Development of Decision Making
Frameworks for Managing Alterations to
the Morphology of Lakes
WFD49a
October 2005
The importance of European lakes for conservation and resource use is
widely recognised, yet a systematic decision-making procedure for
managing lake morphology is lacking. The Water Framework
Directive (WFD) requires that all surface water bodies (including
lakes) should achieve ‘Good Ecological Status’
(GES) by 2015. GES requires hydromorphological conditions
supporting at
worst ‘slight changes’ in the
composition and abundance of key biological quality elements
(phytoplankton, macrophytes and phytobenthos, benthic
macroinvertebrates and fish fauna) relative to the appropriate natural
reference condition or High Ecological Status (HES). For
standing waters hydromorphology is defined by elements of morphology
and hydrological regime.
This report describes the development of a pragmatic decision-making
framework for regulating changes to lake morphology. The
three main objectives of the research were to:
- Define a set of
type-specific morphological reference conditions for the key lake types
defined by the UK’s WFD Reporting Typology;
- Characterise and document
the spectrum of potential morphological impacts affecting lake systems
in the UK;
- Develop a decision-making
framework for evaluating the extent to which morphological alteration
of lake systems is likely to compromise the ecological status of a lake
– both in relation to existing levels of pressures and
impacts and with respect to new development proposals.
The decision-support framework developed for this project was based
around the concept of ‘thresholds of potential
change’, whereby numerical thresholds and criteria of
morphological change were established against a range of recognized
physical pressures. Twelve groups of specific pressures (35
in total) were classified as either ‘whole lake’
where the entire system is affected, or
‘component’, where there is modification to only
part of the lake. Hydrological regime changes which induce
morphological change are also considered. A default set of
threshold values (termed sub-critical,
lower and upper) are defined
for
each group of pressures, assigned on the basis of their nature and
likely significance. The threshold values for a particular
lake are then modified using a ‘Lake Sensitivity
Typology’ scheme, which adjusts default values according to
those site-specific physical attributes (geology, depth, size,
altitude, form and location) perceived as likely to influence lake
ecology sensitivity. Threshold values are increased where
site attributes (such as increased lake surface area) lead to a greater
assimilative capacity, and are reduced where attributes which are
thought to increase ecological sensitivity (e.g. particular lake forms)
are identified.
The decision-support scheme operates through the principle of an
Alteration of Lake Morphology Score (ALMS). Data for the ALMS
must be supplied by a hydromorphological assessment, e.g. by completion
of a Lake Habitat Survey (LHS), which quantifies all specific pressures
with the exception of some hydrological regime data that can be added
into the analysis as it becomes more widely available. The
ALMS can be used to determine whether the morphological pressures at a
site are sufficiently small to permit the site to be classified as
HES. Thereafter, higher ALMS values indicate a progressively
greater risk that a site will fail to achieve GES due to morphological
alteration. This approach readily enables identification of
HMWBs, the eventual designation of which are subject to tests (Article
4.3), and ALMS can also help prioritize the mitigation measures
required to achieve the environmental objective of Good Ecological
Potential (GEP).
Copies of this report are available from the Foundation, in electronic
format on CDRom at £20.00 + VAT or hard copy at £35
.00, less 20% to FWR members.
N.B.
The report is available for download from the SNIFFER Website