R.A. Ayre and T. L. McGrath
SunWater as an owner of 25 major dams in Queensland has completed a programme to update the design flood hydrology of all of its referable structures in accordance with the latest methodology for estimating extreme design floods. This programme ensures the adequacy of existing spillways is included in an overall dam safety portfolio risk assessment in a consistent fashion.
This paper describes the methodology adopted in the re-assessment of the design flood hydrology of the storages. Principally this has meant the use of a design hydrograph approach utilising runoff-routing methods as described in Australian Rainfall and Runoff (1999). Design rainfall inputs have been based on generalised techniques derived by the Bureau of Meteorology such as the Revised Generalised Tropical Storm Method and the Generalised Short Duration Method for the estimation of Probable Maximum Precipitation. These estimates, coupled with the use of a regional design rainfall estimation technique known as CRC-Forge that is used for determining large to rare design rainfall estimates, have been used to derive a complete estimate of the inflow/outflow flood frequency curve for each dam.
The paper also provides an insight into the significant factors and relationships that are involved in the changes resulting from this process. Overall, there has been an increase in design rainfall depth estimates for the extreme events, and a general reduction to neutral change in the large to rare rainfall range. These changes plus the influence of temporal effects and the assignment of Annual Exceedance Probability (AEP) has led to substantial changes from previous estimates of design floods. The implication of these changes is profound for
an organisation such as SunWater.
Now showing 1-12 of 64 2969:
J S Marsden, P H Jacob, R Nathan, R A Davidson and L A McDonald
This paper sets out the principles, practices and issues relevant to the sharing of
costs for dam safety upgrades in southwest Western Australia and other locations.
We examine the impact of applying economic allocation principles to this task and the impact of other criteria such as dam safety obligations, hazards presented by a large dam, community expectations for public safety, the broader public safety, welfare and state and regional economic benefits reliant on dam safety, significant community costs subsidised by irrigation customers, State Government ownership, and the effects on bulk water prices should customers be required to fully fund the necessary dam safety upgrading.
Stephen Newman, Mark Foster
Construction of the Lake Buffalo Dam was completed in 1965. It was to be a temporary dam, required to operate for several years, then act as a cofferdam for the construction of a much larger dam downstream. This larger dam was never built and a risk assessment completed by Goulburn Murray Water (G-MW) in 2001 identified several dam safety deficiencies at Lake Buffalo were among the highest priorities for risk reduction measures across the G-MW dams portfolio. Specifically it identified Lake Buffalo as having inadequate flood capacity and there were also concerns about transverse cracking within the embankment.
This paper describes the detailed investigation and analysis of the embankment cracking including assessing the potential for piping through an embankment having deficient filters and known transverse cracking. The design features of the upgrade are also described including the design of the a filter buttress, a parapet wall raise, Computational Fluid Dynamics (CFD) modelling and spillway anchoring. Construction was completed in 2003.
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.
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 peak
flow). 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.
José López1, Tim Griggs, Robert J. Montalvo, Richard Herweynen and Ernest Schrader
The Burnett Dam is a 50m high Roller Compacted Concrete (RCC) Dam with a total RCC volume of
400,000 m3. It is located on the Burnett River, approximately 50km inland from the town of Childers
in Queensland, Australia. The design of the dam commenced in 2003, construction started in
November 2003 and the dam will be completed by the end of 2005.
This paper discusses the construction processes, the extensive quality control program and the
innovations developed for the RCC dam construction.
Key features of the project discussed in this paper are:
During construction, special emphasis was given to the inspection of the processes of production,
transportation, delivering, placement, compaction and curing of the RCC.