Environmental Engineering Reference
In-Depth Information
Quantification of hydrological impacts of
land management change
catchment scale, that is clearly important in terms
of flood risk assessment, but also raises the possi-
bility that appropriate land management interven-
tionsmight be adopted to reduce downstreamflood
risk. Interventions with potential benefits for
flooding may also be relevant to other aspects of
environmental management, such as the control
of diffuse pollution and habitat improvement to
support improved biodiversity. There has been
increasing recognition in recent years from pol-
icy-makers of the interdependence between land
use and water management. For example, in the
UK, current policy on flood risk management, in
particular Defra's 'Making Space for Water'
(MSW), recognizes that water management is
inextricably linked to land management. There
is therefore an urgent need for guidance concern-
ing the hydrological impacts of landmanagement
to inform agricultural policy.
As a result of the above, land use and manage-
ment as a source of flooding was one of the key
research priority areas identified by the Defra/
Environment Agency (EA) R&D programme
(Calver and Wheater 2002; Wheater 2002), and
subsequently by the Engineering and Physical
Sciences Research Council (EPSRC), following ex-
tensive consultation, in establishing the UK's
Flood Risk Management Research Consortium
(FRMRC). A major review was commissioned by
Defra (O'Connell et al. 2004), which concluded that
the role of land usemanagement in enhancing and/
or ameliorating UK flood risk was an unanswered
question. And although the risk of flooding is con-
centrated in lowland regions, the management of
catchment headwaters, with their generally higher
precipitation rates and flashier response, is of
particular interest for flood runoff generation. To
address this issue, the FRMRC made a major
investment in a multiscale experimental and
modelling programme, based at Pontbren in
mid-Wales. In this chapter we report on the
results of FRMRC Phase 1 (FRMRC1), and intro-
duce preliminary results from the continuing
research in this area, funded under the FRMRC
Phase2 and the Natural Environment Research
Council's (NERC's) Flood Risk from Extreme
Events (FREE) research programme.
As discussed above, there is an urgent need to
quantify the hydrological effects of land use and
land management change, and clearly the poten-
tial for reversal is also important, but available
guidance to represent land management effects is
limited at best.
As noted above, O'Connell et al. (2004) carried
out anextensive review,whichhighlighted the lack
of evidence for local-scale and, particularly, catch-
ment-scale effects. As an interim measure, they
proposed a speculative modification to the Hydro-
logy of Soil Types (HOST) classification of UK soils
to represent the potential effects of soil degradation
on runoff production. JBA (2007) applied the meth-
odology to the Ripon catchment. Results indicated
that, if soil structural degradation were to occur
across the whole catchment, together with addi-
tional maintenance of moorland grips, peak flows
in the town of Ripon would increase by between
20% for smaller scale floods and 10% for more
extreme floods. A less extreme scenario (soil deg-
radation over 30% of the catchment) led to in-
creased peak flows of 10% for smaller scale
floods and 3% for more extreme events. While
these results appear entirely plausible, they are
essentially speculative. However, themethodology
is attractive, and provides the basis for a simple
methodwithnational applicability. Two important
issues arise. First there is a lack of an evidence base
to support the HOST class modifications at either
local or catchment scale; and second, there is po-
tentially a wide range of interventions that can be
considered at local scale, suchas the plantingof tree
shelter belts and the development of farm ponds.
Such interventions could not be directly related to a
notional level of soil degradation.
One option to identify the catchment-scale
effects of land use and land management change
is to interrogate catchment-scale data, and this
has been pursued recently by Beven et al. (2008),
using available UK datasets. The study failed to
identify a clear relationship between land use/
management and river flows. However, it is im-
portant to note that this does not mean that such
