Environmental Engineering Reference
In-Depth Information
Table 2.3
Summarizing historical land use change
Years
Changes
Source
1830
In 1830, the Ubaye river occupied most of the valley bottom, whereas agricultural land use extended
up to the edge of the active channel.
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141
]
Since 1860
The mobility of channel-forest contact the cyclic evolution of the forest margin-active channel
contact during the recent period appears to be controlled by fluctuations in hydrology and bed-
load. The population decreased by 50-60 % in the Barcelonnette basin and by more than sixfold
in the upper valley. Since 1860, when the population peaked in this region, the population has
decreased by 75-80 %.
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141
]
As early as 1892-1905
During this time 3,500 ha were reforested with Austrian black pine while 8,589 ha had already been
reforested (Figs.
2.8
,
2.9
)
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142
]
1920-1925
In 1920 Riparian forestation started. The riparian forest development in the active channel between
1920 and 1925 was the result of reduced rejuvenation processes like peak flow and bed load
supply, mainly due to a slope afforestation policy and torrent correction works undertaken in the
late nineteenth century by the RTM agency (law of 28 July, 1860).
[
141
]
1920-1930
The active channel area was colonized by Pinus Sylvestris. Dendrochonological analysis shows that
forest recolonization of the active channel took place around 1920-1925 based on age of Pinus
Sylvestris. Recolonization was accompanied by fluvial metamorphosis, changing from a braided
pattern to a sinuous single-bed pattern, as well as by bed incision. The topographical cross-
section of this sector demonstrates that the actual bed is 2 m lower than it was 75 years ago.
[
141
]
1941-1957
Close chronological ties with active channel expansion (+12.3 % from 1948 to 1956).
[
141
]
Between the first third of the nineteenth
century and 1948
The area of active channel decreased from 246 to 252 ha to 174 ha.
[
141
]
1948-1973, notably between 1948 and
1956
Vegetative colonization of the active channel primarily affected the segment upstream from
Barcelonnette where the forest decreased by 44 %. Such decreases were also occasionally
observed downstream, but not in any case throughout the entire period. Reduction of forest area
in favour of the active channel area. These changes, lasting only two decades, were in opposition
with the trend observed at the beginning of the century.
[
141
]
(continued)
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