Block B - Theory on Avalanche Release & Risk Control - Avalanche Detection

Samuel Wyssen

Content 1. 2. 3. 4. 5.

Risk analysis Properties of snow Effect of Explosives Hot Spot Theory Residual Risk

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Risk Reduction To reduce the Residual Risk for people travelling along roads or on ski slopes. Res. risk =

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probability of event x probability of presence x extent of damage

Risk Reduction Measures Res. risk = probability of event x probability of presence x extent of damage Res. risk = A x B x C

Type of intervention

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permanent temporary

Effective period

activ Structural: - snow bridges - damms - galleries - tunnels

passiv A B

artificial avalanche release A

Planning - hazard zone planning C Organisational - closures - evacuations

B

Risk Assessment (CH)

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Danger Levels (CH)

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Danger Levels (CH)

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Event Verification of Hazard Maps

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Awareness of the Situation Through artificial avalanche release the awareness … 

the snow and avalanche risk situation at the avalanche starting zones

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awareness of the conditions of the installation

… is guaranteed!

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Advantages of artificial avalanche release + Avalanche at controlled time period + early release to release small portions of snow -> smaller avalanches -> less damage + shorter closures of transport routes

+ no risk for staff + releasing independently of weather during day- or nighttime

+ small investment and running costs Vorname Name

+ environmentally friendly & reconstruction possible Member of

Content 1. 2. 3. 4. 5.

Risk analysis Properties of snow Effect of Explosives Hot Spot Theory Residual Risk

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Properties of Snow

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Properties of Snow The strength of snow is depending on the deformation velocity

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Properties of Snow Slow deformation velocity Viscous deformation No fracture

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High deformation velocity Brittle rupture Fracture

Properties of Snow

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Content 1. 2. 3. 4. 5.

Risk analysis Properties of snow Effect of Explosives Hot Spot Theory Residual Risk

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Explosive effect

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Explosive effect

130m / 5kg

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Field Tests – March/April 2010 & 2011 with Dr. H.U. Gubler, ALPUG Davos

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Selection of type of explosive/gas Explosive above snow

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Max. of air pressure reached after 3ms Vorname Name

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Gas mixture above snow “Gazex”

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Max. of air pressure reached after 11ms

Selection of type of explosive/gas Explosive above snow

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Max. of air pressure reached after 3ms Vorname Name

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Gas mixture above snow “Daisybell”

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Max. of air pressure reached after 11ms

Effective Range The effective range depends on charge position to snow

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Effective range 

Avalanche Tower / Explosive Cableway 5 kg Airblast (Expl. above snow) = 120-130 m

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Manually deployed charge 2,5 kg Expl. on the snow

= 35-40 m

Heli bombing / Daysibell 2,5 kg Expl. in the snow

= 25 m

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Effective Range of different type of explosives

To be veryfied by SLF Vorname Name

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Effective Range PhD work at SLF Davos to compare effective ranges of different releasing methods: - GazEx, Daisybell, Obell’X T.A.S., FR - Avalanche Guard Inauen-Schätti, CH - Avalanche Tower Wyssen, CH

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Choosing the Correct Time for Control Work Avalanche protection work should be carried out:

• Following heavy snowfalls, snow drifting events • If avalanche size is critical, protection work should be done at regular intervals during the snow fall to limit avalanche size.

• Blasting too early can give negative results • Blasting too late may result in too much snow being released • For triggering wet snow avalanches blasting has to be carried out shortly after the highest temperatures have been attained and cooling after sunset has set in. Vorname Name Member of

Content 1. 2. 3. 4. 5.

Risk analysis Properties of snow Effect of Explosives Hot Spot Theory Residual Risk

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Hot Spot Theory

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Hot Spot Theory

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Quelle: www.lawinenlehrgang.de

Hot Spot Theory

Hot Spot

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Quelle: www.lawinenlehrgang.de

Hot Spot Theory

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Quelle: www.lawinenlehrgang.de

Hot Spot Theory

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Quelle: www.lawinenlehrgang.de

Positioning of Charge

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Positioning of Charge

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Positioning of Charge

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Positioning of Charge

The complete potential avalanche starting zone has to be covered by the effective range of the system!

