WS 18 landslides Theo van Asch

Contd… Laprak Landslide The Landslide problem

Theo van Asch: Faculty of Geosciences Utrecht in collaboration with Cees van Westen and Dinand Alkma

ITC Enschede

Landslide

Definition:

Landslide is defined as the movement of a mass of rock, debris or earth down the slope, when the driving (gravity) forces exceeds the frictional resistance of the material.

Landslide hazard analysis

Landslide risk analysis.

Landslide risk management

Risk governance

The Landslide problem

Landslide hazard and risk analyses

• Type?• Where?• How often?• How fast and intense?• How far?• Which elements at risk?• How vulnerable? • Costs?

Hazard assessment

Risk assessment

Landslide classification

The most important characteristics to classify landslides: Material: Rock, Soil Lithology, structure, Geotechnical

properties Landslide geometry: Depth, Length, Height etc. Type of movement: Fall, Slide, Flow etc Water: Dry, wet, saturated Speed of movement: Very slow, slow etc.

Type?Where?How often?How fast and intense?How far?Which elements at risk?How vulnerable? Costs?

Types of movement

Fall

Topple

Slide

Rotational

slide

Translational

slide


Flow

Debris/Mud Flow

Debris avalanche

Velocity of mass movement related to water content and type Type?Where?How often?How fast and intense?How far?Which elements at risk?How vulnerable? Costs?

Translational slide


Rotational slide (Slump)


Rotational slide (Slump)


debris flowType?Where?How often?How fast and intense?How far?Which elements at risk?How vulnerable? Costs?


debris flow


Debris avalancheType?Where?How often?How fast and intense?How far?Which elements at risk?How vulnerable? Costs?

Debris avalancheType?Where?How often?How fast and intense?How far?Which elements at risk?How vulnerable? Costs?

Spatial probability of occurrence

Landslide susceptibility maps

Landslide susceptibility


Landslide susceptibility

How to make a susceptibility map?– Make a landslide map– Determine causing /triggering factors– Make (statistical) correlation between

landslide occurrence and factors– Make a zonation map with probability of

occurrence of future landslides.


Landslide maps


Landslide maps Type?Where?How often?How fast and intense?How far?Which elements at risk?How vulnerable? Costs?

Use of factor maps .

Slope classes

Landuse

Aspect classes

Soil depth

LithologyDistance from river

Weight mapsSusceptibility map Total weight

Statistical correlation techniques with landslide map

Elevation


Susceptibility mapType?Where?How often?How fast and intense?How far?Which elements at risk?How vulnerable? Costs?

The landslide hazard map

Susceptibility map plus temporal frequency

Landslide hazard maps


1D formulation

The driving force and frictional resistance

t

u)h(ρS

x

hkcosαsinαρghc

x

uuc

t

uρh s

sfxxxx

forcenormalαcosghρ

cosα1cosα

ghρσ

force drivingαcossinαghρcosα

1sinα

ghρτ

1*ghρsliceweight

2flfl

flfl

fl

x

z

hi

1m

1/cos

hi-1hi+1

fl,,c,

x x

di-1

977)Cousssot(1uh

3ητ

2

3

ρgh

1'tanαcosS cx

2f

The role of deterministic models

Deterministic (physical ) models are useful to determine the temporal frequency of slope instability


Driving forces

Resisting forces

Groundwater recharge

Precipitation /percolation

Safety factor<1

Slope triggered by rain

Coupled hydrological-slope stability models calculates over time:

Temporal frequency of instability


Δt

uh

ρh

ρSfktanβ

s

1sinαcosαΔtgcuuu

s

Δtculaxu

uh

3ητ

2

3

ρgh

1'tanφαcosSf

nis

in

s1/2ni

ni

ni

ni

n1i

n1i

ni

ni

ni

1ni

1/2nin

icn

i

ni

21/2ni

Δt

uh

ρh

ρSfktanβ

s

1sinαcosαΔtgcuuu

s

Δtculaxu

uh

3ητ

2

3

ρgh

1'tanφαcosSf

nis

in

s1/2ni

ni

ni

ni

n1i

n1i

ni

ni

ni

1ni

1/2nin

icn

i

ni

21/2ni

Δt

uh

ρh

ρSfktanβ

s

1sinαcosαΔtgcuuu

s

Δtculaxu

uh

3ητ

2

3

ρgh

1'tanφαcosSf

nis

in

s1/2ni

ni

ni

ni

n1i

n1i

ni

ni

ni

1ni

1/2nin

icn

i

ni

21/2ni

Δt

uh

ρh

ρSfktanβ

s

1sinαcosαΔtgcuuu

s

Δtculaxu

uh

3ητ

2

3

ρgh

1'tanφαcosSf

nis

in

s1/2ni

ni

ni

ni

n1i

n1i

ni

ni

ni

1ni

1/2nin

icn

i

ni

21/2ni

The role of deterministic models

Deterministic (physical ) models are also useful to determine the speed extent and

