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Agricultural
and environmental engineering research
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CADZIE OBJECTIVES
In January and February of this year record snowfalls along Europe’s mountainous
spine triggered a series of extreme avalanches from the Alps-Maritimes
to the Carpathians. The total number of deaths surpassed the European yearly
average (83). In Austria alone 40 people were killed in Galtür. In
Switzerland more than 100'000 tourists were isolated in mountain communities
as highways and railways were closed due to the fear of avalanches. In
France 11 people were killed as an avalanche destroyed a housing community
in Chamonix.
The extreme avalanche winter of 1999 has caused Europe’s avalanche experts
to rethink existing methods to calculate avalanche runout and prepare hazard
maps. New methodologies, based on modern computer methods presently under
development in all European countries, must be rapidly introduced into
practice in order to be able to manage the extreme avalanche periods better.
When the snow start to slide down the mountain, the avalanche speed
and forces are enormous and destroy all they meet on its path. The high
population density of the Alps makes it difficult for authorities to use
« active » avalanche controls - namely releasing small avalanches
before they become big ones. Where there are crowds, there can be no explosions
and therefore no active avalanche prevention. Only passive – namely defense
structure measures- protection can be efficient in this case.
The expansion of existing communities and construction in newly developed
areas require accurate and convivial tools for avalanche zoning. As land-use
changes and environmental and climatic changes take place existing patterns
of avalanches alter. Thus, protection of existing communities also depends
on the ability to quantitatively understand avalanches. Prevention against
avalanches consists in:
- zoning all exposed areas,
- building defense structures to stop, contain or deviate avalanches
thanks to dams, dissipative structures or galleries to protect roads.
Until now, these studies are essentially based on expert analysis.
It consists of a terrain investigation using the traces avalanches left
as well on the site as in inhabitant’s memories. This allows determining
the historical limits of the major avalanche and depicting the extreme
events having taken place on this site. This approach provides a brief
description based on empirical knowledge that does not allow specifying
the velocity, the height, and the pressure of the avalanche on its path.
This classical method raises two problems:
- It only accounts for avalanches that have been observed or those
that have left permanent tracks
- It doesn’t account for defense structures, or other changes in the
environment.
The aim of this project is to improve the quality avalanche hazard zoning
and the efficiency of defense structures by understanding the physical
process involved in dynamics of catastrophic avalanches and their interaction
with defenses structures. This understanding of process, mechanism will
allow us to develop methods to improve avalanche prevention measures. This
will be developed thanks to the following objectives:
Model calibration, sensitivity analysis and risk management:
Current avalanche models contain physical and/or empirical parameters.
They also need boundary conditions (topographical data) and initial conditions
(snow distribution, snow properties in the starting zone and along the
avalanche path). The outputs of an avalanche model (run-out distance, over-pressure,
deposit depth, extent, etc.) depend in a complicated non-linear way on
these parameters and these initial conditions. The current approach to
choose these parameters is trial and error. This is inefficient, inaccurate
and time consuming since model runs can take an hour or more. Also, only
an expert on the model can do this. The aim of this sub-project is to create
a tool that help the user, using optimization techniques, to find parameters,
in a physically admissible range, which allow the model reproducing a data-set
for an area. The tool should also provide information on the sensitivity
of the model’s predictions to parameter variations.
There is strong need to calibrate and verify the different models,
comparing them with actual avalanches. Each of the participating countries
will therefore supply a set of the available well documented extreme avalanches
so that all the run-out models currently in use, could be calibrated with
real events.
To transfer those models to the end users it is important, to demonstrate
the use of the models for practical problems. Therefore, one task of this
work-package is dedicated to the risk management. In a few sites, that
have been affected during the winters 1999 and 1993 the numerical models
will be applied to produce avalanche hazard maps as well as to calculate
the modification of the hazard when different types of defense structures
would be constructed. This sub-project has several objectives:
- Integration of models in a Geographical Information System,
- Determination of the uncertainty of the models,
- Development of a reliability index for various models and various
application purposes,
- Inclusion of defense structures and their design in the Geographical
Information System,
- Comparison and calibration of models with terrain data from extreme
events,
- Risk Management using the integrated system (G.I.S. + models): Combining
the sensitivity analysis of the model with the probability of an event
to reach an area and the potential damage to get a quantitative estimation
of the risk.
- Illustration of the usefulness of numerical models as a basic tool
for risk management on several European regions based on the experience
of the avalanche events of 1999 and 1993, including cost-benefit analysis
of defense structures.
Quantitative Investigation of Defense Structures:
Defense structures have to some degree been used to protect property and
communities from avalanches. Their cost can be millions of Euro (Taconnaz
in France: 5 M.Euro). Until now their design is entirely empirical and
there is few model that can be used for quantitative design.
This sub-project's aim is to develop a theoretical framework able to
accurately predict avalanche flows, both dense and powder, around defense
structures, and to make this knowledge available to engineers. This will
be achieved in the following way:
- Investigation of different defense structures
- Numerical simulation of flows around defense structures
- Laboratory experiments on small scale models of flows around defense
structures
- Development and implementation of physical simple laws representing
the momentum and the energy losses relating the flow after the defense
structures to this flow before the defense structures.
- Comparison of avalanche run-up heights with different available models.
Evaluation of Existing Structures
In recent years defense structures have been established to stop and deflect
avalanches. Some of them have been hit by avalanches, and valuable experience
is gained in this field in European countries. Moreover, little has been
done to disseminate this knowledge throughout Europe. In Europe many defense
structures have been hit by large avalanches (catching dams, deflecting
dams and channeling dams). In many avalanche sites, large avalanches are
also deflected by natural obstructions. The objectives in this section
are the following:
- Investigation of full scale avalanches and the effects of deflecting
and catching dams,
- Development of a database to be used by the other sub-program to
verify the dynamics models (each avalanche path/terrain will be digitized,
each avalanche record will be mapped digitally and each avalanche will
have a table with detailed measurements and historical photos.
- Comparison between observed and calculated avalanche run-up heights
by use of various available dynamics models,
- Improve the existing dynamics models for better physical description
and practical use
- Implement a 3D terrain model into existing GIS-terrain models with
ability to draw defense
- Structures on digital maps and calculate the volumes, etc.
Dissemination and Practical use of the developed knowledge
This sub-project’s aim is to disseminate the results and systems of the
previous sub-projects from the researchers to the engineers, consultants
and planners. Its aim is to make the results easily accessible to the end
users without compromising their scientific integrity. The results will
disseminated through handbooks, training courses and seminars. We will
ask practitioners what functionarities they want and the decision helping
system to include to facilitate a two-way flow of information and expertise
between researchers and practitioners. This activity will be performed
in close collaboration with engineers who workout with practical solutions
of avalanche problems.
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CADZIE Project