DEVELOPMENT OF ENVIRONMENTAL
STAGE 1 REPORT:
IDENTIFICATION OF HYDRO-MORPHOLOGICAL PARAMETERS TO WHICH THE AQUATIC
ECOSYSTEM IS SENSITIVE
WFD48 Stage 1
Background to research
This project arises as part of a coordinated effort by the UK
environmental agencies to prepare for implementation of the Water
Framework Directive – specifically in relation to water
resources regulation. Its overall aim is to develop methods
for the establishment of regulatory standards for rivers and
lakes. The project excludes Heavily Modified Water Bodies.
Objectives of research
This is a Stage 1 report based on review of the international
literature in order to identify all hydro-morphological parameters
which affect aquatic ecosystems – either being used by water
users/regulators around the world or identified within the research
literature. It includes a gap analysis to report on
parameters which have not been adopted in reported studies or
practices, but which may merit consideration in the UK. It
provides a focus for discussion between members of the project steering
group and the contractors, and a sense of direction for future stages
of the project.
Key findings and
The main outcome of Stage 1 was that the regulatory parameter for
environmental standards for rivers at a broad scale should be flow,
since data on potentially more ecological meaningful parameters such as
depth and velocity are not widely monitored and cannot be determined
with detailed surveys at all sites. Since flow varies greatly
between water bodies, generic flow standards need to be expressed in
dimensionless terms, such as proportions of natural flow or unit flow
per drainage area or channel width. Nevertheless, UK agencies should
develop a hierarchical approach to standards, where broad scales
methods based on flow are used for screening, but detailed scale
methods based on more directly ecologically meaningful parameters, such
as depth and velocity, are used for site level impact assessment and
- Most countries have various methods of determining
environmental flows, each defined for a different purpose, e.g.
strategic analysis, scoping or impact assessment.
- Licensing of reservoir releases and abstractions present
quite different problems and different methods have been developed to
deal with these issues. With reservoir releases, the whole
flow regime (apart from very large floods that by-pass the dam) needs
to be created. Abstractions, by and large, have no impact on
high flows and so the focus is on low flow impacts.
- Where data are scarce, expert opinion is used, and
increasingly a formal structured approach to getting consensus amongst
a group of experts, including academics and practitioners is favoured.
- There is wide acceptance that all parts of the flow regime
have some ecological importance. As a result, there is a growing move
away from single low flow indices.
- Many methods determine environmental flows in relation to
the natural flow regime of the river. Some methods define flow in terms
of site characteristics, such as flow per unit width needed for salmon
migration in Lancashire, but it has not been possible to examine the
data or the basis of these derivations. Other methods define
environmental requirements in terms of more direct hydromorphological
elements, such as water depth and velocity.
- Small scale studies have shown that flow interacts with
morphology to define physical habitat (such as width, depth, velocity
and substrate) for specific organisms. These quality elements vary
spatially; water is deep in pools and shallow on riffle; velocity is
high in riffles and slow in pools. Standards based on these
quality elements at the broad water body scale cannot be readily
defined. To implement standards at the reach scale, site data are
- Implementation of the WFD will require that environmental
standards are applied for all bodies regardless of hydrological and
ecological data available. Consequently, standards are required that
can be applied without having to visit the water body. This
means that standards must be related to parameters than can be obtained
from maps or digital databases, such as river flow, catchment area or
geology. Any resulting standards will have less predictive power at a
local scale and cannot be tested using site data.
- A hierarchical approach may be needed in which a broad
scale approach, perhaps based on flow, is used as a screening tool to
assess all water bodies. A more detailed approach, perhaps
based on depth or velocity, may be applied to a smaller number of sites
identified as requiring close attention.
- The flow regime is complex and is characterised by timing,
magnitude, duration and frequency; all of which are important for
different aspects of the river ecosystem. To produce
operational standards, there is a need to identify a small number of
parameters that capture its most significant characteristics. For
example the number of high flow events greater than three times the
median flow has been shown to be related to the structure of macrophyte
and macro-invertebrate communities in New Zealand (Clausen, 1997).
- The equivalent for lakes is the water level
regime. Water level is of direct ecological relevance since
it determines the area of littoral zone exposed and, given its
variability, the timing and duration of exposure. It is also
directly related to water depth; it influences a range of system state
variables including effective fetch, wave-base and re-suspension of
fine-grained bed sediments; and it is linked to residence
time. As for the river flow regime, there is a need to
identify the most significant characteristics of the lake water level
regime; for example annual or weekly ranges, seasonal maxima or minima,
or rates of rise and fall.
For lakes, water level is the key hydromorphological parameter because
of its integrative role in relation to the volume and dynamics of flow
(including residence time) and its relative simplicity of
measurement. The relative ease of measurement however belies
the paucity of existing long-term data in relation to natural regimes
of lakes across the UK.
Key words: abstraction, flow release, hydrological regime, timing,
magnitude, duration, frequency, hydro-morphology, parameters,
standards, rivers, lakes.
Copies of this report are available from the Foundation, in electronic
format on CDRom at £20.00 + VAT or hard copy at
£25.00, less 20% to FWR members.
N.B. The report is available for download from the SNIFFER Website