Fences against snow
A fence does not stop winter. It moves the place where the snowdrift settles, so that it does not lie on the carriageway. Below is a cross-section: move the fence and see where the outline ends.
Cross-section model: fence, snowdrift and conventional carriageway
No intersection +4.8 m gap to the carriageway edge (model result)
Model diagram, not a measurement and not a map. Horizontal scale in metres (10 m bar), vertical scale exaggerated ×7. The fence is drawn symbolically, model height 1.5 m, conventional carriageway 12 m.Model, not a measurement · vertical ×7 · bar = 10 m
Step 1Where will the fence stand?
The slider moves in 1 m steps, the buttons in 5 m steps. The previous position stays as a thin line.
Step 2How much should it let through?
Front view of the fence: 7 horizontal boards, as in the cross-section. The light stripes are gaps; the more of them, the greater the share of gaps.
Gaps 50%: that share of the fence area is gaps, the rest is boards.
In Tabler’s studies, fences with a porosity of around 40–50% collected the most snow in the conditions tested [2] range to be checked. This sketch draws the extent of the outline, not the volume of snow, so it does not point to an “optimum”.
Step 3Where does the wind blow from?
The outline checked is always the one that could reach the carriageway. With wind from the field, it is the snowdrift behind the fence. With wind from the road, it is the snowdrift in front of the fence, on the road side.
Model resultDoes the snowdrift touch the road?
The outline ends 4.8 m before the carriageway edge
With D = 35 m and 50% gaps, the leeward snowdrift outline (behind the fence, towards the road) is checked: its extent in the model is 30.2 m. It does not reach the assumed 3 m buffer.
This is the result of a geometric sketch with assumed curves, not a recommendation for where to place a fence or an assessment of whether the road is passable.
No trace yet: change any parameter and the previous outline will stay in the drawing as a thin dashed line.
- Ochre: the snowdrift outline being checked.
- Thin grey outline: the other snowdrift, not checked for this wind direction.
- Thin dashed line: the previous setting or the pinned reference.
- Thick bar below ground: the gap between the outline and the carriageway edge. In case of an intersection it is the length of the encroachment, and on the carriageway the ochre covers the part taken.
- Dotted line: the 3 m buffer before the carriageway.
| Parameter | Previous | Now |
|---|---|---|
| Distance D | none | 35 m |
| Gaps | none | 50% |
| Wind | none | from the field towards the road |
| Outline extent L | none | 30.2 m |
| Gap to carriageway | none | +4.8 m |
| Model assessment | none | No intersection |
“None” means there is no previous setting, not a value of zero.
The same fence, four settings side by side
All four drawings use the same scale as the model above. In this sketch the dense fence (C) collects snow mainly in front of itself and has a short outline behind it. The sparse one (D) lets more wind through, so the outline reaches further. This is a property of the assumed curves, not the result of measurements.
Scale as in the model above: horizontal in metres, the bar under each drawing = 10 m, vertical exaggerated ×7. On a phone, the model and these drawings show the same approximate frame of 75 of 114 m. Each drawing is a model diagram, not a measurement or a map.
Why a fence is put up in the field
The fence is meant to collect snow further out than the snowdrift outline reaches. The question for the model is therefore: how many metres are left between the end of the outline and the carriageway?
What a screen does
A screen reduces the wind speed and changes its profile. Snow grains moving near the surface are no longer carried and fall, forming a snowdrift [2] to be checked in the source. With an impermeable obstacle, deposition begins on the windward side, which is why in the model a dense fence has a large snowdrift in front of it.
How it used to be done
GDDKiA lists movable screens made of nailed laths, wooden walls and elements woven from wicker, and alongside them forest belts, fences and hedges [1] to be checked in the source. According to this study, picket fences were put up in the fields before the frosts and taken down in spring, and road workers also drew on experience of clearing snow from railway tracks.
What this sketch does not know
It knows nothing of the terrain relief, embankments, ditches, snow moisture, wind variability or the amount of snow in a season. The snowdrift curves are a didactic assumption, not a fit to measurements.
Limits of the model
- The shape and extent of the outline are the page’s own curves from version V2: didactic, not a design calculator.
- Assumed: fence 1.5 m, conventional carriageway 12 m, buffer 3 m, distance 10–55 m, gaps 10–90%.
- The horizontal scale is in metres, the vertical exaggerated ×7. The fence is drawn symbolically. On a narrow screen (up to 640 px) the drawings show an approximate frame of 75 of 114 m, at the same scale for the model and variants A–D; the fence placed furthest away (55 m) fits in the frame.
- With wind from the road, the snowdrift in front of the fence is checked. V2 always treated this direction as safe, which was a simplification.
- The range of applicability of the sources on porosity and distance should be checked by a specialist. A single percentage is not an instruction for every terrain.
What was removed from V2 and why
- Log of attempts in the browser. Replaced by a “previous / now” comparison and by pinning a reference. The page saves nothing.
- Fence height and snowdrift saturation. They scaled the extent proportionally, so they turned a poster into a control panel. The fixed 1.5 m from V2 remains.
- Four variant buttons. Replaced by four drawings at once, because the difference is easier to see simultaneously.
- Embedded photograph from Wikimedia Commons. A dependence on the network. A link remains in the sources.
- A sentence about railway tracks in cuttings as the first places of large-scale trials. Omitted, because I did not confirm it in this version.
Sources
The links come from version V2. In this version they were not opened or checked again, and their summaries need verification.
- Generalna Dyrekcja Dróg Krajowych i Autostrad [General Directorate for National Roads and Motorways], „Tak kiedyś utrzymywano zimą drogi” [How roads used to be kept in winter], 23 November 2019. Historical forms of wooden and wicker screens, railway experience, manual and horse-drawn methods of winter maintenance. to be checked
- Ronald D. Tabler, „Controlling Blowing and Drifting Snow”, NCHRP, 2003. The mechanics of snow transport, the effect of porosity in the conditions tested (according to V2: ch. 3, pp. 23–24, 46–47). range of conditions to be checked by a specialist
- Chris Light, „Snow Fence 0551”, Wikimedia Commons, photograph of fences in Wyoming, licence according to V2: CC BY-SA 4.0. It is not embedded on this page; it is only a comparison link. rights to be checked again
