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However, it has to be noted that the material composition and important
processes which can initialize a dam failure like piping can hardly be
assessed based on remote sensing and modelling.
Impact of glacial lake outburst ϔloods
As already mentioned GLOFs can present a risk for infrastructures and
even human lives. Therefore it is advisable to calculate the probability of
downstream affects based on modelling of the area potentially affected by
an outburst fl ood, e.g., by using the aforementioned MSF model of Huggel
et al. (2003). Flash fl oods often lead to or transform into debris fl ows. Besides
the availability of loose sediments, a certain velocity of the water is needed
to transport the debris. The kinetics and mechanics of such an extreme
case of fl ooding can be described by the principle of a shallow-water wave
(non-linear differential calculus; Scheidegger 1975). This again depends
mainly on the steepness of the presumptive water channel. Haeberli (1983)
and Huggel et al. (2002) suggested that debris fl ows confi ne if an average
inclination of 11° is reached. According to Allen et al. (2009) lower thresholds
seem advisable, reaching down to an angle of friction of less than 3° (Table
14.3). These thresholds are, however, only rough estimates, and in reality
there exist transitions with different fl ow types occurring within one event
(cf. Table 14.4).
Further models which were used to model fl ash fl oods include RAMMS
(Rapid Mass Movements, Christen et al. 2010) and FLO-2D (O'Brian 1993)
(cf. Mergili et al. 2011).
Thus, the relative probabilities of an affected downstream area can be
calculated (Fig. 14.5). A major decisive parameter, though, is the quality of
the applied DTM.
Table 14.3. Parameters and their thresholds used for modelling of the probability of mass
movements Parameter Rock avalanche (Bolch et al. 2011a).
Parameter
Rock avalanche
(Kaibori 1988)
Ice avalanche
(Alean 1985)
Debris fl ow
(Heaberli 1983,
Huggel et al. 2004)
Floodwave
(Allen et al. 2009)
Slope at the
detachment zone
30º
25°
n.c.
n.c.
Angle of friction
(average incline)
20º
17°
11°
debris fl ows. Notably, large debris fl ows can form during breaching of
moraine dams (Clague and Evans 2000, Haeberli et al. 2001).
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