Andrew Evans, Michael Cawood, Jonathon Reid
Eildon Dam, Goulburn Weir and Waranga Basin in Victoria are owned and managed by Goulburn-Murray Water (G-MW). Eildon Dam and Goulburn Weir are situated on the Goulburn River, while Waranga Basin is an offstream storage supplied from Goulburn Weir.
In November 2004 a dam safety emergency exercise involving the establishment of a central Emergency Coordination Centre at Tatura as well as Emergency Operations Centres at each of these three dam sites was conducted. The exercise presented a variety of emergency situations in stepped time increments, including earthquake, mechanical failure, a hazardous material spill and a terrorism related incident. External agencies were not involved.
The exercise was part of an ongoing G-MW program designed to test and improve dam safety emergency planning and response systems for all of G-MW’s dams and highlighted areas where procedures, situational management and communications can be enhanced.
Outcomes aimed for in G-MW’s program are improvement in Dam Safety Emergency Plans and internal communications, together with clarification of roles, responsibilities and capabilities.
The valuable experiences learned from this dam safety emergency exercise and plans for a larger scale exercise involving other emergency management agencies will be shared with others through this paper.
The Ross River Dam was constructed in 1974 following design by the State Government, including
hydraulic model testing, by SMEC. The maximum spillway discharge at that time was 1100 m3/s.
Latterly, the dam and spillway have come up for a comprehensive review given that the dam is in an extreme hazard category because of its location only a short distance upstream of the city of
Townsville. The revised hydrology has produced outflow hydrographs peaking at over 4 000 m3/s – more than three and a half times the original – to be passed through the 130 ft (39.62 m) wide
The paper describes the hydraulic modelling planned and carried out to determine changes needed to handle such high discharges. The modelling was to provide for the installation of radial gates and piers, and study of the water level, pressure and dissipation conditions in the dissipator for several key discharges through the range to PMF. Pressure measurements included transients, consideration of the potential for uplift of the basin floor slabs, the integrity of the walls to handle the differential loads, and, as a major consideration, the energy conditions in the flow exiting the dissipator and the integrity of the rock downstream to avoid erosion. Each of these aspects will be addressed in the paper both from the modelling and interpretation standpoint and from the civil structural analysis standpoint, together with a description of the strengthening works required to achieve a satisfactory outcome.
Jonathon Reid, Chris Kelly, Bob Wark
One of the most important aspects in the construction of an embankment dam is to be confident that the filter materials placed meet the design intent. The design methodology for filters is now well documented.
However, all too often during construction the filter material, as placed, does not comply with the specified requirements and all parties are faced with costly decisions and delays to the works to determine correction measures and whether the work completed meets the design intent. This paper shares the knowledge gained over a number of projects the authors’ have been involved in and the methods used to improve the properties of the placed filters taking into account some of the practicalities of having these materials produced and placed in a commercial environment
Keywords: filters, specifications, manufacturing, construction, quality assurance.
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.
Ian Hampton, Dr Mohand Amghar and James Willey
The Eildon Dam Improvement Project is being undertaken by Goulburn-Murray Water as part of its dam improvement program that includes an upgrade of the existing Lake Eildon spillway that passes through the left abutment of the dam. The main components of the spillway are a gated concrete gravity overflow section that is 33 m high and 60 m wide, a 435 m long low gradient spillway chute and a hydraulic jump stilling basin.
The spillway was originally designed, including a physical model, in the 1950s to pass a maximum discharge of 3,400 m3/s with a maximum reservoir head of 9.0 m above the spillway crest. This can be compared with the 2003 flood hydrology and flood routing studies that result in a PMF discharge of 6,900 m3/s and a maximum reservoir head of 14.1 m above the spillway crest.
A new physical hydraulic model study was carried out over 2003-2004 as part of the investigations by the Eildon Alliance for the Project. The model was tested with discharges up to and exceeding the upgraded PMF. Very turbulent conditions were observed at discharges exceeding the original design discharge including the formation, build-up and collapse of large diameter vortices in flow over the spillway crest and overflow section. The vortex phenomena resulted in the intermittent formation of high waves and very high transient pressure loadings at the downstream toe of the overflow section and extending to the upstream section of the spillway chute. The paper discusses some scaling issues, presents some of the salient results of the study and discusses their application to the 2003-2004 design of structural modifications for the spillway.
The paper includes a discussion and comparison of the 1950’s model study with the 2003-2004 study. The magnitude of the vortex phenomena could not be predicted from the previous studies, and it is recommended that investigations for upgrades of similar works that involve large increases in design discharges include detail examination of vortex phenomena.