Flood risk analysis and assessment: Case Study Gleisdorf · Modul 2a Risk analysis and assessment...

1Modul 2a Risk analysis and assessment for the city Gleisdorf, Styria

Flood risk analysis and assessment: Case Study

Gleisdorf

H.P. Nachtnebel

River room agenda

Alpenraum


Integrated Flood Risk Managament

Analysis of load Technical Technical Information Measures Measures Warning systems

Analysis of pot. Nontechnical Nontechnicaldamages- Measures Measures Evacuation

Risk Analysis Rescue Measures

Risk Assessment Increaseof Resistance

Reduction of Losses

Prepardness and Awareness

Implementation:Communication with the Public

Design AlternativesAcceptance (Social and Environmental Compatibility)

Construction Works


Some Definitions: Risk Analysis

• Risk Analysis: The systematic use of available information to characterize risk. (Salter 1997-98)

• Risk Analysis: A detailed examination performed to understand the nature of unwanted, negative consequences to human life, health, property, or the environment; (Gratt 1987)

• Risk analysis includes both the estimation of a pdf f(Q) and the estimation of respective damages, losses D(Q)


Some definitions: Risk Assessment

• Risk Assessment:". . .emphasizes the estimation and quantification of risk in order to determine acceptable levels of risk and safety; in other words to balance the risks of a technology or activity against its social benefits in order to determine its overall social acceptability" (Cutter 1993, 2).

• Risk Assessment: Determination of vulnerabilities and hazards in certain location to establish risks and risk probabilities. (D&E Reference Center 1998)


Some definitions: Risk Management

• Risk Management: The process of intervening to reduce risk-the making of public and private decisions regarding protective policies and actions that reduce the threat to life, property, and the environment posed by hazards. Generally, the risk management process attempts to answer the following questions:1. What can be done?2. What options or alternatives are available and what are their associated tradeoffs in terms of costs, benefits, and other (current and future risks?3. What are the effects of current decisions on future options? (Shaw, 1999)


Flood risk analysis and assessmentThe city of Gleisdorf (regional scale)

• Description of the area• Possible scenarios• Risk analysis• Measures• Conclusions


Methodology

• Analysis of flood risk in the city of Gleisdorfanalysis of previous floods (ex post analysis)

• Simulation of possible floods by using a rainfall-runoff model (ex ante analysis)

• Analysis of possible failure cases in the area• 2 D hydraulic model• Damage analysis and assessment• Possible measures for the diminution of the

damages


Impact Assessment

• Establishing a DTM• Generation of an incoming flood (hydrology)• Hydraulic model to calculate propagation of

flood in the project area• Calculation of inundated area, water depth

and flow velocity• Overlay with cadastre map• Identification of exposed objects• Classification of objects


From Laserscan data to a Digital Terrain Model (TDM) by mesh generation


Comparing a DTM with areal photos

Geländenetz (SMS) Orthophoto


Consideration of cross sections is very helpful in generation the DTM


Initial and boundary conditions

• Initial conditions: water depth and flow velocity at t=0 an every location

• Boundary conditions: Inflow hydrograph

• Model parameters: roughness coefficients for each element


Results from the hydraulic model

• Water depth and flow velocity at each location (gridelement)

• Delineation of inundated areas and boundaries ofinundation

• Which scenarios (discharges) ?EU Flood risk directive

a frequent flood HQ30a HQ100an extreme event HQ300


Spatial distribution of water depth for a given time slice (0,1-2m)


Example: flow vectors and depth


Endangered objects for HQ 30/100/300

HQ 30 HQ 100 HQ 300


The location


Analysis of the younger history

• Hydrology• Urban development


Analysis of the Flood Series

Flood series Feldbach

0

50

100

150

200

250

1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001

Annu

al m

axim

a of

the

drai

n Q

[ m

3 /s

]

HQ Trend straight

3


Analysis of the Flood Series

Flood series Feldbach

Flood series Takern

0

50

100

150

200

250

1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001

Annu

al m

axim

a of

the

drai

n Q

[ m

3 /s

]

HQ Trend straight

0

20

40

60

80

100

120

140

160

1968 1974 1979 1984 1989 1994 1999 2004

Annu

al m

axim

a of

the

drai

n Q

[ m

3 /s

]

HQ Trend straight


Development in the RegionLand survey 1787GIS Styria, http://www.gis.steiermark.at/07 -2005

Dykes

FRB

spillway

Dykes

Flood protection project 97-99

Flood release


• The goal was a protection level of HQ100

• Protection of 233 objects and 130 hectares

Inundation area before 1999

Raab: Qmax = 200 m3/sRabnitz: Qmax = 40 m3/s

Newly developed firms


Development within the last few years

• After implementation of the flood protection scheme an intensive development in the valley started

• Construction of some industrial plants• Valley is crossed by several traffic lines: pedestrian,

road, highway, and railway bridge


Scenarios

What would be the situation without any flood protection?What is it like today?Log-jams at bridgesHQ300 floodHQ1000 floodHQ5000 (comparable to the flood in 2002)


Scenario 1Flood area before implementation of flood control structuresRaab: Qmax = 200 m3/sRabnitz: Qmax = 40 m3/sprobability: ~1/100 p.a.

