Markus N. Zimmermann

The 1987 debris flows in Switzerland: documentation and analysis

Abstract A great number of debris flows occurred during the flood catastrophes of the summer of 1987 in the Swiss Alps. Aerial photography, field investigations and eyewitness accounts documented and analysed the events. As an example of the reconstructed major events, the large debris flow in the Varuna valley involved an estimated peak discharge between 400 and 800 m3/s and an event magnitude of 200,000 m3. Several single pulses were observed; the duration of each of them appeared to be not more than a few minutes. Apart from incision into weak bedrock, the maximum erosion depth seemed to depend on the channel gradient. Based on approximately 600 events, typical starting zones and rainfall conditions are discussed with regard to the triggering conditions. Existing and new empirical formulae are proposed to estimate the most important flow parameters. These values are compared to debris flow data from Canada and Japan.

The 1985 catastrophic drainage of a moraine-dammed lake, Khumbu Himal, Nepal: cause and consequences

On 4 August 1985 Dig Tsho, a moraine-dammed glacial lake in the Khumbu area of eastern Nepal, burst above Thame. For the region close to the origin of the outbreak the consequences were catastrophic. The destruction of a newly built hydroelectricp ower plant, 14 bridges, about 30 houses, and many hectares of valuable arable land, as well as a heavily damaged trail network, resulted from 5 million m3 of water plummetting down the Bhote Kosi and Dudh Kosi valleys. The breaching of the moraine was triggered by wave action following an ice avalanche of 150,000 m3 into the lake. The surge had a peak discharge of 1,600 m3/sec; 3 million m3 of debris were moved within a distance of less than 40 km. However, only 10-15 percent of the material left the region as suspended load. The potential hazard of glacial lakes persists and increases. A hazard assessment including an identificationo f source areas and subsequent monitoring of glacial lakes is proposed. It should be incorporated into any development concept for the Himalayan region.

International Frameworks for Disaster Risk Reduction: Useful Guidance for Sustainable Mountain Development?

Abstract In recent decades, a number of global frameworks have been developed for disaster risk reduction (DRR). The Hyogo Framework for Action 2005–2015 and its successor document, the Sendai Framework for Disaster Risk Reduction, adopted in Japan in March 2015, provide general guidance for reducing risks from natural hazards. This is particularly important for mountainous areas, but DRR for mountain areas and sustainable mountain development received little attention in the recent policy debate. The question remains whether the Hyogo and Sendai frameworks can provide guidance for sustainable mountain development. This article evaluates the 2 frameworks in light of the special challenges of DRR in mountain areas and argues that, while the frameworks offer valuable guidance, they need to be further adapted for local contexts—particularly for mountain areas, which require special attention because of changing risk patterns like the effects of climate change and high land-use pressure.

Risk-conscious Reconstruction in Pakistan-administered Kashmir

Abstract The Chakhama Valley, a remote area in Pakistan-administered Kashmir, was badly damaged by the 7.6-magnitude earthquake that struck India and Pakistan on 8 October 2005. More than 5% of the population lost their lives, and about 90% of the existing housing was irreparably damaged or completely destroyed. In early 2006, the Aga Khan Development Network (AKDN) initiated a multisector, community-driven reconstruction program in the Chakhama Valley on the premise that the scale of the disaster required a response that would address all aspects of peoples lives. One important aspect covered the promotion of disaster risk management for sustainable recovery in a safe environment. Accordingly, prevailing hazards (rockfalls, landslides, and debris flow, in addition to earthquake hazards) and existing risks were thoroughly assessed, and the information was incorporated into the main planning processes. Hazard maps, detailed site investigations, and proposals for precautionary measures assisted engineers in supporting the reconstruction of private homes in safe locations to render investments disaster resilient. The information was also used for community-based land use decisions and disaster mitigation and preparedness. The work revealed three main problems: (1) thorough assessment of hazards and incorporation of this assessment into planning processes is time consuming and often little understood by the population directly affected, but it pays off in the long run; (2) relocating people out of dangerous places is a highly sensitive issue that requires the support of clear and forceful government policies; and (3) the involvement of local communities is essential for the success of mitigation and preparedness.

Risk-conscious Reconstruction in Pakistan-administered Kashmir. A Case Study of the Chakhama Valley

Abstract The Chakhama Valley, a remote area in Pakistan-administered Kashmir, was badly damaged by the 7.6-magnitude earthquake that struck India and Pakistan on 8 October 2005. More than 5% of the population lost their lives, and about 90% of the existing housing was irreparably damaged or completely destroyed. In early 2006, the Aga Khan Development Network (AKDN) initiated a multisector, community-driven reconstruction program in the Chakhama Valley on the premise that the scale of the disaster required a response that would address all aspects of peoples lives. One important aspect covered the promotion of disaster risk management for sustainable recovery in a safe environment. Accordingly, prevailing hazards (rockfalls, landslides, and debris flow, in addition to earthquake hazards) and existing risks were thoroughly assessed, and the information was incorporated into the main planning processes. Hazard maps, detailed site investigations, and proposals for precautionary measures assisted engineers in supporting the reconstruction of private homes in safe locations to render investments disaster resilient. The information was also used for community-based land use decisions and disaster mitigation and preparedness. The work revealed three main problems: (1) thorough assessment of hazards and incorporation of this assessment into planning processes is time consuming and often little understood by the population directly affected, but it pays off in the long run; (2) relocating people out of dangerous places is a highly sensitive issue that requires the support of clear and forceful government policies; and (3) the involvement of local communities is essential for the success of mitigation and preparedness.