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Content 1. 2. 3. 4. 5.

Risk analysis Properties of snow Effect of Explosives Hot Spot Theory Residual Risk

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Residual Risk If no major avalanches have been released from a potential release zone, the result can be interpreted as a positive stability test if the following rules have been taken into consideration: • the complete area of the potential release zone has to be covered with the effective ranges of the individual detonations. • reduction of effective ranges by pressure wave shadowing has been taken into consideration • Stability tests are only conclusive for dry snow covers. • detonations must be verified • After negative tests wait at least 15 minutes at high snow temperatures and up to 1 hour at very low temperatures before the zone can be classified as safeguarded (time for mechanical relaxation of the snow cover). Vorname Name

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Residual Risk The residual risk is acceptable if the applied pressure on the potential starting zone is at least:

100 Pa

200 Pa Vorname Name

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• 100 Pa (with 5 kg above the snow ca. 130 m) in case of natural avalanche activity • 200 Pa (with 5 kg above the snow ca. 70 m) in case skiers might cross the area

Guidelines for Artificial Avalanche Control • Basics in risk theory • Basics on the formation of slab avalanches • Basics and experiences about artificial avalanche releasing • Interpretation of releasing success Vorname Name

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Content Block A 

Introduction



Avalanche Control in the Alps

Block B 

Theory on Avalanche Release & Risk Control

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Avalanche Detection

Block C 

Contracting & Organization of Avalanche control Teams

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Reference Projects Vorname Name

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Avalanche Detection With an increase of artificial release systems for the protection of traffic infrastructure, rises the demand for reliable avalanche detection systems. Goals:

1. Verification of artificial avalanche release 2. Detection of spontaneous avalanche activity Vorname Name

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Crucial information for the local avalanche control team

Requirements for operational use Wanted specifications of a detection system: 1. High detection rate (> 90%) 2. High availability (> 90%) 3. Easy to use - Good visualization (PC-Phone) 4. Maintenance only 1/year in summer 5. Remote control, self test 6. Price Vorname Name

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Avalanche Detection Most common methods: • Mechanical monitoring systems • Seismic monitoring • Doppler radar (“Avalanche Radar”) • Infrasound (“IDA©”)

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Avalanche Radar

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Avalanche Radar Historically avalanche detection with radar was not very practical due too: • Big and heavy equipment, not easy to transport and install • High power consumption • False alarms due to bad visibility and precipitation (wrong frequency range) Vorname Name

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Radar-Innovation 

New radar technology, especially developed for avalanche detection (Frequency of 10 GHz)

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Robust and compact design, developed for harsh alpine environments

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Remote control using mobile network, display alarms on PC or mobile phone

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PC-Software “Live Viewer” for data visualisation

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Low power consumption, which enables energy supply with solar panels Vorname Name

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Avalanche Radar Basics • Pulsed Doppler Radar scans endangered areas

• Monitors VELOCITIES from 1km/h – 300 km/h • Output of automatic alarm signal

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Detection Range With an opening roll of 5° range up to 2000 m With an opening roll of 10° range up to 1000 m 5° at 2000 m distance result in approx. 170 m width of the monitored area Vorname Name

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Advantages 

Reliable avalanche detection in real time

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No need for installations in the avalanche track

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Simple installation on a location not harmed by the avalanche activity

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Division of the monitored area into so-called range gates, which minimizes false alarms

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Low weight for mobile and stationary applications

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Great potential in combination with avalanche towers

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Range Gates

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Radar in Ischgl

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Radar in Ischgl

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Monitored area Ischgl

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PC-Software “Live Viewer”

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PC-Software “Data View”

900 m

0 km/h 180 km/h Vorname Name

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1800 m

List of alarms, after two seasons: Season 2012/13

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Season 2011/12 Calibration Time

