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R. E. Saunders, J. Roberts, B. W. Omundson

Ross River Dam is located immediately upstream of the twin cities of Townsville and Thuringowa. The population at risk from failure of the dam is approximately 110,000. A recently completed risk assessment has confirmed earlier studies that the dam does not satisfy current safety criteria and presents high risk levels in a number of areas. Importantly, the risk assessment has enabled the extent of these risks to be clearly identified. This paper summarises the risk assessment highlighting notable methodologies employed and the key findings of the study.

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2000 Papers

2000 – Ross River Dam Risk Assessment – A Summary
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R. E. Saunders, J. Roberts, B. W. Omundson

Ross River Dam is located immediately upstream of the twin cities of Townsville and Thuringowa. The population at risk from failure of the dam is approximately 110,000. A recently completed risk assessment has confirmed earlier studies that the dam does not satisfy current safety criteria and presents high risk levels in a number of areas. Importantly, the risk assessment has enabled the extent of these risks to be clearly identified. This paper summarises the risk assessment highlighting notable methodologies employed and the key findings of the study.
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2004 Papers

2004 – Managing Community, Government and Stakeholders – Ross River Dam Upgrades
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Ken Diehm

Ross River Dam is dam of extreme hazard located immediately upstream of a population in excess of 100,000. A comprehensive review undertaken by a team of international experts (ref 1) identified a number of unacceptable risks that required immediate attention.

The State Government designed and oversaw the construction of the dam that was completed in 1976. NQ Water is of the belief that the problems identified by the team of international experts were a result of poor design by the State and inadequate attention by them during the construction process.

NQ Water developed a comprehensive communications plan (ref 2) with the objective of keeping the community adequately informed, gaining positive media exposure, obtaining the support and confidence of the business community and key stakeholders, and securing State Government funding towards the upgrades.

The climate at the time was characterised by adverse media history in relation to the dam, reluctance by the State Government to take responsibility, and poor brand awareness of NQ Water and its activities.
This paper focuses on the process undertaken by NQ Water in engaging the community, various levels of Government, key stakeholders, and business community, which resulted in securing the necessary funding for the dam upgrades. It will discuss the key elements and components of the communications plan, their objectives, the results achieved, and lessons learnt.
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2005 Papers

2005 – Hydrogeology of the Ross River Dam
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Robert Virtue, Deryk Forster, Jon Williams and Sabina Fahrner

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 water logging 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 damsengineers. 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.
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2005 Papers

2005 – Ross River Dam – Hydraulic Design Considerations for the Spillway Upgrade
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Eric J Lesleighter and Peter F Foster

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 ofTownsville. 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) widespillway.

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 paperboth 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.
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2005 Papers

2005 – Use of No Erosion Filter Design for Control of Seepage in Desiccation Cracks for the Ross River Dam Upgrade
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Jon Williams and Chi Fai Wan

The Ross River Dam was first commissioned in 1974 and raised in 1976. The 8200 m long embankment was not fitted with chimney filters and has suffered extensive desiccation cracking since it was raised. A significant component of the dam upgrade is the retrofitting of filter zones to ensure the embankment meets current dam safety guidelines.This paper describes the process of investigation of the existing desiccation cracks and the use of Hole Erosion Tests (HET) and No Erosion Filter (NEF) tests to validate the design of the retrofitted filter.

A significant challenge in the design is to provide a cost effective solution given the 7500 m length of embankment requiring treatment. Assessment of flow rates within cracks and expected piping erosion along the cracks was used to assess the required drainage capacity. This assessment of expected flow capacity allowed the deletion of the coarse filter inthe design reducing the filter requirement from a triple filter to a single fine filter. Results of this assessment were incorporated into the Risk Assessment based design validation process
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2005 Papers

2005 – Use of Risk Based Design Validation for Justification of the Ross River Dam Upgrades
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Malcolm Barker, Jon Williams and Chi Fai Wan

The Ross River Dam, designed in the early seventies, does not meet current dam safety criteria for overtopping and piping within the embankment or the foundation. The dam comprises a 40m long concrete overflow spillway flanked by a central core rockfill embankment of 130 m on the right bank and 170m on the left bank with a 7620 m long left bank earth fill embankment, which has no internal filter zones for piping protection. The embankment was extensively assessed and treated for foundation deficiencies in 1982, and further assessed in 2000-2002 for appropriate upgrade options.

This paper describes the process of validation of the detailed design using Risk Based Design Criteria.This process included data mining for historical performance and original design intention,comparison of the original design against current and historical investigations and assessment of the upgrades using the large volume of data available from previous work. A design team comprising specialist hydrologists, hydrogeologists, geologists, geotechnical and dams engineers worked within a risk assessment framework at all stages of the design to ensure the design was validated using the design Validation Model. This process incorporated assessment of crest level based on flood risk and wave overtopping, review of 2D and 3D seepage models to assess piping and foundation erosion potential, assessment of fissured soils within the embankment foundation for structural stability and evaluation of spillway model testing for potential spillway failure modes.
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2006 Papers

2006 – Ross River Dam Spillway Gate Reliability and the Impact on the Design
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Malcolm Barker, Barry Vivian and David S. Bowles

Ross River Dam is located approximately 15 km upstream of Townsville and provides a dual role of water supply and flood mitigation. The dam comprises a 39.6m long concrete overflow spillway flanked by a central core rockfill embankment of 300 m in length with a 7,620 m long left bank earth fill embankment, which has inadequate internal filter zones for piping protection. Since completion, design rainfall predictions for the area have doubled, technical data has changed and so, too, have dam safety standards. Dam safety evaluations during 2000-2002 showed that the dam required upgrading in order to bring it up to international standards. As an interim measure, the spillway was cut down by 3.6m.

Upgrade design works were then completed using risk-based design criteria to validate the design, and construction is in progress. The upgrade works comprise spillway anchoring, installation of three radial gates on the spillway, stilling basin modifications, embankment filter protection, and dam crest raising.

This paper presents the options considered, the method of reliability analysis, and how the results influenced the spillway system design and overall risk evaluation for the upgrade design.
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2009 Papers

2009 – Ross River Dam Upgrade – Flood Commissioning Experience
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Rob Ayre, Simone Gillespie, Peter Richardson, Mark Harvey

In November 2007, NQWater (now Townsville City Council) completed the upgrade of Ross River Dam near Townsville. This upgrade included the installation of a Program Logic Control (PLC) operated radial gate structure in the existing spillway. The purpose of the upgrade was threefold; to meet current design standards regarding dam safety and flood capacity; increase the town water supply to Townsville and Thuringowa; and to maintain the flood mitigation benefit of the dam during flood events in the Ross River catchment.

The designers of the dam upgrade completed a risk assessment at the commencement of the design phase and concluded that a PLC operated gated dam posed less risk than an approach that relied purely on dam operators. This is seen as the “new way forward” in gate operated dams by many designers. The regulator of dam safety in Queensland has indicated a preference for an operator to remain on site full time whilst the PLC system is ‘proved’. As a consequence a flood operations team was engaged to monitor the dam during times of flood through the commissioning period of the upgrade.

This paper discusses the lessons learnt from the experiences of the Ross River Dam during its first few flood events and issues associated with the adopted design approach.

Keywords: Dam Safety, Gated Spillway, Flood Operations, Ross River Dam, NQWater, Townsville City Council, SunWater, Queensland.
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