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Planning avalanche defence works for the Trans-Canada Highway at Rogers Pass, B.C. Schaerer, P. A.

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Engineering Journal, 45, 3, pp. 31-38, 1962-05-01

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OGERS PASS, B. C. 11113III 1809002IIIII 11 I~~!~IIII 095 IIII~IIII 2 IIIIII This is a joint paper of @he Departmenst of Public Works and the National Research Council.

REPRINTED FROM THE ENGINEERING JOURNAL, VOL. 45, NO. 3, MARCH 1962, P.P. 31-38

RESEARCH PAPER NO. 152 OF THE DIVISION OF BUILDING RESEARCH

PRICE 25 CENTS OTTAWA NRC 6732 MAY 1962

% -- This publication is being distributed by the Division of Building Re- search of the National Research Council. It should not be reproduced in whole or in part, without permission of the original publisher. The Division would be glad to be of assistance in obtaining such permission. Publications of the Division of Building Research may be obtained by mail- ing the appropriate remittance, (a Bank, Express, or Post Ofice Money Order or a cheque made payable at par in Ottawa, to the Receiver General of Canada, credit National Research Council) to the National Research Council, Ottawa. Stamps are not acceptable. A coupon system has been introduced to make payments for publications relatively simple. Coupons are available in denominations of 5, 25 and 50 cents, and may be obtained by making a remittance as indicated above. These coupons may be used for the purchase of all National Research Council publica- tions including specifications of the Canadian Government Specifications Board.

sion of Building Research, National Research Council, Ottawa, Canada.

4 VALANCHE DEFENCE For The Trans-Canada Highway T ROGERS PASS, B.C.

P. A. Schaerer Former Research Officer, Snow and Ice Section, Division of Building Research, Niltion01 Research Coc~ncil,Ottawa

SELKIRK Mountain range in for the first railway link between of Canada, which is responsible for e interior of British Columbia Eastern Canada and the Pacific Coast. the construction of the Trans-Canlada ne of the major obstacles to be It was in use from 1885 until 1916 Highway through Glacier National the Trans-Canada High- when the Connaught tunnel was built Park, began reconnaissance work f way. Various routes through this and the railway line (through the Pass the highway and organized a prel range have been investigated; that was albandoned. inary survey of avalanche sites an through Rogers Pass was se1ected.l It was known that lavalanches avalanche activity. These avalanch The pass lies 'between the towns of would be one of the major problems observations were under rhe directio Golden and Revelstoke in Glacier for any road built through the Sel- of N. C. Gardner. In 1956 an ava- National Park and was chosen by the kirk range (Fig. l). Accordingly, in lanche observation station was estab- Canadian Pacific Railway as rhe route 1953 the Department of Public Works lished to carry out the more detailed search, co-operated in thc organizn- tion of the avalanche observ:~tion st'?- tion. Bet\\reen 1957 '1ncl 1960 thc a:ithor was in chargc of this st~t~on and was responsible lor p1.1nning the aval~lnche defence. This pqcr tl:,- scribes in brief rhe obscrvatlo~ls\vhich were m,lde 2nd summ'lrucs the dc- fence \vhlch was chosen.

