“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
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.
This paper outlines how Grampians Wimmera Mallee Water (trading as GWMWater) and its consultants managed the upgrading of Bellfield dam’s 43m high, reinforced concrete dry outlet tower and discharge facilities. The upgrading included improvements to operations, the provision of safe person and materials access into the tower and its 1200 mm diameter steel penstock, anchoring the tower with post tensioned cable anchors to resist seismic loads, refurbishing a 1200 mm butterfly valve and penstock corrosion assessments and repair.
Prior to the upgrading, access to all areas was difficult and unsafe to some areas. In particular no provision had been made during the original construction for butterfly valve removal or safe access into vertical sections of the penstock. Overcoming these deficiencies required considerable survey, detailed movement planning and attention to detail.
Deryk Forster and Manoj Laxman
The Stage I construction of the Ross River Dam was completed in December 1973. The reservoir
reached full supply level (FSL) and then spilled in January 1974. In 1976, the left embankment was
raised to Stage II level. Spillway gates were installed in February 1978 with full supply level for
Stage 1A (FSL).
In the years following the first filling of the reservoir after the raising of FSL, salt scalding
downstream of the northern portion of the left embankment occurred. This was attributed to
foundation seepage. Investigations started in 1978 to define what remedial measures were required to ensure the safety of the left embankment. Fissured clays were first discovered in the foundations of the Ross River Dam during these investigations.
Fissures could substantially reduce the overall strength of the soil foundations. Therefore the effect of these fissures needs to be considered when evaluating the acceptable levels of reliability against
embankment failure. More extensive fissuring was discovered during the current investigations and a
cataloguing system was employed to characterise the foundation conditions.
A simplified layer model was adopted early on in the design but did not fully demonstrate the
complexity of the subsurface conditions. Extensive use was made of historical geological data,
current investigation data and the application of GIS systems. The resulting model more clearly
represents the foundation conditions and high degree of variability and was used in subsequent risk
assessments for the upgrade design.
Brett Jones, Brian Mayhew
In preparation for the Corporatisation of the former Snowy Mountains Hydro-electric Authority, an
enquiry was held into the health of the Snowy River below Jindabyne Dam. This enquiry has led to a
range of environmental release requirements being placed on the new entity Snowy Hydro, including
requirements for variable release patterns (daily base flows and periodic flushing flows) and water
Construction works are currently underway to modify the existing Jindabyne Dam structures so that
these releases can be provided. The works include a new intake channel and control structure, a new environmental release tunnel and modifications to the existing spillway, including a concrete lined chute and plunge pool. Provision is also being made for a future mini-hydro power station, which would generate using waters released to provide environmental flows.
This paper discusses the history and background of Jindabyne Dam including the Snowy River
inquiry, details of the environmental flow requirements; design to meet the required capabilities and
the current status of the project.
There is a large stock of embankment dams throughout the world needing the assessment of their
safety as required by modern dam safety regulations. Due mainly to economic and site constraints
associated with potential dam upgrading work, it is imperative that a rational approach be adopted in
assessing their safety and in designing the remedial works. One of the most important criteria is the
selection of appropriate geotechnical parameters under different conditions. Predominant loading
conditions in a dam are much different from those in other structures such as bridge and building
foundations and therefore the direct adoption of traditional approaches may not always be valid. This
paper presents the various aspects of issues associated with the stability assessment of dams including
the rational selection of the parameters and numerical codes available to dan/geotechnical engineers
to assess their safety.