Overall Conclusion and Discussion - Response of Flood Events to Land Use and Climate Change - page 224

RAS model is sufficient. In general, combining the results of modeling both in
1D and 2D domains is necessary. The results of flood propagation in both
models gave us better insight into flood characteristics such as, where the water
moves (inundation) and how fast the water flows (water velocity). These results
are very important as basic information for policy making, decision support, and
flood hazard planning.
Return period
• The results of statistical methods for frequency analysis of the Ubaye River in
Barcelonnette show that the 1957 flood event may, on average, be expected
annually every 11 years with a 90 % lower confidence level, and every 66
and 100 years with a 90 % upper confidence level. In addition, a simulated flood
hazard for a 66 year return period has a 0.015 probability of occurrence; and
100 year return period has a 0.01 probability of occurrence.
Objective (c):
• In case of a maximum discharge of 480 m 3 /s the velocity and water depth
increases in the channel, between the left and right banks in the channelized part
in the city and in the undisturbed river bed. But critical overtopping of the dyke
is observed on both left and right banks in the city area. It shows that with
current morphology of the river and current dyke structure it could protect the
area in case of such designed flood events.
• In a natural environment, the vegetation covering the banks might typically be a
small contribution to the overall flow resistance in the natural reach of the river.
Restoring vegetation along the river would increase hydraulic resistance during
flood events. Higher bed roughness equates to lower near-bank velocity.
Restoring vegetation along the river would increase hydraulic resistance.
Objective (d):
• As an overall conclusion on climate change detection, a significant downward
trend in the precipitation time series at both the Barcelonnette and Allos stations
were distinguished, while an inverse upward trend in the maximum temperature
time series at Barcelonnette was identified. The distribution of discharge in the
channel was normal and no trend was realized in the flow discharge at the
Barcelonnette station. A negative trend in precipitation and a positive trend in
temperature push the research to find other triggering factors which affected the
normal distribution of discharge in the channel.
• The results of the time series analysis between 1961 and 2009 showed that the
highest precipitation occurred in 1977. Therefore, this year was selected to
compare to 2008, the year which the recent flood was occurred. Monthly data of