Terrain The summit of Rogers Pass is 4,300 ft. above se,a level, and t!::. pealts of the Selkirk range risc to 11,000 St. Tlic vallcys ;~ssocinteil\\lii-i~ the Pass are short and comparative-I? steep on the east side, but risc Lo the summit with a g~lilclual climb from Figure 2: Bear Creelc valley on the east side of Rogers Pass. Part of the highway the west. A typical Selkirk valley is can be seen in the left foreground. narrow ancl has steep sides (Figs. 2, 3). The mount~~insides on the Rogers PASSroute have a terrace located be- the river \\dlich flows through the snowfall is usually f0110~r:clby one or tween 5,500 and 6,500 ft. labove sea valley. The lower mountain sides and several d~yswit11 only light snowfall. level (Figs. 4, 5). The terrace goes valle!is are covered with heavy timber During winters of light snowfall three ' gradually over into the scree slopes and clei~sebrush. Trees become scat- storms may occur yielding more than and rockfaces which rise to the moun- terecl on the terrace, leaving space for 16 in. of snow in a three-day period, tdin ridges. Below the tcrrace a sharp alpine meaclows. but during winters of heavy snowfall clrop over cliffs lcacls to talus slopes 10 such sto~msmay occur. Only occa- ancl alluvial fans into the valley bot- Climate sionally, labout once in fhree years, tom \vhich is between 300 ancl 1,000 is there a silowstorm that contributes Rogeis Pass is in thc region popu- more than 36 in. in a three-day peri- Et. wicle. In some plaees the mountain larly kno\vn as the interior wet belt sides are close together, resulting in a od. Most s~lowfallsare accompanied of British Columbia.' High annual by wind which deposits large amounts narrow V-shapecl valley. The highway ~recipitationand heavy snowfall are is cut into the talus slopes and alluvi- of snow on the lee side of the moun- its most distinctive features. The aver- tain ridges. The mlaximum depth of al fans, ancl except tor two short sec- age annual precipitation, measured be- tions is located on the north sicle of snow on the ground in the valley is tween 1921 and 1950, at Glacier close about 100 in., and on the mountain, to the summit of Rogers Pass, is 18 at the 6,700-ft. level, the greatest in. of rain ancl 342 in. of snow, while measured depth of 160 in. was ob- the maximum annual snowfall ever served on May 1, 1959. Figure 3: Illecillewaet valley on the west observed \\.as 680 in., measured dur- Temperature during a snowstorm nor- side of Rogers Pass. The avalanclle sites ing thc winter 1953-54. The magni- mally i>anges bet\veen 20 and 32°F. are the open paths on both sides of the tude ancl frequency of the 24-hour valley. After the storm has ended, it is usual sno\vfalls at Glacier cluring the win- for cloudy weather to continue and ters bet\veen 1953 ancl 1960 are the temperature to change relatively show^^ in Tn:ble I. slo~vlv. Frenuentlv., , however. the Storms \\-it11 '1 high rate of snowfall temperature rises during a sno\vstolm are not frequcnt ancl are usually of ancl the snowfall in the valleys short duration. A day \\-it11 hcavy changes to rain. Tlle temperature falls

TABLE I Frecluency of Snowfalls at Glacie~ Tolal Nzor~ber0.i (lags with m~owl'alls snv~ql'all jor llre Less than winter, I [:int,er 4 fn. . to 1 I 19 lo 20 i.n. 80 in. .in..

