2005 – The Significance of Factors Affecting Secure Yield

Malcolm Nix

“Off-river” storage, Bootawa Dam, receives water pumped from the Manning River to supply a
regional water scheme on the mid-north coast of NSW.

As part of drought planning, short term predictive modelling of future streamflow has been developed
from an analysis of the last 30 years of recorded flow data and “on-line” upstream river gauges.
In the longer view, a comparison was made of th e last 30 years of recorded flow with an analysis of
the previous 80 years of synthetic flow data. There is a downward trend in streamflow in the last 25
years. Is this likely to continue, or is it part of a cycle or some other factor?

Long term fluctuations in the Southern Oscillation Index are compared to rainfall for this region.
Estimates of sustainable yield of the scheme are dependant on many factors, including environmental flows, dam size, turbidity constraints, river pump transfer capacity, river loss, catchment rural demand, accuracy of streamflow data and future climate change.

The affect of each of these factors has been quantified and ranked according to their importance on
sustainable yield.

Buy this resource