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Avalanche research by the National Research Council of Canada

Gold, L. W.

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Avalanche Research by the

National Research Council of Canada

by L.W. Gold

ANALYZED

Reprinted from

Collected Papers from "Science of Snow" Yamagata International Snow Symposium Japan, 30 January

-

2 February 1984 p. 41 -50

(DBR Paper No. 1324)

Price $2.00 NRCC 25013

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Le programme d e r e c h e r c h e s s u r l e s a v a l a n c h e s du C o n s e i l n a t i o n a l d e r e c h e r c h e s a dgbutd

2

l a f i n d e s ann'ees 50 a v e c l a c o n s t r u c t i o n d e l a r o u t e t r a n s c a n a d i e n n e q u i d e v a i t f r a n c h i r l e c o l d e Rogers P a s s e n C o l o m b i e B r i t a n n i q u e . h r a i s o n d e l a f a i b l e d e n s i t ' e d e p o p u l a t i o n d a n s l e s montagnes d e l ' 0 u e s t c a n a d i e n , i l a Q'e p o s s i b l e d ' a p p l i q u e r c e r t a i n e s mgthodes d e p r o t e c t i o n a u b a s d e s c o u l o i r s d ' a v a l a n c h e s . L ' o b j e c t i f du programme du CNRC e s t d e m e t t r e a u p o i n t d e s msthodes d e p r ' e v i s i o n d e s r i s q u e s d ' a v a l a n c h e s e t de d'eterminer l e s c a r a c t ' e r i s t i q u e s d e s s i t e s d ' a v a l a n c h e s e t l e s propri'et'es d e s a v a l a n c h e s elles-mgmes pour p o u v o i r p l a n i f i e r , c o n s t r u i r e e t m e t t r e e n o e u v r e d e s s y s t s m e s d e p r o t e c t i o n e f f i c a c e s . C e t t e comnunication p r ' e s e n t e une d e s c r i p t i o n d e s t r a v a u x e t t r a i t e d e s r e c h e r c h e s pr6eentement en c o u r s .

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Science

of

Snow

Pub.

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Yamagata-ken, Japan,

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AVALANCHE RESEARCH BY T H E N A T I O N A L RESEARCH C O U N C I L OF CANADA

Lorne W.

Gold

A s s o c i a t e Director, D i v i s i o n o f B u i l d i n g R e s e a r c h N a t i o n a l R e s e a r c h C o u n c i l o f Canada

O t t a w a , Canada

ABSTRACT

The avalanche research program o f t h e N a t i o n a l Research Council o f Canada began w i t h i n v e s t i g a t i o n s i n t h e l a t e 1950's f o r t h e r o u t e o f t h e Trans-Canada Highway through t h e Rogers Pass r e g i o n o f B r i t i sh Columbia. P o p u l a t i o n d e n s i t i e s a r e low i n t h e mountains o f Western Canada, making

i t p o s s i b l e t o apply avalanche defence methods i n t h e lower o r run-out zones o f avalanche s i t e s . The o b j e c t i v e o f t h e NRCC program has been t o estab l i s h t h e ava lanche hazard eval u a t i o n methods, t h e c h a r a c t e r i s t i c s o f avalanche s i t e s and t h e p r o p e r t i e s o f avalanches t h a t a r e r e q u i r e d i n planning, c o n s t r u c t i n g and o p e r a t i n g these defence systems. I n f o r m a t i o n

i s presented on t h i s work and on c u r r e n t research a c t i v i t y .

INTRODUCTION

The D i v i s i o n o f B u i l d i n g Research, N a t i o n a l Research Council o f Canada (DBR/NRCC), began i t s avalanche i n v e s t i g a t i o n s i n 1957 when one o f i t s s t a f f , P.A. Schaerer, undertook an o b s e r v a t i o n program f o r t h e Federal Department o f P u b l i c Works i n Rogers Pass i n t h e mountains o f B r i t i s h

Columbia. Rogers Pass i s about 30 km i n length and has about 100 avalanche paths t o t h e Trans-Canada Highway, then under c o n s t r u c t i o n ( 1

,

2 ) . The experience obtained from t h i s work provided t h e b a s i s f o r t h e avalanche research program t h a t was s t a r t e d by DBR a f t e r completion o f t h e highway. The o b j e c t i v e o f t h e program, some o f t h e r e s u l t s o b t a i n e d t o date, and c u r r e n t research a c t i v i t y a r e described b r i e f l y .