-- - 195sj39...... : s5 4 1 3 - 442 1959/60...... 8-1 29 1 - 368 '%Therecol.ds of the wintcr 195-4/55 inclutlc trnlg tllc srlon.fi~llsafter 1 Jar1un1.y1955. below 0°F only a few times during who kindly made available their rec- the winter and this cold weather USII- ords on all avalanches that had af- ally does not coi~tinuefor more than fected railway operation during the a week. period 1910 to 1952. In 1960, when the final plans were Avalanche Survey developed for the first stage of clc- The avalanche survey had to fence, there were available detailed produce the following informatiol~ observations of avalanche activity about the aveilage and very large during seven winters ancl partial ob- avalanches that occur at each site: servations from ano'thel. 40 years. their rupture zone, path ancl terminus; Records of avalanches that occr~rred their depth and width; during the years before 1953 rc- their frequency of occurrence; vealed that therc were periods of more the prevailing conditions responsil)lc than one year in whicll avalanche ac- for thcir occurrence. tivity was a maxiurn. These periods Information was ol~t~~inedby monthly of maximum #activity are associ'~tcd patrols through the area during the with periods of high snowfall and first three years, and after 1956 by high temperature. Unfortunately, the daily and weekly patrols to record present survey was conducted during observations on each av'11anche that what the records indicate to be a occurred, even on those which ter- period of low activity, 'both as to the minated far from the highway. The size and the number of avalanches. Observations taken do not, therefore, rupture zone and path of important Figure 5: Avalanche site Tupper No. 2. avalanches was sketched on photo- cover the worst possible conditions The rupture zone is at the cliffs and gl~aphs and all avalanches that de- which may be encountered. The sur- snowfields below tlle mountain peak; posited snow near or on the highway vey did produce a good picture of the gully is the avalanche path and the right-of-way were traced on location avalanches that may be encountered terminus of the avalanche is on the wide during an aveiiage year, but maxi- alluvial fan. The terrace is above the plans. Infoimation on the conditions cliffs with the waterfall. that cause avalanches was obtiained mum conditions had to be deduced through snow cover and weather db- from the few large avalanches that servations at four observation sites occurred during the observation peri- in the valley and two mountain ob- od and from the incomplete observa- servatories located at an elevation of tions of earlier years. Avalanches slow clown on the alluvilal zvbout 6,800 ft. Precipitation and tem- fan or the talus slope at the lower perature measurements made at Gla- Avalanche Sites part of the mountain, Minor ones will cier previous to 1953 were available stop there 'but major avalanches ad- Avalanche sites can be easily vance into the valley and in some from the Meteorological Branch of the recognized by ,the scars on the tim- Department of Transport. cases reach the opposite side. bered mountainside (Fig. 2). The The narrow valley in Rogers Pass The avalanche survey was completed area where avalanches start to slide by site studies in summer land winter. and the fact that avalanches reach and where 'the bulk of snow origin- the valley floor from both sides made Extent, slope angle, exposure, soil ates is called the rupture zone. The conditions, age of [trees in the rupture it impossible to construct a highway previously descr?bed terrace at la11 that would avoid all dangerous sites. zone, path and terminus were ob- elevation of a4bout 6,000 ft. divides served at each site. Valuable infor- In the 35-mile highway section be- the rupture zone in many of the tween the east boundary of Glacier mation was also obtained from the avalanche sites. The avalanches rup- Canadian Pacific Railway Company, National Park land Albert Canyon on ture in a lower zone on or at the toe d~ewest side 74 avalanche sites had of the cliHs below the terrace to be crossed; 61 of these lie within Figure 4: Avalanche site Cheops No. 2. or in an upper zone on the steep the Park. As the avalanches do not slopes rising to the mountain occur under the same conditions at ridges (Fig. 5). Many of the small each site, and since the topography avalanches b~hich originate in the and area of #therupture zones and the upper zone stop on the terrace. Large avalanche paths may produce avd- avalanches overrun the terrace and lanches of different sizes, the hazard gain a high speed as 'they fall over to the highway varies from one ava- the steep slopes below. There is evi- hnche site to the next. dence that many lower rupture zones The 74 avalanche sites can be class- at Rogers Pass were once covered with ified as follows: timber that prevented the occurrence of avalanches. Fires appear to have Nine sites where minor and major removed these trees and destroyed a avalanches occur frequently ancl very effective niatural defence. where at least one major lavalanche The avalanche path is the track fol- can be expected to reach the Iiigh- lowecl by an avalanche during its de- way every year; scent. The majority of avalanches at Twenty-one sites wllci-e minor Rogers Pass are confined in gullies avalanches occur frequently and usu- which have been carved in the moun- ally reach the highway once or inorc tains by running water (Fig. 5). A than once each winter; the mass of few avalanches reach the valley over the sliding snow is small and may not open, bare slopes (Fig. 4). The ter- cover the whole width of the highway; minus is the area hvllere the main large avalanc~l~esocctu. occasionally body of the avalanche comes to rest. but not cvery winter. affect large sections of simultaneously. highway from these avalanches #would lanches before this amount has been usulally be airborne and little would reached. A continuous snowfall, ex- Spring Thaw Avalanches be deposited on the highway. ceeding 30 in. of new snow, may The most active avalanches are cause unusually large lavalanches. Dry These avalanches occur as a r concentrated in a narrow defile, snow avalanches move on the surface sult of the loss of cohesion of sn about 2% miles long, between Mt. and are accompanied by a cloud of as it melts. They usually occur cycles at many sites simultaneously during a few hot days, but single occurrences were observed also. The avalanches can involve large masses of wet, heavy snow land often slide on the ground. They usually have a lower speed and a smaller range than the dry snow avalandhes, and tend to flow in channels. Wet Snow Direct Action Avalanches Avalanche Defence Methods These avalanches occur when Avalanche c~assifications have snowfalls are fdlowed immediately From the observations made on avalanches and their causes, it was necessary to folmulate a general de- rfence plan for the whole route, land to indicate the defence method that should be applied for each avalanche site within the general plan. To the greatest possible extent the Trans- Canlada Highway was constructed through areas safe !from avalanches. When an avalanche path could not be avoided, \attention was given to locat- ing the highway in such a way as to reduce the effect of the avalanches, e.g. placing the highway near the tip of the avalanche lte~minus where it would be reached infrequently by avalanches or high on rhe mountain- side where the avalanche path is and the defence c'hosen accordingly. deep snow simultaneously at many sites (Fig. 6). narrow and snow clearing to the downhill side easier. Cuts were day- Dry Snow Direct Action Avalanches lighted in order to avoid deep snow The majority of all avalanches Dry Snow Delayed Action Avalanches deposits. Much valuable experience is now available from countries such as Switzerland, Austria land $he United States on various methods of defence against avalanches.

