Analysis of the potential effects of dam break flooding using a GIS-tool for risk assessment in

Transcription

1 1 DACD Dipartimento ambiente costruzioni e design IST Istituto scienze della Terra Analysis of the potential effects of dam break flooding using a GIS-tool for risk assessment in mountain regions. An exploratory study on an hypothetical event: the Val Canaria flood. Mirko Baruffini, Maurizio Pozzoni and Roberto Marzocchi Institute of Earth Sciences, University of Applied Sciences of Southern Switzerland, IST-SUPSI, Campus Trevano, CH-6952 Canobbio (ist@supsi.ch)

2 Contents 2 o Fieldwork and data analysis o Hazard zoning and landslides o Flooding Models FLO-2D R.DAMFLOOD o Risk analysis methodology Risk Assessment tool in ArcGIS Results and considerations o Conclusions and next steps o References

3 Fieldwork and data analysis (1) 3 Geographical setting Canaria valley is located in Northern Tessin, close to the St. Gotthard Alps corridor: a very important area for road and rail connections between North and South Europe. Rutan dei Sassi Föisc Prato di Cè Monti Transport infrastructures: Madrano Highway Main road Railway Airolo

4 Fieldwork and data analysis (2) 4 Because of its particular geological setting the entire region is affected by numerous types of landslides. Val Canaria landslides consist of failed rock masses on both sides of the valley with a total volume of about 80 million m 3. The area is historically known for its instability Presented in session B1 Previsione e monitoraggio frana: September 23rd, 15:45.

5 Fieldwork and data analysis (3) 5 Main recent events: o 2007: a mass of m 3 fell and arrived close to the river without consequences o 2009: a mass of m 3 collapsed; the deposit reached the river and destroyed the nearby road o 2010: landslide deposit + river debris generated a temporary dam that collapsed destroying the road and some cottages o 2011: river debris destroying the road and some cottages The channel of the Canaria stream at the slope s toe is filled with unvegetated landslide debris. A natural dam could form after a landslide event with a possible subsequent disastrous failure and destructive consequences on the important traffic lines passing in the Leventina valley. The complex slide of Oct. 2009

6 Fieldwork and data analysis (4) 6 The dam break scenario, although characterized by a very low probability of occurrence, is nevertheless possible and could have effects on downstream infrastructure A damaged infrastructure would cause serious material damage that t would require extraordinary repairs or restorations. The services inactivity, as a result of a malfunction, would generate important financial losses and problems in essential services supply in the region (Maggi R. et al, 2009). Mud and debris on a stretch of motorway in Ticino Risk analysis of this scenario Motorway chaos after the landslide occurred in Giornico August 29, 2003

7 Hazard assessment (1) Identification of the natural hazards 7 o o Identification of the threatening elements: landslides, rock falls, debris flows, snow avalanches, etc. This is based on the analysis of previous studies and can be completed by regional studies, aerial photo imagery, field surveys, historical data analysis and environmental models. The resulting products are maps of natural hazard phenomena, which identify areas which are prone to the various natural hazards.

8 Hazard assessment (2) Estimation of the hazard level 8 o o The natural hazards that have been identified can be attributed with their degree of hazard, specifying how dangerous a certain situation is. Two main aspects lead to a description of the level of hazard: o How often a hazard occurs Return period Swiss Hazard matrix o With what intensity (the magnitude of the event) o The combination of these 2 parameters, following the Swiss Federal Guidelines (OFAT, OFEE, OFEFP, 1997), lead to the hazard matrix

9 Hazard assessment (3) Estimation of the intensity 9 The intensity is a description of the magnitude of an event and is divided into three classes: high, medium and low intensity. Tab. 1

10 Flooding Models (1) FLO-2D 10 o 2-D physical process model o Conserves volume and reports on it o Combined hydrologic and hydraulic model o Unconfined flooding with no boundary conditions or hot starts o Routes entire hydrograph o Variable timesteps enable fast simulations

11 Flooding Models (2) R.DAMFLOOD o GRASS-GIS module, which aim is to provide a 2D GIS-embedded hydraulic numerical model for the dam break flooding (presented in session S2 Geomatica: September 23rd, 15:45) o Developed in recent years (Marzocchi and Cannata, 2009; Cannata and Marzocchi 2011) by the Institute of Earth Sciences (SUPSI) o Based on the on the numerical solution of the Shallow Water Equations (SWE) using a Finite Volume Method (FVM). 11 Giving as input a Digital Terrain Model (DTM), the initial water depth, the breach geometry and the manning roughness coefficient it give several output (maximum water depth, velocity and intensity, time of occurrence, etc.) that can be directly used for the hazard assessment.

