Environmental Engineering Reference
In-Depth Information
It was recognized early in the research that no
structured approach currently existed within
which to perform the suite of modelling studies
necessary to support integrated catchment
flood risk management planning. The work
then centred on an attempt to fill this void by
developing a practically oriented Framework
for Catchment Modelling Studies (FCMS) that
fulfilled the need identified by Aradas (2001)
for 'a staged and systematic approach to be used
as a template for the development of modelling
exercises to suit the physical characteristics 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 parallels existing
approaches for system-wide geomorphic studies,
environmental assessments and engineering proj-
ect management. Indeed, one of the lessons
learned from the research studies is that geomor-
phic, environmental and engineering investiga-
tions must be closely linked to, and used to
inform, themathematical models used to generate
maps of flood probability.
The applicability and utility of the proposed
FCMS was tested in an Integrated Study of flood
riskmanagement options for the R´o Salado Basin,
with the modelling theme selected to focus on the
flooding mechanism that was critical to flood risk
management in this large, lowland catchment:
groundwater and surface water interaction. It was
found necessary tomodel flooding at both regional
and local scales in order to address the variety of
stakeholder issues, and a coupled modelling ap-
proach was found to be essential to representing
the dynamics of GW-SW interaction at the local
scale. The resulting Flood Probability Maps
(FPMs) proved effective in synthesizing model
outputs in a form suitable to support options
appraisal and identification of sustainable flood
risk management strategies.
The R´o Salado studies revealed that, at a broad
scale, regional modelling must focus on simulat-
ing only the dominant flooding mechanism (in
this case groundwater-induced flooding) in order
that modelling requirements and run times are
Catchment flood risk modelling
The final step is Catchment FloodRiskModelling,
which uses the outcomes of regional and local
flood probability models (together with informa-
tion on flood receptors) to produce catchment-
wide maps of flood risk under current and 'with
proposed flood risk reduction measure' condi-
tions. These results are required at the project
planning phase with the objective of analysing the
flood risk benefits, costs and environmental im-
pacts of proposed options for flood risk reduction
at the basin scale, based on knowledge gained
through local modelling.
Finally, Figure 22.13 summarizes schematical-
ly the above stages of the FCMS for the application
into flood management studies.
Conclusions
Thedesiretodevelopandextendtherepresentation
of physical processes in modelling emerges from
modelling campaigns or literature reviews as a
natural humanaspiration to exploit our constantly
increasing knowledge of hydrological processes to
the greatest degree possible when striving to pro-
duce scientifically credibleflood riskmanagement
plans. However, in practice this aspiration is nec-
essarilyconstrainedbyconsiderationsof cost, time
and data availability. The work reported in this
chapter has attempted to balance the desire to
model inherently complex groundwater and sur-
face water interactions in large lowland areas ex-
plicitlywith theneed toworkwithinstrict budgets
for time and effort through developing amodelling
framework based on practical realism, a challenge
that is often encountered when performing inter-
nationally funded projects in less economically
developed countries (LEDCs). This challenge is
particularly severe in large, low-lying basins
where, besides the need to meet the objectives of
multiple stakeholders, there also exists the need to
overcome difficulties inherent in modelling a va-
riety of flooding mechanisms and their interac-
tions at a variety of scales.
