Civil Engineering Reference
In-Depth Information
new infrastructure is being considered, the model must include capacity to
simulate what would happen to flows with such infrastructure in place. The
planner generally asks the modeller 'what if ?' questions, and expects that the
modeller will provide a response in a form that is useful. The planner needs
to understand broadly the kind of outputs that models can produce, and the
limitations of the model. Examples of model outputs are shown below.
For the Tasmanian River Clyde Water Management Plan 2005, a river
system model was used to simulate different environmental flow rules and
estimate how they might affect water available for extraction. Table 8.1
compares the amount of water that would be available during the period
May to October, with and without the Environmental Water Provisions in
place. Table 8.2 shows how the cease to take rule might affect the volume
available to be taken and the days on which water can be taken during the
winter months when the majority of water is taken into on farm storages.
Three different time periods are used to calculate the availability to show
the impacts of the changes in the system due to the recent drought years and
increases in storage development in the catchment. The three periods are the
whole period of record 1979 to 2003 to reflect the long term range; the period
between 1988 and 2003 which is when significant storage developments were
in place in the catchment and the initial stages of the drought period; and
the period between 1998 and 2003 to reflect the driest period of the record.
In this case the model did not attempt to forecast future flows, but rather
used historic flows and left it to the planners and decision makers to use this
information as a basis for estimating future impacts.
Table 8.3 shows how a model was used to estimate the effect of a change in
system reserve policy would affect allocations in the Goulburn regulated river
system in Victoria. In this case the model compared the effect under three
future inflow scenarios, the base case being a continuation of past average
conditions, scenario B being the climate that is projected for 2055 assuming
a medium level of climate change, and scenario D being the continuation
of the recent low inflow patterns. It can be seen that the proposed policy
has minimal effect on average annual diversions, but trades off a reduced
number of years of very low allocations for a reduction in years with higher
allocations.
Assuming that some sort of model is available, consideration is now given
to methods for relating changes in the water regime to effects on ecosystems,
social, cultural and economic values.
Ecological impact assessment
This involves the estimation of how projected changes in the water regime
for different options will affect the integrity and viability of ecosystems. It is
thus the bridge between model outputs of hydrology changes and the effect
on ecosystems of these changes. In Chapter 5 we discussed methods that
are used to identify and value ecological assets and processes and determine
