Snowdrifts and Winter Ice on Roads

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Snowdrifts and Winter Ice on Roads

Schneider, T. R.

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PREFACE

Many m i l l i o n s o f d o l l a r s a r e s p e n t a n n u a l l y in

Canada t o remove snow and i c e from r o a d s , r a i l w a y s , run- ways and o t h e r f a c l l i t i e s a s s o c i a t e d w i t h t r a n s p o r t a t i o n . U n f o r t u n a t e l y , t h e r e i s l i t t l e i n f o r m a t i o n r e a d i l y a v a i l - a b l e t h a t w i l l guide t h o s e r e s p o n s i b l e f o r k e e p i n g t r a n s - p o r t a t i o n f a c i l i t i e s open i n t h e w i n t e r t o t h e most

e f f e c t i v e means o f d o i n g t h i s under g i v e n c i r c u m s t a n c e s . It i s one of t h e r e s p o n s i b i l i t i e s o f t h e Snow and I c e S e c t i o n o f t h e D i v i s i o n o f . ~ u i l d i n g . ' ~ e s e a r c h t o assemble such i n f o r m a t i o n and make i t a v a i l a b l e i n Canada.

A comprehensive s t u d y of snow and i c e removal from highways was r e c e n t l y undertaken by t h e S o c i e t y o f Swiss Highway E x p e r t s . The Swiss Snow and Avalmche Research I n s t i t u t e , under t h e d i r e c t o r s h i p of D r . M. de Quervain, undertook f o r t h i s s o c i e t y a s e r i e s of i n v e s t i g a t i o n s on methods f o r removing snow and i c e o r c o n t r o l l i n g ; ; h e i r d i s p o s i t i o n . T h i s r e p o r t c o n t a i n s a c r i t i c a l review of a v a i l a b l e lcnowledge and e x p e r i e n c e on snow d r i f t i n g and t h e means by which i t can be c o n t r o l l e d and on t h e forma- t i o n of i c e on highways and t h e means by which i t can be p r e v e n t e d o r removed. T h i s i n f o r m a t i o n vrzs assembled s o

as t o be a v a i l a b l e a s a guide i n developing f u t u r e r e - s e a r c h progranunes. The p r o j e c t was finaficed by a f e d e r a l fund e s t a b l i s h e d i n S w i t z e r l a n d , f o r highway r e s e a r c h .

The D i v i s i o n of B u i l d i n g Research i s p r i v i l e g e d t o have v e r y c l o s e l i a i s o n w i t h t h e Swiss Sno:r and Avalanche Research I n s t i t u t e . In 1948-49 D r . de Q u e r v a i n a c c e p t e d a n i n v i t a t i o n t o v i s i t Canada as a g u e s t worlcer w i t h t h e D i v i s i o n of B u i l d i n g Research, R a t i o n a l Research Council, f o r one y e a r , g i v i n g t h e D i v i s i o n h i s e x p e r t guidance in f o r m u l a t i n g a programme of f u t u r e r e s e a r c h on problems i n v o l v i n g snow and i c e . During t h i s v l s i t he became t h o r o u g h l y f a m i l i a r w i t h t h e s e r i o u s problems t h a t t h e s e m a t e r i a l s c r e a t e f o r Canadian t r a n s p o r t a t i o n f a c i l i t i e s and made s i g n i f i c a n t reconlmendations as t o how t h e s e problems should be s t u d i e d .

The N a t i o n a l Research Council i s p l e a s e d indeed t o have D r . de Q u e r v a i n a g a i n c o n t r i b u t e i n a v e r y r e a l way t o t h e s e s t u d i e s by making a v a i l a b l e r e p o r t s c o n t a i n i n g t h e r e s u l t s of t h e e x c e l l e n t i n v e s t i g a t i o n s by D r . T.R.

Schneider.

It

wishes to record its appreciation to the

Society of Swiss Highway Experts as also to Dr. de

QuervaIn for their permission to have these reports

translated Into English and published In the Technical

~rans1ation'~eries

of the National Research Council.

The Division of Building Research expresses its

thanks also to

Mr.

D.A. Sinclair of the N.R.C. Transla-

tions Section for his work In making this translation.

Ottawa

July,

1962

R.F. Legget

Director

T i t l e :

NATIONAL RESEARCH COUNCIL OF CANADA

Technical T r a n s l a t i o n 1038

Snowdrifts and winter i c e on roads (~chneevervsehungen und wintergl!!t t e ) Author: T.R. Schneider

Reference: ~ i d ~ e n g s s i s c h e s I n s t i t u t f b Schnee- und

Lawinenforschung, I n t e r n e r B e r i c h t N r . 302, 1959. 141 p . , 111 f i g .

TABLE OF CONTENTS

Page

.

I Mechanics of s n o w d r i f t s . . . ~ . . : . . .

I1

.

Snowdrifts n e a r unprotected. n a t u r a l and

...

a r t i f i c i a l o b s t a c l e s

...

I11

.

Measures t o combat s n o w d r i f t i n g

.

...

A The f l a t t e n i n g of s l o p e s of c u t s

...

B

.

R a i s i n g t h e roadway C

.

The e r e c t i o n of f e n c e - l i k e s t r u c t u r e s o r

walls

...

(guide w a l l s . b a f f l e s )

D

.

The e r e c t i o n of p a r a p e t s which conduct t h e

...

wind and snow o v e r t h e o b j e c t

...

.

E The use of rows of t r e e s and hedges

.

F The e r e c t i o n of snow f e n c e s

...

...

.

G The widening of c u t s

...

.

H Makeshift d e v i c e s

.

...

N

Snow f e n c e s

.

...

A Types of fence

...

.

B Departmental experience

...

.

C The e f f e c t i v e n e s s of snow f e n c e s

...

.

D The e r e c t i o n of snow f e n c e s

...

.

E Snow fence i n s t a l l a t i o n s

...

V

.

A d d i t i o n a l means of p r e v e n t i n g s n o w d r i f t s

...

V I

.

P r i n c i p l e s o f p l a n n i n g V I I

.

Wind t u n n e l t e s t s

...

V I I I

.

Summary

...

...

WINTER I C r n G

...

.

I C l a s s i f i c a t i o n of w i n t e r i c i n g

...

A

.

Smooth i c e from meteorological causes

...

B

.

The c a s e of a sub-cooled roadway

...

.

C Wet f o g

D

.

Melt water

...

I1

.

Methods of combatting ice conditions

...

67

A

.

Sanding methods

...

68

...

B

.

Salting methods

...

77

...

.

C

Combined methods 99

D

.

Heating installations

...

102

E

.

Cleaning-off of roads

...

117

...

.

F

Other methods 118

111

.

Requirements and organization of

a

sanding and

salting service

...

118

...

.

IV

Comparison of methods 123

...

.

V

The present situation in Switzerland 125

VI

.

A

few special problems and methods

...

136

...

.

VII

.

Summary 138

...

L m U m 142

SNOWDRIFTS AND WINTER ICE ON ROADS

INTRODUCTION

In

t h i s r e p o r t , which covers t h e work of t h e a u t h o r I n t h e f i r s t semester of h i s r e s e a r c h p r o j e c t , t h e o r i g i n a l i n t e n t i o n w a s t o combine a s h o r t compilation of t h e l i t e r a t u r e with an account of t h e experience gained from d i s c u s s i o n s with departmental a u t h o r i t i e s .

It soon became apparent t h a t t h e l i t e r a t u r e on s n o w d r i f t s and w i n t e r i c e was much more extensive and t h e experience had been much wider than had been supposed a t t h e beginning of t h e study. The a u t h o r t h e r e f o r e decided t o d e p a r t from h i s o r i g i n a l p l a n and t o p r e s e n t a compendium of t h e knowledge c o l l e c t e d i n a s much d e t a i l as p o s s i b l e . The intended d i v i s i o n i n t o " l i t e r a t u r e " and "experience of t h e

a u t h o r i t i e s " has a l s o been discarded, s i n c e t h e experience Is d e a l t with continuously wherever i t d e p a r t s from what i s r e p o r t e d i n t h e l i t e r a t u r e .

