Jim Walker, Jamie Macgregor
The Pukaki Canal Inlet structure is a large gated culvert and stilling basin structure, it is a High PIC appurtenant structure to the Pukaki Dam, located in the Mackenzie Basin area of New Zealand’s South Island.
The 560m3/s capacity inlet structure is founded on glacial moraines. It controls flow from the178 km2 Lake Pukaki storage into the 80m wide, 22km long Pukaki/Ohau canal. It is the owner’s (Meridian Energy) most important valve, as it feeds 1550MW of hydro generation on the Waitaki River.
A risk assessment in late 2009 identified a previously unrecognised trigger for a potential failure mode for the stilling basin. Principally, ongoing erosion of the reinforced concrete base slab could lead to failure of water stops in the slab joints potentially leading to slab uplift, foundation erosion, and ultimately, catastrophic failure of the Pukaki Dam. To better define the risk to the structure, further inspection of the stilling basin was recommended.
A dewatered inspection of the stilling basin was required, as further dive inspections would not improve our understanding of structure condition. Because the stilling basin cannot be isolated from the canal, this requires dewatering the entire Pukaki/Ohau canal, presenting significant risks of damage to the canals from slumping and lining failure. A dewatered outage also has major business revenue impacts.
This paper describes how Meridian were able to take advantage of a transmission network outage, scheduled for just six days after the risk was identified, to plan, safely dewater, inspect, and rewater 22km of hydro canal, and not just to inspect the Pukaki Canal Inlet structure, but also to implement repairs to the stilling basin slab which have successfully mitigated the structure safety and operational risks. This huge undertaking involved mobilising an army of people, plant and materials, and cost over NZ$1.8m. From identifying the risk to the structure, to completing repairs took just 13 (very busy) days.
Lessons learned in the areas of dam safety and asset management are presented. As well as those contributing to the success of the project in seizing an opportunity to mitigate the identified dam safety and operational risks.
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Kristen Sih, Peter Hill, Susan Ryan, Siraj Perera
Although ANCOLD provides guidance on good dam safety practices, in Australia it is the State and Territory Governments’ role to protect the public from dam safety incidents and in many cases these jurisdictions have legally binding regulations in place that dam owners must adhere to. This paper presents a comparative analysis of the dam safety regulations currently in place for Australian states, as well as selected international jurisdictions. The limit of applicability of the regulations, number of dams regulated, content of the regulations and powers and responsibilities of the regulator are all compared. It was found that there is a large range within each of these categories with regulatory approaches varying from light-handed and objective based, to highly prescriptive. The extent to which risk management principles are used in the regulations for each jurisdiction has also been investigated. It was found that in jurisdictions where higher hazard category dams account for a higher proportion of dams being regulated, risk analysis is included in the regulations. Finally, the ANCOLD societal risk criteria and ALARP considerations have been compared and contrasted with those from international jurisdictions and other hazardous industries.
Dr Adam Butler, Robert Rigg, Glen Hobbs
The cost of maintenance is a serious problem. Preventive Maintenance is a good strategy if implemented well, but can led to unnecessary costs if items are replaced unnecessarily. Predictive maintenance can augment preventative maintenance by using real time instrumentation to monitor conditions. These techniques have been effective at recognizing the symptoms of impending machine failure
Glen Hobbs and Associates (GH&A) recently analysed pressure and displacement data from hydraulically actuated hoisting equipment of a large emergency closure fixed wheel gate. Data analysis enabled GH&A to pin-point causes of the gate malfunction. Anomalies in the data waveform corresponded to impacts and squeeze points in the system. Furthermore, comparing recent test data with older data highlighted gate deterioration over time.
Testing, analysis and trending of data enables asset managers to better predict the point at which maintenance really needs to be performed and shows that careful analysis of relevant data can help solve multi-faceted problems.
Keywords: Operations, Maintenance, Asset Management, Gates.
Jiri Herza, Nihal Vitharana, Alex Gower
The Western Australia Water Corporation plans to increase the storage capacity of Millstream Dam, which is located near Bridgetown in the south west region of WA. The existing dam is an 18 m high zoned earthfill embankment constructed in 1962. The dam suffered a block heave of the foundation at the downstream toe during the first filling, probably attributable to high foundation pore water pressures. The dam upgrade will be challenging due to complex and unfavourable foundation soils coupled with these artesian pressures.
The dam is founded on lateritic soil, which is a common weathering profile throughout the region. These soils formed in a tropical environment of fluctuating water tables, severe leaching and translocation of iron oxides over many millions of years. As a consequence some of the lateritic horizons at Millstream Dam have been modified such that they exhibit behaviours that are not consistent with conventional constitutive models and correlations. These are attributed to a complex structure of the soil microfabric, which comprises clay particles bonded together into larger aggregates. The clayey aggregates are also bonded to each other, forming a porous matrix of silty or sandy appearance characterized by low dry density and high void ratio, which may nevertheless disintegrate on working.
Comprehensive geotechnical investigations and extensive laboratory testing have revealed that the foundation materials display characteristics of clayey and granular soils. Under shearing, these soils demonstrate high initial strength, which gradually reduces as the inter-aggregate bonds are broken and the relative position of the aggregates changes. Several soil samples also exhibited significant contractive behaviour on shearing generating high pore pressures under undrained conditions.
This paper presents the investigation and design methods used in the foundation design of the Millstream Dam upgrade with emphasis on unusual behaviour of the foundation media.
Challenges in dam design on lateritic soils
David S. Bowles, Loren R. Anderson, Michael E. Ruthford, David C. Serafini, Sanjay S. Chauhan, Utah State University, Logan, Utah, U.S. Army Corps of Engineers, Sacramento, CA
In 2005 the Sacramento District of the US Army Corps of Engineers implemented an operating restriction to reduce the risk of an earthquake-induced failure of Success Dam, which could cause significant life loss and property damage. This paper describes an update of the 2004 risk-based evaluation of operating restrictions for Lake Success, which incorporated new information obtained by the District and enabled a re-evaluation of the level of the operating restriction and provided a basis for a possible modification of the restriction.
A RISK-BASED RE-EVALUATION OF RESERVOIR OPERATING RESTRICTIONS TO REDUCE THE RISK OF FAILURE FROM EARTHQUAKE AND PIPING
David Scriven, Errol Beitz, Aaron Elphinstone
The Bowen River Weir is located at AMTD 94.4 km on the Bowen River, some 25 km south of Collinsville in North Queensland. The weir is part of the Bowen/Broken Rivers Water Supply Scheme and it provides a pumping pool for pipelines serving two nearby coal mining developments and a power station, and also acts as a regulator for riparian water users downstream until it meets the Burdekin River.
The weir was constructed in 1982 and incorporated a fishway towards the southern (left) bank, the design of which was based on the old “pool and weir” fish ladder type layout, typical of that era, with 48 separate cells containing partial vertical slots and baffles. This design has since been found to be ineffective for Australian native fish. In addition it was often out of service due to cells becoming filled with river sediment and debris. For these reasons it was decommissioned and made safe in late 2008 on the condition that a new fishway be constructed.
In late 2008 agreement was reached with Fisheries Queensland to install a “fish lock” type fishway at the site. This type of fishway has in recent years proved to be reliable and effective (eg. successful fish locks at Neville Hewitt and Claude Wharton Weirs). The preliminary and then final design was undertaken by SunWater (Infrastructure Development) between September 2008 and March 2009. The construction was undertaken by SunWater direct management, commencing in July 2009 and completed in late 2010.
Bowen River Weir Fishway – Design and Construction