Meeting Environmental Outcomes – A Planning Framework - Water and Agriculture: Sustainability, Markets and Policies - page 197

a clearly stated environmental objective or set of objectives that gives rise to measurable
outcomes
technical efficiency such that environmental goals are met at the lowest possible
resource costs, where these costs reflect both productive and environmental values
a clearly specified set of operational rules to provide planning certainty for
environmental managers and consumptive water users — planning certainty is an
important feature of an effective water market.
Specifying the environmental objective
There is a range of potentially complementary and competing management objectives
along a river system. Some of these may be managed independently, but most will need
to be managed jointly, as the supplementation of tributary flows with dam releases is
likely to affect flow regimes all along the river system. From an operational perspective it
is useful to consider a flow regime, and hence the environmental flow objective, at a
specific reference point, remaining mindful that altering this regime will have broader
consequences.
At a given location, an environmental release strategy that reconnects the river and
flood plain environments at appropriate time intervals has at least three elements:
timing or release window of the high flow event — for example, during late winter or
early spring to coincide with breeding cycles;
duration of the high flow event — the number and pattern of days that flow rates are
maintained above a specified level;
minimum and maximum flow requirements ; and
frequency of occurrence — the distribution of return or inter-arrival times between
high flow events.
The first three elements serve to establish the criteria for a desired or successful high
flow event. An environmental release strategy encompasses both access to a volume of
water resources and a set of release rules, to generate a high flow event. For example, in
the context of the discussion in the previous section, the environmental objective may be
specified as maintaining a flow of at least 30 gigalitres a day at Wagga Wagga for a
period of 15 days, commencing in the period from 1 August to 30 September. A
minimum flow rate of a little over 30 gigalitres a day would fill the majority of billabongs
and lagoons in the middle reach of the river, as indicated in Figure B. A maximum flow
rate may also be imposed to avoid upstream flooding at Gundagai.
The criteria for success may reflect ecological imperatives that are ultimately
subjective. For example, a high flow event lasting between ten and 15 days may be
considered a partial success, although the incorporation of partial success into the
planning framework would require the benefits of alternative flow regimes to be given
relative weights. Natural high flow events are still subject to large variability in flows and
the desired event may be better characterised by the processes of filling and flushing the
wetland environments, as opposed to maintaining a minimum flow level. An alternative