This procedure i s j u s t i f i e d because i t o f f e r s t h e b e s t prepara- t i o n f o r t h e r e s e a r c h p r o j e c t and, moreover, a s f a r a s our own

i n v e s t i g a t i o n s a r e concerned, i t provides an e x a c t p i c t u r e of t h e experiments and t e s t s a l r e a d y conducted, t h u s enabling us t o concen- t r a t e in f u t u r e on t h e problems t h a t remain unsolved. In view

p a r t i c u l a r l y of t h e l i m i t e d time a v a i l a b l e i t w i l l be h e l p f u l t o have a s e x t e n s i v e a compilation a s p o s s i b l e a t t h e very beginning s o t h a t o u r own i n v e s t i g a t i o n s can be described i n t h e form of supplements t o t h i s fundamental work.

The a s s o c i a t i o n with t h e departmental a u t h o r i t i e s was a very happy one, because t h e c r e a t i o n of a r e s e a r c h group was welcomed by a l l t h e a d m i n i s t r a t i v e branches. The a u t h o r was given a l l t h e

information he r e q u i r e d and cooperation was asaured everywhere in t h e execution of l a r g e - s c a l e t e s t s . Unfortunately l a s t w i n t e r was a p a r t i c u l a r l y mild one, e s p e c i a l l y i n t h e M i t t e l l a n d . Moreover, a f t e r t h e first h a l f of January t h e r e were no f u r t h e r s u b s t a n t i a l snowfalls and no prolonged c o l d snaps, s o t h a t t h e measurements a t

snow fences and a t t h e t e s t s t r e t c h e s designated f o r combatting winter i c e , whether suggested by t h e a u t h o r i t i e s o r undertaken on our own i n i t i a t i v e , d i d not y i e l d any s a t i s f a c t o r y r e s u l t s . For t h i s reason the s e c t i o n on t h i s s u b j e c t has been dropped i n t h e p r e s e n t r e p o r t , t o t h e g r e a t r e g r e t of the a u t h o r . However, a l l t h e measurements a r e t o be repeated again next winter.

With r e s p e c t t o snowdrifts i t was learned t h a t not only

was

t h e r e a comprehensive theory of d r i v i n g snow, e s p e c i a l l y a t snow fences, but a g r e a t many i n v e s t i g a t i o n s both in t h e wind tunnel and i n t h e f i e l d had a l r e a d y been c a r r i e d o u t , s o t h a t snow fence

research has already reached a high l e v e l . Even t h e i n v e s t i g a t i o n s of t h e s t r u c t u r a l measurements and shapes necessary f o r t h e avoid- ance of snowdrifts have been completed up t o t h e poInt where a l l t h a t Is needed i s a re-examination.

A s f a r a s i c e on roads Is concerned, t h e r e i s s t i l l r e l a t i v e l y l i t t l e experience a v a i l a b l e because t h e use of s a l t o r s a l t and sand combined has been general only f o r t h e p a s t few y e a r s . More- over, comparatively few s c i e n t i f i c i n v e s t i g a t i o n s have been c a r r i e d o u t in t h i s connection. Only t h e e f f e c t of t h e various "sanding" m a t e r i a l s has so f a r been c l a r i f i e d t o any g r e a t e x t e n t .

The rnicroclimate on roads has not y e t been I n v e s t i g a t e d In

d e t a i l , a s i t u a t i o n which we must make every e f f o r t t o remedy In view of the a b s o l u t e n e c e s s i t y of r e l i a b l e I c e f o r e c a s t i n g .

With t h e a i d of t h e p r e s e n t r e p o r t i t w i l l now be comparatively easy t o s e l e c t the most urgent experiments f o r the needs of p r a c t i c e .

SNOWDRIFTS

I. Mechanics o f S n o w d r i f t s

There i s as y e t no complete p h y s i c a l d e s c r i p t i o n of snow d r i f t i n g , which belongs t o t h e group o f phenomena i n v o l v i n g t h e motion o f s o l i d b o d i e s in l i q u i d o r gaseous media. Most a u t h o r s r e f e r t o t h e b a s i c work o f Bagnold (1941) on t h e t r a n s p o r t o f d e s e r t sand by wind. However, s i n c e b o t h t h e s p e c i f i c weight (sand: approximately 2.5 @;/cm3; i c e : 1 . 0 @;/cm3) and t h e g r a i n shape and s i z e , as w e l l a s t h e g e n e r a l p h y s i c a l behaviour of t h e snow cover compared w i t h t h e sand, show s u b s t a n t i a l d i f f e r e n c e s , t h e a p p l i c a t i o n o f B a g n o l d t s i n v e s t i g a t i o n s t o snow d r i f t i n g r e q u i r e s c l o s e c r i t i c a l examination. A number o f a u t h o r s , e s p e c i a l l y i n R u s s i a [Dyunin ( ? ) and Kungurtsev

( ? ) I

and Japan [ S h i o t a n i and Arai

(1952), A r a i , S h i o t a n i and Ogasawara (1953), Shozo and Ogawa (1957)] and i n a more e m p i r i c a l manner Lanlbert (1949) and Pugh and P r i c e

( 1954), have made c e r t a i n i n v e s t i g a t i o n s about t h e r e l e v a n c e of t h e Bagnold t h e o r y t o d r i v i n g snow. A s y e t , however, t h e r e h a s been no

s y n t h e s i s of a l l t h e s e p a r a t e o b s e r v a t i o n s , and t h i s w i l l s c a r c e l y be p o s s i b l e w i t h o u t e x t e n s i v e l a b o r a t o r y and f i e l d i n v e s t i g a t i o n s .

I n what f o l l o w s we s h a l l review b r i e f l y what i s known t o d a t e . D r i v i n g snow i s t h e term u s u a l l y given t o snow t r a n s p o r t e d p a r a l l e l t o t h e s u r f a c e of t h e ground by t h e wind. When t h i s move- ment o c c u r s s l m u l t a n e o u s l y w i t h t h e f a l l i n g o f snow i t i s g e n e r a l l y c a l l e d a snow f l u r r y . If t h e moving snow does n o t r i s e t o human eye l e v e l t h e phenomenon i s c a l l e d sweeping snow.

The d r i v i n g f o r c e o f t h e wind and t h e s t a t i c i n t e r n a l p r e s s u r e o f t h e snow cover i n i t i a t e t h e motion, while g r a v i t y , moment o f l n t e r t i a , t h e geometric form o f t h e i n d i v i d u a l c r y s t a l s and t h e f o r c e o f cohesion w i t h i n t h e snow c o v e r oppose t h e motion. The d r i v i n g f o r c e o f t h e wind depends on i t s v e l o c i t y ; t h e minimum

n e c e s s a r y t o t r a n s p o r t snow i s o f s p e c i a l i n t e r e s t t o t h e i n v e s t i g a - t o r

a able

I ) .

Table I

Author Minimum

wind speed

I

Remarks

- -

-Lawrance ( 19147 )

I

8.3

-

11

1

Wet E n g l i s h c l i m a t e Croce (1943)

Pugh and P r i c e (1954) Shozo and Ogawa (1957)

Dyun i n

Experience of SLP*

The v a l u e s g i v e n by Pugh and P r i c e (1954), and t h o s e g i v e n by Dyunin and t h e e x p e r i e n c e o f t h e SLF* a r e i n good agreement. The d a t a of Shozo and Agarua (1957) and Croce (1943) a r e of t h e same o r d e r o f magnitude, f o r from a h e i g h t of

5

m down t o t h e s u r f a c e of t h e ground a v e l o c i t y d e c r e a s e o f 1 0

-

30% may be e x p e c t e d , a s

i n v e s t i g a t i o n s of Arai, S h i o t a n i and Ogasawara (1953) show ( ~ i ~ . 1 ) . An i d e n t i c a l i n c r e a s e of wind f o r c e w i t h h e i g h t above t h e ground

was found a l s o by Bagnold ( 1 9 4 1 ) . The s u b s t a n t i a l l y h i g h e r v a l u e s of Lawrance (1947) a r e p r o b a b l y due t o t h e c o m p a r a t i v e l y humid

c l i m a t e of England, where t h e normally h i g h m o i s t u r e c o n t e n t of t h e

a i r produces g r e a t e r c o h e s i o n w i t h i n t h e snow c o v e r . F o r c a l c u l a t i n g t h e minimum n e c e s s a r y v e l o c i t y Dyunin g i v e s t h e f o l l o w i n g formula: 7 4 . 3

6

4.6

4 l ) + k 2

-*~-a

k , g d ( p

-

-

'min

-

₁ 10- -!- - l o g 6

5

m above ground

5

m above ground When snow i s f a l l i n g

3

d s e c

*

translator,',^ n o t e : The a b b r e v i a t i o n SLF si. n d s f o r ~ i d ~ c n g s s i s c h e s I r l s t i t u t f u r S c l ~ n e c - und L a ~ ? i n c n f c r s c h u n g (Swiss Snor.? and Avnlnnche Rcscarch I n s t i t u t e ) .

g

-

a c c e l e r a t i o n due t o g r a v i t y h

-

d e n s i t y of t h e c r y s t a l p

-

d e n s i t y o f t h e a i r d

-

g r a i n s i z e v

-

kinematic v i s c o s i t y of t h e a i r flow 8

-

roughness of t h e s u r f a c e

e

-

base of t h e Napier logarithms

k , , k,

-

e x p e r i m e n t a l l y determined c o e f f i c i e n t s .