OBJECTIVES OF THE PROGRAM

The p o p u l a t i o n d e n s i t y i n t h e mountains o f Western Canada i s low. Avalanches a r e a danger p r i m a r i l y f o r highways, r a i 1 ways, power l ines,

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mine s i t e s , r e c r e a t i o n a l a r e a s and t o u r i s t s . There a r e few permanently o c c u p i e d b u i l d i n g s i n t h e p a t h o f avalanches, b u t t h e d e s i r e t o b u i l d i n hazardous a r e a s i s i n c r e a s i n g ( 3 ) . Seven p e o p l e a r e k i l l e d each y e a r i n avalanche a c c i d e n t s , on t h e average, and p r o p e r t y damage ranges from 0.5 t o 1.0 m i l l i o n d o l l a r s p e r y e a r ( 4 ,

5).

Because t h e areas s u b j e c t t o avalanche a c t i v i t y a r e g e n e r a l l y u n i n h a b i t e d and t h e upper r e g i o n s o f avalanche s i t e s a r e r e l a t i v e l y i n a c c e s s i b l e , i t i s u s u a l l y uneconomical t o

i n v e s t i n defence systems i n t h e avalanche s t a r t i n g zone, as i s done, f o r

example, i n Japan and S w i t z e r l a n d . I n Canada i t i s more a p p r o p r i a t e t o

use avalanche defence systems t h a t can be a p p l i e d f r o m v a l l e y l o c a t i o n s

such as avalanche run-out zones. The o b j e c t i v e o f t h e DBR r e s e a r c h program

i s t o d e v e l o p t h e knowledge and defence methods r e q u i r e d t o s e l e c t , design, c o n s t r u c t and o p e r a t e such defence systems.

PLANNING AVALANCHE DEFENCE SYSTEMS

The p o s s i b i l i t y t h a t an avalanche w i l l o c c u r depends o n t h e n a t u r e o f t h e t e r r a i n and o n t h e weather. One o f t h e f i r s t t a s k s u n d e r t a k e n i n t h e r e s e a r c h program was t o e s t a b l i s h t h e methods t h a t s h o u l d be a p p l i e d i n Canada t o d e t e r m i n e t h e danger f r o m avalanches a t a g i v e n s i t e and t h e most

a p p r o p r i a t e defence. An avalanche defence system s h o u l d have maximum

e f f e c t i v e n e s s f o r minimum c o s t (61. I n a r r i v i n g a t a d e c i s i o n c o n c e r n i n g t h e p r o p e r b a l a n c e between e f f e c t i v e n e s s and c o s t i t i s necessary t o s p e c i f y t h e purpose o f t h e defence, t h e r i s k t h a t i s a c c e p t a b l e , and t h e c h o i c e o f s u i t a b l e defence methods. As t h e r e i s u s u a l l y l i t t l e i n f o r m a t i o n on t h e avalanche s i t u a t i o n a t most Canadian l o c a t i o n s , e v a l u a t i o n o f t h e hazard i s n o r m a l l y c a r r i e d o u t i n two stages, p a r t i c u l a r l y f o r z o n i n g d e c i s i o n s w i t h r e s p e c t t o t h e l a n d use t h a t w i l l be p e r m i t t e d ( 3 ) . The m e t h o d o l o g i e s t o be used i n t h i s two-stage e v a l u a t i o n have been developed and demonstrated t h r o u g h a p p l i c a t i o n a t s p e c i f i c s i t e s such a s t h o s e a t Rogers Pass.

The f i r s t s t e p i s t o d e t e r m i n e where t h e avalanches o c c u r t h r o u g h a g e n e r a l survey, u s i n g a e r i a l photographs, t o p o g r a p h i c a l maps and l i m i t e d f i e l d s t u d i e s , i n c l u d i n g , i f p o s s i b l e , o b s e r v a t i o n o f avalanche d e p o s i t s i n t h e s p r i n g a f t e r most o f t h e a v a l a n c h e a c t i v i t y has t a k e n p l a c e . T h i s p r e l i m i n a r y s t u d y p r o v i d e s an a p p r e c i a t i o n o f t h e s e r i o u s n e s s o f t h e avalanche hazard and t h e b a s i s f o r t h e subsequent, more d e t a i l e d survey.

