Subdivision
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ILOCATI0N:
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IThe Timber lFalls Subdivision is located about five miles east oVail, Colorado, south of Interstate 70, and south of Gore Creek
which flows along the highway at this point. The south side of
subdivision extends to the toe of the mountain side and is defi
by the White River National Forest boundary, lt is just south
center of Section 12, f.5 S., R.B0 W.
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f
the
ned
of the
AREA DESCRIPTION:
Gore Creek from Vail, Colorado, upstream to its confluence with Black
Gore Creek some 6 miles east, flows in a glaciated ItU" shaped valley.
The south side of the val ley rising over 2000 feet has been carved
out of nearly horizontal strata of sedimentary rock of I imestone and
sandstone, and is very steep with slopes up to 38o and with l0 to 40
feet vertical cl iffs occurring at some points. The outcrop of re.
sistant sandstone strata forms small falls in the creeks and shelves
on the mountain side. One such shelf is very noticeable in the study
area. The north side of the valley is not nearly as steep and shows
more sculpturing by erosion since the ice age.
The valley itself is not overly wide, never being over 1500 feet
and must allow passage of both Interstate 70 and the creek, together
with rapid development of the valley floor for recreat ion purposes.
The south val ley wall accumulates a sizable blanket of snow during
the winter months as tt does not receive the direct rays of the sun'
In the late spring snow melt water have eroded the steep slopes forming
numerous steep creeks which are mostly dry in the late summer and
fall. These creeks,rhave formed extens ive alIuvial fans on the valley
floor. Due to the steepness of the valley wall mud slides have occurred
on the larger drainage ways and rock.falls have and can occur. Snow
avalanche fol lows the drainages and spills out onto the valley floor
across the alluvial fans. Figure I shows the drainage ways and names
the snow slides fol lowing these waterways.
P.z
TIMBER FALLS AVALANCHE:
The Timber Falls Avalanche is' composedrof two minor slides that in
the past 100 years have not reached the valley floor but stopped on
a shelf some 400 feet in elevation above the val ley floor. The major
slide consists of three branches of which two are welI defined fol low-
ing watercourses which drain the weltern portion of a bowel-shaped
area. The other branch is not so well defined having no watercourse
to follow and is covered with young aspen trees. These Various slide
paths making up the Timber Fall Avalanche have been given a symbol.
irTrr rith a iubscript indicating the particular path. (See Photo l)
Tl EAST RIDGE:
From the val ley floor this slide path looks like a ridge, bare of
trees but it is a slide path with a very minor drainage way. running
along its eastern edge. A rock ou.tcrop (Et,g6OO) about two-th irds
the way up seems to be the trigger for the slide and because of the
steep mountain side (32') an area above the rock has slid in the
Dast. Tr slid last season because snow was present r.rh en inspected
?Jun" zoi lg73l , and 8 to l0 small Engleman spruce trees (3 to B
feet tall) still green were noted. In all probabil ity this was a
wet slide occurring in May. There was very Iittle other older debris
at the end of the path. The shelf where the slide has stopped is
nrrile wide being about 1000 feet with slopes varving from l8o to 25o'
To the east the shelf steepens and to the west it extends as far as
the end of Tc slide but then narrows to the west of the main Timber-
line Slide Cfiute T6. The lower slope of T1 slide contains no trees
but the upper part has some scattered aspen and smal l,spruce' The
width of the path is about 200 feet. Figure 2 taken from 1952 aerial
photos of the Forest Service shows the sl ide paths. Analysis indi-
cates the small waterway cannot carry the volume of snow from a 100
year maximum snow depth but rather the snow would move on a wide front
covering the full width of the path. The scattered timber below the
lower edge of the shelf suggests wet slides have occurred or there was
some spill ouur from soft iiab avalanches. With a large soft slab
slide the shelf would not stop it and it would carry to the valley
floor probably tearing out much of the timber. Table I gives char-
actistics of this sl ide and results of the analysis. The runout
distance from the toe of the mountain was found to be 220 feet for
the probable avalanche associated with a maximum snow dePth (ll0
inches) on the ground having a frequency of once in a-1O0-years'
Figure 3 shows ihe are" covered by the runout f rorn this slide'
p.3
T2 ASPEN SL I DE:
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The. extent of this slide path is difficult to define. At the upper
end it borders T1 slide and is separated from T1 by an island of mature
Engleman spruce. Further down the slope a slight rise in ground level
forms the divide and then a wedge of Engleman spruce, of which some are
12 inches or more in diameter divide T1 and T2. Where it borders on
T3 Lo the west, the division has to be assumed gulded by the fact that
on the shelf below there is a rise in ground plus some large trees
which definitely divide it from T6, slide and its chute. The lower 800
feet of the slide on the shelf contains no trees while the upper slope
supports a growth of aspens I to 3 inches in diameter bel ieved to be
15 to 20 years old.
Like T1 in recent times sl ides' have always stopped on the shelf at
the end of the path. There is a moderate amount of debris pushed into
a grove of large aspens which are scarred and deformed. A smal I ditch
on the east side contained a little water but was not sufficiently
large to channel ize the slide so apparent snow movement is usually
across the fuil width of the path.
Slopes are extremely steep at the upper end being 35', however, the
start of the slide is some 400 feet below the top of the mountain. The
slope above the starting zone is slightly less being about 30o and
supports a heavy qrowth of mature Engleman spruce. The she'l f is narrower
for T2 than T1 with a slope of l8o, but according to analysis will not
stop a very large soft slab avalanche and it was necessary to assume it
spilled over the shelf and down a steep slope of 34' onto the val ley
floor. Similar to T1 the stand of Engleman spruce below the shelf is
sparse, however, there is a very heavy stand between T2 and the major
chute of T5. lt would appear that some large sl ides may have spilled
over the edge of the shelf and ran more-or-less through the trees reach-
ing the valley floor.
The average width of the path is slightly greater than 300 feet with a
length of ISOO feet and contains an area of 1"2,75 acres. An analysis
using the 100 year maximum show depths on the ground of ll0 inches
resulted in a runout distance frorn the toe of the morrntain of 310 feet.
Pertinent data for this sl ide is qiven in Table l.
i nd icated in the
path is not well
T3 EAST SLIDE:
As prev ious I y
of this sl ide
discussion of T2
defined. lt spil
sl ide the definitionls its snow load along
.l'
p. 4
its lower edge into the main chute of Timber Fall Slide and becomes apart of the main chute on the. shelf. A growth of aspen and smal I
Engleman spruce completely covers the path and suggests it is not in-
volved in every slide that runs down the main chute. Because of the tree
cover and the different aspects of its slopes it probably does not
run at the same time as T4 and T5 which have fewer trees and have
narrow chute-l ike paths. Certainly in the case of a large avalanche
cycle T3 would not unload all of its snow cover like T4 and T5.
T3 covers a large area of l2,l acres, part of which is cons idered
to contain the upper part of the main chute from the junction of T4to the shelf. Above its junction with T4 it has a steep slope of 34"but in the past has not extended to the top of the mounta in with slides
starting some 350 feet in elevation below the start of T4, lt islikely that this slide is triggered by T4 slide running and under-
cutting the toe of T3 causing it to follow T4 slide down the main chute.
O T4 WEST UPPER FORK
The large cliff-like rock rnarking the beginning of this slide path is
visible from the valley floor and snow falling from this rock likely
triggers it. (See Photo 2.) From the rock to the valley floor thereis a continuous avalanche part of 4200 feet with a bend where T3 be-
gins to join it at an elevation of about 9500. The path of T4 is de-finitely outl ined by the growth of mature Engl eman spruce and is some-
what wider at its top end probably due to the influence of the large
rock outcrop, The path fol lows a watercourse which is not as wel I de-
fined nor as large as the one that T5 follows, and for the analysis
the effect of the watercourse was not cons idered assurning that snow
movement was across the ful I width of the path.
The general slope of T4 is 3lo but seems to be less steep below the
top and beneath the rock there. lt flattens out at its lower end
havlng a small waterfall just before Tq joins the main chute. The
length of the path is 2000 feet measur6d from the rock to its junction
with T1 and it has a total fall of 1200 feet. lt i,as an arba of 8.4
acres 6eing the smal lest of the paths making up this system of slides.
However, in comparing it to T5 which has a scattered growth of trees
and shows the influence of tfre rock outcrop its path is smoother and
probably is used more often.
At Cross Section X2 on the main chute below the junction of T{ and T5
p.5
the waterway channel is 22 feet wide at the bottom with I to I
sloping banks and about 12 feet deep. There is brush growing on
both banks with some small spruce on the west bank. A channel of
thi.s size can well accommodate a fairly large avalanche.
T5 WEST LOWER F0RK:
This path starts at a ridge which runs out to the north from the
large rock at the head of T4 Slide (pfroto Z). lt follows a well de-
fined waterway which runs on bedrock for a good part of its course-
The extent of the path is fairly well defined by tree growth. At
least four cliff-like rock outcrops cross the path breaking up the
general slope. Scattered trees both spruce and aspen occur throughout
the slide area. The middle portion of the path is wider apparently
because of three rock outcrops. The average width is about 200 feet
and maximum width nearly 350 feet. The path length is 2700r with
a fall of i250' giving an overall slope of 26'. However, due to the
flatter slopes at the beginning and end a slope of 32' was used as
being more representative. Further this slope was deterrnined at Cross
Section X1. ilere the chute was along the east side of the path with
spruce gr5wing on the east bank and brush with some rock outcropping
on the west bank. The bottom of the channel was only 7 feet wide and
the banks had a slope of 1.5 to l.
T6 MAIN CHUTE:
The main chute (see Photo 2) extends from just above the junction of T4
and Tn where a prominent rock outcrop forms a smal I cliff to the valley
floor'following a well defined rrratercourse. There are three bends
in the alignment, one below the junction of T4 and T5 which is at
the beginnlng of the shelf, the iecond one at the end of the shelf and
the third occurs first above the alluvial fan begins and after the
lower rock outcrop. The last bend is a part of the outcrop and likely
is an extension of it. lt is this bend covered by a steep solid bank
that guides the slide into the valley floor turning it to the east to-
wards a rise in ground surface that may have been part of a glacier
moraine (see Fig. 3). The alluvial fan beginning at the end of the
bend is very steep (Slope =.15') and the western portiofl is covered
with brush ihrough which th6 runoff from the chute flows down to Gore
C reek.
p. 5
The four smal I waterfal ls below the shelf make for a very rough pathfor either water or moving snow. They will retain much inow Fror unyslide. The slope was found tb be 30o from the last outcrop to thelower edge of the shelf at the upper waterfall. 0n the shelf the slopeat cross section x4 was measured to be 27* upstream and 21" downstream.
The G,S, Contour map showed the chute to have a slope of 20. acrossthe shelf. Cross Section XL at the narrowest portion of the chutelocated on the shelf shows i bottom width of lb feet with a depth of
30 feet and bank slopes of nearly 1.5 to l. Further down below thefirst rock outcrop Cross Section Xq shows a bottom width of 2e feetwith 1.5 to I sloping bank and a d6pth of J0 feet. Cross Secrion Xg
about one-half the way down from the shelf shows a channel 26 feet
wide with bank slopes steeper than l* to l. At all cross sections the
channel was full of brush and quite irregular also. The ground rises
from the top of the bank to the edge of the sl ide path on a slope of
about 4 to lwhich adds more cross sectional areas to the chute tocarry an avalanche wi thout spilling snow out into the adjacent tree
covered s I opes.
ANALYS IS OF SL I DES:
A report by A. Voellmy on the rrDestructive Force of Avalanche't pub-
lished in 1955 and translated into Engl ish 1964 contained mathematical
formula and suggested coeffic!ent so that the speed, fcrce, end runout
distance for avalanches can be computed provided slope, snow depth,
avalanche path size, shape and roughness are known together with the
type of avalanche expected and certain snow characteristics.
To begin an analysis, a snow depth must be assumed. This was done by
using records from the nearby avalanche station started in 1953
by the writer and using the snow course records from the Vail Pass
Station surveyed at the end of eabh winter month by the Soil Conser-
vation Service (see Figure 4). By taking into account the elevationof the stations and extending the line on logarithmic paper it is
found that the maximum snow depth on the ground that would occur in a
100 year period is ll0 inches and willoccur the last of March orfirst of April. The:nean elevation of the slide path is about 10,000
feet, however, snow:depth increase from Vail Pass Station upon going
west, perhaps due to.. greater orthographic effect of the mountains upon
storms moving in from the wegt.
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p.7
Winds with veloci ty above l2 mph transport snow and their direction
together with the aspect of the avalanche catchment area, will result
in an uneven snow depth distribution oter the slide path' However
the assumption is made that the depth is uniform over the catchment
area. The size and shape of the paths and catchment area is determined
from aerial photos enlarged and traced on to a map of suitable scale
(see Photo I E FiS. 2). Path areas are planimetered to obtain areas
which are given in Tables I E 2.
The avalanche slopes are determined from contour maps and a profile
fol lowing the main course of the slide down its path is drawn from
which the slope for any portion of its path can be scaled. Also
slopes were measured by an Abney hand level in the f ield. For a study
of this type the U.S.G.S. quadrangle map should have closer contour
interval s and smal ler scale ratios.
Past experience in the high alpine zone in Colorado has indi.cated
that all of the larger more dangerous slides are from slab avalanche.
Further at Vail at these moderate elevations they have been of the
soft slab type. While airborne avalanches do occur in Colorado they
are associated with larger slides and those moving on a wider front
than those under study. The assumption is made that the largest
slides occurring in a 1OO-year period will be a ground avalanche
starting from soft slab snow in the catchment area.
To determine the runout distance it is first necessary to determine
Lhe avalanche velocity when it reaches the toe of the mountain where
the runout begins. Factors determining this velocity are snow depth,
slope angle, sl iding surface, roughness and internal shear within
the snow mass. Both surface roughness and internal shear are diffi-
cult to evaluate but the internal shear has the most influence and haS
received less attention by experts. However Voel Inry and others have
given guides for selection of proper coefficients for surface roughness
ind iniernal shear which have resul ted in computed velocities that
corresponded to those observed in avalanches in Europe under conditions
similar to those at Vail.
FOr a sl ide having no chute or large enough watercourse to concentrate
the moving snow a.unrt wide strip is assumed exten,jing from the start
of the slide to the end of the runout. Tl, f2, T3 and T4 are such
slides and the computed velocities and unit discharge can be found In
Tables I E 2 for the upper 5lope, the shelf, and at the toe of the
mountain where the runout begins.
when using a unit width and a change in slope occurs both snow depth
and veloci ty changes as a function of the cosine of the two slope angles.
These changes are noted in the referenced tables. Note for a unit width
snow dischirge (q) tit given in cubic yards per second per linear yard'
p.8
t/here the snow concentrates in a watercourse or chute an adjustment
must be made in the procedure. A cross section of the chute is
required and the snow depth is replaced by the hydraulic radius which
is the area of the cross section at a given depth divided by the wetted
perimeter. Total discharge is computed as the product of area and
velocity. The computation is very similar to computing the hydraul ics
of open flow channels and requi res arrcut and try procedure or the
use of curves. The velocities, snow depth in the chute, and total
discharge are s hown for those sl idepaths having a sizable chute in
Table 2.
The runout distance is primarily a function of the slide velocity
and the slope of the runout together with the internal shear. Again
the internal shear is very important as shown in the fol lowing table
where the critical angle at which the avalanche for practical purPoses
will not stop is computed in terms of internal shear.
Interna I Shear Met r ic
units (Kelm3)
Avalanche will not stop
if angle is greater than:o 5.7"
7. l'
8. 5"
9.8'll.l'
I {. U-
16. 1"
. 100
.125
. 150
.175
.200
.25n
.300
The runout is also sonewhat influenced by the sl iding
and the daming effect or height the snow will rise as
The latter term is a function of the initial velocity.
give runout distances for the various sl ides.
I
surface roughness
it slows down.
Table | 6 2
slope where the avalanche broke through
ZQZ of the snow would remain on the
Where soft slab avalanches start on a smooth slope they usually break
above the ground and leave some snow in place at the top of the slide.
Farther down due to the accumulation of snow and weight they usually
remove all snow to the ground. lf there is a growth of brush or asPen
the amount of snow left is greater- For the upper pert of 'T2 Aspen
slide down to the upper edge of the shelf the assunption was made that
25% of the ll0 inch depth would remain' 0n the shelf all of the ll0
inches of snow was assumed to move. This same assumptioh of the aspen
growth holding back 25% of ihe snow was made for T3 East Side Slide'
For T1 East Ridge on the lower
the trees it was assumed that
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p. 9
slope and on the shelf not being involved in the runout. The shelf
had many pockets which would hold back. snow. For T2 such an assumption
was not made. Where the slid'e had to irove through 6rush or aspen the
roughness coefficient was decreased from 500 to 400, and where theslide moved through mature trees it was further decreased to 300.For the main chute where cross sections were requi red a roughnesscoefficient of 400 was used being reduced from the standard coefficientof 500 because of brush and ledge rock. One exception was eross
Section Xq where a coefficient of 300 was used because of the four
waterfal l6 above it and the extreme rough nature of the chute.
For the main chute with three slides feeding into it these d ifferent
assumpt ions were made: First cons idered that only T4 and T5 movedin such a manner as to cffiii-e their peak volume in dhe mai6 chute,
thus assuming that T{ ran later or not at all. Second the assumption
b/as that the three slides ran in such a manner thaT-Il-ei r peak flows
would be combined but that 20% of their vol ume was lost or deposi Led
along the main chute before they reach the runout. Third the assumptinn
was the same as the second except no snow was lost i;-tIE chute.
Because the slope of the ground was so important in computing the run-out distance, profiles of the runout area were made from the site
Layout l4aps for Timber Falls Subdivision which has a contour intervalof 2 feet and a scale of I inch = 50 feet. This map gives much moredetail than the U.S.G.S. Vail East Quadrangle, which has contour intervalsof 40 feet:nd a scale of | lnch = 2000 feet.
For the main chute, because of the steep upper portion of the runo*ut,
and using Cross Section X7 (see Fig. 3) just below the last waterfal ls,
runout distances were excess ive (Table 2). lt seemed proper to move
down to where the l5o slope flattened out which was at contour 8540.
The avalanche would spread out on the alluvial fan after leaving Cross
Section X7 and an effective width at contour 8540 of 300 feet was
assumed with the velocity in the center of the cross section being l*
times the average velocity. Using these assumptions the runout distance
was found to be from 346 to J28 feet measured from contour 8540, depending
upon which of the three assumptions were used as to volume of snow in
the slide, These runout distances place the edge of the slide runout
about l30t closer to the toe of the mountain than the computations
using Cross Section.-X7. (Note runout distance is measured from cross
section where velociti is determined.)
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D I SCUSS ION:
To make a study of this type many assuolptions have to be made before
it is possible to draw a line on Fig. 3 to indicate the extent of
runout from avalanches that have an indicated frequency of happening
once in a hundred years, The various assumptions were given in the
preceding section on analysis. The maximum depth of snow on the
ground of Il0 inches for a 100 year period is perhaps one of most
accurate figures. 0f more concern is its deposition on the sl ide
catchment areas as effected by wind deposition, Even with the snow-
fall that would occur once in a 100 years it is likely some of the
slides might be triggered one or more times before the maximum deposit
was reached, and would be less violent than assumed in the study. How-
ever to be practical some type of snow loading and reactions must be
assumed.
The values used of coefficients of internal shear and surface rough-
ness are open to criticism but have given realistic results when
appl ied with experience and judgment.
The avalanches of Gore Creek, Fig. l, do not have an accurate record
of sufficient length to determine a meaningful frequency for them.
Nick Kiahtipes, a rancher, has been in the valley for many years and
reported that during the active avalanche cycle of 1950-51 season'
the Racquet Club slide came to the valley f loor and some avalanches
ran as far as the creek. Since 1952 when Vail came into existence
there have been no major si icies ai though in the season oi i967-68 Timber
Falls (T6) ran and deposited some debris high up on the alluvial {an..(Estimated to be about at contour 5840.) lt is extremely important that
an accurate record be kept of these slides, especial ly is this true as
some structures are being placed very close, if not within the runout
areas of some of the other avalanches. Along with these observations
the wet slides, sluffs and snow deposition in the catchment should be
observed.
There are many physical features that cannot be translated into mathe-
matical equations. Notable is the mature Engleman spruce on the lower
slopes of T1 and T2, Also the natural pockets that occur at the toe of
the mountain to the west of T1 and the pocket Iike depress ions on the
shelf of T1. AlI these are negative and would reditce the runout dis-
tance. There are probably some positive factors btrt I do not know of
them.
This study has made use of the latest maps and
date procedures to predict an avalanche runout
physical on-site measurements and slopes and di
good aerial photos and reliable maps.
used t ire most up-to-
area. lt is based on
stances obta i ned from
o
p. ll
Having made an estimate of the runout area the question arises - is
there anything that can be done to decrease its extent or alter its
shape so as to develop the prpperty that it may embrace? The Swiss
have developed structures to shorten the runout distance and structuresto divert the avalanche runout to a different area. The Canadians
have also used structures in the runout zone to protect the National
Transcontinental Highway through Glacier Park. A few years ago
Hans Fruitiger spent a year with the Forest Serv jce advising them and
the Colorado State Highway Department on avalanche problems and has
continued to work with structural designs to protect property and to
stabil ize the avalanche catchment area. The latter is a very costlyprocedure, lt is possible that the runout areas shown which are con-
sidered unsafe for permanent dwel lings or use during the winter andearly spring could be decreased in size or their shape change so that
some of the area could be used for dwell ing units. You may wish to
investigate thi s possibility.
In recent years the wet slides that occur late in the season have been
observed along the toe of the mountain. Chan Welin at Vail has a
record of these. During the past season just west of Clubhouse a wet
slide had a width of 100 feet and a runout length of nearly 150 feet.
Because of this hazard and that of rock fall cons ideration should be
given to leaving a belt-like zone 150 feet wide along the toe of the
mountain free of permanent dwel I ings, There are some Iocations wherethis zone is not needed where mature spruce are especially thick and
there are no cliffs with loose rock above.
The forest cover of the mounta in side anchors the snow to the steqpslopes. lf it deteriorates or is removed avalanches will increase in
number, size and frequency. Every effort should be made to maintain
the forest and vegetat ive cover, and if possible, to improve it.
Either fire or insect infestation can produce changed conditions and
cause new and more violent slides.
CONCLUSIONS AND RECOMMENDATIONS:
(l) The area shown on Figure 3 indicating the estlnated extent of
avalanche runout that can occur with a max imur':" snowfal I with a
100 year frequency should be kept free of perrnanent dwel lings and
should be considered unsafe for occupancy during the period of
December to mid-April.
(2) There is the possibility of using structures to decrease the
avalanche runout area or to change the shape of it
the avalanche in the runout zone.
(3) The whole avalanche area should be watched for theof new chutes or changes in the ones now active.
o$\;rh.,rCr,.RA${s\.
Wh i tney )1. Bor I and
P.E. No. 3300 Colorado
July 27, 1973
by
p. l2
diverting
deve I opmen t
(4) The forest cover including vegetative cover of chutes and slide r.
paths should be preserved and improved if feasible.
(5) A record should be kept of avalanche activity, extreme snow depth,
and high wind causing deposition in the catchment areas. Thereis no substitute for basic observations and experience.
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,TIMBER FALLS AVALANCHE
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TABI&1
TI MEER .FALLS !'ALANCHE
SUMMARY OF ANALYSIS FOR T. AND T^ SLIDEStz
I
VELOCITY.
MPr-.1
UNIT DISCHARGE
q
N/sEc/YD
RUNOUT DISTANCE
FT. .qI TNtr PATH
East RIoce T,:___-__--J-
UPPER SL0PE
Snrur
TOTAL FOR SLIDE
LowER Sr-ope
RuNout
aqptrNr q.l T ntr T .
UPPER SLOPE
SnElr
TOTAL FOR SLIDE
LowER Sr-opE
RUNOUT
AREA
A
ACRES
6.82
3.44
1O.26
8.97
3.78
12.75
SLOPE
Ntr/:DtrtrC
200
AVE.
l'llIDTH
b FT.
191
200
t94
300
308
LENGTH
' 750
' 2300
1250
1800
SNOv,l
DEPTH
h FT.
