Controling Snowdrifts

Transcription

1 Controling Snowdrifts Masaru Matsuzawa, Ph.D. Civil Engineering Research Institute for Cold Region, Public Works Research Institute, JAPAN

2 Contents I. Characteristics of blowing/drifting snow Snowdrift

3 I. Characteristics of blowing/drifting snow Modes of Snow Transport Wind Suspension Creep Saltation Takeuchi (1990)

4 I. Characteristics of blowing/drifting snow Modes of snow transport Saltation Tabler (1986) Suspension

5 I. Characteristics of blowing/drifting snow Weather conditions under which blowing snow occurs continuous suspension intermittent suspension predominant saltation (Takeuchi et al., 1986)

6 Snow transport rate 吹雪量 ( g/m s) I. Characteristics of blowing/drifting snow Horizontal distribution of snow transport rate U 100 : wind velocity at 1 m in height U 100 = 8. 4 m/s U 100 = 5. 2 m/s U 100 = 8. 7 m/s snow transport rate wind U 100 = 7. 3 m/s Fetch (m) 400 U 100 = 7. 2 m/s 吹走距離 ( m) Takeuchi (1980)

7 I. Characteristics of blowing/drifting snow Typical snowdrift formation Wind velocity decreases near obstacles, so the transport force is weakened and snow starts accumulating. Turbulent eddies cause snow particles to separate from the airstream. The particles accumulate to form snowdrifts. Snowdrifts often form around obstacles such as cuts, buildings and cars. Photo by the Hokkaido Development Bureau

8 I. Characteristics of blowing/drifting snow Snowdrift formation at a cut section Tabler (2003) Tabler (2003)

9 Contents I. Characteristics of blowing/drifting snow Snowdrift

10 1. Snow fence Wyoming USA Japan Snow fence CERI (2011)

11 Characteristics of a snow fence Bottom Gap: the space between the ground and the bottom of the slats Porosity: the ratio of open area to total frontal area excluding the bottom gap Porosity Ratio = Opening to frontal area Bottom Gap

12 Snow depth (cm) Snow fence porosity and snowdrifts Wind Porosity Price (1961) Distance from snow fence Porosity: 30% (Japan) - 50% (USA)

13 Porosity: 30% Bottom gap and snowdrift Fence 柵 (m) ( m) 柵高 Fence =3. height 41 = 3.41m m 3 下部空隙 Bottom gap = = m 55 m 2 3 Mar. 月 28 日 1 2 Feb. 月 15 日 Jan 月 31 日 3 柵高 Fence =3. height 41 = 3.41m m 下部空隙 Bottom gap = = m 15 m Distance 柵から from snow の距離 fence ( m) Bottom gap: m, to prevent burial, to maintain effectiveness

14 Effects of ground slope on the shape of equilibrium snowdrifts Tabler (2003)

15 I-80: Site of 5 fences Copyright 2001 Tabler & Associates

16 Before snow fence installation (1971) I-80 Wyoming, U.S.A. Copyright 2001 Tabler & Associates

17 After snow fence installation (1972 present) I-80 Wyoming, U.S.A. Copyright 2001 Tabler & Associates

18 Solid barrier CERI (2011)

19 Location of solid barrier Too far from the road Too close to the road Proper Location of Solid Barrier CERI (2011)

20 2. Snowbreak woods

21 Basic structure of snowbreak woods The Highway Snowstorm Countermeasure Manual (2011 edition), Japan wind deciduous trees willow work path evergreen trees 23.0 m fir, pine, spruce deciduous trees snow-piling area 7.5 m road 4.0 m 3.0 m CERI (2011) Mean annual snow transport Width of woods 20-30m 3 /m ( t/m) 11.0m 30-50m 3 /m ( t/m) 23.0m 50m 3 /m or more (17.5t/m - ) 32.0m

22 3. Drift-free cut Provides a gradient of 1 : 3 on the windward slope Wind

23 Drift-free cut Before improvement (1969) Wind Snow (m) After improvement (1980) Ishimoto (1985) (cm)

24 Annual snow transport (t/m) Slope length of a drift-free cut Slope length 7 Ishimoto (1985) Slope angle (degrees)

25 4. Drift-control fill The fill height is 1.3 times the average maximum snow depth. Takeuchi(1973)

26 4. Drift-control fill (with a gentle slope) Tabler (2003)

27 Before Comparison of snowdrift between a fill section and a cut section Feb. 07, 2012 Before Fill section Cut section After Feb. 09, 2012

28 References Controlling Blowing and Drifting Snow with Snow Fences and Road Design; R. D. Tabler The Highway Snowstorm Countermeasure Manual (2011 Revised Edition -Abridged Edition- ; Civil Engineering Research Institute for Cold Region (CERI), PWRI. Thank you for your attention! Gracias por su atención!