Results - Response of Flood Events to Land Use and Climate Change - page 164

6.10.2 River Change Scenario
According to the literature and the RTM report, in contrast to the period of
1970-1990, the active channel was characterized by reduced peak flow and
vegetative re-colonization (+5 %) of the active channel (Fig. 6.31 ). The evaluation
of the active channels' average width and annual peak flow from 1945 to 1990 on
the middle of the Ubaye River is shown in Fig. 6.28 .
River change detection was estimated for 1957, 1982, 1995, 2000, and 2008
according to available aerial photos, land use maps and discharge values. The
results of this analysis are as follows:
Flood 1957: Due to the lack of access to any data regarding past events, it was
not possible to obtain references and increase the accuracy of the results. For
instance, the flood event of 1957 has been recorded in every commune that was
affected by flood and the consistency in the reports varies in different communes.
The 1957 flood occurred on June 14. Various geomorphic phenomena along with
climatic factors enhanced the damaged cause by this severe event. Climatic factors
such as precipitation, snowmelt, and wind triggered the flood in this area. Other
factors such as debris accumulation and particle size varying from mud to several
cubic meters also affected this flood event. Based on the available literature, local
snow jams and snow melting at an elevation between 2,000 and 2,500 m, followed
by approximately 13 showers a day, also allowed the debris studded streams to
flow down the valley at a very high speed wherever the slope was moderate to
high. The uncertainty behind the 1957 flood simulation has to do with the lack of
observed data and information about this event. The data were missing because the
equipment was damaged and there was an interruption in reading the data [ 1 ].
Based on the limited data in some reports, the maximum discharge of this event
was 480 m 3 /s. The peak of the hydrograph reaches toward the end of the event
Fig. 6.31 Evaluation of active channel average width and annual peak flow between 1945 and
1990 on the middle Ubaye River (after Hydro bank data and aerial photograph (Source RTM)