The second s t a g e i s a d e t a i l e d i n v e s t i g a t i o n o f each s i t e a t w h i c h a s e r i o u s a v a l a n c h e may o c c u r t o o b t a i n t h e i n f o r m a t i o n r e q u i r e d f o r d e c i s i o n s c o n c e r n i n g l a n d use and defence systems. O b s e r v a t i o n s a r e made on t h e

c h a r a c t e r i s t i c s o f t h e a v a l a n c h e path, i n c l u d i n g t h e a c c u m u l a t i o n , s t a r t i n g , and r u n - o u t zones. Evidence i s o b t a i n e d f r o m v e g e t a t i o n and o t h e r sources o f t h e e x t e n t o f t h e area t h a t may be a f f e c t e d ( 6 , 7 ) . A l l r e l e v a n t

c l i m a t o l o g i c a l and h i s t o r i c a l d a t a t h a t may p r o v i d e i n f o r m a t i o n o n t h e o c c u r r e n c e and degree o f hazard a r e c o l l e c t e d . An example o f t h i s i s t h e c l i m a t o l o g i c a l and avalanche o c c u r r e n c e s t u d y c a r r i e d o u t by F i t z h a r r i s and Schaerer f o r Rogers Pass area, c o v e r i n g t h e p e r i o d 1909 t o 1977 (8, 9 ) .

I d e a l l y , t h e i n f o r m a t i o n from t h i s i n v e s t i g a t i o n would a l l o w t h e p l a n n e r and e n g i n e e r t o d e t e r m i n e t h e extreme v a l u e s o f t h e i m p o r t a n t p r o p e r t i e s o f avalanches a t each s i t e , f o r example, t h e mass o f an avalanche w i t h a r e t u r n p e r i o d o f 10, 30, o r 100 y e a r s (1 01, o r t h e maximum run-out d i s t a n c e and

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p r o v i d e s t a t i s t i c a l data, and f o r most l o c a t i o n s i t has n o t been p o s s i b l e

t o develop such a r e c o r d . Through i t s r e s e a r c h program, DBR i s s e e k i n g ways

i n which s a t i s f a c t o r y d e s i g n v a l u e s can be o b t a i n e d f r o m s h o r t - t e r m o b s e r v a t i o n s .

AVALANCHE C L A S S I F I C A T I O N

r There i s a c o n s i d e r a b l e d i f f e r e n c e o f o p i n i o n as t o how avalanches

s h o u l d be c l a s s i f i e d ( I l l . The approach a p p l i e d s u c c e s s f u l l y i n Canada i s t o c l a s s i f y them a c c o r d i n g t o t h e i r p o t e n t i a l d e s t r u c t i v e e f f e c t s when

I moving a t t h e i r e s t i m a t e d maximum o r t e r m i n a l speed ( s e e T a b l e I ) .

I m p o r t a n t f a c t o r s d e t e r m i n i n g t h e c l a s s i f i c a t i o n a r e mass, l e n g t h o f path, and f r e e w a t e r c o n t e n t . A l t h o u g h t h i s method i s s u b j e c t i v e , i t i s m e a n i n g f u l

i n t h a t i t r e l a t e s t o t h e e x t e n t o f p o t e n t i a l damage; t h e s i z e o f t h e o b j e c t t h a t c o u l d be a f f e c t e d i n c r e a s e s w i t h i n c r e a s e i n c l a s s i f i c a t i o n number.

TABLE I . Canadian Snow Avalanche S i z e C l a s s i f i c a t i o n System

and T y p i c a l F a c t o r s

Typ i c a l T y p i c a l Path T y p i c a l Impact

S i z e D e s c r i p t i o n Mass Length, m Pressures, kPa

I R e l a t i v e l y harmless <I O t t o peop l e 2 Could bury, i n j u r e , 1 0 2 t 100 o r k i l l a p e r s o n 3 C o u l d b u r y a c a r , 1 0 3 t 1000 d e s t r o y a smal l b u i l d i n g , o r b r e a k a few t r e e s 4 Cou l d d e s t r o y a r a i l w a y car, l a r g e t r u c k , severa l b l dgs., o r a f o r e s t w i t h an area o f up t o 4 ha (40,000 m2) 5 L a r g e s t snow

ava l anches known; c o u l d d e s t r o y a v i l l age o r a f o r e s t o f 40 ha