impact of landslides


Rapid gravitational debris/mudflowsSource area

Remaître 2006

Faucon creek French Alps 2003 event


Rapid gravitational debris/mudflowsTransportation and deposition area


Faucon creek French Alps: 2003 eventFaucon creek French Alps: 2003 event

Rapid gravitational debris/mudflowsSource area


Faucon creek French Alps: Faucon creek French Alps: 2003 event2003 event

Rapid gravitational debris/mudflowsScouring in transportation area


Rapid gravitational debris/mudflowsDeposition area



Coh = 1 kPa, K = 5.0E-2 m kPa.s-1

Average velocity: 6 m s-1

Model simulation in deposition area Faucon Barcelonette



Wartschenbach 1997 (Austria)Wartschenbach 1997 (Austria)

Rapid gravitational debris/mudflowsDeposition area



Simulation of an earthflowType?Where?How often?How fast and intense?How far?Which elements at risk?How vulnerable? Costs?

• All objects, persons, animals, activities and processes that may be adversely affected by hazardous phenomena, in a particular area, either directly or indirectly.

What are elements at risk?


Different elements at risk

Physical elements HousingInfrastructure (roads, railways.airport etc )Critical facilities (schools hospitals police..etc )Utilities (Power supply ,transport services,governmental services..etc)

Economic elements Buseness and trade activities, access to work,agricultural land, work force,

Societal elements Moving people, vulnerable age categories,Low income groups,homeless people, disabled ,gender

Environmental elements Resources: like air, water, fauna, flora ,biodiversity,


• Buildings are one of the most important groups of elements at risk.

• They house the population. The behavior of a building under a hazard event, determines whether the people in the building might be injured or killed.

Important elements:buildings


Important element:population

• Static characteristics: – Relate to number of inhabitants, the densities of the

population and the age compositions;

Dynamic characteristics: – Relate to the activity patterns of the people, and the

distribution of the population in space and time. – One of the most important socio-cultural vulnerability

indicators is the time-distribution of the population.


Rockfall on school:

1400 deaths

Landslide on neighborhood:

800 deaths

Flood caused by a landslide dam

Debris flow on 14/9 destroying the remains of Old Beichuan

City of Beichuan, deserted after the earthquake on 12 MayType?Where?How often?How fast and intense?How far?Which elements at risk?How vulnerable? Costs?

Types of vulnerability

• Physical Vulnerability:

• Economic vulnerability: • Social vulnerability• Environmental vulnerability


Types of vulnerability


• Vulnerability curves:

– Are constructed on the basis of the relation between hazard intensities and damage data

– Relative curves: they show in the degree of damage (between 0 and 1) of a property

How to express physical vulnerability?

Low vulnerability

curve

High vulnerability curve


Landslide vulnerability assessment is still in its infant stages

• There is a wide variety of processes • Lack of historical damage databases

Vulnerability assessment for mass movements


Damages due to various landslides.


Damages due to various landslides.


Quantitative risk assessment

Risk = Hazard * Vulnerability * Amount

= Temporal frequency (H)

* Degree of loss to elements at risk (V)

*Cost quantification of elements at risk (A)

Quantitative Risk


A=US $ 50.000

V = 0.1

RP = 10 yearsH=0.1

A=US $ 200.000

V = 0.5

V = 1

A=US $ 100.000

Specific quantitative risk

Specific Risk =0.1 * ((0.1 *50.000)+(0.5*200.000)+(1*100.000))

Landslide

Quantitative specific Risk = H*V*A


Landslide risk map of the Arno river basin over a period of 30 years. The risk is expressed as economic losses due to landslides for each terrain unit (from Catani et al. 2005)


Risk map Arno river basin Italy

Education

WS 18 landslides Theo van Asch