Methodology - Response of Flood Events to Land Use and Climate Change - page 81

propagation results, depth of water and velocity were estimated and simulated in
the HEC-RAS model based on two different DEM resolutions. To this purpose, the
hydrograph of flood events of 2008 was used because there was the chance to
calibrate the model based on observed information from that event.
3.10.2 River Change Scenario
In the river change scenario, the river morphology was first digitized according to
available aerial photos for different years. Six series of vertical aerial photographs
were used: 1956, 1974, 1982, 1995, 2000 and 2004. These series of photographs
were applied to historically and quantitatively assess the area occupied by different
land cover in the whole study area, and to get a feeling about the river channel
changes over the time. Then, in hydrodynamic modeling, different hydrographs
were applied to approximate how river channel changes affect flow propagation.
3.10.3 Dyke Scenario
A high percentage of the world's population lives close to oceans, seas, lakes, and
rivers. In many cases, the life of these people, coupled with their personal property
and belongings, depend on flood defense systems [ 83 ]. In 2004, a commission of
the European communities reported that river floods may occur whenever the
capacity of the channel or man-made drainage system is unable to cope with the
volume of water generated by rainfall or when flood defenses fail [ 70 ]. In recent
years, extreme river floods across the world and all over Europe occurred due to
the breaking of these flood defense systems and the protection of infrastructures.
For example, during the August 2002 floods, more than 130 dyke breaches
occurred in Germany along the Elbe river which caused a total damage of
15 billion € [ 84 - 87 ]. In another example, in the Netherlands, the floodplain area
has often historically been faced with the threat of several floods from the sea, as
well as from rivers, which were mostly due to flood defense failure Möllmann
et al. [ 87 ]. Also, the failure of dykes around the city of New Orleans during
Hurricane Katrina turned a bad hurricane into a major urban catastrophe. Major
damage was due to the dyke failure along the Industrial Canal [ 88 ]. Usually, floods
have high damage potential due to the growth of urban areas or industrial sites in
floodplains. In many cases, these areas are protected by river dykes. Depending on
the characteristics of the river, the floodplains, dykes, and characteristics of the
dyke breach, such as the location and width of the breach, significant volumes of
water may spill over into the dyke hinterland, reducing the peak of the flood wave
downstream of the breach location [ 84 , 89 - 91 ]. River beaches protected by dykes
exhibit high damage potential due to a high value accumulation in the hinterland
areas. While providing efficient protection against low magnitude flood events,