Bourkes Gorge/Bogong Creek and Geehi River Aqueducts are large aqueducts that contribute to the
inflows for the operation of Snowy Hydro Ltd (SHL), hydroelectric plant in the Murray operational region.
The region has endured one of the longest and worst drought sequences of recent times and the efficient
used of water is becoming of increasing importance. The drought sequence has led to a low number of
medium to high inflow events to analyse, only one in the Bourges Gorge Aqueduct through the period of
study.

To determine what events occur at the intakes to the aqueducts, several representative sites had water level
monitoring instrumentation installed. Sites selected were Three Rocks Creek and Watsons Creek/Gorge
intakes on the Geehi aqueduct and Bourkes Gorge/Bogong Creek intake on the Bourkes Gorge aqueduct.
It has been found through the course of this investigation that water is lost from the aqueduct system when
there is capacity for water to be carried in aqueducts. For the single event in the Bourkes Gorge Aqueduct
93% of the volume spilt could have been accommodated in the aqueduct. Geehi aqueduct results varied
more and were difficult to evaluate due to the aqueduct configuration containing multiple intakes. There
was, however, significant scope for gains during some precipitation events.

On Geehi Aqueduct, the Three Rocks Creek intake has been found to have discharge over the spillway
much earlier than that at Watsons Creek and earlier than the flood peak that reaches the aqueduct metering
station. The time difference has been recorded as on average between 5-6 hours or greater and as such has
the potential to be a valuable site as an early flood warning station for maintenance crews to visit sites.
Data from Three Rocks Creek on the Geehi Aqueduct also revealed small spill events occurring in fair
weather. This differs from the general belief that spills occur only in inclement weather. It also adds to the
potential use for the site as an early warning station as if the intake is blocked and spilling from increased
flows due to snow melt a precipitation event under the same conditions would result in a much higher
percentage loss of water.

Data suggests that when spill events occur there is a significant loss and the volumetric and monetary
potential for gains is substantial and if appropriate water saving options were employed they would pay for
themselves in a relatively short period of time (several years). Large scale engineering solutions would
currently be expensive and would take a long time for them to pay for the capital and installation costs.