Dan Forster, Murray Gillon
A robust and defensible dam surveillance process is considered to be the ‘front-line of defence’ in ensuring dams do not present an unacceptable risk to people, property and the environment. The concept of a ‘Quality Chain of Dam Surveillance’ describes the surveillance process as a multi-linked chain where each step in the process forms a critical link. Without rigorous attention given to quality assurance links in the chain can become tenuous or broken and thus compromise the integrity of the whole chain. Hydro Tasmania is currently re-engineering its existing surveillance process using the Quality Chain of Dam Surveillance as a basis.
This paper presents the concept of the quality chain and uses the Hydro Tasmania improvement initiative as an example application of the concept. The paper is intended to provide a fresh perspective on what is sometimes considered a stale topic and reinforces the need for a considered approach to dam surveillance.
2011 – The Quality Chain of Dam Surveillance
G. Hadzilacos, ML. Ng, K. Taske, A. Small and B. Loney
Alteration of flow patterns by constructing a dam may have an irreversible impact on ecosystems depending on the timing, duration and frequency of these flows. As part of an Environmental Impact Study, carried out for a proposed mining operation in Australia that included an earth dam on a pristine ephemeral creek, an appropriate waterway management scheme was proposed that required the establishment of measurable instream flow requirements. This paper describes an environmental flow analysis (EFA) carried out to identify flow regimes that achieve the desired ecological outcomes for the affected waterways. The EFA methodology was based on the range-of-variability approach using a calibrated rainfall-runoff model to form the hydrologic basis. The study established a relationship between flow components and ecological variables based upon which the flow requirements were estimated using a simple methodology.
2011 – A case study of an initial Environmental Flows Assessment for an earth dam on a pristine stream in Cape York
Rob Campbell, Tom Kolbe, Ron Fleming, Christopher Dann
Hinze Dam is an Extreme hazard category water supply dam situated in the Queensland Gold Coast hinterland, owned and operated by Seqwater (formerly owned by Gold Coast City Council). The Hinze Dam Stage 3 works involved raising the previously 65m high central core earth and rockfill embankment approximately 15m to a maximum height of approximately 80m.
The Stage 3 works included a program of foundation curtain grouting, consisting of six discrete grout panels, five of those beneath areas where the embankment was extended and one beneath part of the spillway enhancement works. Five of the six grout panels were essentially single row panels, with one or more partial rows added in specific areas of high grout take. The remaining grout panel (Panel 4) was constructed as a triple row panel.
A number of challenges were encountered and overcome during the Stage 3 foundation grouting works due to highly variable foundation conditions, ranging from extremely low strength residual soil to highly fractured and permeable high strength rock.
The grouting works were undertaken using downstage grouting techniques, with manual recording of data, manual control of grout pressures and injection rates and use of predominantly neat cement grout mixes.
A key issue in the execution of the foundation grouting works was the maximum grout pressures applied to the foundation and this was discussed in detail between the project design team and external review panel. This paper presents the results from project specific grout trials and production grouting to demonstrate that closure of the foundation was consistently achieved (with one exception discussed herein), which supports the grouting approach employed and the adopted grout pressures.
This paper presents a case study description of the Stage 3 foundation curtain grouting works, including a summary of key learnings which may be of benefit to future dam foundation curtain grouting projects.
Amanda Ament, Jon Williams, Malcolm Barker
Aplins Weir is located on the Ross River in Townsville, downstream from the Ross River Dam. Previous work had identified Aplins Weir as exhibiting factors of safety below 1.0 under normal operating conditions, with over 1000 persons at risk today in the event of failure. Originally constructed in the early 1920s, Aplins Weir has been upgraded and repaired following various failures on a number of occasions. The end result is a complex reinforced concrete and steel sheet pile composite structure reliant for stability on a number of unreliable components. This paper presents the historical data describing the current configuration of the weir, and the analyses required to evaluate the extisting structure, leading to the design of the proposed upgrade works. The final design involves a retrofit of large diameter cast-in-place lined piles and a heavily reinforced base overlay slab designed to completely bypass all existing vulnerable substructure elements.
2011 – Where is our Weir going – an Unusual Upgrade!
Awoonga Dam is the sole source of water for the City of Gladstone and the heavy industries in the region. The area’s distribution reservoirs hold little more than a day’s supply. Extended water supply disruption could have severe economic impacts.
The nine large valves in the inlet tower and river outlet of the dam cannot be inspected or maintained without shutting down the entire water abstraction system. Consequentially limited maintenance has been carried out in the 25 years since the valves were installed.
Recent Dam Safety inspections carried out for the dam owner, the Gladstone Area Water Board (GAWB,) noted some deterioration of the valves and recommended that the valves should be removed, inspected and refurbished as necessary
GAWB was thus presented with a daunting challenge to refurbish valves at Awoonga Dam, as it was generally believed that their removal for refurbishment would not be possible within the time limitations imposed by the system and customer requirements.
In 2008 GAWB commissioned GHD to develop a strategy to refurbish the valves within a 12 hour shutdown period. The strategy proposed and adopted required a rigorous risk management approach and close collaboration between GAWB’s operational staff, two contractors and the consulting engineers. The work was successfully completed during 2011.
This paper discussed the strategies and processes developed and how the project planning, supervision and execution was driven by the risk management based approach. It also highlights some of the experiences and lessons learnt during the project.
2011 – Refurbishing Outlet Valves utilising Shutdown Periods
Krey Price, Mike Harvey, Bob Mussetter, Stuart Trabant
The California Department of Water Resources, Division of Dam Safety (DWR-DSD), has determined that San Clemente Dam on the Carmel River in Monterey County, California, does not meet seismic safety standards. Several alternatives have been considered to decommission the dam and eliminate the hazard, including thickening of the 25-m-high, concrete arch structure, lowering the dam, and complete removal. At the present time, the upstream reservoir that had an original storage capacity of about 1.8 GL, is essentially filled with sediment. The 29-km reach of the Carmel River between the dam and the Pacific Ocean passes through urbanised areas within the upscale Carmel Valley; flooding and channel stability in these areas are significant concerns. The Carmel River also contains habitat for the endangered steelhead and red-legged frog that could be positively or negatively affected by the decommissioning.
After an extensive series of hydraulic and sediment transport modelling studies, two actions remain under consideration: (1) dam thickening, which will require reconstruction of the existing fish ladder and construction of an adjacent, 3-metre diameter sluice gate to prevent sediment build-up from blocking the ladder outlet, and (2) removal of the dam and rerouting the river into a tributary branch of the reservoir, which would isolate approximately 65 percent of the existing sediment deposits from future river flows and eliminate a significant fish-passage problem. Both options were modelled extensively in hydrologic, hydraulic, and sediment transport applications. Since available models do not adequately represent sediment dynamics at the sluice gate, a special sediment routing model was formulated to evaluate this aspect of Option 1. Option 2 is currently preferred by the resource agencies, since it would optimise endangered species habitat; however, this option would be three to four times more expensive than Option 1, and funding limitations may impact the alternative selection. Evaluation efforts are ongoing, along with approaches to address liability issues associated with the decommissioning actions for the privately owned facility, while optimising the benefits and costs of the selected action.
Modelling Studies to Design and Assess Decommissioning Actions for a Seismically Unsafe, Concrete Arch Dam