Environmental Engineering Reference
In-Depth Information
with a steady increase in the discharge level throughout the period. The initial
period of the curve flattening may be attributed to the steady rise in the river water
as a result of the water flow constantly accumulating from several streams from the
upstream. The high increase of the peak discharge may be associated with sudden
snow melt attributed to warm wind from the south, leading to an increase in the
water level several folds within a very small period of time.
An essential factor that affected the intensity of the event was the amount of
debris that was transported with the running water down the slope and blocked the
river flow path [ 1 ]. But there were no available data for the quantity of debris
accumulation during this event. Based on the assumption that all other factors are
constant, only the estimated discharge data were used as input to the model and the
changed conditions (e.g., dykes) were incorporated within the DEM. The results of
the 1957 flood simulation (Fig. 6.32 ) were validated based on the photographs
available from RTM.
There were no data regarding velocity or depth of water during this event.
Therefore, a model calibration for these parameters without any observed data was
almost impossible. The 1957 flood is validated at two points with available pho-
tographs as shown in the Fig. 6.32 . These validations gave at least some clarity
about the severity of the flood. The maximum estimated velocity was *6.32 m/s
and the maximum water depth was *3 m in the channel.
Flood 2008: In May 2008, the Ubaye River exhibited a peak discharge of
205 m 3 /s. If no major flooding occurred, some damages were observed: a bridge
had been destroyed, and in some specific areas, river ridges have been scored
(Fig. 6.33 ). Based on the RTM, the triggering factor for this event was heavy
rainfall and actively melting snow in the upper part of the slopes, a similar
situation to the 1957 flood.
During this event, the floodplain was not affected by inundation like the 1957
flood. The water stayed within the banks, but in some places the banks became wet
and overtopped. The bridge of ''Pont de l'Abattoir'' where the measuring station was
located had its scale a few centimeters out of the river flow (Figs. 6.34 and 6.35 ).
The DEM that was used in this simulation was adjusted by increasing the
heights of the dyke by 0.5 m from that of the 1957 event. Figure 6.32 represents
the model results in the city area of the Ubaye River. The maximum estimated
velocity for the 2008 flood in the channel was *3 and had a maximum water
depth of *2.7. At cross section 12 located exactly at the Abattoir Bridge, the
maximum water depth in the near bank was 1.7 m. This result shows the best
agreement between measured and observed data. This means that the model cal-
ibration was done in the right way to access more accurate and real results.
Other simulations (1982, 1995, and 2000): Based on the available data, the flow
propagation was simulated for the river case study for flood events in 1982, 1995,
and 2000, and was compared with the river morphology of 1957 and 2008. The
idea behind this kind of simulation was to know how much river channel changes
affect flow propagation.
The maximum discharge for all of these years was less than the 2008 flood, and
there was also no report about any inundation during these years. Then again, the
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