With t h i s formula he a r r i v e s a t t h e value given In F i g . 1.

The complexity o f t h i s formula shows c l e a r l y t h a t very intri-

c a t e l y r e l a t e d f a c t o r s a r e Involved i n t h e occurrence o f d r i v i n g snow. F o r p r a c t i c a l purposes a mean v a l u e of 4

-

4 . 5 d a e c as

obtained from Table I w i l l s u f f i c e .

The g r a i n s i z e o c c u r r i n g i n t h e formula was o b t a i n e d by Dyunln with t h e a i d o f s c r e e n a n a l y s e s ( ~ 1 ~ . 2 ) . The p r o p o r t i o n N o b t a i n e d f o r a given mesh s i z e i s c a l c u l a t e d according t o t h e f o l l o w i n g

formula :

l o g N =. log l o g Di-lP- l o g Dl

where p

-

p e r c e n t by weight of t h e f r a c t i o n recovered i n a s c r e e n

Dl

-

mesh s i z e of two s c r e e n s used one a f t e r a n o t h e r .

I n i n t e r p r e t i n g t h e curves i t should be borne i n mind t h a t some of t h e s o f t snow c r y s t a l s w i l l be broken by t h e s c r e e n i n g p r o c e s s ; f o r , as Dyunin showed very c l e a r l y , t h e g r a i n s i z e d e c r e a s e s w i t h Increasing d u r a t i o n o f t h e s c r e e n i n g p r o c e s s and t h e d i s t r i b u t i o n becomes more uniform ( F i g .

3 ) .

Dyunin a l s o showed t h a t t h i s aame p r o c e s s can be observed i n d r i v i n g snow, because h e r e a g a i n reduc-

t i o n and more uniform d i s t r i b u t i o n of t h e g r a i n s i z e i s obaerved w i t h i n c r e a a l n g d u r a t i o n . Grain s i z e d i s t r i b u t i o n curves similar t o t h o s e ln F i g .

3

a r e o b t a i n e d . The damage t o t h e snow f l a k e s occura when t h e y c o l l i d e with one a n o t h e r i n t h e a i r o r on f a l l i n g back t o t h e ground; f o r , as Bagnold (1941) demonstrated In h i s w.Wd t u n n e l t e s t s

and a s h a s been confirmed by v a r i o u s a u t h o r s (pugh and P r i c e , 1954;

~ y u n l n ) , t h e f o l l o w i n g p o s s i b i l i t i e s e x i s t f o r each s e p a r a t e f l a k e , depending on i t s s i z e , shape, t h e wind f o r c e and t u r b u l e n c e :

1. If t h e s t e a d y r a t e of f a l l i s c o n s i d e r a b l y l e s s t h a n t h e upward motion due t o t h e t u r b u l e n t wind flow, t h e f l a k e becomes

suspended i n t h e a i r .

2 . I f t h e s t e a d y r a t e of f a l l becomes g r e a t e r t h a n t h e upward motion t h e f l a k e e x e c u t e s a hopping motion.

3 .

With s t i l l s m a l l e r wind v e l o c i t y t h e f l a k e s r o l l a l o n g t h e s u r f a c e . Within a s i n g l e s n o w d r i f t a l l t h r e e c a s e s can o c c u r s i m u l t a n e - o u s l y . To i n i t i a t e t h e d r i f t i n g i t i s n e c e s s a r y f o r t h e f i r s t f l a k e s t o be s e t i n motion by t h e d r a g g i n g f o r c e of t h e wind; t h e n t h e hopping and r o l l i n g f l a k e s c a r r y o t h e r p a r t i c l e s a l o n g w i t h them, u n t i l a k i n d of e q u i l i b r i u m s e t s i n between t h e c r y s t a l s t h a t come t o r e s t and t h o s e t h a t keep moving.

The q u a n t i t a t i v e v e r t i c a l d i s t r i b u t i o n of d r i f t i n g snow h a s been I n v e s t i g a t e d by A r a i , S h i o t a n i and Ogasawara

(1953)

f o r h e i g h t s from 0

-

5 m. F i g . 4 shows t h e c u r v e s o b t a i n e d from one o f t h e i r s e r i e s o f t e s t s . F o r t h e r e l a t i o n between t h e h e i g h t from t h e ground ( 2 ) and t h e amounts of d r i f t i n g snow a t two d i f f e r e n t mass p o i n t s (M,, M,) t h e y g i v e t h e f o l l o w i n g formula: 2 Z = a ( ~

-

l o g

-

_M, 100) a,K = c o n s t a n t s . T h i s formula, of c o u r s e , i s o f o n l y l i m i t e d v a l u e . In .the f i r s t p l a c e i t a p p l i e s o n l y t o h e i g h t s of l e s s t h a n 100 cm, and s e c o n d l y t h e c o e f f i c i e n t s a ( 3 5 . 0

-

9 0 . 0 ) and K ( 2 . 5 5

-

4 . 0 4 ) a r e v e r y i m p e r f e c t l y known. A s F i g . 4 and F i g .

5

from S h i o t a n i and

A r a i f s (1952) work show, most of t h e blowing snow i s c o n f i n e d t o a h e i g h t o f l e s s t h a n 150 cm above t h e s u r f a c e , a r e g i o n which h a s been e s p e c i a l l y i n v e s t i g a t e d by Kungurtsev. H i s r e s u l t s a r e assembled i n Table 11. The d e f i s i t y d i s t r i b u t i o n i s p r a c t i c a l l y independent of t h e wind v e l o c i t y . The a u t h o r e x p r e s s l y s t a t e s , moreover, t h a t even a t wind v e l o c i t i e s of 20 d s e c t h e d e n s i t y

Table I1 Height above ground 100

-

200 50

-

loo

3 0

-

50

20

-

30 1 0

-

20 0

-

l o

Minimum

1

Minimum 0

-

10 0

-

20 S l i g h t wind

( 6

n J s e c ) snow d e n s i t y $ S t r o n g wind (16 m/sec) snow d e n s i t y $ D r i f t i n g d u r i n g snowfall snow d e n s i t y $

d i s t r i b u t i o n remains t h e same, so t h a t considerably h i g h e r v e l o c i t i e s a r e r e q u i r e d i n o r d e r t o keep t h e snow c r y s t a l s suspended w i t h i n an

a i r s t r a t u m of any g r e a t t h i c k n e s s . Most of t h e c r y s t a l s more o r l e s s r o l l along t h e s u r f a c e . Even when snow i s f a l l i n g t h e d e n s i t y d i s t r i b u t i o n remains t h e same up t o 20 cm above t h e ground. Because o f t h e continuous supply from above, however, i t i s i n c r e a s e d some- what above t h a t of o r d i n a r y d r i f t l n g snow. Kungurtsev has a l s o

i n v e s t i g a t e d t h e d i s t r i b u t i o n i n t h i s t h i n , bottom l a y e r (Table 111). Table I11 0 = S u r f a c e of snow

I

I

Height (cm) $ d i s t r i b u t i o n of q u a n t i t y of snow i n t h e l a y e r from

o

-

12 cm (=

lo&)

0

64

T h i s confirms what was a l s o demonstrated by S h i o t a n l a n d A r a i (1952) i n t h e i r p r i n l a r i l y t h e o r e t i c a l worlc, narilcly t h a t most of' t h e t r a n s p o r t o c c u r s i n a coinparatively t h i n l a y e r above t h e ground, and because of t h e low wind v e l o c i t y i t does n o t t a k e p l a c e i n t h e form of a s u s p e n s i o n i n t h e a i r , u u t by hopping and p r i r ~ n r i l y by r o l l i n g . In t h i s r e s p e c t t h e r e i s no essential d i f f e r e n c e between d r i f t i n g snow and d r i f t i n g s a n d .