Is of 10 in. when accompanied observation of the snow cover and Active Defence Structures and vegetation (per- manent measures) Rekining 'barriers Snowfences and wind- bahfles Braking barriers: Earth mounds, Catching ed action avalanches unstable snow cover, dams snowfall and wind over Diverting dams a long period of time. Snowsheds high temperatures Reforestation Explosives (temporary mea- sures)

8 Avalanche warning (temporary measure) Highwdy closures Avalanche detection All metl~ocls may be applied alone or in combination. They arc cle- scribecl below ancl rationalizecl for the defence at Rogers P'lss. Retaining ban iers a1 e constlucted in the rupture zone mlcl contiol av'l- lanches at their source. Thcy can create a completely sale site. It was touncl that costs for barriers in rhe renlote and llarge rupture zones ivhicli occur at Rogels Pass iilere prohibitive. Retaining ba~ricrscoulcl 1)e built eco- llomically only at minor av'11anche sites where thc rupture zone is close to the highway, e.g. on long, steep banks fro111 which significant anlounts of snow may slicle and cover the Figure 6: Ternlinus of a wet snow direct action avalanche on the future highway highway. The sno\v is 45 feet deep.

structures wvhich can be usccl, earth awlnlanclles were slowecl down whi mouncls ancl catching clams wwJere passing between the monnds an judgecl to be suibable. terminated just beyoncl; spring th Earth mounds are built in twvo avalanches stopped at the first row or more roivs in a checkered arrange- mounds. It wvas decided that moun ment on the flat section of the pakh sl~oulclbc built as clefence against \I \\here the avalanches woulcl normally snow avalanches ancl smaller dry sno have sloivecl down considerably (Figs. avalanches at othcr sites where not 7, 8). At Rogers Pass, the alluvial illore than three avalanches per winter fans at the tcrminus of the avalanche are likely to occur. Because construc- sites have low slope angles and are tion costs are low, they can be built as a suitable location for mounds. A clefence against large dry snow ava- series of experimental mounds wvas lanches also. In this case, it is not constructecl in 1957. Obscrvntions ex~ecteddlat thc mounds will stop (luring thc following three winters the avalanches completely, but they shonrecl that at locatio~lswhere the shoulcl retain 'a great part of the n~ou~lclswvcrc constructecl dry snow\. lleavicr slicling snow and reduce the

Figure 7: Avalanche site Cheops No. 1 Figure 8: Earth inoui~cl~with deposited avalanche snow. with earth mounds in the terminus.

Snowfences and winclbafflcs con- trol in the rupturc zone the clrifting snow that may create an aval~u~che hazard. It was considerecl that this defence is not suitable for Rogers Pass, because the structures must be built at high elevations ancl on ex- posed mountai~l ridges ivhcrc con- struction ancl maintenance are clif'l'i- cult. This defence does not prevent dry or wet snow clirect action lava- lanches that are not accompaniecl by wind. Furtl~ermore,it is possiblc that deep snow would soon cover the structures. U~akingbarriers are obstaclcs in the avalnnche path wwrhicll slo\w~clown or stop the avalanches belorc they reach the highway. Of tllc various here not more than two struction methods have changed dur-

