Civil Engineering Reference
In-Depth Information
response of the ecosystem in terms of the services it provides. For rivers, the
linkage between water regime and biodiversity has been described by Bunn
and Arthington (2002) in terms of four principles:
1 major flow events drive geomorphic processes, determine the form of
habitat available for plants and animals and therefore set limits to those
that can continue to exist in a river system;
2 the plants and animals associated with a river have evolved responses that
match the opportunities and pressures provided by the natural flow;
3 many animal species in rivers, and plant and animal species adjacent to
rivers, require the periodic connections that occur during floods if they are
to survive, disperse and prosper; and
4 changes to the flow regime reduce the competitive advantage of endemic
species and encourage colonisation by exotic and introduced species - and
possibly also dominance of a sub set of the existing range of species.
Fundamentally, changes to the flow regime will increase the likelihood of
change to the biological and other elements of the river ecosystem. A range of
assessment methods has been developed to provide more specific information
on the relative importance of particular aspects of the flow regime. Such
assessments assume that a certain amount of modification to the flow regime
can occur without incurring excessive risk of loss of valued services. Tharme
(2003) identified over 200 methods from 44 countries. The methods vary
greatly with respect to their objectives, complexity, and the data, technical
and scientific inputs they require.
Some methods focus on preservation of particular species, typically fish.
These methods focus on minimum flows for maintaining habitat and for
spawning and migration. Others are more holistic, and aim to address the
support of the ecosystem as a whole.
The 'FLOWS' methodology, developed in 2002 by the Victorian
government in Australia, uses a 'bottom-up' 'building blocks' approach (see
DNRE 2002). It identifies flow dependent environmental assets, identifies
flow component characteristics (standard component types are used) which
are required to maintain or enhance them, and assesses the extent to which
those characteristics are currently present. Using hydraulic and hydrologic
models, the current river flow characteristics can be compared to the required
characteristics to assess where there are gaps. For each assessed river reach,
the extent to which the current flow component meets the recommended
parameters is expressed on a six point scale, ranging from 'mostly' to 'never'.
A 'top-down' approach to environmental flow assessment, such as the
Benchmarking Methodology (see Brizga 2007; Quinlan
et al
. 2004), uses the
natural or existing flow regime as a starting point, and examines the conse-
quences of altering or removing various components of the flow regime. This
compares with the bottom-up FLOWS approach, which identifies minimum
flow characteristics needed to support important values. Both of these
