Study Area - Response of Flood Events to Land Use and Climate Change - page 117

marls, black schist's, and limestone (84 %) at the base of the foot slopes, the area
is susceptible to landslides and erosion [ 6 ].
Another prominent influence is the high variability of lithologic structures.
Erodible structures like black marl and flysch affect the slopes with severe gully
erosion and explain the 17 zones of instability. This lithology dates back to the
Jurassic period. Mountain areas mostly consist of calcschistes, sandstone, and
conglomerate (16 %) with the age start of Cretaceous [ 8 ].
Weber [ 6 ] explained the presence of Quaternary deposits topped with recent
alluvial deposit carpets, saying they begin to form on the surface of dark Limon
after being deposited during major floods. It is also important to mention changes
in land use from agricultural clearing practices and the unstable climatic factors
which have caused damages in the area [ 8 ].
4.8 Soil
It is known from past research on marly landscapes that mass-waste processes and
rill erosion affect formations with similar morphological and sedimentological
characteristics differently. [ 14 - 16 ]. Mass wasting was often found to be prevalent
in more cohesive soils because of their higher retention capacity, whereas gully
erosion is commonly observed on more silty soils [ 17 ]. Extensive erosion from the
slopes has contributed to the main types of soils in the area. Weathering produces
massive blocks of sandstone and limestone which disintegrates to form sandy and
loamy regolith. Flysch produces smaller or massive plates which break down as
sandy and loamy regolith, while marls produce silts or clayey regolith in the area
[ 18 ]. There is presence of some isolated arms of old meanders with clay deposits
and moraines in the higher slopes [ 6 ].
In order to better understand the soil surface and the influence of infiltration
through the surface, several studies have been carried out in the large mudslide
area [ 10 ]. The case study includes some parts of the Barcelonnette, Faucon-De-
Barcelonnette, Saint-Pons, Uvernet-Fours, and Les Thuiles subbasins. Different
types of soils (Fig. 4.20 ) are distinguished in this area, such as moraines, torrential
deposits, weathered marls, limestone, and Flysche, which covered 53, 33, 8.13, 3,
and 2.8 % of the whole area, respectively. Several factors over the past decades
have contributed to torrential floods and debris flows, such as the removal of
natural vegetation and increasing tourism. By removing natural vegetation, the
likelihood that soil will move down steep slopes increases, resulting in sedimen-
tation of rivers and a higher probability of flash floods.