International ScienceInternational Workshop, Snow Davos Science 2009, WorkshopProceedings Davos 2009

Artificial Release above Settlements

Stoffel Lukas1,* and Stefan Margreth1 1 WSL Institute for Snow and Avalanche Research (SLF), Davos, Switzerland

ABSTRACT: In the Swiss Alps with triggering by explosives is widely used in ski areas and also along traffic routes. New methods for artificial avalanche release have been developed during the last years. Autonomous devices allow remote triggering of independently of visibility and with a good detonation effect. In Switzerland the standard methods for protecting settle- ments are snow supporting structures and earth . Some endangered settlements or group of houses still have no protection with structural defence measures due to high costs. At some of these locations, artificial avalanche release has been applied successfully since the 1950s. Local avalanche control services are interested in improving the safety measures. Therefore the application of artificial avalanche release for the protection of settlements is also discussed for new locations. In general, artificial release above settlements should be applied with extreme caution and should remain an ex- ception. The main risk of artificial release above settlements is triggering a too large avalanche caus- ing damage. For such applications the avalanche situation must be studied in detail. Important points are the evaluation of the terrain features in regard to the effectiveness of artificial avalanche release, the potential for triggering secondary avalanches and the existing damage potential. We developed a technical guideline which defines the most relevant factors for evaluating the safety aspects.

KEYWORDS: Snow avalanche, avalanche protection, avalanche control by explosives, temporary protection measures.

these locations additionally also artificial ava- 1 INTRODUCTION lanche release is used – occasionally since the 1950s. The integral risk management includes land- The extraordinary avalanche winter 1998/99 use planning (hazard mapping), structural (per- clearly demonstrated the importance of tempo- manent) and temporary protection measures rary avalanche protection measures. Many acci- (SLF 2000). Preventive road closures, closures dents in the Swiss alps were prevented with the and evacuation (also curfew, persons can stay evacuation of endangered settlements, road in their houses) in inhabited areas and artificial closures or artificial release of avalanches (SLF, avalanche release are examples of temporary 2000; Wilhelm et al., 2001). At some locations measures. In the Swiss Alps, avalanche control avalanche control was successful due to fre- by explosives is widely used in ski areas and quent use of explosives (Fig. 1, 2). It proved to also along traffic routes. In these cases, artificial be important to attempt artificial release also release usually does not endanger persons during bad weather conditions even when it was since the endangered areas can easily be not possible to evaluate its results. Therefore closed. Sometimes, damage to infrastructure often mortars were used, which have the disad- (e.g. pylon of a chair lift) can not be avoided. vantage that the detonation effect is rather small The standard methods for protecting settle- (detonation within snow cover) and that for ments are snow supporting structures and earth safety reasons the targets often are well below dams (Margreth, 2009). Some endangered set- the ridge which is quite far away from the opti- tlements or group of houses still have no suffi- mal detonation point. Usually helicopter bomb- cient protection with structural defence meas- ing (dropping charges) was done as soon as the ures mainly because of too high construction weather conditions were good enough. At most costs. To guarantee an acceptable safety level locations a combination of mortar fire and heli- at these locations, local avalanche control ser- copter bombing was applied. Also with fre- vices evaluate the hazard and arrange tempo- quently avalanche control, bigger avalanches rary measures such as evacuations. At some of were triggered with a size corresponding to a return period of about 10 years. Two very large ______avalanches caused damages in Leukerbad (Fig. Corresponding author address: Lukas Stoffel, 3) and at the Lukmanier Pass (power line). In WSL Institute for Snow and Avalanche Research both cases due to a too long period without at- SLF, Flüelastrasse 11, CH-7260 Davos Dorf, tempts, a big powder snow avalanche was trig- Switzerland; gered. Also secondary releases occurred (e.g. in tel: +41 81 417 0126; fax: +41 81 417 0110; the release area Laschadura, Fig. 4). email: stoffell(at)slf.ch

572 InternationalInternational Snow Science Snow Workshop Science DavosWorkshop, 2009 Davos 2009, Proceedings

Remotely controlled avalanche release sys- tems such as Gazex, avalanche tower or ava- lanche guard (Fig. 5) allow the frequent use of explosives independently of weather conditions and guarantee a good detonation effect at the chosen location in the release area. These autonomous systems represent a major devel- opment and are one of the reasons why the arti- ficial release above settlements attracted a lot of interest recently. Local avalanche control ser- vices are interested to improve the safety meas-

ures. Therefore the desire is increasing to apply Fig. 1: Klosters Tallawine: Large, steep (≥35°) the artificial release more frequently also above release area; artificial release since 1967, 5 settlements. Consequently, the need emerged mortar targets, also helicopter bombing (since to provide recommendations on how to proceed 2007 catching in runout zone). when evaluating the applicability of artificial re- lease above settlements.