Radar Ischgl

Radar References • • • •

Sedrun, Switzerland – Road & Railway Ischgl, Austria – Road Kaunertal, Austria – Road St. Anton, Austria - Skiresort

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Radar Review • Radar works operational • “Calibration Time” 4-6 weeks of monitoring, including 23 avalanches are required before alarms can be set

• Line of sight is needed • Restrictions by detection range (max. 2000 m) and width

(max. 200 m) of the radar Vorname Name

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Infrasound Detection of Avalanches - IDA©

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Infrasound Detection of Avalanches History Various infrasound systems have already been tested around the world:

• • • • •

Arfang-Switzerland, in the 90’s Scott-USA, since 2000 Uhu-Switzerland, since 2008 Item-Italy (“IDA”), since 2009 Item and Wyssen-Austria (“IDA”), since 2012

With a great variability of equipment, type of installation and detection algorithm!

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Infrasound Detection of Avalanches

Advantages: + Monitoring a wide area + No installations in the avalanche track necessary + Positioning of avalanche events + Good visualization of the detections on maps

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Disadvantages: − Very sensible to wind noise − Problems with detection of small avalanches − Many interfering signals (Helicopters, planes, etc.)

Infrasound-Facts • low frequency sound waves (1 Hz – 20 Hz) propagating through the air at the speed of sound (ca. 344 m/s) • frequency is below the audible range for human beings • propagates very big distances (hundreds of km) • produced by many sources (Volcanoes, explosions, planes, etc.)

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Infrasound of Avalanches

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Infrasound Detection of Avalanches - IDA® • Custom made high sensitive Infrasound sensor • Fibre-optic cable connections for harsh alpine environment • Low energy consumption • Proved in many installations around the world (Iceland, Italy, Turkey, etc.) • Advanced detection algorithm Vorname Name

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Infrasound Detection IDA® 4 to 5 Sensors (microphones) installed in triangular shaped array with a spacing of ca. 150 m

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Infrasound Detection IDA®

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IDA®- Raw data view

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IDA®- Map view

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IDA-Review • IDA has been used in Italy (Val d’Aosta) for detection of avalanche activity for forecasting purposes (r= 10 km) • First tests with IDA in Austria for precise avalanche detection are promising (r = 2 km) • Supplier has experiences with infrasound detection for many years Vorname Name

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Comparison between Radar & Infrasound Detection Radar • works well for distances up to 2km • Has narrow observation window: ~ 170m • detects very accurate & reliable • can be used for verification & alarms Infrasound • works up to 10 km distances • global observation (any direction) • detects more generally than accurate • can be used for verification & "forecasting" Vorname Name

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Seismic Detection  

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Snow avalanches produce seismic signals travelling in the ground

These signals can be monitored with different seismic sensors (Geophones, Seismometers,..)

Signal Amplitude, Frequency and Waveform are highly depending on the characteristics of the ground Installations close to avalanche track get best signal and minimize influence of the ground The possible application of seismic detection systems is highly depending on the ground characteristics of the test site.

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Seismic Detection Detection based on:

• Amplitude • Duration • Frequency of the seismic signal

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Mechanical Detection Systems • Pendulum, pressure plates, ropes, etc. Advantages: + Simple system + Good detection capabilities + Reliable

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Disadvantages: - Time- and cost intensive installation in the track - After alarm reinstallation of the trigger mechanism required - Mostly yes/no information - High risk of damage due to process activity - High maintenance costs

Mechanical Detection Systems

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Summary • Different detection systems available • Every system has different advantages/disadvantages • Most reliable detections with the avalanche radar within the narrow observation window

• Infrasound can be used for avalanche forecasting • The combination of artificial release and detection systems has high potential for avalanche control work

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Content Block A 

Introduction



Avalanche Control in the Alps

Block B 

Theory on Avalanche Release & Risk Control



Avalanche Detection

Block C 

Contracting & Organization of Avalanche control Teams

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Reference Projects Vorname Name

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Break 

Questions?

Samuel Wyssen