Hydraulic protection of territory
The main topics are:
- danger hydrologic in mountain land
- nivology
- snow mechanical behavior
- analysis of motions
- protection structures
What is mean danger?
Danger is assessed as a risk hydrologic, it is connected at slope instability, by geologic aspects. Meteorological and climate events influence that assessment, because they characterize water cycle.
The risk is regarding the protection of population and citizen. A risk value is the product between frequency of events and damages which an event can make.
To reduce the risk value of a territory, exist some different ways:
by protection, through building of structures active or passive,
by prevention, through activities non-structural,
by prevision, through danger maps.
Do you know the snow?
There are species of snow, it depending on its formation and temperature and pressure values during its growth.
AINEVA expresses the snow formation into a cloud by the vapor pressure, because the snow is formed by water drops. Therefore, with a temperature under zero degrees and through the nucleation, we have an ice crystal (homogeneous or heterogeneous). Then we can have the reverse sublimation which forms a snow crystal (as the picture).
From a snow crystal, it is born a snowflake by aggregation, a new snowflake by reverse sublimation or edged crystal by edging.
After the snow fall, there are different conditions during a day, these variations can modify the kind of snow: through the metamorphism, it is studied how a snow structure growth depending from its dry level. In this case, it is so important know the gradient of temperature from soil to surface (G).
If we have a dry snow, if G<5 c/m it is a destructive growth, else (G>5 c/m) it is a constructive growth.
If we have a wet snow, if it is quite wet it is stable, else it is very wet it is unstable.
The analysis of mechanical behavior is so important to understand what is snow: many studies reports that there is a great difference between compression and traction resistances, by main important is know slice resistance, to understand coulomb behavior.
By these knowledge it is possible to understand how a great mass of snow can move, such as the avalanches.
The avalanche analysis is very difficult: an avalanche is a rare consequence of many factors, naturals or artificial. So there, the study by frequency (or returning time) is different from rain analysis.
First of all, it is necessary understand what avalanche is: is it a fluid or a solid? Both kind of study are important to know where and how an avalanche is developing along a slope.
Through several types of motions, we know velocity, starting point and arriving point of a snow mass. This thanks the hypothesis of Newtonian fluid or Coulombian solid with turbulent fluid. Although these difficulty, it is possible know the velocity with the balance system of energy and mass.
In this case, some models are used, such as PCM, Vollmy, Vollmy-Salm and AVAL 1D - RAMMS 2D (analytical model). That last model uses the technique of Godunov time discretization and Riemann problem, through the hypothesis of two shock waves.
There are many kind of structure for protection of a slope, all that are specific for the land. For instance, we have supporting structures, deflectors for wind effects, deviation and stopping structures. Finally it is important know the rules by a Swiss law which includes dimensions and distances of works.