Environmental Engineering Reference
In-Depth Information
Table 22.1
Baseline Scoping Modelling - Comparison
surface flooding was identified as the dominant
flooding mechanism in the most economically
important part of the basin (the Northwest -
Region A) and could, therefore, be defined as the
catchment theme. It followed that simulation of
GW-SW interaction emerged as the dominant
modelling theme, as explained in the previous
section.
matrix
Ground
water-induced
surface
ooding
Rainfall-
runoff
Fluvial
ooding
Rainfall-runoff
3
3
Fluvial
ooding
1
1
Groundwater-induced
surface
ooding
3
2
Baseline scoping model
The Baseline Scoping Model identifies all the rel-
evant variables and flooding mechanisms that
operate at the catchment scale and defines the
roles they play within the conceptual risk model
(s) developed in the initial conceptualization. The
analytical tools applied in this step constitute
'interpretive' or 'generic' rather than 'predictive'
models (Anderson and Bates 2001). This is the
case because these tools should not necessarily
require calibration as they are used mainly to
guide development of a conceptual framework for
exploring the sensitivities of the flooding system
to the uncertainties inherent in different future
scenarios.
Examples of the types of analytical tools that
might be applied include:
.
lumped rainfall-runoff models;
.
simple tank models applied at the sub-regional
scale;
.
coarsely gridded, 3-D groundwater models;
.
GIS-based regression models linking inputs
(hydrometeorological data) with outputs (ground-
water head responses).
A possible outcome of this stage could be a
comparative matrix suitable for representing
knowledge acquired concerning interactions
between the dominant hydrological processes in
the basin. This can then be used to determine
which interactions are sufficiently strong to
merit coupled modelling. An example is
presented in Table 22.1. Once linkages
between hydrological processes have been
identified, it should also be determined whether
they operate at the regional, sub-regional or
local scales.
Key:
1 Process A has low impact on Process B and no coupling is required.
2 Process A has medium impact on Process B and a weak coupling is
required.
3 Process A has a high impact on Process B and a strong coupling is
required.
Regional modeling
Regional modelling is performed to simulate the
main flooding mechanisms identified in the Base-
line Scoping Modelling step at a broad scale. Such
operational models (which may be applied at the
catchment or subcatchment scales) concentrate
on simulation of the relevant components of
the terrestrial hydrological cycle, with variable
degrees of coupling, as indicated by the matrix
developed in Step 3 (Table 22.1).
Local modelling
Local modelling is performed to explore and elu-
cidate coupling between hydrological processes
that are not simulated in the regional models.
This step has two specific objectives: first, to
gain deeper insights into the operation of key
hydrological processes that can be fed back into
one or more of the regional models (see feedback
arrow inFig. 22.9); and, second, to evaluate options
for flood risk management, with the findings
passed on to the final, Catchment Flood Risk
Modelling step.
