ProAlp Final Meeting ISPRA Hazard Modelling: Methods and results of mapping Avalanche Protection Forest (APF) HR DI. Dr. Karl Kleemayr, DI Frank Perzl Department Natural Hazards and Timberline Federal Research Centre for Forests, Natural Hazards and Landscape - BFW

Content – basics and main operational steps: BFW – Federal Research Centre for Forests and Natural Hazards 1.Definition of avalanche and avalanche protection forest – basics of mapping APF 2.Mapping of APF in detail: Mapping and characterizing potential avalanche starting zones (PRAs) in forests Detection of the damage potential - modelling of potential transit and run out zones 3.Results of mapping APF

Definitions: (snow) avalanche BFW – Federal Research Centre for Forests and Natural Hazards An avalanche is a rapid down slope movement of a large mass of snow. Avalanche motion: J. Berger, Verbund AHP Werksgruppe Kaprun-Salzburg 2008 © BFW 2008 ©

Definitions: (snow) avalanche – hazard zones BFW – Federal Research Centre for Forests and Natural Hazards Avalanche hazard zones: 1.Starting zone with potential release areas (PRAS) - initiation 2.Transit zone - motion 3.Run out and deposition zone - deposition

Definitions: avalanche classification BFW – Federal Research Centre for Forests and Natural Hazards Many (main) criteria of avalanche classification: Size and damage potential: sluff – large avalancheSize and damage potential: sluff – large avalanche Manner of starting: loose snow, slab avalancheManner of starting: loose snow, slab avalanche Form of movement: flow – powder avalancheForm of movement: flow – powder avalanche Position of gliding surface: surface layer – full-depthPosition of gliding surface: surface layer – full-depth Liquid water in snow: wet-snow – dry-snowLiquid water in snow: wet-snow – dry-snow Form of path: unconfined – channelled avalancheForm of path: unconfined – channelled avalanche Land use of starting zone: open land – forest avalancheLand use of starting zone: open land – forest avalanche

Definitions: avalanche classification – size BFW – Federal Research Centre for Forests and Natural Hazards termrun out classification damage potential classification quantitative classification Size 1sluff small snow slide that usually cannot bury a person but push over a cliff relatively harmless to people, (may injure/kill a person) length < 50 m volume < 100 m 3 Size 2 small avalanche stops within the slope may bury, injure or kill a person length < 100 m Volume < 1000 m 3 Size 3 medium avalanche runs to the bottom of the slope may bury and destroy a car, damage a truck, destroy a small building or break a few trees length < 1000 m volume < m 3 Size 4 large avalanche runs over flat areas (significantly less than 30°) of at least 50 m in length, may reach the valley bottom may bury and destroy trucks or trains, large buildings and forested areas length > 1000 m volume > m 3

Definitions: avalanche classification BFW – Federal Research Centre for Forests and Natural Hazards Deposition of a large avalanche Sluffs and small slab avalanches Medium slab avalanche

Definitions and basics: avalanche initiation factors BFW – Federal Research Centre for Forests and Natural Hazards Basic susceptibility Tendency (almost) constant in time Slope gradient, medium snow depth – climatic zone/altitude, geomorphology Variable susceptibility Fluctuating tendencyDaily snow depth, temperature, radiation, vegetation System impactsExtraordinary loadsHeavy snowfall, temperature increase, rainfall, mechanical impacts on snowpack Risk management (day-by-day- evaluation) Land use planning

Definitions: avalanche protection forest BFW – Federal Research Centre for Forests and Natural Hazards Avalanche protection forest APF (Lawinen-Objektschutzwald): forest use areas (FUA) with a basic susceptibility for initiation of avalanches with a damage potential Main protection effect of forest: avalanche release prevention Only secondary: deceleration of avalanches (just smaller avalanches) Evaluation of the deceleration effect of forests is difficult and not solved sufficiently 1 – PRA above timberline: no APF 2 – PRA is FUA (clearcutting), damage potential: APF 3 – PRA is FUA (clearcutting), no damage potential: no APF 4 – FUA in the transit zone, damage potential: no APF by definition

