Environmental Engineering Reference
In-Depth Information
for a flood height of 4 m, good-quality houses can suffer damage of 0.2 (i.e. 20 %
of damage risk) whereas a lower-quality house will reach damage figures almost
equal to 1 (complete destruction, since they correspond to 100 % of damage risk).
For a flood height of 3 m, the mean damage value is about equal to 0.6, whereas it
is about equal to 0.3 for a height of 0.9 m. Flood height and velocity can be derived
from numeric simulations depending on the river's discharge and the local topogra-
phy of the floodplain and river-banks. GIS maps of structural risk of failure are
obtained from the fragility curves. They can be drawn up for various flooding sce-
narios in order to make sensitivity analyses for decision-making, because socio-
economic consequences and restoration costs may vary greatly depending on the
location of the construction in the floodplain and the hazard scenario.
As a result of flooding, various kinds of waste can be generated in excessive
volumes and quantities. This waste may represent more than ten times the yearly
volume of waste generated during normal use. Several years' work and important
socio-economic costs may then be required to remove, evacuate and process flood
waste. In order to predict waste, a database has been created and 6 typical dwelling
houses have been studied taking two scenarios into consideration: flooding lasting
under 2 days and flooding lasting over 2 days. Fragility curves vs. floods height
were developed for four individual and two collective typical French houses show-
ing that the volume of waste generated by a flood period lasting over 48 h is almost
twice the volume of that created during a shorter period. The volume of waste
generated by a flood 3 m high is almost three times the volume of waste generated
by a flood 1 m high.
For coastal industrial plants containing metal tanks with various kinds of prod-
ucts, fragility curves were developed on the effects of tsunamis. The height and
velocity of the tsunami flow was described by a simplified model valid at the shore-
line (at normal sea level) and inland inasmuch as the terrain is flat. Mechanical
failure of tanks was investigated, showing that failure may occur from sliding, buoy-
ancy uplift, buckling or overturning. New fragility curves vs. tsunami height were
developed for five typical tanks ranging from 8 to 30 m high and from 10 to 80 m in
diameter, used for oil storage. Results showed that sliding has more severe effects
on tanks than buckling, buoyancy or overturning in the case of small tanks, even if
their level of content was not low when the tsunami hit. Large tanks' resistance to
sliding is also very weak if no precautions are taken by installing a lateral protective
barrier.Withoutprotectivebarriers,tankscouldslideandthepipesconnectedtoit
could break even if the tsunami is less than 3 m high; whereas they could withstand
tsunamis of almost 10 m before buckling and 15 m before they are damaged by
buoyancy or overturning effects.
Sensitivity analysis studies may prove very useful for helping risk managers to
prepare themselves in the face of potential hazards such as floods and tsunamis, as
well as for designing protective systems i.e. barriers, early warning and alert devices
and dikes. Taking these points into consideration is particular important when building
new structures during reconstruction processes.
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