F o r t h e amount of snow t r a n s p o r t e d p e r u n i t l e n g t h and u n i t time Dyunin g i v e s t h e f o l l o w i n g formula which has l a r g e l y been con- f irrned by experiment

v,

Q = 5 -

(YJ-

1 ) " ( d m s e c )

V, = wind v e l o c i t y 1 m from t h e ground.

S i n c e t h e q u a n t i t y of snow t r a n s p o r t e d v a r i e s w i t h t h e cube of t h e wind v e l o c i t y , even s l i g h t changes of v e l o c i t y may g r e a t l y

i n f l u e n c e t h e d r i v i n g power. T h i s f a c t i s used t o combat snow d r i f t i n g .

A s a l r e a d y mentioned, t h e c o h e s i o n w i t h i n t h e snow c o v e r p l a y s a b a s i c p a r t i n t h e i n i t i a l s t a g e s of d r i f t i n g snow. Hard c r u s t s can form on t h e s u r f a c e , depending on t h e t e m p e r a t u r e v a r i a t i o n and t h e s o l a r r a d i a t i o n . The cohesion between i n d i v i d u a l g r a i n s o f t h e c r u s t i s v e r y s t r o n g . T h i s i s a c o n d i t i o n which r a r e l y o c c u r s i n d e s e r t s a n d . The wind i s a b l e t o t e a r a t b e s t o n l y a few i s o l a t e d c r y s t a l s from a c r u s t e d s u r f a c e . Like a c t u a l snow s q u a l l s , t h e r e - f o r e , s n o w d r i f t s o c c u r predominantly under c o n d i t i o n s of prolonged

I I

c o l d and h i g h wind ( i n S w i t z e r l a n d what i s c a l l e d b i s e " w e a t h e r ) . C e r t a i n minimum d e p t h s of snow a r e a l s o n e c e s s a r y , s i n c e o t h e r w i s e s u r f a c e i r r e g u l a r i t i e s ( b l a d e s of g r a s s , bushes, furrows i n f i e l d s , e t c . ) a c t as o b s t a c l e s and form n e s t s i n which t h e moving snow soon t a k e s s h e l t e r . The snow can be t r a n s p o r t e d o v e r r e l a t i v e l y l a r g e d i s t a n c e s o n l y when t h e s u r f a c e of t h e ground h a s been c o m p l e t e l y smoothed o v e r .

11. -.-- S n o w d r i f t s Near Unprotected, N a t u r a l and A r t i f i c i a l O b s t a c l e s

-

S i n c e t h e t r a n s p o r t c a p a c i t y of t h e wind, a s a l r e a d y mentioned, depends on t h e cube of t h e wind v e l o c i t y , even a s l i g h t d e c r e a s e of v e l o c i t y w i l l r e s u l t i n t h e d e p o s i t i n g o f c o n s i d e r a b l e q u a n t i t i e s o f t h e d r i f t i n g snow on t h e ground a g a i n . The r e s u l t i n g mounds have a c h a r a c t e r i s t i c s h a p e , t h e i r p r o f i l e b e i n g s i m i l a r t o t h e shape o f a f i s h ' s back. A s a consequence C o r n i s h (1902) c o i n e d t h e t e r m " i c h t h y o i d " f o r t h e s e forms.

D r i f t i n g snow i s t h e r e f o r e always d e p o s i t e d a t p l a c e s where o b s t a c l e s i n t e r f e r e w i t h t h e normal p a s s a g e o f t h e wind. In f r o n t o f t h e o b j e c t i n q u e s t i o n t h e h o r i z o n t a l component o f t h e wind v e l o c i t y i s reduced by t h e b a f f l e e f f e c t and behind i t by v o r t e x f o r m a t i o n , and t h e snow p r e c i p i t a t e s . On e i t h e r s i d e o f t h e

o b s t a c l e t h e wind v e l o c i t y i n c r e a s e s a c c o r d i n g t o B e r n o u i l l i ' s l a w

because of t h e c o n s t r i c t e d c r o s s - s e c t i o n . The r e s u l t i n g i n c r e a s e d d r i v i n g f o r c e o f t h e vrind h a s an e r o d i n g e f f e c t which produces t h e dug-out forms which a r e a l s o c h a r a c t e r i s t i c . The d e p o s i t s around a

bush ( F i g . 6 , ) , a t r e e ( F i g . 7 ) and a house (FIG.

8,

9)

s t a n d i n g i n t h e open a r e r e p r e s e n t e d a s found by C o r n i s h (1902) i n Canada.

D e p o s i t s a l s o o c c u r a s a r e s u l t o f v o r t e x forrnation a t p l a c e s where g r a d e s change. V a r i o u s c o n d i t i o n s e x i s t on r a i l r o a d and highway embankments, depending on t h e i r h e i g h t . A s F i g . 10 shows, most a u t h o r s a g r e e t h a t t h e r e i s no depositing on low embankments r i s i n g

j u s t above t h e s u r r o u n d i n g snow c o v e r . On h i g h embankments w i t h

s t e e p s l o p e s ( F i g . l l ) , however, a v o r t e x form o c c u r s on t o p and l e a d s t o t h e f o r n i a t i o n of mounds. S i m i l a r c o n d i t i o n s a r e p r e s e n t on c u t s in t h e s i d e of h i l l s ( F i g . 1 2 ) . Wlnd v e l o c i t y d i s t r i b u t i o n s on t h e vrindward and l e e s i d e s of a n embankment w e r e measured by

Benterud (1947) (,Fig. 13 )

.

D e p r e s s i o n s ; i n t h e ground and c u t s can a l s o v e r y e a s i l y be d r i f t e d i n ( ~ i g . 1 4 ) . Kungurtsev s t u d i e d t h e p a t h of a n I n d i v i d u a l snow c r y s t a l a l o n g w i t h t h e ,wind d L s t r i b u t i o n ( F i g . 1 5 ) . H i s

a r e t a k e n from t h e lowermost l a y e r s of t h e atmosphere by t h e v o r t e x forming i n t h e d e p r e s s i o n . The d e p o s i t s i t u a t e d on t h e s i d e n e a r e r t h e wind grows r a p i d l y . T h i s a u c t i o n e f f e c t , o f c o u r s e , does n o t e x t e n d t o

a

v e r y g r e a t h e i g h t . The h e i g h t above t h e s u r f a c e of t h e ground i s equal t o o n l y about one-half t h e depth o f t h e d e p r e s s i o n . Although t h e r e i s a comparat1.vely high wind v e l o c i t y on t h e bottom o f t h e c u t i t i s n o t g r e a t enough t o e j e c t t h e a r r i v i n g snowflakes.

It i s s t r o n g l y emphasized by v a r i o u s a u t h o r s ( ~ s c h i r w i n s k y ,

1931;

P e t e r s e n , 1942) t h a t c u t s more t h a n

6

-

8

m deep a r e n o t s u b - j e c t t o d r i f t i n g , because t h e r e is s u f f i c i e n t room on t h e s i d e s t o accommodate t h e d e p o s i t e d rnaases o f snow ( ~ i ~ . 1 6 ) . In F i g . 14 S c h u b e r t (1903) g i v e s an i n c l i n a t i o n of 1 : 8 on t h e windward and

1 : 6 on t h e l e e s i d e f o r t h e s l o p e s of n a t u r a l l y formed snow

d e p o s i t s . These v a l u e s a r e of g r e a t irnporta.nce f o r d e s i g n purposes,

as w i l l be d i s c u s s e d more f u l l y in a subsequent s e c t i o n ; because f o r , d e p o s i t s do n o t o c c u r on t h e s i d e s and s l o p e s o f c u t s f o r which t h e s t e e p n e s s does n o t exceed t h e s e v a l u e s . The aame a p p l i e s t o a l l c u t s t h a t r u n p a r a l l e l t o t h e wind. d i r e c t i o n .

