Theoretical Background - Response of Flood Events to Land Use and Climate Change - page 38

Fig. 2.14 An evolving land
use: during the twentieth
century (source [ 93 ])
2.10 Physical Characteristic of Flood Hazard
In the frame of hazard assessment, flood events are analyzed by means of recur-
rence intervals and spatial-temporal flood characteristics [ 128 ]. Flood hazard
estimation is based on the factors such as the triggering factors causing the hazard,
their spatial extent, duration and time of onset, including their frequency and
magnitude of occurrence, and secondary events influencing the event if any [ 129 ].
The flood characteristic creates a clear understanding of the flood plain, and gives
the understanding to the flood hazard behavior. The flood characteristic is not only
described by flood inundation, but also by inundation depth, flow velocity, inun-
dation duration; volume of water, surface area, stream power, and so on. Access to
all this information is possible by flood simulation using hydrodynamic modeling.
Alkema [ 130 ] emphasized that the hazard estimation is also based on the output of
the model simulation in the form of parameter maps such as flood velocity, depth of
water, and flood impulse. The pre-requisite for flood hazard is estimated by its fre-
quency analysis or return period calculation [ 131 ]. Hydrographs for different return
periods are the basis for understanding the hydrologic response of the basin [ 132 ].
The following characteristics are important in terms of the physical hazard
posed by floods event:
a. The depth of water and its spatial variability;
b. The extent of inundation, and in particular the area that is not normally covered
with water;