Results - Response of Flood Events to Land Use and Climate Change - page 172

Fig. 6.40 The location of the left dyke and right dyke in urban reach of the Ubaye River with
some photo of city and natural part of the river (Source of photos Google Earth and RTM)
has a modified and natural river bed. These two parts include a canalized channel
in the city and an undisturbed river bed without any infrastructure. The dykes are
located in urban reach of the river, having an approximate height of 2 m and a
length of 3.5-4 km. Using different criteria, critical flooded areas were deter-
mined. By comparing with aerial photos from the region, areas potentially affected
by damages in different scenarios could be estimated (Fig. 6.40 ).
In this section, HEC-RAS was used to model the dyke break scenarios over the
case study area. Geometric inputs were achieved with HEC-GeoRAS (ArcGIS
extension) and additionally, ArcGIS 9.3.1 was applied for spatial processing of the
input and modeling processes, and also to visualize the outputs. Then, the HEC-
RAS model was run to investigate the effects of a dyke break in the area. For this
purpose, the dyke break was considered on the right and left bank in the city part
of the river. The model results show the maximum inundation depth around the
dyke break to be about 0.12-1.48 for the 2008 flood event and 0.58-3.20 for the
1957 flood. The following figures show overtopping of the banks as a result of a
dyke break in one cross section. The applied analyses include the following
scenarios:
Scenario (1): Modeling of the 2008 flood event showed a maximum discharge
of 205 m 3 /s with the dykes. In case of this scenario (1), normal retention water
depth and velocity was shown in the channel-water flow was kept between the
banks. The model indicated that the maximum water depth and velocity in the