ProAlp Final Meeting ISPRA 2008-12-10 Hazard Modelling: Methods and results of mapping Avalanche Protection Forest (APF) HR DI. Dr. Karl Kleemayr, DI Frank

ProAlp Final Meeting ISPRA 2008-12-10

Hazard Modelling: Methods and results of mappingAvalanche Protection Forest (APF)

HR DI. Dr. Karl Kleemayr, DI Frank PerzlDepartment Natural Hazards and TimberlineFederal Research Centre for Forests, Natural Hazards and Landscape - BFW

Content – basics and main operational stepsContent – 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) avalancheDefinitions: (snow) avalanche


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 zonesDefinitions: (snow) avalanche – hazard zones


Avalanche hazard zones:

1.1. Starting zone with Starting zone with potential release areas potential release areas (PRAS) - initiation(PRAS) - initiation

2.2. Transit zone - motionTransit zone - motion

3.3. Run out and deposition Run out and deposition zone - depositionzone - deposition

Definitions: avalanche classificationDefinitions: avalanche classification


Many (main) criteria of avalanche classification: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-snow Liquid 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 Land use of starting zone: open land – forest avalancheavalanche

Definitions: avalanche classification – sizeDefinitions: avalanche classification – size


term run out classificationdamage potential

classificationquantitative

classification

Size 1 sluffsmall snow slide that usually cannot bury a person but push over a cliff

relatively harmless to people, (may injure/kill a person)

length < 50 mvolume < 100 m3

Size 2small

avalanchestops within the slope

may bury, injure or kill a person

length < 100 mVolume < 1000 m3

Size 3medium

avalancheruns 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 mvolume < 10000 m3

Size 4large

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 mvolume > 10 000 m3

Definitions: avalanche classificationDefinitions: avalanche classification


Deposition of a large avalanche

Sluffs and small slab avalanches

Medium slab avalanche

Definitions and basics: avalanche initiation factorsDefinitions and basics: avalanche initiation factors


Basic susceptibility

Tendency (almost) constant in time

Slope gradient, medium snow depth – climatic zone/altitude, geomorphology

Variable susceptibility

Fluctuating tendency Daily snow depth, temperature, radiation, vegetation

System impacts Extraordinary loads Heavy snowfall, temperature increase, rainfall, mechanical impacts on snowpack

Risk management(day-by-day- evaluation)

Land use planning

Definitions: avalanche protection forestDefinitions: avalanche protection forest


Avalanche protection forest APF (Lawinen-Objektschutzwald):

forest use areas (FUA) with a basic susceptibility for initiation of avalanches

with a damage potentialMain 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

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Mapping APFMapping APF


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 potentialCharacterizing PRAs: avalanche hazard potential


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 AHPCharacterizing PRAs: ranking of the AHP


Levels of avalanche hazard potential (basic susceptibility of the starting zone)Key

numbercolour

Notation Description

0-whiteNo or very low basic susceptibility

Events are improbable

1-yellowLow basic susceptibility

Small and infrequent events are possible. They occur only under highly unfavourable variable system conditions.

2-blueMedium basicsusceptibility

Events are possible more frequently; under highly unfavourable variable system conditions medium events are possible, large events are improbable - they are expected seldom.

3-redHigh basicsusceptibility

Events are possible frequently; small to large events are possible also under more favourable variable system conditions.

Mapping and characterizing PRAs – indicators of AHPMapping and characterizing PRAs – indicators of AHP

BFW - Bundesforschungszentrum für Wald, Naturgefahren und Landschaft

Indicator Austria France Germany Slovenia Switzerland

Model / guideline ISDW GSM 2006 expert ZRC-SAZU SilvaProtect

Minimal altitude [m](climatic zone)

700 - 1250 1000, 1300 800 1200 900/1100/1200

Depth of snow cover [m] ≥ 0.7 ≥ 1

Slope gradient > 25° 28°- 55° 25°- 55° 21°- 60° 28°- 60°Minimal length of starting zone [m]

50 50 50

Minimal area of starting zone [m²]

500 5000

Large scale geomorphology(plan curvature)

x

Medium scale geomorphology(slope length)

x x

Low scale geomorphology

x x

Surface roughness x xGround vegetation x x x

Exposition x x x

Durability of snow cover ≥ 75 days

Mapping and characterizing PRAs – indicatorsMapping and characterizing PRAs – indicators


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 potentialProAlp indicators of avalanche initiation potential


ProAlp indicators of avalanche initiation potentialProAlp indicators of avalanche initiation potential