111. Measures t o Combat Snow D r i f t i n g

It i s e v i d e n t from what h a s been s a i d above t h a t t h e f o l l o w i n g two p o s s i b i l i t i e s of combatting s n o w d r l f t s e x i s t :

1. The o b j e c t may be g i v e n a form such t h a t no d e p o s i t s a t a l l can o c c u r , o r a r t i f i c i a l means can be p r o v i d e d s o t h a t t h e snow i s blown o v e r t h e o b j e c t t o be p r o t e c t e d o r i s conducted p a s t i t . 2. By t h e e r e c t i o n of o b s t a c l e s o r by s u i t a b l y a l t e r i n g t h e shape o f t h e ground t h e wind v e l o c i t y is d e c e l e r a t e d s o t h a t t h e d r i v - i n g snow i s p r e c i p i t a t e d . Ln t h i s c a s e s u f f i c i e n t s p a c e is allowed i n t h e d e s i g n of t h e p r o t e c t i n g i n s t a l l a t i o n f o r t h e snow t o be d e p o s i t e d .

Thus a wide v a r i e t y of means i s a v a i l a b l e which a r e rnore o r l e s s e f f e c t i v e , depending on l o c a l c o n d i t i o n s .

In most c a s e s f i n a n c i a l c o n s i d e r a t i o n s w i l l be t h e c h i e f f a c t o r s t h a t must be t a k e n i n t o account i n s e l e c t L q g t h e measures t o be a d o p t e d . I n t h e c a s e of roads t h e airn i s u s u a l l y t o c r e a t e

c o n d i t i o n s s o t h a t snow c l e a r i n g equipment can p a s s e a s i l y a l o n g t h e e n t i r e s t r e t c h I n q u e s t i o n and w i l l n o t need t o be o p e r a t e d a t times when t h e r e i s no s n o w f a l l . I n p a r t i c u l a r , t h e use of s p e c i a l equipment f o r t h e removal of d r i f t s which g e n e r a l l y a r e of s h o r t d u r a t i o n w i l l n o t be economical i f t h e d r i f t s a r e s i t u a t e d beyond a c e r t a i n d i s t a n c e from t h e equipment garage.

Condit i o n s a r e d i f f e r e n t

,

however, on superhighways and expressways, s i n c e any i n t e r r u p t i o n i n t r a f f i c means economic l o s s e s , s o t h a t h e r e o n l y t h e maximum p r o t e c t i o n a g a i n s t snow i s adequate.

I n o u r i n t e n s i v e l y c u l t i v a t e d country i t i s f r e q u e n t l y d i f f i - c u l t t o o b t a i n t h e a r e a of ground r e q u i r e d f o r t h e e r e c t i o n of permanent p r o t e c t i v e s t r u c t u r e s . A t some l o c a t i o n s , indeed, It i s o u t of t h e q u e s t i o n . A t such p l a c e s one must make do with temporary p r o t e c t i v e d e v i c e s which a r e s e t up every y e a r , although a c t u a l l y t h e s e a r e o n l y a l a s t r e s o r t . Within t h e two main groups of p r o t e c - t i v e d e v i c e s , t ~ h i c h a r e completely d i f f e r e n t I n t h e i r e f f e c t , we may d i s t i n g u i s h t h e following measures:

1. I n s t a l l a t i o n s a t which t h e snow i s blown over o r p a s t t h e p l a c e t o be p r o t e c t e d

A . The f l a t t e n i n g o f f o f t h e s l o p e s o f c u t s ;

B. The r a i s i n g of t h e roadway t o a h e i g h t where i t w i l l be swept by t h e wind;

C . E r e c t i o n of f e n c e - l i k e s t r u c t u r e s o r w a l l s which guide t h e wind s o t h a t i t sweeps o v e r t h e o b j e c t t o be k e p t c l e a r and

c a r r i e s t h e snow with it (guide w a l l s , b a f f l e s ) ;

D. P a r a p e t s which guide t h e wind and t h e snow over t h e o b j e c t .

2. I n s t a l l a t i o n s which cause t h e d r i f t i n g snow t o be d e p o s i t e d b e f o r e i t reaches t h e o b j e c t :

--

E . Rows of t r e e s and hedges;

F. The e r e c t i o n of snow fences;

Q . The widening of c u t s ;

H . Makeshift devices;

1. Snow wa1l.s made from blocks of snow;

2. Snow dykes;

3.

E a r t h dykes;

The f i r s t group i n c l u d e s o n l y d e v i c e s which by reason of t h e i r s i z e and c o s t of e r e c t i o n belong e n t i r e l y t o t h e c l a s s of permanent i n s t a l l a t i o n s which i f a t a l l p o s s i b l e a r e provided f o r when a

r o u t e i s f i r s t planned, o r must be e r e c t e d subsequently and t h e n g e n e r a l l y a t g r e a t e r expense. The u n d e r l y i n g p r i n c i p l e i s t o main- t a i n o r even i n c r e a s e , e . g . by an a r t i f i c i a l l y induced nozzle e f f e c t , t h e v e l o c i t y and hence t h e d r i v i n g f o r c e of t h e wind. _, Harmful

v o r t e x formations due e i t h e r t o o b s t a c l e s o r a b r u p t changes of g r a d i e n t , a r e avoided a s f a r a s p o s s i b l e .

Some of t h e measures l i s t e d i n Group 2 a r e pernlanent ( s t r i p s of t r e e s , hedges, w a l l s , e a r t h dykes, widening of t h e c u t s ) . Except f o r t h e emergency i n s t a l l a t i o n s it i s mainly t h e snow f e n c e s which a r e e r e c t e d o n l y p e r i o d i c a l l y .

I n what f o l l o w s t h e s e p r o t e c t i v e means a r e d i s c u s s e d i n d e t a i l . A . The F l a t t e n i n g of Slopes o f Cuts

A s mentioned i n S e c t i o n 11, Schubert (1903) has a l r e a d y

e s t a b l i s h e d t h a t n a t u r a l s n o w d r i f t d e p o s i t s form a n g l e s of s l o p e of 1 : 8 t o 1 :

6 .

Tschirwinslcy (1931) g i v e s a value of 1 : 10. This c h a r a c t e r i s t i c can be u t i l i z e d i n combatting s n o w d r i f t s , by making t h e s l o p e s f l a t enough s o t h a t no d e p o s i t accumulates on them. A d e t a i l e d i n v e s t i g a t i o n of t h i s problem w a s c a r r i e d o u t by Finney (1939). The r e s u l t s of h i s wind t u n n e l r e s e a r c h , which were con- firmed by o b s e r v a t i o n s i n n a t u r e , a r e reproduced i n Fig. 17, 18 and

19.

For s l o p e s w i t h s h a r p a n g l e s i n c l i n a t i o n s o f a t l e a s t 1 : 6 a r e needed. I f t h e s h o u l d e r and f o o t a r e rounded o f f , however, f l a t t e n i n g t o 1 : 4 i s a l r e a d y adequate.

These measures c o n s t i t u t e one of t h e most advantageous ways of p r o t e c t i n g c u t s , b u t of course t h e y a l s o i n v o l v e heavy c o s t s

because o f t e n i t i s n e c e s s a r y t o move c o n s i d e r a b l e amounts of e a r t h . The i n c o r p o r a t i o n of a l a r g e r a r e a i n t o t h e t o t a l road i n s t a l l a t i o n and t h e consequent i n c r e a s e d consumption of a r a b l e land i s a b a s i c disadvantage; f o r i t i s p r e c i s e l y i n ground t h a t i s c u t up t o a c o n s i d e r a b l e degree t h a t t h e consur~lption of s o i l r i s e s t o enormous p r o p o r t i o n s . On t h e o t h e r hand, such an arrangement represc!llts a

g a i n f o r t h e e n t i r e i n s t a l l a t i o n , s i n c e v i s i b i l i t y and l a n d s c a p i n g i s g e n e r a l l y inlproved. In many p l a c e s i n America where f r e q u e n t d r i f t i n g o c c u r r e d , t h e f l a t t e n i n g o f f of t h e s l o p e s h a s been c a r r i e d o u t even on e x i s t i n g r o a d s , and, as Finney (1939) showed v e r y

c l e a r l y , improvements were always forthcoming. These o b s e r v a t i o n s t o some e x t e n t c o n t r a d i c t Schubert s f i n d i n g s (1903 )

,

who recommends a s l o p e a n g l e of n o t more t h a n 1 : 1 0 and f u r t h e r s t a t e s t h a t when low d r i f t i n g o c c u r s (snow sweeps) d r i f t s can s t i l l form. It i s e a s i e r t o b e l i e v e F i n n e y l s well-founded i n v e s t i g a t i o n s (1939), f o r i n s t a t i n g h i s r e s e a r c h p l a n he i s more c a r e f u l inasmuch as he s u g g e s t s a r a t i o o f 1 :

6.5.