Fig. 5: Remote systems Gazex, Inauen-Schätti avalanche guard, Wyssen tower (from left to

right). Fig. 2: Walenstadt: Large powder snow ava- lanche, Feb. 2003 (triggered by mortar fire). 2 PRINCIPLES In general, artificial release above settle- ments should be applied with extreme caution and should remain an exception. The main risk of artificial release above settlements is trigger- ing a too large avalanche causing damage. The strategy is to trigger frequently small avalanches in order to avoid a large destructive avalanche. The closure and control of the endangered area in the runout zone during the control operation can be difficult and needs a particular effort.

Using artificial avalanche release above set- Fig. 3: Leukerbad: The roof of a well constructed tlements recommends (1) a detailed evaluation house was damaged as result of a helicopter of the safety aspects and (2) a well organized bombing operation, Feb. 1999. local avalanche control service with established working procedures based on a safety concept. If the installation of a detonation method is sub- sidized by Swiss government, a report regarding the safety aspects is necessary.

1 2 3 APPLICABILITY OF ARTIFICIAL AVALANCHE RELEASE ABOVE SETTLEMENTS

The applicability of artificial release has to Fig. 4: Zernez: Primary avalanche path Barcli (1) contain the evaluation of (1) the terrain in regard and secondary area Laschadura (2), flat ridge to the effectiveness of artificial avalanche re- between. lease (incl. the potential of triggering secondary avalanches) and (2) the existing damage poten-

573 International Snow ScienceInternational Workshop, Snow Davos Science 2009, WorkshopProceedings Davos 2009 tial (Tab. 1). In addition, the following points weather and snow data available for the ava- must be considered: (3) possible detonation lanche hazard evaluation (e.g. automatic methods, (4) required safety measures (tempo- weather station). rary closure of endangered areas) and (5) the

Tab. 1: Factors to be considered for the evaluation of the applicability of artificial avalanche release above settlements (most important factors italically represented)

Criteria Positive (favourable) Negative (unfavourable) 1. Terrain Per part of re- 1.1 Part of release area >35° > Approx. 30% of the < 30% of the area lease area (higher release probability) area (total area: …..ha (total area: …..ha > 35°: …..ha) > 35°: …..ha) 1.2 Topography, altitude, aspect con- Depression, plane, Small-scale strong struc- cerning the avalanche release prob- evenly bent, north as- tured, change of inclina- ability pect, tion, convex, south as- > 2200 m 1 pect, < 2200 m 1 Total release 1.3 Release area (concerning poten- ≤ Approx. 10 - 20 ha 1 > Approx. 20 ha 1 area tial avalanche size) (total: …..ha) (total: …..ha) 1.4 Topography regarding maximum Well separated release No separated release avalanche size areas areas Track 1.5 Predictability of the flow direction Defined, e.g. gully Undefined, several flow directions possible 1.6 Inclination regarding braking < 20° 1 > 20° 1 Runout zone 1.7 Inclination regarding runout dis- < 10° 1 or uphill > 10° 1 tance / altitude < 1000 m 1 > 1000 m 1 Secondary re- 1.8 Existence of secondary release No Yes, number of areas lease areas areas 1.9 Separation between primary and Steep slopes on both Other topography e.g. secondary area regarding inadvertent sides (prim./sec. area), flat ridge between release (per area) well separated prim./sec. area 1.10 Preventive measures in secon- Supporting structures Not existing dary area (per area) or artificial release 1.11 Avalanche record (per area) No coincidental re- coincidental release lease known known 2. Damage potential (natural avalanche return period without artificially triggered avalanches) Avalanche path 2.1 Damage potential of a 10yrs. ava- Zero to low Medium or higher and secondary lanche (e.g. range land; forest (few inhabited, unpro- areas damage hardly possi- tected houses; barns, ble) uninhabited houses, power lines), important forest (with protection capacity) 2.2 Avalanche return period (T) to reach settlement area (most exposed T > 20y T < 20y buildings) 2.3 Damage potential until and includ- Low to medium High to very high ing most exposed buildings (few inhabited houses, (settlement, infrastruc- barns) ture and industry) 2.4 Damage potential of a 100yrs. Low to medium High to very high avalanche (few inhabited houses, (settlement, infrastruc- barns) ture and industry) 2.5 Preventive measures (direct pro- Existing Not existing tection of buildings, dams) on track / runout of a 100y avalanche

