Avalanche Defences for the Trans-Canada Highway at Rogers Pass Schaerer, P
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NRC Publications Archive Archives des publications du CNRC Avalanche defences for the Trans-Canada Highway at Rogers Pass Schaerer, P. A. For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous. Publisher’s version / Version de l'éditeur: https://doi.org/10.4224/20358539 Technical Paper (National Research Council of Canada. Division of Building Research), 1962-11 NRC Publications Archive Record / Notice des Archives des publications du CNRC : https://nrc-publications.canada.ca/eng/view/object/?id=c276ab3a-c720-4997-9ad8-ff6f9f9a7738 https://publications-cnrc.canada.ca/fra/voir/objet/?id=c276ab3a-c720-4997-9ad8-ff6f9f9a7738 Access and use of this website and the material on it are subject to the Terms and Conditions set forth at https://nrc-publications.canada.ca/eng/copyright READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site https://publications-cnrc.canada.ca/fra/droits LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB. Questions? Contact the NRC Publications Archive team at [email protected]. If you wish to email the authors directly, please see the first page of the publication for their contact information. Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à [email protected]. Ser TH]. N21t2 no. Ll+l e.2 BI,D8 ilIiluill tilu|uilJiilLru uuuu iillII NATIONAL RESEARCH COUNCIL CANADA DIVISION OF BUILDING RESEARCH AVALANCHE DEFENCES FOR THE TRAI{S.GANADA HIGHWAY AT ROGERS PASS by ANALYZED P. Schaerer This is a joint paper of the Department of I Public Worke and the NationaL Research Gouncil Technical Paper No. l4l of the Divieion of Building Research OTTAWA November L962 AVALANCHE DEFENCES FOR THE TRANS-CANADA HICHWAY AT ROGERS PASS by P. Schaerer TABLE OF CONTENTS Page FUNDAMENTAL CONSIDERAT IONS I TERRAIN z GLIMATE 3 Snowfall 3 Snow Cover 4 Temperature 4 Wind 5 AVALANCHES 5 AVALANCHE SURVEY 6 AVALANCHE ACTIVITY I AVALANCHE CLASSIFICATION 9 Dry Snow Direct-Action Avalanches 9 Wet Snow Direct-Action Avalanches IO Dry Snow Delayed-Action Avalanches l0 Spring Thaw Avalanches It AVAI.ANCHE DEFENCE METHODS II Retaining Barriers I3 Snowfences and Windbaffles I3 Braking Barriers T4 Earth rnounds I4 Wedges of concrete L4 Cable nets in the avalanche Path I4 Catching darns and benches t4 Diverting Darns I5 Snow Sheds I6 Refores tation l6 Explosives I6 Hand planted charges r8 Pre-plzrnted charges . IB Artillery fire l8 Highway Closure zo Avalanche Detection zo GENERAL DEFENCE PLAN ..... zo Basic Considerations zo First Stage of Defence . ZL Highway location ZT Structures . zz Explosives ?z Highwayclosures... Zz Avalanche detection ?'3 Second Stage of Defence . ?3 Third Stage of Defence . 23 LTST OF AVALANCHE SITES WITH RECOMMENDED DEFENCE z5 ACKNOWLEDG MENTS 3? REFERENCES 35 APPENDIX A LIST OF OBSERVATIONS ON ACTUAL AVALANCHES APPENDIX B EXPERIMENTAL EARTH MOUNDS APPENDIX C EXPERIMENTAL BENCHES APPENDIX D DESIGN OF SNOW SHEDS AVALANCHE DEFENCES FOR THE TRANS-CANADA HIGHWAY AT ROGERS PASS by P. Schaerer FUNDAMENTAL CONSIDERATIONS In the early l95O's consideration was given to the use of Rogers Pass as a possible route for the Trans-Canada Highway through the selkirk Range. The Pass is located between the towns of Golden and Revelstoke in British Colurnbia, with its surnmit near the town of Glacier in Glacier National Park. It was discovered during surveys preceding construction of the Canadian Pacific Railway and was narned after Major Rogers, Chief Engineer of the Mountain Division of the Railway. The valleys associated with the Pass are narrow with steep sides. Because the snowfall is heavy avalanches occur each winter and spring. Accordingly, in I953 the Departrnent of Public works, which was responsible for the construction of the highway in Glacier National Park, began making observations on the location of each avalanche site and the conditions under which avalanches forrn. These studies were under the direction of Mr. N. C. Gardner. In I956, when the decision had been rnade to construct the highway through the Pass, the Departrnent of Public'Works established an Avalanche Observation Station at Glacier. The previous observation prograrn was enlarged so that the inforrnation necessary for the specification and design of the defence systern could be obtained. An avalanche lnazard evaluation and forecast service was established for the protection of the avalanche observers, surveyors and construction crew during the construction period. The Division of Building Research of the National Research Council co-operated in the organization of the Avalanche Observation Station. Initially it contributed inforrnation and instruments for taking necessary weather and snow cover observations, but