B. Raising t h e Roadway R a i s i n g t h e roadway o v e r t h e l e v e l o f t h e s u r r o u n d i n g t e r r a i n , as a l r e a d y mentioned i n S e c t i o n 11, p r o v i d e s e x c e l l e n t p r o t e c t i o n a g a i n s t d r i f t i n g snow. T h i s method i s used everywhere t o d a y i n new r o a d s b u i l t o v e r f l a t c o u n t r y . Most a u t h o r s a g r e e on t h e r e q u i r e d h e i g h t , s t a t i n g t h a t i t must be a t l e a s t as h i g h as t h e maximum

d e p t h of snow t o be expected under non-windy c o n d i t i o n s . To p r e v e n t s n o w d r i f t s on t h e crown, a c c o r d i n g t o Finney (1939) t h e embankment s l o p e s s h o u l d have a n i n c l i n a t i o n of 1 : 4 ( F i g . 2 0 ) . A s i m i l a r

c r o s s - s e c t i o n , where t h e roadway i s a d d i t i o n a l l y p r o t e c t e d by e a r t h embankments, w a s given by Benterud (1947) f o r t h e road from Smolensk t o Minsk i n Russian ( F i g . 2 1 ) .

C . The E r e c t i o n o f F e n c e - l i k e S t r u c t u r e s o r Walls ( h i d e Walls, ~ a f f l e s )

These i n s t a l l a t i o n s a r e i m p o r t a n t c h i e f l y i n h i g h l a n d r e g i o n s s i n c e h e r e t h e very l a r g e q u a n t i t i e s of d r i f t i n g snow r e n d e r t h e e r e c t i o n of f e n c e s , which a r e o f t e n blown f u l l a f t e r a few h o u r s , of l i t t l e a v a i l . S t r u c t u r e s of t h i s k i n d can be e r e c t e d , of c o u r s e , o n l y a t p l a c e s where a w e l l - d e f i n e d wind d i r e c t i o n i s known; even a t s l i g h t d e v i a t i o n s from such d i r e c t i o n s t h e y become i n e f f e c t i v e , and under c e r t a i n c i r c u m s t a n c e s even d i r e c t a d d i t i o n a l snow o n t o t h e o b j e c t t h e y a r e i n t e n d e d t o p r o t e c t .

Schubert (1903) was t h e f i r s t t o mention such devices. He suggests e r e c t i n g s l a b s with a s l o p e i n t h e wind d i r e c t i o n of 30

-

45', i n which case an a r e a extending a d i s t a n c e of

8

m behind t h e s l a b s , if t h e s e have a h e i g h t of 1 . 5 m, w i l l become heaped up, s i n c e a s o r t of unloading w i l l occur a s a r e s u l t of t h e d e c r e a s i n g wind flow ( ~ i g . 2 2 ) . Unfortunately he has n o t h i n g t o s a y about t h e width of t h e t r a c k t h a t i s f r e e of snow. This system has n o t been taken up by l a t e r a u t h o r s , s o t h a t t h e r e a r e no p o s s i b i l i t i e s of comparison.

A more u s e f u l system c o n s i s t s i n t h e e r e c t i o n of v e r t i c a l w a l l s g e n e r a l l y s e v e r a l metres high in such a d i r e c t i o n t h a t they d e f l e c t t h e wind (guide w a l l s ) and cause t h e snow t o de deposited o u t s i d e t h e i n s t a l l a t i o n t h a t i s t o be p r o t e c t e d . One of t h e b e s t examples of t h i s i s found along t h e Parsennbahn, two s e c t i o n s of which a r e shown diagrammatically i n F i g . 23 ( s e e a l s o Fig. 91-93). It w i l l n o t be p o s s i b l e t o determine t h e e x a c t form of the d e p o s i t here u n t i l next autumn a f t e r t h e f i r s t snows. According t o t h e r a i l r o a d

employees t h e s e i n s t a l l a t i o n s have made i t niuch e a s i e r t o keep t h i s s t r e t c h of r a i l r o a d open. O f course, s e v e r a l y e a r s experimenting by t r i a l and e r r o r was necessary b e f o r e s a t i s f a c t o r y r e s u l t s were

obtained. The c o n d i t i o n s were favourable in t h a t t h e wind which b r i n g s t h e l a r g e s t amount of snow follows t h e ~ o r f t g l i r a t h e r e x a c t l y and t h u s blows p r a c t i c a l l y p a r a l l e l t o t h e r a i l r o a d l i n e .

B a f f l e s c o n s i s t of h o r i z o n t a l wooden p a n e l s o r staggered boards i n c l i n e d somewhat towards t h e wind s o t h a t t h e r e s u l t i n g nozzle

i n c r e a s e s t h e wind v e l o c i t y ( F i g .

2 4 ) .

There a r e no r e p o r t s about experience with them, although t h e s e devices a r e mentioned r a t h e r f r e q u e n t l y . D e t a i l e d i n v e s t i g a t i o n s should be c a r r i e d o u t here, f o r in t h e view of t h e a u t h o r they might be u s e f u l on t h e troublesome h i l l s i d e roads i n t h e a l p i n e r e g i o n s .

Here, f o r t h e sake of completeness, we should a l s o mention t h e hollowed s l a b s , and t h e guide walls, b a f f l e s , e t c . used i n avalanche c r i b b i n g , although they a r e never used i n road construc- t i o n . T h e i r purpose i s t o prevent e ~ c e s s i v e accwnulations of snow in f r a c t u r e zones. The snow i s conducted by guide w a l l s i n t o l e s s

dangerous areas, o r t h e grooved s l a b s a r e used t o reduce the t h i c k - ness of the snow cover.

D. The Erection of Parapets Which Conduct the- Wind and Snow Over t h e Object

Enormous q u a n t i t i e s of d r i f t i n g snow a r e c a r r i e d by t h e wind e s p e c i a l l y along mountain s l o p e s when i t blows i n t h e d i r e c t i o n of t h e g r a d i e n t . On t h e Gotthardstrasse t h e author observed, f o r

example, a f t e r the removal of snow a few cm deep, t h a t a depression

20 cm wide and

15

cm deep running p a r a l l e l t o t h e slope was

completely f i l l e d i n again i n 10 minutes. Keeping roads of t h i s kind open with snow blowers o r ploughs i s extremely uneconomic i f a t a l l p o s s i b l e . For t h i s reason t h e railways, which a r e p a r t i c u - l a r l y i n t e r e s t e d i n the continuous maintenance of t r a f f i c , use snow sheds t o p r o t e c t t h e i r l i n e s i n some a r e a s ( e . g . Berninabahn,

Wengeneralpbahn, Gornergra tbahn, Parsennbahn )

.

However keeping t h e entrances t o t h e snow sheds open remains something of a problem. They f r e q u e n t l y have t o be p r o t e c t e d by snow fences o r guide w a l l s

( e

.

g. Parsennbahn, Fig. 2 6 ) .

Schubert (1903) r e p o r t s on a p r o t e c t i v e i n s t a l l a t i o n on t h e former d s t e r r e i c h i s c h e ~fidbahn in Karst between Laibach and T r i e s t e , where walls

6

m high d e f l e c t t h e wind so t h a t t h e snow i s blown over t h e c u t (Fig. 2 5 ) . Such i n s t a l l a t i o n s , however, a r e e f f e c t i v e only above a c e r t a i n wind speed, a p o i n t t h a t i s p a r t i c u l a r l y emphasized by Schubert (1903). He a l s o mentions t h a t on c e r t a i n Russian r a i l - roads, snow ramparts a r e produced by means of movable panels on both s i d e s of the l i n e . The panels h e l p t h e u s u a l l y s t r o n g wind t o

blow t h e snow over t h e road. Since e i t h e r of these systems o f f e r s only doubtful s e c u r i t y they a r e no longer considered f o r the

e s s e n t i a l l y higher demands which a r e made today on t h e maintenance of communications.

