Peter F Foster and Peter K Silvester
Clyde Dam, the largest concrete gravity dam in New Zealand, was constructed in the 1980’s on the Clutha River in New Zealand. Lake Dunstan, which is the reservoir formed by the dam, reached its full operating level in 1993, some 21 years ago.
This paper summarises the performance of the dam over this period, the changes in operations that have been undertaken and looks to future challenges. The performance and management of the landslides around Lake Dunstan that were remediated prior to lake filling is outlined. The large floods experienced in the Clutha River in the 1990’s highlighted aspects of the flood management procedures that needed amending to capture lessons learned and some modifications to appurtenant structures have been completed. Changes to the environmental management in moving from water rights to consent conditions under the Resource Management Act are addressed.
Over the last 21 years a sediment delta has progressed down Lake Dunstan, as expected, and a long term sediment management plan has been developed for both Lake Dunstan and Lake Roxburgh which is downstream of Clyde Dam. A summary of the plan is discussed. The seismic hazard at the dam site is currently under study to update the seismic assessment parameters for the dam.
This paper outlines lessons learned from 8 years of regular operations and testing of 111 gates at 22 sites. It points out that the implementation challenges involved are not only technological in nature, but also encompass human factor and organizational issues. This is perhaps understandable since the initiative is part of the cultural shift to sustain gate reliability long-term.
An increase in gate testing frequency has led to the identification of more performance anomalies, ranging from deficiencies to operational failures. This finding may not be unique to a single dam owner. It leads to the following question to the general dam owner community: Are we testing our gates enough?
Leonard Wiliem, Rob Keogh, and David Thomas
Progressive rope creep on the steel ropes which hold 14 counterweights in tension on the seven spillway gates was monitored regularly. The 2011 annual inspection identified that the creep had taken the lower guide wheels of the suspended counterweights beyond the extent of the wheel guides.
A programed project to extend the guides was delayed due to Workplace Health and Safety concerns on confined access and working under a suspended load. A study was commissioned to deliver a safe method of extending the guides. Because regular testing and two flood events had proved the gates were functioning well, the risk of failure in gate operation during flood event was considered low and a lower priority was assigned to rectification work.
Callide Dam is a SunWater owned dam located in Central Queensland. It has a similar spillway gate mechanism as Coolmunda Dam. The only difference is that Callide Dam gates work in pairs with one counterweight attached to each gate.
In January 2013 due to heavy rainfall caused by the ex-cyclone Oswald, Callide Dam experienced a flood event which triggered a gate operation. During the draining phase, the gates operated abnormally sustaining damage to the structure and to the automatic gate opening mechanism. SunWater undertook investigations to identify the cause of the abnormal operation and found that the primary cause of the gate abnormal operation was due to jamming of the suspended counterweight on the end of the guides. This was due to cable stretched over 26 years of service to the extent that the lower wheel assembly was beyond the guide rails at the time of the flood event.
The event at Callide Dam was a wake up call for SunWater to re-evaluate the risk assessment for Coolmunda Dam. This re-evaluation recommended to assign the highest priority on the rectification of the wire rope creep issue on the radial gate as the risk of failure in gate operation during flood event was high.
This paper discusses the actions in re-evaluating the risks at SunWater’s Coolmunda Dam and the measures taken to quickly undertake remedial action on both dams and the challenges involved with each.
Gavan Hunter, David Jeffery and Chris Kelly
Laanecoorie Reservoir, located in central Victoria, passed 3 significant floods in late 2010 to early 2011; the last flood being the highest on record since 1909. Significant cracking and deformation of this 100 year old puddle core earthfill embankment occurred. A series of longitudinal cracks up to 25 mm in width opened up in the crest over a length of 70 m and crest settlements were up to 70 mm; very large for a dam of this age. A significant difference at Laanecoorie compared to other similar dams is that it experiences high tail water levels during major flooding.
Investigations into the embankment following the January 2011 flood encountered several defects
including a decomposed tree root hole (large void up to 90 mm) that almost fully penetrated the raised section of puddle core, permeable gravel layers within the puddle core and transverse cracks up to 2 mm wide. The encountered defects and performance of the embankment many years after construction highlighted the deterioration that can occur with aging of these older embankments and the issues associated with poor past practices in tree management adjacent to dam embankments.
Dam safety upgrade works were undertaken in 2013 to address the identified piping and stability risks.
The works included construction of a filter buttress, replacement of a length of the raised puddle core and construction of a buried gabion wall on the left abutment to provide protection against scour should the secondary spillway fail or overtop.
GMW implemented a series of actions during the flood events in accordance with the Dam Safety
Emergency Plan (DSEP) to address cracking and deformation. Once aware of the dam safety risks, interim actions were implemented including increased frequency of monitoring, together with set up and measurement of crack pins, and temporary survey markers on the embankment.
Luke Toombes and Rob Ayre
Many large dams are built as multi-purpose structures, providing both flood mitigation and bulk water storage, but requiring a trade-off in functionality between those purposes. In response to the Millennium Drought (2001 to 2009) closely followed by devastating floods in 2011, the State of Queensland initiated a comprehensive review of the operation of its flood mitigation dams. Part of this study involved development of an Integrated Assessment Methodology to provide an informed and unbiased assessment of the competing factors affecting dam operations. The methodology assessed the primary variables of flood damage and other impacts, future bulk water infrastructure and water security requirements in the form of a net present cost/benefit. The study concluded that modification of the dam flood release strategy to reduce flood damage during large events would come at the expense of increased frequency of minor flooding, or vice versa, with minimal net benefit. Similarly, reducing bulk water storage to increase flood mitigation would increase water supply costs by a similar magnitude to the flood damage prevented.
Guresh Ahuja, Brian Cooper, Olaf Rutgrink and Andrew Thomson
This paper presents details of the State Water Corporation of NSW Australian first temperature control curtain project aimed at dealing with the environmental issue of cold water pollution in dam offtakes. This is a key project focused on dealing with a known environmental issue and reflects changing environmental and social expectations for dam operators. In the concept phases this project was part of the NSW Rivers Environmental Restoration Program (RERP) sub-program ‘better delivery of environmental water’.
The paper presents the development of the design concept including early concept screening and selection, scale model testing, concept design development, hydrodynamic, structural and computational fluid dynamic analyses leading to the final design that has now being constructed. The concept design work was completed in 2011 and following a tender process a design and construct contract was let for the detailed design and construction of the temperature control curtain system. This phase of the work was recently completed and the temperature control curtain is now fully operational. The actual performance and effectiveness of the temperature control curtain will only become evident after a few years of operation and will also hinge on the degree of stratification in the dam.