Environmental Engineering Reference
In-Depth Information
modelling being undertaken in the Flood Risk
Management Research Consortium (FRMRC) and
other related research programmes. The problem
of modelling and predicting impacts at the catch-
ment scale is reviewed, and the major challenges
associated with filling key gaps in knowledge
are discussed. New modelling concepts such as
information tracking are introduced, and their
application to vulnerability mapping and
Source-Pathway-Receptor modelling for policy
and decision support in catchment flood risk
management planning is demonstrated.
example, with changes in land use type such as the
switch from grassland to arable, changes in farm-
ing practices such as intensive mechanization
within a given land use type, or changes in field
infrastructure such as the installation of field
drains or the removal of hedges. In turn, these
pressures can change the
state
of rural catch-
ments, reducing the integrity and resilience of
environmental characteristics and processes with
potential to increase runoff, soil erosion and pol-
lution. If unchecked, this can result in negative
impacts
on people and the environment and the
loss of welfare that this implies. A particular
feature of runoff (and water-related soil erosion
and pollution from rural land) is that impacts,
when they do arise, are mainly 'external' to the
site of origin and are borne by third parties usually
without compensation. In this respect, land man-
agers may be unaware of, or may have little per-
sonal interest in alleviating, the potential impacts
of runoff, unless they are instructed otherwise.
Concern about impacts justifies
responses
in the
form of interventions that variously address high-
level drivers, land management pressures, protect
the state of the environment andmitigate impacts.
Responses, which may involve regulation, eco-
nomic incentives, or voluntary measures, are
more likely to be effective, efficient and enduring
where they modify drivers and pressures, rather
than mitigate impacts (O'Connell et al. 2005).
This chapter uses the DPSIR framework as
a starting point to demonstrate how land use
management fits within a broad strategic research
framework for flood risk management at the
catchment scale. Catchment scale modelling and
prediction is of central importance to assessing
impacts withinDPSIR, and is also central to asses-
sing the effectiveness of mitigation response
measures. The current status of the capacity to
model impacts will therefore be a central feature
of this chapter. First, the historical context for
land use management changes is set out, and the
evidence for impacts at local and catchment scales
is summarized. A strategic modelling framework
for flood risk management based on DPSIR is
then mapped out, which includes an integrated
programme of multiscale experimentation and
Historical Context: Runoff Generation
and Routing in Changing Landscapes and
the Evidence for Impacts
Changes in land use and management
Since the SecondWorldWar, theUK landscape has
undergonemajor changes as a result of the drive for
self-sufficiency in food production, and the effects
of the Common Agricultural Policy:
.
loss of hedgerows, and larger fields;
.
cultivation practices causing soil compaction to
a greater depth;
.
land drains connecting the hilltop to the
channel;
.
cracks and mole drains feeding overland flow to
drains and ditches;
.
unchecked wash-off from bare soil;
.
plough lines, ditches and tyre tracks concentrat-
ing overland flow;
.
tramlines and farm tracks that quickly convey
runoff to watercourses;
.
channelized rivers with no riparian buffer zones.
In this landscape there are several interacting
factors that will have induced changes in the
generation of runoff and its delivery to the channel
network, such as the extent of soil compaction,
the efficiency of land drains, and the connectivity
of flow paths. A key factor is the impact that soil
structure degradation (due to compaction) can
have on runoff generation. By influencing the soil
structural conditions that determine the inherent
storage capacity within the upper soil layers, and