1 General values, to be adopted depending on situation

574 InternationalInternational Snow Science Snow Workshop Science DavosWorkshop, 2009 Davos 2009, Proceedings

Criteria Positive (favourable) Negative (unfavourable) 3. Detonation method and detonation points (target locations) General 3.1 Applicability of the method (time Guaranteed Visibility required, of detonation) (weather independent) location not easily acces- sible 3.2 Detonation effect Medium to high Small (Detonation on (>2kg) (Detonation in snow or above snow surface) cover, < 2kg) 3.3 Slope inclination at detonation point (per point) >35° <35° 3.4 Number of detonation points in Sufficient coverage Insufficient coverage regard to the effective detonation (main part of release (main part of release area range area along most prob- along most probable frac- able fracture line > ture line < ca. 60% cov- approx. 60% covered) ered) Remotely con- 3.5 Location of the system regarding No danger or small in- Big intensities (protection trolled ava- to impacts of avalanches, snow pres- tensities (protection difficult or impossible) lanche release sure and rock fall possible) systems 4. Closure measures / evacuation Effort (for little 4.1 Closures, curfew Small effort Medium or big effort to medium (few roads, few houses) (several roads, settlement snowfall) with many inhabitants) 4.2 Evacuation Not necessary Necessary 5. Weather data and check of detonation result Snow and 5.1 Automatic weather station Existing Not existing weather data nearby or information from nearby ski area Check of deto- 5.2 Visibility Observation possible, No observation because nation result e.g. from the valley of terrain (e.g. helicopter necessary) 5.3 Technical support Installation existing or No installation available (e.g. Geo- phone) 6. Possibly: experience of a local avalanche control service 6.1 Available experience with artifi- Existing (successfully Not existing (no artificial cial release in the area use of artificial release release until now) since several years) 6.2 Documentation (e.g. records of Existing Not existing detonations and avalanches). (Benefit of a record: knowledge of frequent release areas and runouts)

ondary releases, experience with trig- 4 TECHNICAL GUIDELINE FOR ARTIFICIAL gering if done in the past, conclusion) AVALANCHE RELEASE ABOVE - Applicability of artificial avalanche re- SETTLEMENTS lease (see Tab. 1; conclusion with posi- tive and negative factors) The technical guideline describes the proce- - Possible alternative protection measures dure on how to assess the applicability of ava- - Safety concept for temporary measures lanche triggering at a certain location (Stoffel, (if in request contained) Margreth, 2009). - Recommendation.

The evaluation report should contain the fol- It is also possible to describe the avalanche lowing elements (concerning the safety as- situation (terrain of the avalanche path, ava- pects): lanche record) and to simply fill out Table 1. Ad- - Introduction (area of evaluation) ditionally, a conclusion should be made with an - Basic documents (maps, hazard map, overview of possible alternative protection existing reports) measures. - Analysis of the avalanche situation (ter- rain, avalanche record, observed sec-

