2: View of the St Barthélémy forested fan with the gorges
and the Cime de l’Est on the background (Peak on the right).
3: View of one of the first dams erected in the 1920' along the
channel to avoid bed incision. The talus slope on the left is probably
the remains of an old debris cone.
flows during the period from 26 September, 1926 to 9 October, 1926
brought down to the Rhone river approximately 106 m3
of material. More recently (~1995) despite the construction of two
concrete dams in 1975 and during the eighties (Fig. 3), a debris flows
had partially obstructed the Rhone river. Today maintenance works
are currently planed for an amount of 3 Mio Swiss francs.
4: Present state (17.08.2003) of the riverbed of the St Bathélémy.
Note the amount of sediments that are prone to create debris flows.
4b: View of the deposit within the channel joining the accumulation
zone and the fan (Picture E. Bardou).
4c: A cross-section within a debris flow nicked by the river (Picture
that enhance the activity of this catchment are most probably linked
slope of the catchment and lower order stream sufficiently flat
for debris accumulations (Fig. 4)
of moraines (Fig. 3)
small size of the catchment
geological setting that make large rockfalls possible (Fig. 5)
geological setting implying high erodability
stream is situated at the contact of the gneissic basement and with
the helvetic carbonate series.
implying clays minerals occurrence
5 : Geological map (from BRGM 1 :250'000 ;
Map Thonons-les-Bains) of the St Barthélémy catchment (in blue the
be said that the neighboring catchement of Mauvoisin had not built
such an important fan although its settings are similar. Even if the
current process of erosion is to be related with bed load transport,
it seems that it could be due to a venturi effect of the Rhône before
the St-Maurice cluse.
d'une lave torrentielle. CREALP page.
E. (2002): Méthodologie de diagnostic des laves torrentielles
sur un bassin versant alpin. Thèse EPFL.
G.H. & Clague
J.J. (1984): Destructive mass movements in high mountains: hazard
and management - Geol Soc. of Canada, Paper 84-16, 230 p.
F. (1927): Le réveil des Dent du Midi (Coulées de 1926 et de 1927).
Le Globe, Genève, 66, 1-15.
F. (1930): Les coulées de 1930 au St-Barthélémy (Suisse). Mat. Cal.
6, 25, 239-251.