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S I Z E AND FREQUENCY OF AVALANCHES

One o f t h e p r i n c i p a l aims o f t h e DBR r e s e a r c h program i s t o develop methods o f p r e d i c t i ng t h e frequency o f o c c u r r e n c e and s i ze o f ava lanches

a t a g i v e n s i t e based p r i m a r i l y o n i n f o r m a t i o n o n t e r r a i n and weather ( 7 , 10). The b u i l d - u p o f a c o n d i t i o n t h a t may r e s u l t i n avalanches depends on a

p a r t i c u l a r sequence o f s e v e r a l weather e v e n t s , and t h i s sequence w i l l v a r y from r e g i o n t o r e g i o n .

I t has been found t h a t t h e frequency o f o c c u r r e n c e o f avalanches a t Rogers Pass, f o r example, depends p r i m a r i l y on t h e mean i n c l i n e o f t h e avalanche p a t h from t h e f r a c t u r e l i ne t o t h e t o p o f t h e r u n - o u t zone and on t h e square o f a "wind exposure index" ( 1 0 ) . The w i n d exposure index c o v e r s a s c a l e o f i n c r e a s i n g w i n d e f f e c t i n t h e a c c u m u l a t i o n zone, from c o m p l e t e l y s h e l t e r e d ( i n d e x No. I ) t o f u l l exposure on t h e l e e s i d e o f a wide r i d g e ( i n d e x No. 5 ) . I n g e n e r a l agreement w i t h s t u d i e s i n o t h e r p a r t s o f t h e w o r l d , t h e mean p a t h i n c l i n e has t o be g r e a t e r t h a n a b o u t 25 deg f o r

ava I anches t o occur. F o r i n c l i nes g r e a t e r t h a n a b o u t 42 deg, frequency i s independent o f i n c l i n e . F a c t o r s such as o r i e n t a t i o n , w i d t h and roughness o f t h e avalanche p a t h have l i t t l e i n f l u e n c e o n f r e q u e n c y a t Rogers Pass,

b u t t h e y c o u l d be i m p o r t a n t i n o t h e r r e g i o n s .

One c h a r a c t e r i s t i c o f t h e measurements made i n t h i s s t u d y , and o f a l l measurements o f avalanche p r o p e r t i e s , avalanche s i t e s and weather, i s t h e i r g r e a t v a r i a b i l i t y . T h i s v a r i a b i l i t y r e q u i r e s c a r e f u l t r e a t m e n t when s e e k i n g r e l a t i o n s h i p s among avalanches, t e r r a i n , and weather.

The p r o p e r t i e s o f an a v a l a n c h e t h a t can be e s t i m a t e d a f t e r i t has o c c u r r e d a r e t h e s i z e and average d e n s i t y o f t h e d e p o s i t , t o t a l mass, w a t e r

c o n t e n t and r u n - o u t d i s t a n c e . DBR has been making such e s t i m a t e s i n Rogers Pass s i n c e 1966 and has developed a method o f p r e d i c t i n g t h e mass o f maximum avalanches f o r t h a t r e g i o n f r o m i n f o r m a t i o n on snowfal l and t e r r a i n . I t has been found t h a t a b o u t once i n 12 y e a r s avalanches w i l l o c c u r w i t h a mass much g r e a t e r t h a n t h e annual average maximum.. Such m a j o r avalanches a r e t r e a t e d a s a s e p a r a t e p o p u l a t i o n i n s t a t i s t i c a l analyses; mass, M, o f t h e s e l a r g e avalanches can be expressed as:

where C i s a c o e f f i c i e n t t h a t depends on t h e i n c l i n e o f t h e s t a r t i n g zone and t h e r e t u r n p e r i o d o f t h e l a r g e avalanche,

S i s t h e 30-year maximum w a t e r e q u i v a l e n t o f t h e snow c o v e r i n t h e a v a l a n c h e path, and

A i s t h e s u r f a c e a r e a o f t h e p a t h .