575 International Snow ScienceInternational Workshop, Snow Davos Science 2009, WorkshopProceedings Davos 2009

5 CONCLUSIONS 7 REFERENCES The importance of avalanche control with Bründl, M., H.J. Etter, M. Steiniger, C. Klingler, explosives increased with the newly developed J. Rhyner, and W. Ammann, 2004: IFKIS – autonomous installations such as Gazex, ava- a basis for managing avalanche risk in set- lanche tower or guard. These methods allow the tlements and on roads in Switzerland. Nat. frequent delivery of explosives under almost any Hazards Earth Syst. Sci., 4, 257-262. weather conditions and guarantee a good deto- Margreth, S., 2009: Permanente Lawinen- nation effect at the chosen locations in release schutzmassnahmen in der Schweiz: Er- areas. kenntnisse und Entwicklungen aus dem In general, artificial release above settle- Lawinenwinter 1999. Wildbach- Lawinen- ments should be applied with extreme caution verbau 73, 162: 36-40. and should remain an exception. Using artificial McClung, D.M. and P. Scharer, 2006: The ava- avalanche release above settlements recom- lanche Handbook. 3rd ed. The Mountain- mends (1) a detailed evaluation of the safety eers Books, Seattle WA, U.S.A., 342 pp. aspects and (2) a well organized local ava- SLF, 2000: Der Lawinenwinter 1999 – Ereignis- lanche control service with established working analyse. Swiss Federal Institute for Snow procedures based on a safety concept. If the and Avalanche Research, Davos, Switzer- installation of a detonation method is subsidized land, 588 pp. by the Swiss government, a report regarding all Stoffel, L., 2001: Künstliche Lawinenauslösung. safety aspects is demanded. Praxishilfe. 2. überarbeitete Auflage. Mitt. Table 1 describes the most important factors Eidgenöss. Inst. Schnee- Lawinenforsch. which must be considered regarding the appli- 53, 66 pp. cability of artificial avalanche release and the Stoffel, L., 2004: Künstliche Lawinenauslösung safety aspects. The evaluation of all these fac- – Rechts- und Versicherungsfragen – Pra- tors indicates if the artificial release is suited or xishilfe. Vollzug Umwelt. Bundesamt für not. The decision, if artificial avalanche release Umwelt, Wald und Landschaft, Bern, 31 pp. above settlements is possible or not, is often not Stoffel, L. and J. Schweizer, 2007: Praxishilfe – easy. For the decision also the cost-benefit ratio, Arbeit im Lawinendienst: Organisation, Be- the overall situation (e.g. along a road section) urteilung lokale Lawinengefährdung und and the general acceptance have to be taken Dokumentation. Schweizerische Interes- into account. Also permanent measures or a sengemeinschaft Lawinenwarnsysteme combination of temporary and permanent (SILS), Münster; WSL, Eidg. Institut für measures (e.g. artificial release and an ava- Schnee- und Lawinenforschung SLF, Da- lanche dam) should be considered. vos; Bundesamt für Umwelt, BAFU, Berne, It is recommended to attempt triggering after Switzerland, 8 pp. already small amounts of snow accumulation Stoffel, L., S. Margreth, 2008: Avalanches: (e.g. during snowfall) to avoid large destructive Safety concepts for temporary measures avalanches. If a too large avalanche must be and application of artificial release. Ex- expected, it is advisable not to trigger. tended abstract, Interprävent 2008 Dorn- Open issues that must be investigated in the birn, 398-399. near future are the remote control of the endan- Stoffel L., Margreth S. 2009: Künstliche Lawi- gered area and the automatic detection of the nenauslösung oberhalb von Siedlungen. triggered avalanches (both specially for bad Teil 5.4 und Anhang A9 zu Teil 5 des weather conditions). At present the SLF studies „Handbuch NFA im Umweltbereich“. Mittei- different methods such as acoustic and radar lung des BAFU als Vollzugsbehörde an systems for the automatic detection of artificially Gesuchsteller. Bundesamt für Umwelt, triggered avalanches. Bern: 15 pp. Wilhelm C., T. Wiesinger, M. Bründl, and W.J. 6 ACKNOLEDGEMENTS Ammann, 2001: The avalanche winter 1999 in Switzerland – an overview. Proceedings We would like to thank the members of the International Snow Science Workshop, Big Expert Commission for Avalanches and Rockfall Sky, Montana, U.S.A., 1-6 October 2000, (EKLS), Reto Baumann (Federal Office for the Montana State University, Bozeman MT, Environment BAFU) and our colleagues Hans- U.S.A., 487-494. Jürg Etter, Hansueli Gubler, Hanspeter Hefti, Jakob Rhyner, Jürg Schweizer, Thomas Stucki who have contributed to the development of the guideline.

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