Environmental Engineering Reference
In-Depth Information
Dyke failure width
Dyke crest elevation
Horizontal failure
Vertical failure
Floodplain elevation
Fig. 3.14
Simplified dyke failure in a schematic representation
dykes may fail under the load of extreme water levels and long flood durations.
Losses arising from subsequent inundation may be dramatic, not only because of
the high value concentration in the dyke protected floodplain, but also because of
the fast water level rise and high flow velocities caused by rapid breach outflow
[ 2 ]. Dyke failure occurs in different conditions:
• Dykes can fail by overtopping or by being inundated at a prescribed elevation
for a specified duration.
• Dykes can fail to a prescribed elevation different from the floodplain elevation.
• Specify dyke breach width and,
• Specify a rate of failure both vertically and horizontally (Fig. 3.14 )
The dyke scenario simulation results are beneficial for the authorities, and
planners should know about the possible effects of failure, finding critical places
which are more vulnerable before an extreme flood occurs in the case study. In this
study, in case of dyke failure, the aim was to find how strong the dykes and
channel modification are in both the city and natural sectors of Ubaye River. In this
context, simulations of different failure scenarios applying various hydrograph
propagations are useful to investigate the river behavior during flood events.
Ubaye River is divided to two parts; modified/channelized and natural river bed.
These two parts are included in a channelized part of the city and the undisturbed
river bed without any infrastructures. The dykes are located in urban reach of the
river having an approximate height of *2 m and a length of *3.5-*4km
Ramesh [ 92 ]. Potential affected areas from damages in different scenarios could be
estimated by comparing the results of the simulation derived from different dyke
scenarios with available aerial photos.
Dyke scenarios were applied to the situation with and without dykes, giving a
rough idea of the flood defense effects of dykes. HEC-RAS hydraulic modeling
was used to execute unsteady flood river routing of dyke breach hydrographs
through the upstream and downstream channels. SOBEK hydrological modeling
was applied to estimate the flow propagation in floodplain in case of dyke breach
and overtopping of the banks and inundation occurrence. Input data such as RAS-
geometry was achieved with HEC-GeoRAS (ArcGIS extension) and additionally,
ArcGIS 9.3.1 was applied for spatial processing of the input and model of data,
and to visualize the outputs. The applied analyses include the following scenarios:
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