E. The Use o f Rows of Trees and Hedges

The p l a n t i n g of hedges. and rows of t r e e s forms an e f f e c t i v e p r o t e c t i o n a g a i n s t t h e snow, and u n l i k e a l l o t h e r i n a t a l l a t i o n s i t

i s t h e l a r g e amount of space involved. Often people suppose t h a t a f t e r t h e s e have.been p l a n t e d t h e y can be l e f t t o themselves. The c o n t r a r y i s t h e case; f o r without continuous c a r e t h e y w i l l never provide optimum p r o t e c t i o n . However, a c c o r d i n g t o a s t a t e m e n t I n

"Engineering and c o n t r a c t i n g " (1920) t h i s method c o s t s o n l y

o n e - t h i r d t o . o n e - h a l f a s much a s t h e annual r e - e r e c t i o n of wooden f e n c e s , and moreover a f t e r

7

y e a r s t h e y become more e f f e c t i v e t h a n f e n c e s .

U n t i l t h e arrangement h a s reached f u l l e f f e c t i v e n e s s t h e

endangered s p o t s must be p r o t e c t e d w i t h snow f e n c e s . This has t h e a d d i t i o n a l advantage t h a t t h e most favourable arrangements can be determined by means o f t h e s e f e n c e s in experiments t h a t extend over s e v e r a l y e a r s . An experiment of t h i s kind i s t o be a t a r t e d n e x t y e a r by M r . R e g l i

a ant.

Tiefbauamt T e s s i n ) i n t h e B e d r e t t o t a l . In s e l e c t i n g t h e p l a n t s t h e f o l l o w i n g p o i n t s must be considered (Finney, 1937 ) : 1. The c l i m a t e and t h e n a t u r e of t h e s o i l 2 . B i o l o g i c a l f a c t o r s : ( a ) Maximum h e i g h t ( b ) Density ( c ) L i f e expectancy ( d ) A d a p t a b i l i t y ( e ) R e s i s t a n c e t o wind ( f ) Moisture consumption (g) Ease of p l a n t i n g

( h ) S u s c e p t i b l i t y t o s l e e t , h a i l , heavy snow loads ( I ) Cost of maintenance

3.

Economic f a c t o r s : ( a ) E f f e c t i v e n e s s a s a snow s h i e l d ( b ) Usefulness of wood f o r b u i l d i n g o r b u r n i n g

4.

S u s c e p t i b i l i t y t o damage: ( a ) By i n s e c t s ( b ) By d i s e a s e : 1. S u s c e p t i b i l i t y t o c e r t a i n d i s e a s e s 2. L i a b i l i t y t o a c t a s .a h o s t f o r c e r t a i n d i s e a s e s o f u s e f u l p l a n t s o r f r u i t s

( c ) S u s c e p t i b i l i t y t o rodents

5.

Aesthetic f a c t o r s :

( a ) Appearance along t h e roadside ( b ) Adaptation t o t h e whole landscape

6.

Value a s a p r o t e c t i o n and source of food f o r wild l i k e

7.

Cost of r e a r i n g

8.

Number of years required f o r maintenance.

Schubert (1903) suggests t h e use of c o n i f e r s ; f o r according t o t h e experience of t h e South Russian r a i l r o a d s deciduous t r e e s

( a c a c i a s ) r e q u i r e s t r i p s a s wide a s 30 m ( c o n i f e r s w i l l not grow i n

these r e g i o n s ) . Moreover, p r e c i s e l y during t h e time when they a r e needed a s p r o t e c t i o n deciduous t r e e s show t h e i r lowest d e n s i t y . A

disadvantage of c o n i f e r s i s t h e dying o f f of t h e lower branches under t h e required conditions of dense growth, s o t h a t a f t e r a c e r t a i n

time t h e d e n s i t y in the important lower p a r t s f r e q u e n t l y becomes inadequate. This condition can be combatted by progressive r e f o r - e s t a t i o n o r by t h e i n s t a l l a t i o n of wooden w a l l s .

The author made t h i s i d e n t i a l observation on t h e ~ S d o s t b a h n a t Altmatt where t h e r e was a 30

-

40 year old p r o t e c t i v e screen of fir

c o n s i s t i n g of two rows of t r e e s p l a n t e d a t i n t e r v a l s of 1 m from t r e e t o t r e e . Large gaps were showing c l o s e t o t h e ground. The r e a r i n g of t h e s e t r e e s was s a i d t o have been troublesome from t h e very beginning because t h e marshy s o i l i n which they had been p l a n t e d was too wet f o r them. Since today t h e grove i s of only l i m i t e d

e f f e c t i v e n e s s wooden w a l l s have a l r e a d y had t o be b u i l t in p l a c e s . Thus a poor choice of v a r i e t y here had r e s u l t e d i n t h e u s e f u l n e s s of t h e grove becoming impaired a f t e r a comparatively s h o r t time.

P r o t e c t i v e s t r i p s o r i g i n a l l y p l a n t e d a l l t o g e t h e r must l a t e r o f t e n be improved by thinning and r e p l a n t i n g . Schubert (1903)

mentions t h a t such arrangements a r e indeed c o s t l y , but t h a t they pay i n the long

run.

Croce (1943) i n h i s s e r i e s of t e s t s t r i e d a beech hedge, and a low and a high pine hedge f o r comparison with snow fences. He comes t o the following conclusions :

The d e p o s i t s a t t h e hedges were i n a l l c a s e s g r e a t e r t h a n a t t h e f e n c e s , b u t of c o u r s e t h e g r e a t e r h e i g h t o f t h e hedges may have had a c e r t a i n i n f l u e n c e . He could g i v e no d i r e c t proof, b u t i s

convinced t h a t a t l e a s t a n e q u a l e f f e c t can be o b t a i n e d w i t h hedges a s w i t h f e n c e s , even though t h e beech hedge i n p a r t i c u l a r , was

r a t h e r l o o s e l y c o n s t r u c t e d . There i s a c e r t a i n d i f f i c u l t y i n d e t e r m i n i n g t h e r e q u i r e d d i s t a n c e from t h e o b j e c t t o be p r o t e c t e d because c o n d i t i o n s change w i t h time owing t o t h e growth of t h e

p l a n t . The a u t h o r l e a v e s t h i s q u e s t i o n open, because f u r t h e r t e s t s would be r e q u i r e d t o s e t t l e i t .

Finney (1337) h a s c a r r i e d o u t v e r y e x t e n s i v e i n v e s t i g a t i o n s b o t h i n t h e f i e l d and i n t h e wind t u n n e l i n t o t h e problem of u s i n g p l a n t s . F o r t h e p l a n t i n g of c o n i f e r s he s u g g e s t s t h e arrangement shown in F i g . 27. The number of rows can be v a r i e d a c c o r d i n g t o t h e i n t e n s i t y of t h e d r l v i n g snow. The rows a r e p l a c e d

1.5

m a p a r t , t h e t r e e s b e i n g s t a g g e r e d from row t o row. I f p e r i o d i c t h i n n i n g of t h e grove i s planned an i n t e r v a l of

60

t o 7 0 cm i s chosen f o r t h e

d i s t a n c e between t r e e s ; o t h e r w i s e i t can be i n c r e a s e d t o 1 . 2 m, i n which c a s e t h e rows a r e spaced

3

m a p a r t . A b a s i c a l l y s i m i l a r arrangement i s used w i t h deciduous t r e e s . In a d d i t i o n , however,

bushes must be p l a n t e d in o r d e r t o a v o i d t o o much p e n e t r a t i o n between t h e t r u n k s ( F i g .

2 8 ) .

F i g u r e 29 i l l u s t r a t e s t h e shape of t h e snow d e p o s i t w i t h i n a p r o t e c t i v e grove. The e x c e l l e n t e f f e c t of a s t r i p of v e g e t a t i o n i s due t o t h e s t r o n g d e c e l e r a t i o n of t h e wind speed, which, as F i g . 30 shows, i s reduced t o a few p e r c e n t of i t s unchecked v a l u e . From h i s wind t u n n e l t e s t s Finney (1937) a l s o determined t h e e f f e c t of t h e l e n g t h of t h e v o r t e x zone, and hence t h e r e l a t i o n

between t h e l e n g t h of t h e d e p o s i t and t h e h e i g h t ( F i g .