T h i s e q u a t i o n i s now b e i n g e v a l u a t e d f o r a p p l i c a t i o n i n o t h e r r e g i o n s i n t h e mountains o f Western Canada.

AVALANCHE RUN-OUT DISTANCE

I n f o r m a t i o n o n t h e run-out d i s t a n c e s o f avalanches i s e s s e n t i a l f o r d e c i s i o n s on t h e l o c a t i o n o f highways, b u i l d i n g s , and o t h e r s t r u c t u r e s near an a v a l a n c h e s i t e . Models o f t h e r u n - o u t d i s t a n c e s o f l a r g e avalanches based on t h e dynamics o f t h e m o t i o n and t h e c o e f f i c i e n t o f s l i d i n q f r i c t i o n

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between a v a l a n c h e and a v a l a n c h e p a t h a r e b e i n g t e s t e d ( 1 2 , 1 3 ) . The

a p p l i c a t i o n o f t h e s e models i s l i m i t e d , however, because o f l a c k o f i n f o r - m a t i o n o n t h e c o e f f i c i e n t o f s l i d i n g f r i c t i o n , t u r b u l e n t d r a g c o e f f i c i e n t , and mass o f ava l anches.

A second approach i s b e i n g i n v e s t i g a t ' e d i n c o l l a b o r a t i o n w i t h t h e

Norwegian G e o t e c h n i c a l I n s t i t u t e . T h i s i s based o n a s t a t i s t i c a l c o r r e l a t i o n between r u n - o u t d i s t a n c e and c e r t a i n p r o p e r t i e s o f t h e t e r r a i n . The

a n a l y s i s i n d i c a t e s t h a t t h e maximum r u n - o u t d i s t a n c e r e l a t i v e t o a r e f e r e n c e p o i n t up t h e s l o p e can b e p r e d i c t e d w i t h i n g i v e n c o n f i d e n c e l e v e l s , u s i n g t h e p a t h l e n g t h above t h e r e f e r e n c e p o i n t and o t h e r t e r r a i n v a r i a b l e s .

PROPERTIES OF AVALANCHES I N MOTION

One o f t h e f i r s t p r o j e c t s u n d e r t a k e n i n t h e DBR r e s e a r c h program was t o measure t h e speed and i m p a c t p r e s s u r e s o f a v a l a n c h e s . F i g u r e I shows p r e s s u r e c e l I s s e t up i n t h e c e n t e r o f an a v a l a n c h e p a t h . The c e l I s were e n c l o s e d i n c y l i n d r i c a l , s t r e a m l i n e d h o l d e r s and mounted on a s t e e l frame a b o u t 5 m i n h e i g h t . Two s i z e s were used; t h e sur-face a r e a o f one s e t was 645 mm2 and t h a t o f t h e second s e t was 6450 mm2. More r e c e n t l y , p r e s s u r e - m e a s u r i n g d e v i c e s w i t h a s u r f a c e a r e a o f 200,000 mrn2 have been i n s t a l l e d .

F i g . I S t e e l frame w i t h two l o a d c e l I s

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The motion o f avalanches i s very complicated and has n o t y e t been descr i bed s a t i s f a c t o r i l y. The measurements show t h e ex i stence o f t h r e e zones: a dense f l o w a l o n g t h e ground surface, a middle zone o f " I i g h t flow," and an a i r b o r n e , powdered snow zone ( F i g . 2 ) (14). The dense, f l o w i n g zone c o n t a i n s most o f t h e mass o f t h e avalanche. I t produces an i n i t i a l peak pressure t h a t subsequently drops t o a r e l a t i v e l y c o n s t a n t value t h a t remains as long as t h e dense snow f l ows p a s t t h e ce l l s.

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D E N S E F L O W

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F R O N T A L S P E E D 2 7 . 7 rn

r - '

S C A L E , m

F i g . 2 P r o f i l e o f t h e avalanche 10 February 1977 a t t h e load c e l l mount (Reproduced from t h e Journal o f G l a c i o l o g y by permission o f t h e l n t e r n a t i o n a l G l a c i o l o g i c a l S o c i e t y )

The middle zone o f l i g h t , f l o w i n g snow i s composed o f powder and o f lumps up t o 60 mm i n diameter t h a t a r e thrown upward by t h e t u r b u l e n t motion o f t h e dense f l o w . Pressures were observed whenever a snow lump s t r u c k a gauge, b u t were zero o r very low a t o t h e r times. The avalanching snow appeared t o flow i n waves, as i l l u s t r a t e d i n F i g u r e 2. A t y p i c a l pressure record i s presented i n F i g u r e 3.