to be built in the of smaller Diverting dams which confine the width of the avalanches. A snowshed ilt in the path of the avalanches. avalanches, were designed for deposit loacls of 450 p.s.f. and 150 p.s.f. and 300 p.s.f. moving load. A paper giv- ing cletailecl information on the de- sign of sno~vsheclsis being prepared. Reforestation in the rupture zone serves the same purpose as retaining barriers. Rcforestatio~l projects must be associated with tempomry retain- ing barricrs, cvliich because of expense were not collsiclered for Rogers- Pass. Explosives are a temporary de- fence nleasurc that is cheap and ver- satile. When tlie avalanche hazard dictates avalancl~es can be released uncler control by detonating explo- sives in the rupture zone. Under cer- tain circumstances, particularly when therc is 3 hazard for dry snow de- layecl action avalanches, the explosion call creatc a sk,~blesnow cover with- out proclucing an avalmche. b1~1ch experience on this method of ava- telmine wlvhen explosives should be the U.S.A. and in ~witzerlland,where used and wvhen the highway must bc it has proved effective and economi- closed or reopened. An avalanche is observation station in the Rogers Pass cal against direct action avalanches causecl by cliMerent faotors associated area made snow cover and w and clry snow delayecl action 'ava- with terrain, snow cover, snokviall, observations iand evaluated dai lanches, although not against spring wind and temperature, (all in close avalanche hazard. The testing me thaw avalanches. relationship. Certain rules have been was usecl as the basis for evalua The normal technique is to use established through experience on the Weather condi~tions that cc~used projectiles fired from an lartillery wea- dependence of avalanche hazard on lanches at specific sites were an pon. Studies and experiments indi- these factors. Haaarcl can be evaluated lysed and rules for forecasting dire cated that the 75-mm. and 105-mm. quite accurately 'for the time of ob- action avalanches were found. 0th howitzer are most suitable for ava- servation, but the prediction of future studies were made to establish a ru lanche control at Rogers Pass. Some hazarcl is only as good as the weather of thumb for the hazard evaluati rupture zoncs are too rugged for eco- forecast. In practice, the avalanche of spring thaw avalanches. In 19 nomionl firing and at a few avalanche hazard forecaster has to assume that the responsibility for avalanche evalu- sites no suitable firing position coulcl weather will follow a certain pattern ation and prediction was transferre be found. Since firing must often be and his prediction is based 011 ?his. to the Department of Northern done cluring snowstornls when main- The evaluation of the avalanche fairs and National Resources. The tenance personnel are already busy hazard can be approached by two perience gained in combining with snow removal \\rork, and be- different methods, called here the testing method with (the anal cause a large portion of the highway testing method and the anlalytic methocl has been passed 011 to t is in the Natiolllal Park wvhich should method. Department. not be converted into an artillery The testing method has been de- range, it was decided that artillery velopecl in S~itzerland;~evaluation Defence Plan fire should be used only against ava- of the avalanche hazard is based on Study of avallanche defence f lanches that cannot be controlled eco- snow cover observations. Stability of the Rogers Pass route indicated bh nomically by orher methocls. Hancl- a snow cover can be tested directly the cost of a defence that wou placed ancl preplantecl explosive from time to time and weather factors guarantee a continuously open hig charges were found unsuitable at such as snowfall, wind and tempera- way would be unreasonably high. Rogers Pass because of the remote- ture used to determine its stability was realized also that the required ss of the rupture zones. between observations. With expen- structures for such a defence ]could Highway closure for the duration ence and tests, it has been found not be built before rhe scheduled of dangerous avalanche conditions is \vhich factors may lead to a fracture completion clate of the highway. On a simple protective measure. It re- and which conclitions contribute to the other hancl it was recognized that quires an organization to study snow stabilization. a passive clefence only would not cover ancl weather, evalulate avalanche The analytic method is the tech- avoid frequent and Iong closures, hazard and order closure and re- nique used in the U.S. Forest Ser- which coulcl not (be accepted for the opening as necessary. It was con- vice.5 Most avalanche sites with which Trans-Canlada Highway. Based on sidered that although the Rogers Pass this service was concerned produced these consiclerations a plan with three route must be open for the whole direct action avalanches. Observations stages of defence const winter, short closures would be per- over a few winters indicated the wea- bining active defence wibh pas ther and snow cover factors mainly defence by highway closures, An lavalanche cletection system responsible for creating them. By cle- chosen. The length of time that consists of an electronic device which termining the magnitude of each fac- highway woulcl probably be close detects an avalanche as it occurs and tor, it was possible to evaluate ava- each winter woulcl be decreased operates warning signals. 111 a long lanche hazard. This method requires the completion of each st path, an lavalanclle may be cletectecl more acculate weather observations The first stage of some time before it reaches the high- than the testing methocl, but plocluces be in operation when the way and traflic sig~ials coulcl warn better results. opened, and the other sta oncoming vehicles before they enter In practice, both methocls are introduced later wvhen more the dangerous area. In short paths the device may only signla1 avalanche occurrence to the maintenance head- TABLE I1 quarters. The former use of the sys- Corllparison of the Different Defences tem may be feasible at a later stage Based on 1960-19f31 Prices of defence at a few selected lavalanche Clost~reof Iiighwal~ sites at Rogers Pass, but d~elatter Est~nzatedCosts in an Average VVint use of the system was chosen for two sites where frequent sn1'1ll avalanches may cover the highway. The Radio and Electrical Engineering Division of rho National Research Council has built an avalanche detection device First Stage: For Rogers Pass that is now being caoinbined active and tested. passive defencc 5,300,000 52,000

Avalanche Hazard Evaluation and Prediction Defence by means of explosives Third Stagc: ancl highway closure requires the active defencc only 4,400,000 70,000 Konc evaluation of avalanche hazard to de-

11 t 12 hours af

e First Stage of Defence

ction at sites:

snowfalls yielding less than 16 quently than once in 10 years. Ad- in. new snow when iaccom- ditional snowsheds, retaining barriers panied by wind, or less than in rupture zones close to the highway,

- where spring thaw avalan- be built. ches were observed .to have