Flexible steel net barriers that hold the snowpack in the starting zone before an avalanche forms, instead of stopping it further down the slope. The design follows from the extreme snow height, slope angle, aspect, and the creep and glide factors.
Systems
- SPIDER Avalanche snow netGeobrugg, imported
- Anchors and micropilesInstalled by Artusa
The problem
An avalanche is expensive to stop once it is moving and comparatively cheap to prevent in the starting zone. The starting zone is the steep upper section where the snowpack tends to slide under its own weight; when the snow layer loses its bond with the ground a fracture surface forms and the whole cover starts to move. Below are road corridors, mountain villages, tourism facilities and power lines. A closed road is a recurring cost.
The warning signs are read in winter and in summer alike. In winter: cracks opening in the snowpack, sliding snow slabs, cornices, a weak layer between new and old snow, wind-loaded lee slopes behind a ridge. In summer: tree trunks bent downslope, no trees above a certain elevation, avalanche chutes cut into the slope, a mixture of rock and timber piled at the toe. These traces tell the location and width of the avalanche path before an event is ever seen.
How we decide
What we measure and compile: the boundaries of the starting zone, slope angle and aspect, the regional value of the extreme snow height, snow density, ground roughness and vegetation, the wind-loading direction, the width of the avalanche path and the position of the target. The load the snowpack imposes grows with the square of the snow height; an error in the height estimate goes straight into the design.
| Observation | Criterion | Decision |
|---|---|---|
| Starting zone defined and accessible | Slope angle within the avalanche formation range | Barrier lines in the starting zone |
| Starting zone wide and scattered | Barrier area not economical | Deflection dams, a gallery or road regime below |
| Wind loads a particular ridge | Loading direction can be measured | Snow fences behind the ridge, plus barriers |
| No snow height measurement record | Regional data uncertain | A snow measurement station and an observation period first |
| Rockfall on the same slope in summer | Two hazards threaten the same line | A shared line, assessed separately for each hazard |
The barrier height comes directly from the extreme snow height; the line spacing is calculated from the slope angle and the barrier height. Lines are built overlapping, not in isolated segments: the end gap of one line must be covered by the body of the line above, otherwise snow leaks through the gap and the line fails at its own edge. Seismic action enters the anchor design under the applicable national code.
System family
| System | When it fits | Source |
|---|---|---|
| Flexible snow net barrier | Holding the snowpack in place in the starting zone | Geobrugg, imported |
| Cable anchors and micropiles | Tying the barrier feet into rock or soil | Installed by Artusa |
| Snow fences and deflection structures | Drift management and road protection | Assessed project by project |
| Ring net panel | Local reinforcement, made to size | Made by Artusa |
Because flexible net barriers are light compared with rigid steel or concrete snow bridges, they can be carried by helicopter and by hand; on slopes where no road can be built this is decisive. The geometry and strength of the system are dimensioned with the coefficients that describe the creep and glide behaviour of the snowpack; these vary with ground roughness, vegetation and aspect and are not taken as fixed at the desk. Outside the snow season the same barrier also holds small fragments, but this is secondary behaviour: a snow net carries no rockfall energy class.
Installation
Installation happens in a short seasonal window: it starts after the snowmelt and finishes before the first snow. Transport of material is the most critical item; where there is no road, helicopter rotations are planned and the weight and package size are split accordingly.
- Setting out: marking line axes and foot points, overlap check.
- Anchors and micropiles: drilling, cleaning, grouting, setting time record.
- Feet and post installation: alignment perpendicular to the slope and level check.
- Net and cables: panel laying, pre-tensioning, tightening of connectors.
- Close-out: ID tag plate, as-built survey, repair of transport tracks.
Control points: anchor pull-out test, foot spacing and vertical barrier height, line spacing and overlap length, cable pre-tension, coating integrity. Work at height is organised under EN 795 and EN 365.
Acceptance and maintenance
The handover file holds the as-built line plan, anchor pull-out test results, barrier height measurements, line spacing and overlap checks, the cable pre-tension list and the corrosion protection documents (in the frame of EN ISO 1461). The extreme snow height used in the design and its source are written down as well, to be compared with the values actually measured in later inspections.
Maintenance takes place after the snowmelt. Checked: settlement or slippage at feet and anchor heads, bending in posts, breaks in nets and cables, loosening of connectors, damage to the coating. If afforestation has started on the slope it is recorded; a mature forest shares the barrier's load in the long run.
Frequently asked
- Does a snow net stop an avalanche? It does not stop it; it prevents it from forming. Once movement has started, other structures such as deflection dams or galleries are needed.
- In which season is it installed? In the window between snowmelt and the first snow.
- Does the same barrier hold rockfall? It helps against small fragments but carries no rockfall energy class. Where both hazards are present the line is assessed separately under rockfall protection criteria.
System and product pages (Turkish)
Field record
4 projects in this family in our records, 2012–2025: Türkiye. Under confidentiality agreements, project and client names are not published.