ProAlp indicators of AHP: altitude thresholdsProAlp indicators of AHP: altitude thresholds


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 thresholdsProAlp indicators of AHP: altitude thresholds


Example: snow cover regions and altitude thresholds of Austria

Alpine RegionAvalanche hazard

potentialCode Region 1 2

Austria Altitude thresholdsA100 Vorarlberg ≥ 700 m ≥ 900 mA210 Northern Alps – West Zone ≥ 800 m ≥ 1 000 mA220 Northern Alps – Middle Zone ≥ 750 m ≥ 1 000 mA230 Northern Alps – East Zone ≥ 700 m ≥ 900 mA310 Western Central Alps – West Zone ≥ 900 m ≥ 1 100 mA320 Western Central Alps – Middle Zone ≥ 1 250 m ≥ 1 700 mA330 Western Central Alps – East Zone ≥ 900 m ≥ 1 400 mA400 Eastern Central Alps ≥ 800 m ≥ 1 000 mA500 Southern Subcontinental Alps ≥ 950 m ≥ 1 200 mA600 Austrian Southern Alps ≥ 700 m ≥ 1 100 mA700 Austrian Southeaster Alps ≥ 1 100 m ≥ 1 600 mA810 Northern foothills – West Zone ≥ 900 m ≥ 1 100 mA820 Northern foothills – East Zone ≥ 800 m ≥ 1 200 m

Indicators of AHP: interpolation altitude thresholdsIndicators of AHP: interpolation altitude thresholds


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 AHPIndicators of AHP: altitude zones of AHP


Creation of a map of altitude zones with AHPfrom DEM and GRIDs of interpolated altitude thresholds

AHP indicators: mapping altitude zones of AHPAHP indicators: mapping altitude zones of AHP


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 gradientAHP indicators: slope gradient


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 slopeAHP indicator: mapping AHP because of slope


AHP indicators: mapping AHP - plan curvatureAHP indicators: mapping AHP - plan curvature


Threshold values of plan curvature: - 2 > plan curvature ≤ 0.2

AHP indicators: combination of indicatorsAHP indicators: combination of indicators


Combination matrix of indicators:

Climaticavalanche

hazard potential

(Altitude)

Slope gradient

- 28° >28 – 34° >34 – 39° >39 – 55° > 55°

Avalanche hazard potential of slope gradient and curvature

0 1 2 3 0

Avalanche hazard potential (AHP)

0 0 0 0 0 0

1 0 0 1 1 0

2 0 2 3 3 0Intersection of layers:

altitude slopegradient

curvature

Map of PRAs and of the AHPMap of PRAs and of the AHP


Map of AHP of forest use area - FAHPMap of AHP of forest use area - FAHP


Intersection of the AHP with the forest use area

Mapping APF: detection of the damage potentialMapping APF: detection of the damage potential


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 trackMethods for calculation of the avalanche track


Energy line method - geometric angle (Heim 1932)

Geometric angle of avalanches: 17° - 47°, mean 28°

Methods for calculation oft the avalanche trackMethods for calculation oft the avalanche track


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)Map of the APF (start areas and tracks)


Results of mapping and characterizing APFResults of mapping and characterizing APF


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 PRAsResults of mapping and characterizing PRAs


Halsl-avalanche, Tyrol/Axams: 09.02.1984:4 people dead, 12 injured, 8 cars destroyed, 1 building damaged



Wolfsgruben avalanche, St. Anton a. A. /Tyrol:15.01.1959: damage of a fright train (no people injured)13.03.1988: 7 people dead, 23 injured, 3 residental buildings destroyed



Forest avalanche, Schnann / Tyrol:24.03.2006, buried 70 m of the railway, destroyed the power supply



Gries im Sellrain / Tyrol:Forest avalanche “Gaislehnertal”:01.20.1951, 1 haystack destroyed

Calculation of run out length and mapping APFCalculation of run out length and mapping APF


Forest avalanche “Gaislehnertal” : no APF, today no main infrastructures endangered

AHP APF

Calculation of run out length and mapping APFCalculation of run out length and mapping APF


“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 forestPRAs and potential tracks

area of protection forest mitigation project„Juds- and Wolfstal avalanches“

TIRIS ©

Conclusions:Conclusions:


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.

Documents

ProAlp Final Meeting ISPRA 2008-12-10 Hazard Modelling: Methods and results of mapping Avalanche Protection Forest (APF) HR DI. Dr. Karl Kleemayr, DI Frank