Civil Engineering Reference
In-Depth Information
O
developing flow deviation - ecological response relationships for each river
type using a combination of existing scientific studies, expert knowledge
and representative field studies, and thereby estimating the current threat
to ecosystems and what would be needed to reduce that threat;
O
recognising that there will always be a level of uncertainty and therefore
applying an adaptive monitor - evaluate - revise approach to refine
understanding of ecological responses over time (Poff
et al
. 2010).
It should be noted that estimates of water requirements for ecosystems will
always have a level of uncertainty. Assessments provide values of parameters
that are estimated using available knowledge to support the ecosystem. For
this reason, water requirements may best be expressed as a range representing
high to low likelihood of damage or loss, rather than a single value. Decisions
made later in the planning process can then take into account this likelihood
of damage in weighing up alternative management options.
Risk and vulnerability
As discussed earlier, risk can be considered a combination of the likelihood of
a threat and the consequence of that threat to benefits. In the above discussion
of assessments, threats to water resource benefits have been discussed in
terms of times when identified water requirements for the benefits are not
met. We have also discussed estimating the consequences of the threat in
terms of the economic value of benefits lost or reduced, where such valuation
is possible. For cases where economic valuation is less straightforward (e.g.
important natural assets) valuing can be based on non-economic criteria that
prioritise assets in terms of such things as biodiversity, naturalness, as well as
any non-consumptive economic benefits. Risk is assessed by combining the
likelihood of a damaging event (e.g. a severe water shortage) occurring with
an assessment of consequences.
Risk assessments can be improved by adding in assessments of vulnerability
to the threat. For example, a town may be very vulnerable if the water resource
is its only source of water, but less so if it has alternative supplies available.
Similarly, a groundwater-dependent ecosystem can be more vulnerable to a
water shortfall if this has been a rare or non-occurring event in the past than
if it is already adapted to periods without water. Likewise, a community may
be more vulnerable to flooding if it has no evacuation plans or individuals
have no insurance.
In NSW Australia a technique using river geomorphology characteristics
was used to classify and map river reaches ecosystems that are more and less
susceptible to being impacted by human activity (see Hamstead 2010, Cook
and Schneider 2006). This 'fragility' classification was defined as the suscep-
tibility/sensitivity of certain geomorphic categories to physically adjust/
change when subjected to degradation or certain threatening activities. Three
categories were derived:
