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The avalanche defence on the Trans-Canada Highway at Rogers Pass
Schaerer, P. A.
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t //q7Y
THE AVALANCHE
DEFENCE
ON TF{E
TRANS.
CANADA
HIGHWAY
AT ROGERS
PASS
BY
PETER SCHAERER
A I . J A
I . Y T E D
A R E P O R T O F A P R O J E C T C A R R I E D O U T J O I N T L Y B Y T H E D I V I S I O N O F B U I L D T N G R E S E A R C H A N D T H E D E P A R T M E N T O F P U B L I C W O R K s . C A N A D A ,/
R E P R T N T E D
F R o M
/
P R O C E E D I N G S O F T H E 2 8 T H A N N U A L M E E T I N G O F T H E
W E S T E R N S N O W C O N F E R E N C E , A P R T L 1 9 6 0 , P , 7 1 . 7 A .
T E C H N I C A L P A P E R N O . I 1 1 O F T H ED I V I S I O N O F B U I L D I N G RESEARCH
OTTAWA
D E C E M B E R 1 9 6 0
P R I C E
1-4q18
/
2 5 C E N T S
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7T
TI{E AVAI^ANCI{E
DEFENCE
ON THE m.ANS-CA}NDA
}TIGHyIAY
AT NO@RS PASS
By
Peter Schaer:eJ/
stuttARY
the lbans-Canada Highrcy is to be constructed over Rogers Fass in Glacier l,trational Park, B. C.
About tuenty-four
miles of the hlghrey which inclrdes the Pass is threatened by arralanches. In 1953
an avalanche surv€y res organized to obtain the jnfomtlon
r.equired for the desi.gn and construction
of the highmy defence uorks ard for the firture avalanche warning senrice.
Awlanches neaching the
proposed highmy route rere surweyed and recotded.
For each avalanche site a defence res chosen
according to the size and frequency of the analanche.
Sncnrsheds will
be used for protection against
the large and frequent avalanches. Earbh nounds and dans rritl be constructed at the sites of s@ller
avalanches.
No protection uas planned for those avalanches sites that threaten the hlghmy onl;r once
in every three to five years.
lhe Selkirk Range is one of the more fornidable obstacles to ground transportation
betreen British
Colunbia ard the rest of Canada. Within the Selki-rk Range is beautlful-
G.Lacier t'lational
Park, still
large\y a virgi-n vrllderness (fig.
f).
In the Fark, near the town of Glacier, is Rogers Fass. The
discovery of this Fass in 1881 by l4aJor A. B. Rogers during his surwey for the Canadlan Pacific iailrray
Conpany established
for this conpany the route over uhich the first
lailrey
llnk betvreen Eastern Canada
and the West Coast rias completed ln 1885.
the Fass never yas hospitable to the ralhay
durlng its constructlon
or later use.
ltre tr."acks
crossed nuterous paths of snow avalanches, which r€quired the constructlon of sheds w'ith a total length
of 5 nl1es.
But even the sheds could not protect the railrray lile
complete\r and eventually the
rail-rray decided to build an altemative
Ilne.
In 1916, the construction
of the 5-nlle-long
Connaught tunnel through Mt. lihcDornld ras conpleted
and the rail$ay J:ine through the Fass abandoned. For about 40 years the Fass les IefL to neture ard
the old €ihey
line feII into decay.
I^ 1956 the decision las nade to use the Fass as the route
through the Selkirks for the first
ll"ans-Canada tEghlay (Figs. 2 and 3).
Snorrfall at Rogers Pass
Glacier is one of the highest snowfall areas in Canada. the average total snowfall for the rinter
neasured over I tuenty-year period at the rest end of Fogers Pass is 342 inches.
Ihe mximun total
snowfall neasured during the winter of 1953-54 ms 680 inches.
Snowfall beg"ins usuallJrat
the end of
October ard ends at the end of Apri1.
Ther.e are no year\r recurring perlods of naxirm:n snowfall
jl-tensity.
Snowfalls have been recorded on every day il one nonth and periods of tro ueekst duration
have occurred without snowfall.
Dnring rinters
of light
snorrfall tuo storrs By occur yielding
l2
inches of snow fu a 24-hour period.
For winters of hea\ry snorrfall, eight to ten such stoms By occur.
Only occasional\r
ls there a snowfall w?rich contributes nore than 18 ilches of snow il a 2{-hour period.
Storms with a high rate of snowfall are usually of short durgtion.
In the records that have been
studied, no storm res recorded which yieJded 12 jlches of snow in a 24-hour period for nore than 3
qonsecutive days.
the mxj-nun snowfall for a Jday period r,es jrr.st under 7O inches.
It is possible that once in 25 to J0 years, a nlnter wlth very heavy snowfall could occur when
the above-nentioned snowfall amounts arne exceeded. On both ?2 atd 26 January ot I935t 35 jlches of
snow in a 2.la-hour period vere record.ed but thj.s e:<tr.ere rate has not been observed since.
the tenperature during a snowstorn nor@lfy firnges betvreen 4F
Lo 32"F. There is usualltr no
drop in teroperature irlnediately
after a snowfalJ.. Most of the snotrfalls are accompanied by souther\r
and r{esterly uj-rds with variable speed.
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I A M T S I R D O N A L DFigure 3. The sunrnit of Rog3rs Pass with the abandoned railuay grade on the right side end the clear€d right-of-uay of the highuay on the left. In the backgrourd, Mt. Roger is on the left; Mt. Tupper on the right.
Figure {. East ridge of Mt. Tupper uith avalanche paths. The highriay is located at the bottoro of the photograph. (lhotogreph: Bruno Engler)
?5
The Avalenche Sunpy
the Departrent
of hrblic
Works of Caneda is responslbLe for the design ard constnrction
of the
ltans-Canada higttmy through Glacier llational
Fark. In L953, tlre Depadrent
of Rrbllc Works began to
@ke absenatlons
on the avalanche activlty
in the nog€rs Fass area.
Slace 1957, the lbtional
BEsearch
Council of Canada through Lts Division of Building REsearch has assisted rith these observations.
After the initial
sttdies on the Rogers Pass route and the first
recorueissance work for the
highlay,
a closer suffey of the anaLanches les organized.
During the three rinters
betreen )-953 ard
1956 occasional trips were made over the Fass, ard the location and size of the ar,'alanches that had
occuned rrene recorded.
Silce 1956 obsenrations on the avalenches, snow conditS.ons, ard weather have
been mde irr the rinter
by a crew located at Glacler.
It res the responsibility
of this crew to:
(1)
Surrrey and reeord the ti-ne of occurrence a.nd the location of all the avalanches near
the proposed higtney route.
(2)
Recoumerd.
the nost econonlcal defence for each avalanche ard to locate and assist in the
deslgn of the defence stnrctures.
0)
CoILect e:<periences jn for.ecasting the a\ralanches trhich uould be of value for the future
avalanche r'erning senrice.
ltp avalanches that occurred riere suneyed on frequent tr5.ps along the proposed highr'ey route
ani the locatlon of each aralanche reaching the higlney Ule ras plotted on location plans.
the
accu-rnrlatlon area, the sllrls pa.!h, ard the terminus of sore ilportant
avalanches rpre traced on to
photo-g€phs.
In an average w-inter about 120 avalenches corre close to the future highral
and hane to be
su:nreyed ard r€corded.
the Avalanches in the Rogers Fass Area
the section of the proposed hlghmy threatened by avalanches is 24 niles long.
$re nost active
analanehos are concentrated in tuo sectionsl
(1)
Below Mt. T\rpper betueen nite lO and U (from the eastern bourdary of the Park) (Fj.g. 4).
(Z)
On a $ nj.1e sectlon Just outside the rlestem bourdary of the Park.
Avalanches reach the highray at both sections durhg ard after every si-grrlficant snorvfall and
particu-Iar\r
after snovrfalls of nore than 1O lnches acconpanied by wind. Betueen these two sections ard rest
of the second, the avalanches ane nore scattered ard reach the highr,ay under bad conlitions
only.
Dangerous avalanches can occur at these siteE after snowfalls of nore +,ban 2l+ jlches total and during
the snor'melt period.
I?rere ate two arralanche periods each year.
In the first
period between the begiruring of November
and the end of February the arralanches are rtsinly caused by snor'rfalls and wirrl, and most of the
ava-Ianches ans of dry onorr. the second avalanche period beglns u-ith the nonth of April and ends about
the niddlE of I'hy.
the avalanches during this period are caused by the snow Delt ard are of uet snow.
In the nonth of brch,
betr,cen the two periods, the avalanche activity
is general\r Iow.
Avalanche Defence
It rras recognlzed from the surrey that it noutd be impossible to obtain for the highr'ey 10O per cent
protection
from analanches uslng protective
structures.
Sheds could be built at those sites where the
path is well defired and avalanches threaten trafflc
on the average more than once errery vrinter.
At
other sites,
earth nounds, benches, and divertlng
dans could be constructed which uould impede and
ditrert the arrala^nche. Such structures do not offer complete protection norrelly
but rrill
retain nost
of the avalanches that occur and certalnly
reduce the arlount of snow r.eaching the highrray.
There are
nurerous avafanches for which, becar:se they occur ilfrequent\r
or the cost of protection neasures is
unreasonab\r high, no defence structures could be planned. Under unfavourable conditions, these
avalanches nould deposit snow on the hlghrrey.
the avalancheE were divlded into different
classes accorrling to the defence nost suitable.
Ttre
classes of analanche and the defence proposed are as follovrsr
Class 1 Avalanches. - ltris class includes the avala.nches that occur frequently and reach the highuay
one or nore tires each rrjnter.
At these sites it is proposed to protect the highley w'ith snowsheds.
Elght snousheds rrith a total length of 4500 feet have been reconoended,
ltre decision as to the t;rpe
of constnrction
ls still
to be niade. It is expected that one Ehed with a length of 30O feet rrlll be
constr:ucted in the su.m6r 195O ard the other sheds one year later.
7 6
Unfortunately, rnost of the sheds have to be built in the terrninal zone of the arralanche, wtrere the aralanche snow will accumrfate to a great depth on the shed roof. lte mxinm design load used I'as 1OOO lb,/sq. ft. for the vertical component and a 35O lb/sq. ft. for the horizontal. A lighter type of shed to be built in the path of snall-er avalanches r,as designed for a vertical load of 5O0 lb,/sq. ft. and a horizontal- load of 20O lb/sq. ft. To minj:nize the length of the shed the avalanches will be confined by earth dans. the darrs will be 20 Lo 25 feet high. In tuo of the avalanche paths it vas possible to dig trenches, 45 feet deep and I5O feet w'ide at the botton, which fonn a channel- for the arralanches. the earth exeavated from the trenches uas used for the construction of fill for the highvray (nig. i). the trenches werre cornpleted before the rrinter I959-6Ot observations during this winter have shown that the channels uere successful ln confiling the avalanches to a narrow section of the proposed highuay.
Class 2 Arralanches. this class includes the arralanches that occur frequently but where the nass of the sliding snow is slrEll and tnost ti-nes the arralanche stops before reaching the highuay. In the avalanche paths of this Class the highvay is protected by less expensive earth strrrctures, such as diverting dans and nounds.
Ttre mourds are between 15 and 25 feet high with a distance of 60 to 80 feet between centres. the size and the arrangenent of the nounds depends on the local conditions, such as norrml size of the analanches and the inclination of the arralanche path. One group of mounds uas buil-t in the sumner ]-957
(Fig. 6). Observations during the past three winters have shown that the mourds have a protective capracity of three avalanches per winter. After three avalanches had occurred the space betueen and above the mounds vas filled with arralanche snow and the defence becane ineffective. This woul-d indicate that mourds are not suitable in places where more than thrnee avalanches per winter are e:qgected.
Another forn of earth structures are benches which are built across the avalanche path. It is obvious that the bench u-ill- soon fill with snow and that only small and slow avalanches will be stopped by them. Ihe capacity of the bench can be i-mproved if a dara of snow is built on the edge of the bench. this dam, about 10 feet high, can be built by bulldozers using the snow fronr snowfalls ard avaLanches. Benches must be at least 90 feet w-ide to be effective. In rnost cases it wiII be nore econonrical if mounds are buil-t instead of benches. In Rogers Pass benches w-i1l be effective in stopping avalanches at a few sites onIy. Ttre benches now in use are either naturral or arre the abandoned raifuay grade, requiring onJ-y little improvement.
Class 3 Avalanches. this class inchdes aval-anches that occur only under sevene conditions and not rnore frequently than once in two years. the avalanches ney deposit a large anount of snow on the highuay. Because of the low frequency of these avalanches, the high cost for defence stnrctures is not justified.
The amount of snow deposited by these avalanches ley, however, create sore snor,r-clearing problens that couLd delay the opening of the highuay after the hazarri has decreased. Earth nounds wlIL be con-structed where the l-ocal conditions reke then feasible. ft is not ercpected that the rnounds will stop the avalanches conpletely, but they should retail a great part of the heavier snow sliding at the bottorn of the arralanche. the accompanying cloud of J.ight snow will not be affected by the rnounds and will probably reach the highle.y but it should not deposit much snow. In lany cases it should be pos-sibl-e to r€-open the highuay by snowplows. Ttre mounds should be effective for ground arralanches of heavy r.et snow carrying rock and ti-uiber. This type of arralanche is the nost difficult to rernove fron the highray.
Class 4 AvaLanches. I?ris class jlcLudes avalanches that occur under severe conditions only and not more frequent than once j-n two years. The snow that would reach the highlay frorn these arralanches would usually be airborne and little would be deposited on the highuay. No special protection is planned for avalanche paths of this class.
Avalanches fr.on the unprotected sites need not occur on the sane day or even in the same perlod during the wjnter. Often snow from one only uill reach the highuay during a 2{-hour period. At the unprotected sites it is estjxated that 2510@ cubic lards from six a@Ianches within tuo days would be the naxirnrn anount of snow that would have to be rernoved from the highvay. this anount my be exceeded under exLr.enely bad conditions that could occur once in 20 Lo 30 Jrears.
Other Methods of Arralanche D,efence
I'Iany arralanehes of Class I and Class 4 can be controlled by gunfire. It is not yet knom which type of r{eapon witl be used in the future. Successful- trials uere nade w'ith the 4.2-inch nortar, the 75-rm hou'itzer and the lo5-nm howitzer. ltre 105-nm recoill-ess gun, bei.ng used for the arralanche
shooting in the llnited States, is not suitable for the condltions in Aogprs Pass. the angle of elevation required to reach the high elevated targets ls too high.
7 7
Eigure 5. Dams and excavated channels for the avalanches at Mt. Tupper
+_
Figure 6. Earth mounds at the botton of an avalanche pa.th. (More mounds are to tle built on the right side.)
(Photograph: Bruno Engler) ACIOId{LEDGI{ENTS: The author vrishes to acknowledge the contribution of N. C. Gardner who organized the arralanche surwey and recorded the avalanches before 1957 and Bnrno Engler who photographed the avalanche ar.eas and the ayafanches. He also wishes to exprress his appreciation to H. R. Srigley, J. P. Priolland, E. J. Strrith, J. C. Carl-and and J. Tasko, nenbers of the avalanche survey staff of the Depart-rent of Public Works, who nade snow and avalanche observations often urder difficult and hazardous conditions. This is a contri-bution fron the Division of Building Research, National Research Council, Cenada, and is published wlth the approval of the Dirrector of the Division.
7 8
Obher methods of arralanche defence, such as supporting strrrctr:res in the accumrl-ation area, w'ild baffles, snow fences, and breaking structures of steel cabl-es r',ere studied for the different avalanche paths. A11 these structures proved to be either too ereensive or not effective. Supporting structures built in the accumulation area of the avalanches are considered the best and safest method of defence, but they were found to be nore el<pensive than sheds.
Organization of the Arralanche Wamine
Since the highuay wilL not be protected agailst all avalanches but will be closed vthen avafanches are likely to occur in unprotected arreas, an effective warnilg service is essential-. The avalanche hazard forecast, the control of trsffic and operration of the completed highmy through the National-Park lrill be the responsibility of the I'lational Farks Branch of the Departnent of Northern Affai.rs and National- Resources.
During the survey and constrrrction of the highuay, an observatory with a snow test plot ltas located at the sumrit of Rogers Pass, altitude 4350 feet. Daily snow and ueather obserwations r,vere taken there. A second obselvatory uas constrrrcted on Mt. Abbott at 6800 feet, the altitude where most of the large arralanches originate. this obserrratory vas visited about once each r,eek and the snow profile studied. Occasionally an observer slayed at the Mb. Abbott observatory during a snow storn and reported snow and ueather conditions by radio to the nai,n canp at Gfacier.
A test plot and observatory were established also at the sururit of Balu Fass, about 3 rniles I'rest of the snow pt-ot at the surunit of Rogers Pass. Ttre altitude of this site is about 69OO feet. Ttre access to this site llas not aluays safe and so obsenrations r.,ere not made as frequently as at the other sites. In the faII of I959t special wind telemetering equipnent developed by the Division of Radio and Electrical Engineering of the I'lational Research Council vas install-ed at the Balu Pass obserrratoly. Infosrnation on w'ind speed and direction is ttansndtted by radio to the base camp at Glacier. Sone difficulties were encountered in the use of this equipment during the first winter of field trials but these have been largely overcore.
During the past four winters, contirruing obserwations have been nade at the test plots and obser-vatories and using the nethods practi-ced by the U. S. Forest Service, Swiss A\,'alanche Ser'rice and others, the avalanche hazard uas forecasted as if the highvay uere in operation. The inforrF.tion collecied ard experience gained during the past four years will be made available to the Department responsible for the avalanche prediction and traffic control of the future hightay.
Avalanche I€zard Forecasting
The studies on the conditions contributing to the avalanche hazard showed that the aval-anches l',el€ caused by the sane factors as have been obserwed elsewhere, for e>ample Switzerland. The studies show the following facts:
(1) A snowfall of more than ]O inches of new snow creates a moderate avalanche hazard and avalanches na)r occur at areas now protected by snowsheds or other defence structures. A contisuous sntwfaU of lO lnches or more w'ith little or no wirtd nay cause large avalanches in unprotected areas. r,{ith strong winds large avalanches occur before this ancunt of new snow is deposited. the density of the new snow has a najor ilfluence. the average density of the new snow is 0.082. New snow w'ith a density l-ower than O.0? is more like1y to cause avalanching.
(2) the wjld his an important influence on the build-up of the avalanche hazard for most of the avalanche pths. T?re direction of the prevailing wind deterrnines whether certain ava-lanches will occur. The r+ind cr€ates local- snow accunrlations on the 1ee side of mountain ridges. the [vlindslabrt comnon in the United States avalanche areas uas obserwed on\r occasionallv.
0) the temperalure has to be observed during and after a snowfall- and during the snow neltfug period. It vras found that avalanches occur during the snow nelting period on the first or second day with a nean daily ternperature of 32"F and above. Before any such avalanche occurs, houever, the tenperature between the grourd and the surface of the snow must have n e a c h e d ? 2 " F .
(4) The snowfalls are uel1 distributed over the winter and the re1-atively high tenperatures create a stable snow cover on the ground. Not reny unstable layers w"ith netanorphized crystals coul-d be observed. In the w-jlter nonths an avalanche caused by the fracture of an internal unstable snowlayer is rarely obserwed. It is only in spring that big avalanches start to slide on internal unstable layers.