ZT Turk 1995 & 1997


Scenario 2Flood areas,DepthsRaab: Qmax = 200 m3/sRabnitz: Qmax = 40 m3/sprobability: ~1/100 p.a.


Scenario 3

Existing flood protectionDepth of inundationlog jam at the bridge


Scenario 4inundation area anddepthRaab: Qmax = 245 m3/sRabnitz: Qmax = 56 m3/sflood probability:~ 1/300


Scenario 5Inundation area and depth Raab: Qmax = 310 m3/sRabnitz: Qmax = 82 m3/sflood probability: ~ 1/1000


Scenario 6Inundation area anddepthRaab: Qmax = 400 m3/sRabnitz: Qmax = 97 m3/sflood probability: ~ 1/5000


Estimation of the possible damages

• object (structure, infrastructure ...)• contents (equipment ...)• Induced damages


Property damages

Building, heating systems, electric and electronic infrastructure.

Vehicles

Goods, products, stock levels

Operating equipments, EDP ...

Loss due to service interruption: losses in sales volume and profit

Location disadvantages

Environmental consequences

Classification of Damages of Enterprises


Damage potentialsBuildings in a GIS

Representation of the scenarios

Assignment damage functions to classes Individual estimation of damages via nterviews and local analysis

Damage estimation

Building

Equipment

Creation of value losses (duration, €)

Environmental hazards

Resultant effects

Not monetary damages Damage estimate about combination with flood

depth of the scenarios

Unity damages per object

(Method point values)

representation of damages

Additional elevation

Industry, large trade All buildings:

Reference values

Attributs of the object qualities, classification, point layer

Damages per area unit

(Method area values)

Attributis of the flood depths of the scenarios, post-processing


Consideration of hydraulics, topography and land use


Damage potentialsEstimation based on reference values

Method to BUWAL (1999) & BWG (2002)Converted & discounted Austria p., 2004Damages in €/building & damages in €/m2


Damage potentials in industrial sectors:

Damage typesdamages of propertylosses in productioncompetitional disadvantagessubsequent damages

...Analysis at the site

Information (presentation, informative material, distribution of a questionnaire)

Contacting technical managersCommon inspectionDamage estimation.


Estimation of damage potentials

Questionnaire

1st what can happen?

2nd description in monetary units

3rd mitigation


Damage potential in the industrial sector:Results from interviews

10 companies respondedamong them the 4 largest ones:

Management and insurance companies are interested one company: internal mitigation measuressome of them have an insurance: property and losses in productionsensible topic (losses when the companies vulnerability would be identified from outside)difficult to get reliable response from the companies


Measures to reduce losses:

• Protection of objects (houses)• Protection of companies (internally organised)• Information, raising the awarness• insurance• Reduction of sensible points in the region• Dikes should be redesigned (inundable) and

consideration of runoff in the Hinterland


• Information about possible scenarios & local measures (eg. Water proofing of objects)

• Training for a flood event: What to do ? Removing cars, water tight closing of doors and windows, clearing the basement, closing sewers...)

• Improved warning and forecasting

• Insurance

Precautionary Measures Privat & Companies


Water proving of objectsopenings (doors, windows, sewers, garages, ventilation systems...

Protection of Objects

Typical flooding of objects (BMVBW, 2002)

Windows in the basement (BMLFUW , 2004)


Risk of dam failure and over topping

Therefore, we have to consider also the failures of dikes !!


Integration of spillways into dykes

• According to the hydrological longitudinal profile several spillways have to beconsidered

• Where to locate them?Where large retention capacity is availableAfter each tributaryWhere wetlands existed in the pastEven in areas with dense population


General schem of the location of spillways

Wirkungsbereiche

spillways

river kilometer

Tributary


Runoff in the Hinterland

Combination of DTM and hydraulic model


Spillways for Dikes

• If possible, simple spillways over a fixed dam crest

• Reduces the uncertainty in g(X*), inundation starts slowly, we know where and when and what happens in the Hinterland, and therefore lower damages will result

X*Flood water table

Dam crest


Increase of the Safety of Dikes

• Hochwasserschutz an der Gail• Überströmstrecken bei Rückstaudeichen an

der Donau (Wallsee, Altenwörth, Greifenstein..


Summary and Conclusions

• Flood risk analysis• Flood risk assessment methodology for the village of

Gleisdorf• Generation of scenarios• A methodology for the assessment of damages

(consideration of national and international documents)• Information of the public is also required


Thank you for your attention !!

Flood risk analysis and assessment: Case Study Gleisdorf · Modul 2a Risk analysis and assessment...

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Transcript of Flood risk analysis and assessment: Case Study Gleisdorf · Modul 2a Risk analysis and assessment...