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1 - - - i 1 u S M A L L L O A D C E L L . 0 . 3 7 m A B O V E B E D S U R F A C E w u n! L I G H T F L O W -D I -+ D E N S E F L O W - 3 I

,,,

L A R G E L O A D C E L L , 0 . 5 8 m A B O V E B E D S U R F A C E 1 TIME, s

F i g . 3 lmpact p r e s s u r e r e c o r d i n g s o f avalanche No. 3 o n 10 December 1977 (Reproduced f r o m t h e J o u r n a l o f GI a c i o l o g y by permi s c ' I on

o f t h e I n t e r n a t i o n a l G l a c i o l o g i c a l S o c i e t y )

The o b s e r v a t i o n s have been analysed, assuming t h a t p r e s s u r e , p, i s g i v e n by t h e f o l l o w i n g e q u a t i o n :

where v i s v e l o c i t y o f f l o w (ms'l)

p i s dens i t y o f t h e f l o w i n g snow ( k g m'3)

c i s a c o e f f i c i e n t t h a t depends o n t h e p r o p e r t i e s o f t h e snow and t h e s i z e o f t h e p r e s s u r e gauge.

Values o f d e n s i t y were e s t i m a t e d f r o m measurements o n t h e d e p o s i t e d snow. Values o f c c a l c u l a t e d f r o m measurements o f t h e peak p r e s s u r e and t h e

r e l a t i v e l y c o n s t a n t p r e s s u r e imposed by t h e dense, flowing-snow l a y e r a r e g i v e n i n T a b l e I I . These v a l u e s a r e based on few o b s e r v a t i o n s . Many more a r e r e q u i r e d t o e s t a b l i s h t h e r e l a t i o n between impact p r e s s u r e and avalanche speed and t o d e t e r m i n e t h e f a c t o r s r e s p o n s i b l e f o r t h e wide v a r i a t i o n i n t h e p r e s s u r e s t h a t were observed.

TABLE 1 1 . C o e f f i c i e n t s o f Impact P r e s s u r e

I n i t i a l Peak Pressure Base Pressure

Number o f Mean Number o f Mean Observations = I Observations C b Small load c e l l Dense flow 8 1.68 8 0.48 L i g h t flow 7 1.50 Large load c e l l Dense flow 2 1.14 4 0.43 L i g h t flow 6 0.99

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One o f t h e i m p o r t a n t f a c t o r s r e q u i r e d f o r c a l c u l a t i n g p r e s s u r e s and run-out d i s t a n c e , u s i n g a dynamic model, i s speed o f t h e avalanche. The DBR research group have measured avalanche speed v i s u a l l y and by t i m i n g t h e passage o f t h e avalanche u s i n g geophones s e p a r a t e d b y a known d i s t a n c e 5 6 Experiments a r e now b e i n g conducted on measurement o f avalanche speed u s i n g r a d a r . Measurements have been analysed u s i n g t h e f o l l o w i n g e q u a t i o n : where v i s v e l o c i t y (ms-l) 5 i s c o e f f i c i e n t o f t u r b u l e n t f r i c t i o n (mse2) R i s h y d r a u l i c r a d i u s (m) a i s i n c l i n a t i o n o f s l o p e p i s c o e f f i c i e n t o f k i n e t i c f r i c t i o n a i s a c o e f f i c i e n t o f r e s i s t a n c e t h a t i s independent o f speed. The a n a l y s i s i n d i c a t e d t h a t f o r t h e s i t e s s t u d i e d t h e c o e f f i c i e n t o f r e s i s t a n c e , a, was small and c o u l d p r o b a b l y be n e g l e c t e d . The c o e f f i c i e n t , v, appeared t o decrease w i t h v e l o c i t y and good agreement was found by

s e t t i n g i t equal t o 5/v. F i g u r e 4 g i v e s t h e r e s u l t s o f t h e a n a l y s i s o f o b s e r v a t i o n s made f o r dry, damp, and wet snow c o d i t i o n s . A l e a s t squares f i t o f e q u a t i o n ( 3 ) t o t h e s e o b s e r v a t i o n s g i v e s an average v a l u e o f

5 = 1420 m ~ ' ~ . Geophones have been i n s t a l l e d t o p r o v i d e a b e t t e r v a l u e o f t h e speed a t t h e t i m e t h e avalanche s t r i k e s t h e p r e s s u r e c e l l s .

