Graeme Hannan, David Jeffery
Lake Mokoan is a 365 GL capacity off-stream storage in the Broken River basin in northern
Victoria. Lake Mokoan will be decommissioned to provide 44 GL of water savings to benefit the
River Murray and the Snowy River. The Victorian Government has committed to maintain
reliability of supply in the Broken River supply system by implementing a package of offset projects.
The paper describes the community engagement process implemented by Goulburn-Murray Water
to steer the selection and implementation of the offset projects.
A reference committee of Broken systems irrigators was established in late 2004 to provide advice
to Goulburn-Murray Water and the Department of Sustainability and Environment on the package
of offset measures to be implemented to maintain the supply reliability once the 365 GL capacity
Lake Mokoan was decommissioned, leaving the 40GL capacity Lake Nillahcootie as the sole
storage in the Broken River irrigation system.
A REALM based system simulation model was refined to test the sensitivity of the parameters
defining the system reliability and to assess proposed offsets measures. The paper describes the
modelling which was undertaken and the evaluation and ranking of offset projects priorities.
The community engagement process is described. The paper concludes with commentary of the
lessons learned from this process.
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A risk assessment was performed for the Sacramento District of the U.S. Army Corps of Engineers to explore the justification for imposing an operating restriction on Lake Success to reduce the
probability and consequences of an Earthquake-induced dam failure. The potential for both a sudden overtopping failure and a delayed “seepage erosion through cracks” failure were considered.
The risk assessment focused on the seismic performance of the dam, the potential life loss and
economic consequences of Earthquake-induced dam failure, and the estimated residual risk and
degree of risk-based justification for the Existing operating regime, a range of Potential Operating
Restrictions, and an Indicative Improved Warning and Evacuation System. Risk assessment inputs
were supported by seismic deformation analyses under various Earthquake loadings and pool
elevations, dam break-inundation modelling, and reservoir simulation.
Evaluations against tolerable risk guidelines from the USBR, ANCOLD, and the UK HSE, together
with insights into the relationship between pool elevation and dam failure risk, provided important
inputs for the decision to implement an operating restriction.
Steven Fox, Robert Cooper, Shane McGrath
The Project Alliance delivery model is becoming more popular within the dams industry as owners, designers and constructors seek more effective ways to deliver upgrades that are needed to meet
contemporary community expectations whilst managing the significant safety and commercial risks
typical of these projects.
The Eildon Alliance has recently completed the Eild on Dam Improvement Project on behalf of Goulburn- Murray Water. This $52 M project involved reconstruction and raising of the upper portion of the 80 m high embankment, works to strengthen the spillway chute to cope with larger flood events and refurbishment of the original 50 year old spillway mechanical equipment.
The Eildon Alliance was responsible for the detailed design, construction, commissioning and project
management of this major upgrade. To be successful, a project alliance requires
the alliance partners to adopt a cooperative approach throughout the project. This paper de
tails the benefits that this cooperation provided at Eildon, reasons for selecting the alliance project delivery model and the outcomes achieved.
Peter Hill, Kristen Sih, Rory Nathan, Phillip Jordan
This paper presents a number of innovative hydrologic investigations undertaken for the recent detailed design of upgrades for Ross River Dam in North Queensland. A key issue for estimating extreme floods in the tropics is the estimation of flood events of long critical durations. The implication is that there is an increased focus on estimating the correct volume (not only the peakflow). This paper describes the regional analysis of flow volumes that was used to validate the estimated flood volumes.
Another issue of considerable importance is the assumed relationship between inflows and initial reservoir level. The analyses described in this paper showed that inflows are independent of reservoir levels for the more frequent events but for more extreme events they are correlated. This has important implication on how the initial reservoir level is incorporated in the hydrologic analysis. The final aspect covered by the paper is the derivation of seasonal flood frequency curves. This is particularly important given the highly seasonal nature of rainfalls in the tropics and the results are important for assessing risks during construction and scheduling the upgrade works
“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
Basic pre-construction foundation investigations for the Ross River Dam were done in the late ‘60s to early ‘70s but a more detailed hydrogeological assessment was carried out to investigate and manage waterlogging and salinity, which developed immediately downstream in the late 1970s.
As part of the 2005 Stage 2 to 5 upgrade design, detailed conceptual and numerical hydrogeological modelling was required to predict aquifer response along the embankment and downstream. This required “data mining” and additional drilling and aquifer testing to fill in data gaps, with the filtered and re-interpreted data used to build a 3D conceptual model of the embankment and underlying geology, by a design team comprising specialist hydrogeologists, geologists, geotechnical and dams engineers. This was converted to a 10-layer, 2-million cell numerical model, to enable high-resolution modelling of groundwater behaviour for a range of aquifer properties, flood hydrographs and seepage management options. As well as a design tool, the model is a valuable monitoring tool in confirming the performance of seepage management systems and to provide early warning of seepage management failures.
The study emphasised the need to capture data for a wide range in aquifer stress, to have simple
preliminary spreadsheet models to provide a “sanity check” and to collect data away from the
embankment to allow a 3D interpretation of the geology, to the assumption of “layer cake” models.