12 Flooding Models (3) Model and work objective 12 o Model the potential flooding (due to the breaking of the natural dam), to predict inundation areas in the upper Leventina valley, with a particular attention to the highway route. o Evaluation of the two models was performed by comparing simulation results against each other, with the aid of a GIS. Landslide model result Localization of the natural dam 200 m

13 Flooding Models (4) Model reference scenarios - Dam features 13 o Different types of scenarios, with dam height vary form 15 to 35 meters o Reference scenario: dam maximum height of about 30 m, according to the results of a landslide scenario, modeled with MassMov2D (presented in session S2 Geomatica: September 23rd, 15:30) o 2 types of breaching the dam, without taking consideration of debris flow (next step) Scenario Flooding model Number of failure element (8x8m) Dam elevation [m] Dam maximum height [m] Water volume [m 3 ] 1-FLO 2D FLO 2D FLO 2D FLO 2D R.DAMFLOOD r.damflood R.DAMFLOOD r.damflood Tab. 2

14 Flooding Models (5) Comparison of model results 14 o Good agreement between the 2 models: first cross-validation of R.DAMFLOOD o Main differences due to different methods of dam break FLO-2D R.DAMFLOOD

15 Flooding Models (6) From model results to the hazard map (FLO-2D) Combining flow depth and flow velocity map, we obtain the intensity map (for a given return period) and then the hazard map. The operation could be done directly in Flo-2D or exporting model output in ArcGIS 15

16 Risk analysis methodology (1) BUWAL recommendations 16 QUALITATIVE: protection deficit QUANTITATIVE: global values Three stages may be applied individually according to the analytical depth required. Together, however, they form a unit. QUANTITATIVE: object values The stages from 1 to 3 are increasing in analysis resolution and data requirements.

17 Risk analysis methodology (2) Risk Assessment tool in ArcGIS 17 o The tool allows studying the risks deriving from natural hazards along transportation corridors. o The tool organizes the various data and calculates the quantitative object and collective risks (BUWAL, 1999), quoted in relation to persons (number of fatalities) and material assets (property damage in Swiss Francs). o Simulation environment developed within ArcObjects, the development platform for ArcGIS o The topic of ArcObjects usually emerges when users realize that programming g ArcObjects can actually reduce the amount of repetitive work, streamline the workflow, and even produce functionalities that are not easily available. o in ArcGIS. We have adopted Visual Basic for Applications (VBA) for programming ArcObjects, because VBA is already embedded within ArcMap and ArcCatalog.

18 Risk analysis methodology (3) Risk Assessment tool in ArcGIS Risk analysis: data recording and import Just click a button! 2 - Risk analysis: a numerical procedure 3 - Risk analysis: visualisation of the results

19 Risk analysis methodology (4) Result of the analysis 19 The quantitative analysis based on investigations specific to the object according to BUWAL (1999) can be performed using Risk Assessment tool in ArcGIS on purpose developed. Risk analysis parameters: Hazard type Flooding Return period (1/he) [yrs] 300 Object type Highway Velocity (v) [km/h] 90 Daily Traffic (DTV) [nb of auto] Vehicle occupancy (β) [people/auto)] 1,59 Lethality (λ) 10-8 Scenario 1 A2-Highway Hazard Level high medium low Tab. 3 r ij collective risk DTV he * pra * * g * * v* f Number of fatalities Year Hazard zone

20 20 Risk analysis methodology (5) Discussion and conclusion o The risk analysis gives for all the four scenarios a numerical results which is < number of fatalities/year. o This is due to: the low value of lethality considered, the lethality is higher if we consider another type of risk k(debris bi flow), and dif we have an high hintensity. it the limited dimension of the object at risk with medium intensity the high value (300 years) of the return period of the considered events. Scenario Intensity Length (g ) [m] Risk [Death/year] 1-FLO 2D Medium/Low 193 < FLO 2D Medium/Low 194 < R.DAMFLOOD Low 193 < R.DAMFLOOD Low 194 < Tab. 4

21 21 Conclusion and next steps o Good agreement between the 2 flooding models o Better knowledge of potentialities and limits of the 2 models o Obtain an overview of the interests and the need to act to reduce vulnerability and the hazardous nature of the Gotthard corridor. o The lack of protection of identified risk is an useful indicator to plan for risk reduction measures. o It is possible to limit the vulnerability with protection measures referred particularly to sensitive objects. Another possibility is to limit the danger of the corridor with measures that restrict the probability of occurrence of a hazard. NEXT STEPS o Perform a simulation with FLO-2D considering the debris flow option and consequently reevaluate the risk. o Further tests and improvement in the risk assessment tool, taking into account also other types of vulnerable objects.

22 References 22 BUWAL 1999: Risikoanalyse bei gravitativen Naturgefahren - Methode, Fallbeispiele und Daten (Risk analyses for gravitational natural hazards). Bundesamt für Umwelt, Wald und Landschaft (BUWAL). Umwelt-Materialen Nr. 107, Cannata and Marzocchi 2011: Two-dimensional dam break flooding simulation: a GIS embedded approach. Natural Hazard, accepted for publicationnatural Hazards Maggi R. et al, 2009: Evaluation of the optimal resilience for vulnerable infrastructure networks. An interdisciplinary pilot study on the transalpine transportation corridors, NRP 54 Sustainable Development of the Built Environment, Projekt Nr , Final Scientific Report, Lugano. Marzocchi and Cannata, Two-dimensional dam break flooding simulation: a GIS embedded approach.proceedings of FOSS4GIS 2009 OFAT, OFEE, OFEFP (1997), Recommendations Prise en compte des dangers dus aux mouvements de terrain dans le cadre des activités de l'aménagement du territoire, 42 pages.

23 23 THANKS FOR THE ATTENTION