Environmental Engineering Reference
In-Depth Information
Fig. 22.6 Interaction between
relict aeolian features and fluvial
flooding in the Lower Salado. (See
the colour version of this figure in
Colour Plate section.)
which is consistent with the relatively low hy-
draulic conductivity, the very gentle regional gra-
dients and the relative high groundwater salinity.
Figure 22.7 shows a conceptual representation of
the groundwater-induced surface flooding process.
Based upon this conceptual understanding
of the surface water-groundwater system, the
flow balance for the basin can be formulated as
follows:
Approaches and Techniques: The Role
of Mathematical Modelling
Approaches and techniques
Having conceptualized a flood risk model that
encompasses the various flooding mechanisms
operating in a large, lowland catchment, the
next step is to develop a modelling approach
that accurately transfers the embedded concepts
into a practical assessment of current and
future flood probabilities and risks. A generic
approach (successfully applied to the R´o Salado
Basin) is proposed in Figure 22.8. In this
figure, parallels are set between the conceptual
understanding of the processes that lead to
flooding, the tools required to simulate these
processes and the components of the flood risk
model.
A key output of the modelling approach is the
Flood Probability Map (FPM). The FPM is a spatial
representation of the probability of flooding asso-
ciated with events of given magnitudes. This is
often expressed in terms of the return period of an
event, i.e. the inverse of the annual frequency of
exceedence of that event. By definition, an FPM
Precipitation
¼ runoff þ infiltration þ
interception storage þ
evaporation
fromopen surfaces
with the interceptedwater
Infiltration
¼ actual evapotranspiration
fromtheunsaturatedzone þ lateral
subsurface flow ð interflow Þþ
recharge
¼ recharge groundwater flow
actual evapotranspiration
fromthe saturatedzone
groundwater discharge to rivers ;
wetlands and lakes
Change in
groundwater
storage
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