Environmental Engineering Reference
In-Depth Information
land plains (Chapman 1984). This compilation
also placed special emphasis on the unique
features encountered within the plains of
Buenos Aires Province, which includes the R´o
Salado Basin.
The preceding introductory discussion sum-
marizes some key issues related to large lowlands,
recognizing that low energy is the main feature
responsible for the small horizontal water fluxes
and the prevalence of vertical fluxes involving
evaporation, infiltration and, in particular, the
exchange between the shallow aquifer and the
unsaturated zone. This prevalence of vertical over
horizontal water movementsmakes lowlands par-
ticularly sensitive to climate change and human
interventions in the hydrological system. This
sensitivity is clearly demonstrated by the recently
increased frequency and duration of flooding in
the Northwest area of the R
´
o Salado Basin, which
is discussed in detail in later sections.
That introduction (UNESCO 1984) also identi-
fies several fundamental issues that are explored
in more detail with a case study of the R´o Salado
Basin more generally. For example, the multi-dis-
ciplinary nature of flooding mechanisms, their
modelling and their management in lowland
catchments require that groups of specialists work
together in developing an integrated, conceptual
approach right from the beginning of a study,
rather than working in series or in parallel
throughout the duration of the assignment, and
this is addressed through the Framework for
Catchment Modelling Studies (FCMS) proposed
in a later section (see 'Modelling framework for
flood risk management'). Other issues that are
explored include the need to develop broad-scale
flood risk maps using remote sensing (UNES-
CO 1993); the importance of adopting water bal-
ance models that clearly identify the dominant,
driving variables at a variety of scales; the key role
of groundwater-surface water interaction; and, in
particular, the role of groundwater storage in act-
ing as the 'memory' of the system through its
lagged response to hydroclimatic trends and cy-
cles. The latter is clearly depicted by relatively
modern, groundwater-induced flooding in the
Northwest area of the R´o Salado Basin, which is
interventions in the flooding system. When deci-
sions must be made concerning future manage-
ment of flood risks, the situation is further
complicated by uncertainties concerning the tim-
ing and severity of climate change, the existence of
multiple alternative scenarios for socioeconomic
development, changes in public perceptions and
expectations with respect to flooding, and the
possibility of technological developments in flood
damage mitigation that cannot at present be
predicted (Evans et al. 2003; Thorne et al. 2007).
Consequently, integrated flood risk management
studies, encompassing the conditional probability
of inundation from a variety of flooding mechan-
isms, risk tolerability [e.g. the ALARP principle
promoted by theUK'sHealth and Safety Executive
(HSE 2001)] by individuals and society, and the
sustainability of different management strategies,
emerge as a vital discipline to support decision-
making. For example, increasing awareness of
climate change places ever increasing emphasis
on dealing with future uncertainties, as demon-
strated by the Risk and Decision Making Frame-
work developed by the UK Climate Impacts
Programme (UKCIP; Willows and Connell 2003).
The iterative and tiered nature of this framework
is a reflection of the need for management to
be both flexible and adaptable in order that it
can deal effectively with unpredictable problems,
respond to changing stakeholder wishes, and re-
spond effectively to feedback from the benefici-
aries of river basin projects.
In this context, this chapter presents flood risk
concepts and modelling techniques that are
selected to be particularly suited to applications
in large, low-lying basins, and examines these
concepts and techniques from the perspective of
broad goals for catchment development.
The hydrological attributes inherent to large
plains have been extensively treated in a very
interestingcompilationof studies (UNESCO1984,
1993) covering conceptual aspects (Fertonani and
Prendes 1984; Kovacs 1984; Mull 1984; Paoli and
Giacosa 1984) and international case studies, such
as the shallow aquifers of East China (Shi and
Ke 1993); the Caspian Sea Basin (Velikanov 1993)
and the Australian approach to hydrology of low-