when the author joined the staff of the Snow and Ice Section of the Division it assurned the following responsibilities: z- to rnake recon:rrnendations on the type, location and design of the defence for each avalanche site; Z. to assist in the organization and taking of the observations required for the recornrnendations. InApriI of 1957 the author was seconded to the Departrnent of Public Works and joined the Avalanche Observation Station at Glacier on a full-tirne basis. I{e was engaged in field work there until Novernber 1959. On Z October 1959 responsibility for snow and weather observations and for avalanche hazard evaluation and forecast was transferred frorn 'Works the Departrnent of Public and the National Research Council to the National Parks Branch of the Departrnent of Northern Affairs and National Resources. During the winter of I959'60 the Departrnent of Public 'Works rnaintained a survey crew at Glacier which continued the avalanche observations and reported to the author. This observation station ceased its operation in June 1960. This report contains a surnrnary of the observations that were rnade and presents recornrnendations for the avalanche defence required for the protection of the Trans-Canada Highway in winter. Details of snow cover and weather observations, and of experience gained in evalu- ating avalanche lnazard and rnaking forecasts during the period when the National Research Council was associated with taking the field observations have already been published (I). TERRAIN The Setkirk range, with peaks rising to 11,000 ft, is one of the interior ranges of British Colurnbia and lies within the big bend of the Colurnbia River. The lateral valleys on the east side are cornparatively short and steep, whereas those to the west drop gradually to the Colurnbid River. The surnrnit of Rogers Pass is the lowest point in the water divide of the Selkirk range, reached on the east side through Bear Creek VaIIey and on the west through the Illecillewaet Valtey (Table I). These are typical Selkirk valleys, narrow with steep sides (Figs. L,Zl. The valley bottorns are between 500 and I,000 ft wide and consist of silty sand, gravel deposits and bogs. In sorrre places the rnountain sides are aknost V-shaped. One of these narrow defiles is between Mount Tupper and Mount MacDonald on the east side of Rogers Pass; another is forrned -3- by the sides of Fidelity Mountain and Fortitude Mountain at the west boundary of Glacier National Park (Fig. 3). The mountains on the Rogers Pass route have a terrace between 5,500 and 6,500 ft above sea level (Fig. 4l) that leads gradually into steep scree slopes and rock faces rising to the rnountain ridges between 7,000 and 10,000 ft. Below the terrace a sharp drop Ieads to talus slopes and alluvial fans and the valley floor. Heavy tirnber and dense brush cover the lower rnountainsides and valleys, with alpine rneadows and scattered trees on the terrace at 6,000 ft. Tirnberline is generally about 6,800 ft. The steep slopes and heavy timber rnake access to the mountains very difficult. CLIMATE Rogers Pass is located in the southeast interior region of British Columbia, popularly known as the Interior Wet Belt (2); high annuaL precipitation and heavy snowfall are its rnost distinctive features. Frorn the point of view of avalanche conditions, the rnountain area in the western United States has been divideti into three different clirnatic zones. The Selkirks,in the northern extension of the rniddle zone, are characterized by heavy snowfalls of moist to dry sncw, rnedium tempera- tures only occasionally below zero degrees Fahrenheit, and strong wind action on the mountains. During the winters frorn I953 to I960 snowfall, snow depth and temperature were lneasured at Glacier, Stoney Creek and Flat Greek. Snowfall, snow cover ternperature and wind were observed on Rogers Pass surnrnit and on Mount Abbott frorn 1957 to 1960. Records of pre- cipitation and ternperature rneasured at Glacier during the years before 1953 were available frorn the Meteorological Branch of the Departrnent of Transport. Snowfall The average annual precipitation at Glacier, rneasured over the 30-year period between 19ZI and 1950, is lB.0 inches of rain and 342 inches of snow. The largest total snowfall observed was 680 inches, rneasured during the winter of I953-54. Once in l0 years a snowfall of 450 inches or rnore can be expected. There are noyearly recurring periods of maxirnurn snowfall intensity. Storrns with heavy snowfall are infrequent. During winters of light snowfall three rnay occur that yield rnore than l6 inches in a -4- 3-day period; and for winters of heavy snowfall, ten such storrns rnay occur. Only occasionally is there one that contributes rnore than 36 inches of snow in a 3-day treriod.