31)

and width of t h e p r o t e c t i v e grove ( F i g . 3 2 ) , a r e l a t i o n s h i p of g r e a t importance i n p l a n n i n g . To be s u r e , t h e a u t h o r s a y s n o t h i n g whatever about t h e s c a l e c o n d i t i o n s of h i s i n v e s t i g a t i o n s . The r e s u l t s a r e t h e r e f o r e , as w i l l be e,xplained l a t e r i n more d e t a i l , t o be t a k e n w i t h a c e r t a i n c a u t i o n . A s a mean d i s t a n c e from t h e o b j e c t t o be p r o t e c t e d ,

however,

15

t i m e s t h e expected h e i g h t of t h e t r e e s can be t a k e n as c o r r e c t . Finney (1937) a l s o i n v e s t i g a t e d t h e u s e f u l n e s s of niany

coniferous and deciduous v a r i e t i e s i n America. For t h e r e s u l t s of t h i s work, however, we must r e f e r t h e r e a d e r s t o t h e o r i g i n a l

l i t e r a t u r e .

I n summing up i t may be emphasized t h a t - t h e use of t h i s

n a t u r a l type of p r o t e c t i o n a g a i n s t d r i f t i n g , which g e n e r a l l y blends well with t h e landscape, should be encouraged. In cases.where t h e o r i g i n of t h e d r i f t i n g snow i s known, t h e combative measures should be c a r r i e d o u t i f p o s s i b l e a t t h e source of t h e t r o u b l e . Often even a s p a r s e r e f o r e s t a t i o n o r t h e d i v i d i n g up of l a r g e r f i e l d s by means of hedges w i l l be q u i t e e f f e c t i v e . I n our t e r r a i n , w h i c h , i s o f t e n very c u t up, and l a r g e f i e l d s a r e comparatively r a r e , such "sources of d r i f t i n g snow" should be r a t h e r easy t o l o c a t e and n e u t r a l i z e .

F. The E r e c t i o n of Snow Fences

Since t h i s type of p r o t e c t i o n i s t h e most conlrnonly used of a l l today, and i t s d e s c r i p t i o n i s t h e r e f o r e r a t h e r long, t h i s m a t t e r w i l l be d e a l t with s e p a r a t e l y in another s e c t i o n .

G. The Widening of Cuts

This measure i s p r a c t i c a l l y i d e n t i c a l with t h a t described under A , s i n c e t h e same p r i n c i p l e s hold. By widening t h e s l o p e s , however, t h e i n t e n t i o n i s n o t s o much t o c a r r y t h e snow away over t h e road as t o provide s u f f i c i e n t space on t h e s l o p e f o r t h e

d e p o s i t i n g of t h e snow. The observations of Gloseys (1946) i n Dakota and E a s t Montana, U.S.A., a r e p a r t i c u l a r l y i n t e r e s t i n g . H e

found t h a t v e r t i c a l o r almost v e r t i c a l c u t s a r e considerably l e s s d r i f t e d than f l a t ones. This confirms t h e observations of

Tschirwinsky (1931), who could f i n d no d r i f t i n g a t s l o p e s s t e e p e r than 1 : 1.5. Deep c u t s a r e t h e r e f o r e n o t modified, a s a r u l e , but f l a t ones with an angle of more than 30' a r e normally d e a l t with by t h e method advocated by Finney (1939). I n deep c u t s a r u l e of thumb i s t o spread o u t t h e s l o p e s t o 2.5 t i n ~ e s t h e i r h e i g h t . I n o r d e r t o g a i n a d d i t i o n a l space f o r t h e masses of snow accuniulating i n t h e course of c l e a r i n g o p e r a t i o n s , t h e f o o t of t h e slope i s g e n e r a l l y c u t back 1 t o

3

m from t h e edge of t h e roadway.

H. Makeshift Devices

Various makeshift devices f o r p r o t e c t i o n a g a i n s t snow were employed, p a r t i c u l a r l y i n t h e Russian campaign, but a r e h a r d l y con- s i d e r e d f o r c i v i l i a n purposes. They a r e l i s t e d h e r e c h i e f l y f o r t h e sake of completeness ( p e t e r s e n , 1942).

1. Walls made of blocks of snow

If t h e snow cover had s u f f i c i e n t cohesion blocks were c u t w i t h

dimensions of

35

35

.

20 cm and were s t a c k e d i n rows 2 t o

3

blocks high.

2 . Snow mounds

These a r e u s u a l l y c o n s t r u c t e d from non-cohesive snow covers. According t o Smith (1946), t h i s i s indeed one of t h e p r i n c i p a l methods employed i n Antrim County, North Michigan. The average annual snowfall t h e r e i s

3.5

m, but t h e d r i f t s normally appear only a f t e r t h e heavy f a l l s which occur towards t h e end of t h e w i n t e r . Thus, during t h e time when ploughs and snow-clearing machines a r e n o t otherwise occupied t h e y a r e used t o c o n s t r u c t a s e r i e s of

d i t c h e s and ramparts running p a r a l - l e l t o t h e roads ("snow t r a p s " ) . This work i s s a i d t o be p r o f i t a b l e because i t saves many hours of ploughing and r e n d e r s unnecessary t h e time-consuming e r e c t i o n of

snow fences; f o r a t o t a l of 650 k m of roads 100 km of snow fences would be r e q u i r e d . The county i s a l s o employing f o r c e d growths of evergreens and hedges. Approximately 40,000 t r e e s and bushes have a l r e a d y been p l a n t e d , but of course d i f f i c u l t i e s f r e q u e n t l y a r i s e with t h e farmers who have t o be compensated f o r the l o s s of land. The method o f t e n employed fo6merly i n Russia f o r t h e formation of snow ramparts by means of snow fences w i l l be r e p o r t e d on i n t h e n e x t s e c t i o n .

3 .

E a r t h ramparts

E a r t h ramparts c o n s t i t u t e an extremely p r i m i t i v e form of pro- t e c t i v e i n s t a l l a t i o n . In Russia, however, where g e n e r a l l y enough space i s a v a i l a b l e , they a r e f r e q u e n t l y r e s o r t e d t o ( F i g . 21) and t h e y have t h e advantage of r e q u i r i n g no maintenance.

4. Walls made from branches of f i r , p i n e , o r from r e e d s

This extremely p r i m i t i v e and n o t very e f f e c t i v e d e v i c e i s

r e s o r t e d t o i n c i v i l i a n use o n l y in c a s e s of extreme urgency.

IV.

Snow Fences

The e r e c t i o n of snow f e n c e s i s t h e commonest means of p r o t e c - t i o n a g a i n s t d r i f t i n g used today because compared with o t h e r

methods i t has c e r t a i n b a s i c advantages:

1. When p r o p e r l y e r e c t e d t h e y a r e q u i t e e f f e c t i v e .

2. T h e i r e f f e c t i v e n e s s can be improved o v e r t h e y e a r s by r e l o c a t i o n without a d d i t i o n a l c o s t .

3 .

No a r a b l e land i s l o s t because t h e f e n c e s a r e e r e c t e d o n l y in t h e non-growing season.

4.

The c o s t s p e r running metre a r e comparatively low, although of course a n n u a l l y r e c u r r i n g o u t l a y s have t o be made f o r e r e c t i o n and s t o r a g e .

A disadvantage, however, i n common with most o t h e r t y p e s of p r o t e c t i o n i s t h e s t r o n g d i r e c t i o n a l e f f e c t .

A . Types of Fence

I n former y e a r s fences were u s u a l l y manufactured by t h e

a u t h o r i t i e s themselves o r by l o c a l tradesmen, s o t h a t t h e r e a r e a g r e a t many types which u s u a l l y vary fromone a d m i n i s t r a t i v e d i s t r i c t t o t h e n e x t . Only r e c e n t l y , with t h e development of f a c t o r y - b u i l t f e n c e s ( ~ i c o fence, coco f i b r e f e n c e ) has t h e r e been a t r e n d towards

a c e r t a i n s t a n d a r d i z a t i o n , because most a d m i n i s t r a t i o n s when

r e p l a c i n g e a r l i e r equipment o r p r o c u r i n g new ones t e n d t o purchase f i n i s h e d p r o d u c t s .

Despite t h i s g e n e r a l s t a n d a r d i z a t i o n t r e n d we s h a l l i l l u s t r a t e and d e s c r i b e a number of t y p e s , which w i l l c l e a r l y show t h e v a r i e t y of s o l u t i o n s t h a t have been attempted f o r t h i s one problem and

i n d i c a t e t h e continuous s t r i v i n g f o r improvement. In o r d e r t o d i s t i n g u i s h between t h e many types and t o avoid subsequent compli- c a t e d circumlocutions, d i f f e r e n t f e n c e s w i l l be given geographic