Mapping APF BFW – Federal Research Centre for Forests and Natural Hazards Required information for mapping APF: PRAs (position, size, potential release depth) forest use area damage potential of PRAs in forests: assets (position, value, vulnerability, presence likelihood of people) potential transit and run out zone avalanche pressure along the track Operational steps: 1.Mapping and characterizing of areas with basic susceptibility for avalanche initiation (PRAs) 2.Intersection of PRA with the forest use area 3.Detection of the damage potential: calculation of the avalanche track and intersection with the assets (settlements, infrastructures)

Characterizing PRAs: avalanche hazard potential BFW – Federal Research Centre for Forests and Natural Hazards Avalanche hazard potential (AHP) of a starting zone (PRAs): Probability of the occurrence/initiation of an avalanche from certain magnitude without consideration of forest and defense constructions AHP = f(probability, magnitude) But: no frequency-mass-functions for AHP quantification are available Question: Is it useful to quantify the AHP ? Yes, because probability of an avalanche release depends on site factors But: only a qualitative ranking of the AHP is possible

Characterizing PRAs: ranking of the AHP BFW – Federal Research Centre for Forests and Natural Hazards Levels of avalanche hazard potential (basic susceptibility of the starting zone) Key number colour NotationDescription 0-white No or very low basic susceptibility Events are improbable 1-yellow Low basic susceptibility Small and infrequent events are possible. They occur only under highly unfavourable variable system conditions. 2-blue Medium basic susceptibility Events are possible more frequently; under highly unfavourable variable system conditions medium events are possible, large events are improbable - they are expected seldom. 3-red High basic susceptibility Events are possible frequently; small to large events are possible also under more favourable variable system conditions.

Mapping and characterizing PRAs – indicators of AHP BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft IndicatorAustriaFranceGermanySloveniaSwitzerland Model / guidelineISDW GSM 2006expertZRC-SAZUSilvaProtect Minimal altitude [m] (climatic zone) , /1100/1200 Depth of snow cover [m] Slope gradient> 25°28°- 55°25°- 55°21°- 60°28°- 60° Minimal length of starting zone [m] 50 Minimal area of starting zone [m²] Large scale geomorphology (plan curvature) x Medium scale geomorphology (slope length) xx Low scale geomorphology xx Surface roughnessxx Ground vegetationxxx Expositionxxx Durability of snow cover 75 days

Mapping and characterizing PRAs – indicators BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Main indicators of PRAs (AHP): 1.Altitude (climatic region) – indicator of potential avalanche release frequency and magnitude: correlation with snow depth surrogate of release depth correlation with kinetic head 2.Slope gradient – indicator of potential avalanche release frequency but no or only weak correlation with the magnitude 3.Plan curvature, indicator of potential avalanche release frequency and magnitude; effects on snow depth release depth snow pack

ProAlp indicators of avalanche initiation potential BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft

ProAlp indicators of avalanche initiation potential BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft

ProAlp indicators of AHP: altitude thresholds BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft 2 levels of AHP: altitude thresholds dependend from climatic region: level 1: lower zones – mainly sluffs and small avalanches possible level 2: high-altitudes – common avalanche terrain Definition of snow cover regions by expert

ProAlp indicators of AHP: altitude thresholds BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Example: snow cover regions and altitude thresholds of Austria Alpine Region Avalanche hazard potential CodeRegion 12 Austria Altitude thresholds A100Vorarlberg 700 m 900 m A210Northern Alps – West Zone 800 m m A220Northern Alps – Middle Zone 750 m m A230Northern Alps – East Zone 700 m 900 m A310Western Central Alps – West Zone 900 m m A320Western Central Alps – Middle Zone m m A330Western Central Alps – East Zone 900 m m A400Eastern Central Alps 800 m m A500Southern Subcontinental Alps 950 m m A600Austrian Southern Alps 700 m m A700Austrian Southeaster Alps m m A810Northern foothills – West Zone 900 m m A820Northern foothills – East Zone 800 m m

Indicators of AHP: interpolation altitude thresholds BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Because of the breaks of the altitude threshold between snow cover regions interpolation is necessary Grid of altitude threshold: Resolution: 200 m Interpolation: Focal Mean function (50 Cells), resample to 25 m Grid of interpolated altitude thresholds: Resolution: 25 m

Indicators of AHP: altitude zones of AHP BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Creation of a map of altitude zones with AHP from DEM and GRIDs of interpolated altitude thresholds

