Geoscience Reference
In-Depth Information
The important aspects of this definition are that
it deals with the both quality and quantity of the
water, in terms of the distribution, or variability in
time and space; that it links the ecosystem to the
people; and that it acknowledges the non-scientific
choice of environmental objectives. Environmental
flows have a long history - people have always
been aware of the importance of flow as a
governing process of river ecosystems, but it was
first formalized by Tennant (1976) in his simple
but much-used Montana assessment system,
essentially an instantaneous look-up table. Since
then, more than 200 methods have been developed
for environmental flow assessment (Tharme,
2003), and these can be grouped, in relation to
level of detail and resources required, into four
broad groups: hydrology based; hydraulic rating;
habitat simulation; and holistic. Table 4.1 describes
the general process of assessing, negotiating
and implementing environmental flows using a
holistic methodology. Despite the wide diversity
of methods, all use the same type of data (or
sub-sets of it): habitat and process requirements
linked to hydrology via hydraulic models. The
Table 4.1
The various stages and tasks (common to most holistic methodologies) by which environmental flows are
assessed and implemented (modified from O'Keeffe, 2009).
STAGE A: SCOPING
Assess the area of interest, to try to identify issues of particular importance, and to draw up an initial plan for the
assessment.
STAGE B: PREPARATION FOR THE ASSESSMENT WORKSHOP
Task 1
Initiate EFA assessment (level of detail, define methodology, appointment of the specialist team)
Task 2
Zone the study area
Identify reaches of the study river in which physical and ecological conditions are likely to be similar.
Task 3
Habitat integrity
Assess the condition of the area of interest by classifying sections of the river in terms of how much they have
been modified from natural conditions.
Task 4
Site selection
Select sites within the study area for detailed analysis based on: ease of accessibility; habitat diversity; sensitivity
of habitats to flow changes; suitability for modelling; proximity to a flow gauging site; representation of
conditions in the river zone; and critical flow locations.
Task 5
Surveys and measurements
These surveys are intended to augment information and fill in gaps that have not been covered in previous
studies:
Biological Surveys —
To identify flow-sensitive species (e.g. fish, macroinvertebrates, diatoms, riparian
vegetation) and define their seasonal habitat requirements in terms of current velocity, depth, substrate type
and wetted perimeter.
Hydraulic survey and analysis —
To provide the link, via rated cross-sections or habitat simulation, between
ecological habitat requirements and flows.
Hydrological analysis —
To check that the recommended flows are within reasonable limits of flows
experienced in the river, and is therefore a check on the realism of the process, rather than a motivation for
recommended flows.
Geomorphological survey —
To assess the sources and types of sediment in the river, analyse the channel
morphology (the geomorphic features and their stability) and predict the consequences of changing flows on
the sediment input-output and therefore the channel shape and substrate types.
Water quality analysis —
To assess possible problems related to flow modification and to identify point and
diffuse runoff impacts.
Social survey —
i) To identify people who are directly dependent on a healthy riverine ecosystem (e.g.
subsistence fishermen, farmers, withdrawers of domestic water, and anglers); ii) To consult with stakeholders
and identify preferences for the management objectives for the river.
