Theoretical Background - Response of Flood Events to Land Use and Climate Change - page 31

infrastructure planning and implementations reduce flood damage from small and
medium floods; they can induce catastrophic floods when they start to fail. For
example, if dykes or levees fail, they can cause a false sense of security on public
and residential parts in flood-plain areas. As noted by Eiker et al. [ 120 ] for flood-
mitigation projects, the question is not if the capacity will be exceeded, but what
are the impacts when the capacity is exceeded. Thus, land-management planners
and the public must fully understand the consequences when the dykes or dam
fails.
2.9 Historical Changes in Land Use in Barcelonnette Area
One of the reasons for deforestation during the seventeenth century in France was
that the forests were considered as an economic resource spatially for the con-
sideration of warships. The dramatic consequences of deforestation led to
increasing of land degradation and mass movement occurrence [ 121 ]. Many
authors have addressed in their investigations to deforestation in the floodplains of
the rivers in south-eastern France in the late eighteenth and nineteenth centuries
[ 122 ]. In contrast, with the vegetation explosion of the early twentieth century,
changes were observed over shorter time periods and in smaller areas, in the
riparian forest active channel contacts. Table 2.3 summarizes previous investiga-
tions on land use, channel morphology and population change during eighteenth,
nineteenth, and twentieth centuries in whole catchment:
Bravard [ 123 ] by investigation on previous research concluded that anthropo-
genic factors played a major part in initiating active channel restriction at the turn
of the century, with climate change as a secondary factor. Slopes were stabilized
through extensive reforesting, torrent control measures, and progressive aban-
donment of agro-pastoral activities, thereby reducing peak flow and bed-load
supply. Bravard [ 123 ] also confirmed the importance of natural and anthropogenic
factors in riparian vegetation in his research. The evolution of the Ubaye Riverbed
at the turn of the twentieth century provides an instructive example of short-term
watershed influence on a river segment. As shown by Schumm [ 124 ], channel
geometry is equally adjusted to external factors and is modified at the same time as
riparian vegetation. Channel deepening and narrowing on the major part of the
Ubaye course was noted, as well as channel pattern modification. By increasing
hydraulic roughness and favoring bar stabilization, forest expansion exerts an
internal control on the alluvial mosaic and contributes to a reduction in bed width.
The genesis of a floodplain forest is, in fact, accompanied by the development of
tree units within the active channel, and therefore rivers draining forest corridors
are generally not as wide as those located in prairie sectors [ 125 ]. Internal factors,