Managing debris flow risks: security measures for a hazard-prone resort in Switzerland.

Abstract Debris flows represent a widespread threat to villages and small towns in the Swiss Alps. For many centuries people “managed” such risks by trying to avoid hazardous areas. However, major debris flow and flood events in the last 25 years have revealed that the degree of freedom to engage in this type of risk management has substantially decreased. This became especially evident during the 1999 disasters in a number of places in Switzerland. The winter of that year was unusually wet. In February heavy snowfall triggered destructive avalanches. In May high temperatures caused heavy snowmelt, with excessive rainfall contributing more water to the already saturated soils. Landslides, debris flows and floods were triggered in many locations, including Sörenberg. Hazard prevention and disaster management have a long tradition in Switzerland, although an integrated approach to risk management is rather new. Only in recent years have methods and tools been developed to assess hazards, define protection goals, and implement disaster reduction measures. The case of Sörenberg serves as an example of how todays approaches to disaster reduction are implemented at the local level.

Murgänge erkennen und bewerten

Murgange, auch Rufen oder Laui genannt, gehoren zu den dominanten Massenverlagerungs-prozessen in den Alpen. Sie konnen grosse Schuttmengen innert kurzester Zeit uber weite Strecken transportieren. Deshalb sind auch Siedlungen oder Verkehrswege in den Talboden, weit entfernt vom Ursprungsort der Muren, erheblich gefahrdet. Fur die Verantwortlichen in Forst- und Wasserbau, sowie naturlich fur die Bewohner selber waren Rufen schon immer bekannt und gefurchtet (z.B. Berlepsch 1861). Die Forschung hingegen beschaftigt sich erst seit den 1970er und 1980er Jahren intensiv mit dieser Naturgefahr (z.B. Takahashi 1978, Costa 1988). In der Schweiz gaben sogar erst die Diskussionen um das Waldsterben (VAW/EAFV 1988) und die Unwetter vom Sommer 1987 einen entscheidenden Forschungsimpuls (Haeberli et al. 1990, BWW 1991).

Analysis of Weather- and Climate-Related Disasters in Mountain Regions Using Different Disaster Databases

Mountains are fragile ecosystems with global importance, providing key ecosystems services within mountainous areas but also for the lowlands. However, mountain regions are prone to natural disasters and exposed to multiple hazards. In this chapter, we present four disaster databases (EM-DAT, NatCatSERVICE, DesInventar, Dartmouth) that store information about spatiotemporal occurrence and impacts of natural disasters in mountain areas. Quality and completeness of the four databases are compared and analyzed regarding reliability for weather- and climate-related natural disasters. The analysis identifies the numbers of fatalities as the most reliable loss parameters, whereby the number of people affected and the economic loss are less trustworthy and highly dependent on the purposes of each database. Main limitations regarding sustainable mountain development are the inhomogeneity in database definitions, spatial resolutions, database purposes and lack of data registration for human and economic losses. While some individual disasters such as the Kedarnath flood in northern India in 2013 have been robustly linked to changes in climate, there is generally insufficient evidence to attribute any overall increasing disaster frequency to climate change. Damage due to hazard in mountain regions will increase irrespective of global warming, in regions where populations are growing and infrastructure is developed at exposed locations.

Modelling of individual debris flows using Flow-R: A case study in four Swiss torrents

Recently, an empirical debris flow model called Flow-R has been added to the broad range of existing debris flow modelling software. While Flow-R’s applicability on regional scale has been confirmed in several studies, it’s potential in local debris flow modelling has not yet been evaluated. In this study, Flow-R’s potential in debris flow modelling on local scale is tested via an application in four debris flow torrents in Switzerland. Obtained results are validated by comparison to documented debris flow events as well as model results from the commonly used hydraulic debris flow model RAMMS. Results show that due to the nonhydraulic model conception, the potential of Flow-R in individual debris flow modelling is limited. Plausible debris flow patterns are only achieved on torrents showing a low to moderate channelization, i.e. incision on the fan. Computed process velocities are unreliable due to the inability of the model to account for debris flow mass. Moreover, modelled debris flow magnitudes are biased by the compulsory non-volumetric definition of magnitudes.