Flood risk analysis and assessment: Case Study Gleisdorf

Transcription

1 Flood risk analysis and assessment: Case Study Gleisdorf H.P. Nachtnebel River room agenda Alpenraum 1

2 Integrated Flood Risk Managament Risk Assessment Increase of Resistance Reduction of Losses Prepardness and Awareness Analysis of load Technical Technical Information Measures Measures Warning systems Analysis of pot. Nontechnical Nontechnical damages- Measures Measures Evacuation Risk Analysis Rescue Measures Implementation: Communication with the Public Design Alternatives Acceptance (Social and Environmental Compatibility) Construction Works 2

3 Some Definitions: Risk Analysis Risk Analysis: The systematic use of available information to characterize risk. (Salter ) 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) 3

4 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) 4

5 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) 5

6 Flood risk analysis and assessment The city of Gleisdorf (regional scale) Description of the area Possible scenarios Risk analysis Measures Conclusions 6

7 Methodology Analysis of flood risk in the city of Gleisdorf analysis 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 7

8 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 8

9 From Laserscan data to a Digital Terrain Model (TDM) by mesh generation 9

10 Comparing a DTM with areal photos Geländenetz (SMS) Orthophoto 10

11 Consideration of cross sections is very helpful in generation the DTM 11

12 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 12

13 Results from the hydraulic model Water depth and flow velocity at each location (grid element) Delineation of inundated areas and boundaries of inundation Which scenarios (discharges)? EU Flood risk directive a frequent flood HQ 30 a HQ 100 an extreme event HQ

14 Spatial distribution of water depth for a given time slice (0,1-2m) 14

15 Example: flow vectors and depth 15

16 Endangered objects for HQ 30/100/300 HQ 30 HQ 100 HQ

17 The location 17

18 Analysis of the younger history Hydrology Urban development 18

19 Analysis of the Flood Series 3 Annual maxima of the drain Q [ m /s] HQ Trend straight Flood series Feldbach

20 Analysis of the Flood Series HQ Trend straight Flood series Feldbach 3 Annual maxima of the drain Q [ m /s] Annual maxima of the drain Q [ m /s] HQ Trend straight Flood series Takern

21 Development in the Region Land survey 1787 GIS Styria, Flood protection project spillway Dykes FRB Flood release Dykes 21

22 Inundation area before 1999 Newly developed firms The goal was a protection level of HQ 100 Protection of 233 objects and 130 hectares Raab: Qmax = 200 m 3 /s Rabnitz: Qmax = 40 m 3 /s 22

23 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 23

24 Scenarios What would be the situation without any flood protection? What is it like today? Log-jams at bridges HQ 300 flood HQ 1000 flood HQ 5000 (comparable to the flood in 2002) 24

25 Scenario 1 Flood area before implementation of flood control structures Raab: Q max = 200 m 3 /s Rabnitz: Q max = 40 m 3 /s probability: ~1/100 p.a. ZT Turk 1995 &

26 Scenario 2 Flood areas, Depths Raab: Q max = 200 m 3 /s Rabnitz: Q max = 40 m 3 /s probability: ~1/100 p.a. 26

27 Scenario 2 Flood areas, Depths Raab: Q max = 200 m 3 /s Rabnitz: Q max = 40 m 3 /s probability: ~1/100 p.a. 27

28 Scenario 3 Existing flood protection Depth of inundation log jam at the bridge 28

29 Scenario 4 inundation area and depth Raab: Q max = 245 m3/s Rabnitz: Q max = 56 m3/s flood probability:~ 1/300 29

30 Scenario 5 Inundation area and depth Raab: Q max = 310 m 3 /s Rabnitz: Q max = 82 m 3 /s flood probability: ~ 1/

31 Scenario 6 Inundation area and depth Raab: Q max = 400 m 3 /s Rabnitz: Q max = 97 m 3 /s flood probability: ~ 1/

32 Estimation of the possible damages object (structure, infrastructure...) contents (equipment...) Induced damages 32

33 Classification of Damages of Enterprises 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 33

34 Damage potentials Buildings in a GIS Attributs of the object qualities, classification, point layer Attributis of the flood depths of the scenarios, post-processing Representation of the scenarios All buildings: Reference values Additional elevation Industry, large trade Assignment damage functions to classes Individual estimation of damages via nterviews and local analysis Unity damages per object (Method point values) Damages per area unit (Method area values) Damage estimate about combination with flood depth of the scenarios Damage estimation Building Equipment Creation of value losses (duration, ) Environmental hazards Resultant effects Not monetary damages representation of damages 34

35 Consideration of hydraulics, topography and land use 35

36 Damage potentials Estimation based on reference values Method to BUWAL (1999) & BWG (2002) Converted & discounted Austria p., 2004 Damages in /building & damages in /m2 36

37 Damage potentials in industrial sectors: Damage types damages of property losses in production competitional disadvantages subsequent damages... Analysis at the site Information (presentation, informative material, distribution of a questionnaire) Contacting technical managers Common inspection Damage estimation. 37

38 Estimation of damage potentials Questionnaire 1st what can happen? 2nd description in monetary units 3rd mitigation 38

39 Damage potential in the industrial sector: Results from interviews 10 companies responded among them the 4 largest ones: Management and insurance companies are interested one company: internal mitigation measures some of them have an insurance: property and losses in production sensible topic (losses when the companies vulnerability would be identified from outside) difficult to get reliable response from the companies 39

40 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 40

41 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 41

42 Water proving of objects Protection of Objects openings (doors, windows, sewers, garages, ventilation systems... Windows in the basement (BMLFUW, 2004) Typical flooding of objects (BMVBW, 2002) 42

43 Risk of dam failure and over topping Therefore, we have to consider also the failures of dikes!! 43

44 Integration of spillways into dykes According to the hydrological longitudinal profile several spillways have to be considered Where to locate them? Where large retention capacity is available After each tributary Where wetlands existed in the past Even in areas with dense population 44

45 General schem of the location of spillways Tributary Wirkungsbereiche spillways river kilometer 45

46 Runoff in the Hinterland Combination of DTM and hydraulic model 46

47 Spillways for Dikes If possible, simple spillways over a fixed dam crest Dam crest X* Flood water table 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 47

48 Increase of the Safety of Dikes Hochwasserschutz an der Gail Überströmstrecken bei Rückstaudeichen an der Donau (Wallsee, Altenwörth, Greifenstein.. 48

49 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 49

50 Thank you for your attention!! 50