9.15
9.74
10.56
54.40
47.87
42.73
4.2.9
'42.9
38.25*x
4A.77
36.91
36.91
97.O4
,90,79
87.55
31"
. 30
3o
1.0. 9
'10.9
9.3s
A. a^+
iJ.5v
c, . c:,
91.4'
9'I .4.
7.O.72**
65. 25'r'
<a 7?
55.49
59.72
t)5.lc
63. 15
2s7.
zno**
usE 220
309
usE 3i0
50
26"
lg"
z6
5.+
5.50
-l
t-m
.
* 25% REDUCTION FOR ASPEN.
** 20% REDUCTION FOR DEPOSITION TREES & ON SHELF.
SLIDE PATH
AREA
A
ACRES
SLOPE
DEGREES
TrrqBER oot'iIuiro*r*
SUMMARY or RrunIyW T3, T4, T5 & T6
AVE.
hIiDTH
b
Ft
SN0f,/ DEPTH
LENGTH ON SLOPE IN CHUTE VELOCITYL h .H VFT FT FT MPH
DISCHARGE RIJNOUT--UN-IT-----FiAI- DISTANcEqQS
cy/sec/yd cylsec FT
T3 SLIDE PATH 12.73
Ta SLIDE PATH 8. 37
cross section X2
T5 SLIDE PATH
cross section X3
To MAIN CHUTE 5.4s
?
'FShel f
cross section X4ll rr vr,. '' x6, , X6ll rr Y-r'\I.,nx7
l r y-
I
RUNOUT USING X7.ir tt x7r || v-l\l
coNTouR 8540
34"292 i900
decreased
by 25%
3l " lB2
12.17 32"196
f . i5
6. 89
9.15
50.44
43.76
47 .7?
55.03
48. 65
57.9
90.0
58. 76
85.'14
86.80
4780
4321
9070
4750
'4750
b00
27A0 9.15
3l .2
28.6
4UO
2A2
1 150
70020.
23'
20"
30'
30"l5'l5'.l5"
i0'l0'l0:
t.o-
7.6"
1 F,o
25.75
29.52
34.18
13850
9070*
9070*
9070*
I I I20**
9070*
I I 120**
'13850
9070 *
lll20 **
13850
9070**
I I
.l20**
13850
568
613
666
246
285
328
SJO use
40.6
J9.t
?04
JO. v
4t .0
33.5
36.9
41 .0
53.7
5t .5
54. I
56.4
40.0
4t .5
43.4
40.0
4t .6
43.4
32.0
34.5
36.9
-{
rFI
t$
rJt
* from T4 & T5 on1y.
T4, & T5 with 20% deposited on shelf & c'liffs.
c0J eonc
I
i
I
I
I
I
I
I
I
I
I
r-'1L-JoFFrcg
CRF4
aqo
II
E
A
LEGEND
AVALANOHE PATHS.
LOT NUM BER
TRACT LETTER
o{60
ga rO
18o
1-\,2
xzl cnoss sEcrroN
"t""
)
\---?-
8500
go
"""""5no -
g55o - .
":::"
I WET SLIDE AND ROCK FALL
zoNE r50 FT. ltrtDE.
__\*
-r- | |--== | lr'-- j__ ^i---'ltl\=i:::t___t_
-'.- ,-... - -1--_\oc'o
j
T
Tl
-.III
I
T2
TIMBER FALLS CORPORATION
gIGHORN AREA
TIMBER FALLS
vArL I coLoRADO.
SUBD IVI S TON
AVALANCHE STU DY
W.M. Borlond
P.E. NO, taOO COLO.
July lt, 1973
JAY UDDEI oeNrg=
trl p H.3j
>':___f
--/l-l-----:<r 'L
\__---.---_.Io
/;
-\SLOPE, PLUS
R3
SHELF. SLOPE
18 " TO 25"
PLUS 3oO
ROCx
300
L
s
/
Re I
Rr
ON
TI
AVALANCHE
I ta rqoo rloo
rct Lr r FEat. 1.. 600'
W. M. Borlond.
P. €. NO, :'tOO COLO.
'l'--- ---t'-._ rl ^ I iJrri Rr EcrE i A ltri
MBER FALLS CORPORATION
BTGHoRN AREA VAtLr COLORAOO
ST U D Y
TIMBER FALLS SLTDE
July 2, 1973