Fig.4 Observed avalanche speeds (Reproduced t h r o u g h t h e c o u r t e s y o f t h e l n t e r n a t i o n a l A s s o c i a t i o n o f H y d r o l o g i c a l Sciences)

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CONCLUDING COMMENTS

I n a d d i t i o n t o o b t a i n i n g i n f o r m a t i o n r e q u i r e d f o r t h e s e l e c t i o n , design, and c o n s t r u c t i o n o f avalanche systems, t h e DBR avalanche r e s e a r c h group has f a k e n a l e a d i n g r o l e i n t h e development o f e d u c a t i o n a l programs.

I t has h e l p e d t o p r e p a r e m a t e r i a l f o r c o u r s e s o n avalanche h a z a r d e v a l u a t i o n and p r e d i c t i o n and t o p r e p a r e guide1 i n e s f o r o b s e r v a t i o n o n weather, snow c o n d i t i o n s , and avalanches (17). T h i s work i s c o n s i d e r e d t o be o f g r e a t

importance because o f t h e i n c r e a s i n g need f o r t e c h n i c a l p e o p l e t o become more knowledgeable c o n c e r n i n g avalanche c o n d i t i o n s i n t h e mountains o f Western Canada. I t i s a l so necessary i n o r d e r t o compi l e t h e r e c o r d s o f weather, t e r r a i n , and avalanche o b s e r v a t i o n s t h a t a r e r e q u i r e d by t h e land use p l a n n e r and t h e e n g i n e e r .

REFERENCES

I

.

Schaerer, P.A. Ava I anche defences f o r t h e Trans-Canada Hi ghway a t Rogers Pass. N a t i o n a l Research C o u n c i l Canada, D i v i s i o n o f B u i l d i n g Research, NRCC 7020, 1962.

2. Schaerer, P.A. The avalanche hazard e v a l u a t i o n and p r e d i c t i o n a t Rogers Pass. N a t i o n a l Research C o u n c i l Canada, D i v i s i o n o f Bui l d i n g Research, NRCC 7051, 1962.

3. Freer, G.L. and P.A. Schaerer. Snow-avalanche hazard z o n i n g i n B r i t i s h Columbia, Canada. J. G l a c i o l . , 2 6 ( 9 4 ) , 345-354, 1980.

4. Stethem, C.J. and P.A. Schaerer. Avalanche a c c i d e n t s i n Canada.

I . A s e l e c t i o n o f case h i s t o r i e s o f a c c i d e n t s , 1955 t o 1976. N a t i o n a l Research C o u n c i l Canada, D i v i s i o n o f B u i l d i n g Research, NRCC 17292,1980. 5. Stethem, C. J. and P.A. Schaerer. Avalanche a c c i d e n t s i'n Canada.

I I . A s e l e c t i o n o f case h i s t o r i e s o f a c c i d e n t s , 1943 t o 1978. N a t i o n a l Research C o u n c i l Canada, D i v i s i o n o f B u i l d i n g Research, NRCC 18525, 1980. 6. Schaerer, P.A. P l a n n i n g defences a g a i n s t avalanches. Can. Geotech. J.,

7 ( 4 ) , 397-404, 1970.

7. Schaerer, P.A. Analyses o f snow avalanche t e r r a i n . Can. Geotech. J., 16(3), 281-287, 1977.

8. F i t z h a r r i s, B.B. and P.A. Schaerer. Frequency o f ma j o r avalanche w i n t e r s . J. G l a c i o l . , 2 6 ( 9 4 ) , 43-52, 1980.

9. F i t z h a r r i s , B.B. Frequency and c l i m a t o l o g y o f m a j o r avalanches a t Rogers Pass, 1909-1977. N a t i o n a l Research C o u n c i l Canada, D i v i s i o n o f Bu i l d i ng Research, NRCC 19020, 198 1

.