AHP indicators: mapping altitude zones of AHP BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Detail view of hazard potential because of altitude Paznauntal Yellow area: Low altitudes – little AHP Red area: High altitudes – higher AHP Black line: Border between two snow cover regions with different altitude thresholds

AHP indicators: slope gradient BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Evaluation of the hazard potential because of slope gradient: threshold values of potential release areas: 28° - 55° Slope gradient Level of hazard potential - 28° 0 – no hazard potential > 28 – 34° 1 – low hazard potential > 34 – 39° 2 (1-3) – medium hazard potential > 39 – 55° 3 – high hazard potential > 55°0 – no hazard potential

AHP indicator: mapping AHP because of slope BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft

AHP indicators: mapping AHP - plan curvature BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Threshold values of plan curvature: - 2 > plan curvature 0.2

AHP indicators: combination of indicators BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Combination matrix of indicators: Climatic avalanche hazard potential (Altitude) Slope gradient - 28°>28 – 34°>34 – 39°>39 – 55°> 55° Avalanche hazard potential of slope gradient and curvature Avalanche hazard potential (AHP) Intersection of layers: altitude slope gradient curvature

Map of PRAs and of the AHP BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft

Map of AHP of forest use area - FAHP BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Intersection of the AHP with the forest use area

Mapping APF: detection of the damage potential BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Data requirement: map of forest with AHP (FAHP) map of the assets (settlements and main infrastructures) map of the potential run out and transit zones of avalanches from forest area Methods for calculating run out zones of avalanches: statistic (topographic) models: energy line method, αβ model Models which require the release depth (and the area of the PRA) 1D models: Aval-1-D 2D models: Aval-2-D, ELBA 3D models: SamosAT

Methods for calculation of the avalanche track BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Energy line method - geometric angle (Heim 1932) Geometric angle of avalanches: 17° - 47°, mean 28°

Methods for calculation oft the avalanche track BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft General gradient approach (geometrisches Gefälle). Model: Alphamodell_2 (Klebinder K., Fromm, R. & F. Perzl 2006, BFW) Input: (forest with) AHP (avalanche starting zones in forest, asc file) DTM (asc file) layer of infrastructures (asc file) Alphamodell_2: Calculation of the flow path from each start pixel. Intersection of the geometric decline with the flow path for estimation of the run out length. Intersection of the avalanche tracks with the infrastructure and selection of tracks (and start zones) which endanger infrastructures Determination of the start pixel of this avalanches APF

Map of the APF (start areas and tracks) BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft

Results of mapping and characterizing APF BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Evaluation of the results is difficult because of data lake: Possibilities for evaluation: comparison with well-known dangerous avalanche release areas (damage events, areas with avalanche defense constructions) forest use area and run out length: evaluation is difficult because of the protection effect of forest by expert 1.Mapping of the PRAs (AHP): 2.Calculation of run out length and mapping APF

Results of mapping and characterizing PRAs BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Halsl-avalanche, Tyrol/Axams: : 4 people dead, 12 injured, 8 cars destroyed, 1 building damaged

Results of mapping and characterizing PRAs BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Wolfsgruben avalanche, St. Anton a. A. /Tyrol: : damage of a fright train (no people injured) : 7 people dead, 23 injured, 3 residental buildings destroyed

Results of mapping and characterizing PRAs BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Forest avalanche, Schnann / Tyrol: , buried 70 m of the railway, destroyed the power supply

Results of mapping and characterizing PRAs BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Gries im Sellrain / Tyrol: Forest avalanche Gaislehnertal: , 1 haystack destroyed

Calculation of run out length and mapping APF BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Forest avalanche Gaislehnertal : no APF, today no main infrastructures endangered AHP APF

Calculation of run out length and mapping APF BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft Juds- and Wolfstal avalanches: avalanches from this terrain reached the main street and destroyed and damaged buildings 1951, 1952, 1970 Protection forest mitigation measures were required insufficient forest protection effect map of the protection forest PRAs and potential tracks area of protection forest mitigation project Juds- and Wolfstal avalanches TIRIS ©

Conclusions: BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft TIRIS © Evaluation of the results of mapping APF The result of modelling starting zones is good, well know dangerous avalanche release areas in Tyrol were worked out It is difficult to evaluate the results of the modelling of the run length of the avalanches (most of them are potential avalanches) - the results are plausible.