Environmental Engineering Reference
In-Depth Information
proaches, tools and linkages. This is necessary
in order that the methodological platform:
1 supplies the deliverables that are actually
required to support integrated catchment studies
to guide the development process;
2 ensures that the model outputs are compatible
with the requirements of decision-makers not
only at the end but also at each intermediate stage
of the study;
3 avoids
encompasses representation of
the following
elements:
1 The spatial distribution of hydrometeorological
stresses (rainfall, evapotranspiration).
2 The response of the physical environment (soil
layer, aquifer, fluvial corridor) to the hydromete-
orological stresses.
3 The spatial representation of hazard; e.g. flood-
ing/no flooding and waterlogging/no waterlogging
situations in the basin.
4 The calculation of the probability of occurrence
of a particular event (groundwater-induced flood-
ing, waterlogging, fluvial flooding).
Mathematical models provide the basis for gen-
eration of FPMs and, in this context, it is impor-
tant to note that while the first element (point 1
above) is a direct function of the availability of
temporal and spatial records of precipitation and
evapotranspiration, the other three elements are
functions of themodelling strategy adopted for the
studies.
The FPM yields, for every discrete element
(raster element) of an area, the number of times
during a specified period that the water level is
expected to rise to a given elevation above ground
level (for groundwater-induced surface and fluvi-
al flooding) or just below it (for groundwater-
induced waterlogging). The general approach to
calculating the flood frequency is set out in
Box 22.2.
expending monetary
and human
resources unnecessarily.
Current flood risk management policies
demandanintegratedmodellingplatformor frame-
work, but despite this there remains anabsenceof a
formalized modelling framework. Aradas (2001)
proposed a Framework for Catchment Modelling
Studies (FCMS) as 'a staged and systematic ap-
proachtobeusedas a template for thedevelopment
of modelling exercises to suit the physical charac-
teristics of a basin and the level of detail required at
each stage of a project, trying to strike a balance
between project needs, cost and human resources.'
The resulting FCMS recognizes three distinct
blocks of activities, coinciding with the three
stages proposed by Mitchel (1989), to guarantee
a timely and cost-effective project planning pro-
cess. The blocks are:
1 Normative level: identifying and examining
general issues regarding the hydrological, geomor-
phological, land-use and flooding systems in the
basin.
2 Strategic level: comprehensive analysis of land
and water interactions at a variety of scales
throughout the basin.
3 Operational level: integrated modelling of se-
lected, key flooding mechanisms in the basin.
The proposed FCMS (Fig. 22.9) parallels existing
approaches to geomorphic studies, environmental
assessments and engineering project management
(Thorne 1998). Indeed, one of the lessons learned
from research performed to develop the FCMSwas
the need to better account for geomorphic process-
es and landforms in the mathematical modelling.
For example, in the R´o Salado Basin it emerged
that the proper representation of the hydrological
impacts of the different types of relict dune field
present in theNorthwest (RegionA) is an essential
Modelling framework for flood risk
management
The importance of carrying out integrated studies
and developing flood risk management plans at
the basin scale when seeking sustainable solu-
tions to flooding problems is now widely recog-
nized. However, the requirement to generate and
incorporate multiple inputs from a range of cog-
nate disciplines leads inevitably to the develop-
ment of ever more complex mathematical
models that seek to simulate as closely as possi-
ble the physical processes that occur in nature.
This makes it increasingly important that a
sound methodological platform is used to under-
pin selection of the appropriate modelling ap-