10. Schaerer, P.A. and B.B. F i t z h a r r i s . E s t i m a t i o n o f t h e mass o f l a r g e snow avalanches. Can. J. C i v i l Eng., 1 1 ( 1 ) , 79-81, 1984.

I I . McClung, D.M. and P.A. Schaerer. Snow-avalanche s i z e c l a s s i f i c a t i o n , I n Proc. o f Avalanche Workshop, Vancouver, B.C. N a t i o n a l Research Council Canada, A s s o c i a t e Comnittee on Geotechnical Research, TM 133,

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12. McCl ung, D.M. and P.A. Schaerer. D e t e r m i n a t i o n o f avalanche dynamics f r i c t i o n c o e f f i c i e n t s f r o m measured speeds. Annals o f G l a c i o l . , 4,

170-173, 1983.

13. McClung, D.M. D e r i v a t i o n o f V o e l l m y ' s maximum speed and run-out e s t i m a t e s f r a n a c e n t e r o f mass model. J. G l a c i o l . , 29(102), 350-352,

1983.

14. Schaerer, P.A. and A.A. Salway. Seismic and impact-pressure m o n i t o r i n g

o f f l o w i n g avalanches. J . G l a c i o l . , 2 6 ( 9 4 ) , 179-187, 1980.

15. Schaerer, P.A. F r i c t i o n c o e f f i c i e n t s and speed o f f l o w i n g avalanches. Proc. Symposium on Snow Mechanics, G r i n d e l w a l d , 1974, IAHS P u b l i c a t i o n No. 114, 1975, p. 425-432.

16. Salway, A.A. A s e i s m i c and t r a n s d u c e r system f o r m o n i t o r i n g v e l o c i t i e s and impact p r e s s u r e s o f snow avalanches. A r c t i c and A l p i n e Res.,

1 O( 4 1, 769-774, 1978.

17. G u i d e l i n e s f o r weather, snowpack and avalanche o b s e r v a t i o n s . N a t i o n a l Research Counci l Canada, A s s o c i a t e Committee on Geotechn i ca l Research, TM 132, 1982.

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T h i s p a p e r , w h i l e b e i n g d i s t r i b u t e d i n r e p r i n t form by t h e D i v i s i o n of B u i l d i n g R e s e a r c h , remains t h e c o p y r i g h t of t h e o r i g i n a l p u b l i s h e r . It s h o u l d n o t be r e p r o d u c e d i n whole o r i n p a r t w i t h o u t t h e p e r m i s s i o n of t h e p u b l i s h e r . A l i s t of a l l p u b l i c a t i o n s a v a i l a b l e from t h e D i v i s i o n may be o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o n , D i v i s i o n of B u i l d i n g R e s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l of C a n a d a , O t t a w a , O n t a r i o ,

KIA OR6.

Ce document e s t d i s t r i b u 6 s o u s forme de t i r e - 3 - p a r t par l a D i v i s i o n d e s r e c h e r c h e s en bbtiment. Les d r o i t s d e r e p r o d u c t i o n s o n t t o u t e f o i s l a propriCti5 de l t i 5 d i t e u r o r i g i n a l . C e d o c u m e n t n e p e u t t t r e r e p r o d u i t en t o t a l i t 6 ou en p a r t i e s a n s l e consentement de l t 6 d i t e u r . Une l i s t e d e s p u b l i c a t i o n s de l a D i v i s i o n p e u t C t r e o b t e n u e en g c r i v a n t

a

l a S e c t i o n d e s p u b l i c a t i o n s , D i v i s i o n d e s r e c h e r c h e s e n b a t i m e n t , C o n s e i l n a t i o n a l de r e c h e r c h e s Canada, Ottawa, O n t a r i o ,

K1A

OR6.

Figure

TABLE  I .   Canadian  Snow  Avalanche  S i z e   C l a s s i f i c a t i o n   System  and  T y p i c a l   F a c t o r s

TABLE I .

Canadian Snow Avalanche S i z e C l a s s i f i c a t i o n System and T y p i c a l F a c t o r s p.6
TABLE  1 1 .   C o e f f i c i e n t s   o f   Impact  P r e s s u r e

TABLE 1

1 . C o e f f i c i e n t s o f Impact P r e s s u r e p.10

Références

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