Robert Wark, R.N.M. Nixon
Sediment inflows to Lake Argyle, the reservoir formed by the construction of the Ord River Dam, were seen as a significant threat to the Ord Irrigation Project when the scheme was being developed through the 1960s. Sediment monitoring was built into the operation of Lake Argyle when the Ord River Dam was completed in 1971. The paper describes the strategies that have been in place to assess sediment loads and monitor sediment build up in the reservoir.
Spectacular reduction in sediment flows has been achieved through developing a comprehensive catchment management program. The program commenced in the early 1960s and was adapted and modified as progress was made. The paper describes the steps taken to identify the areas of the catchment at risk, the measures implemented and the current status of the catchment.
A key feature of the catchment management program has been the willingness to critically review progress and adapt the program. A variety of sediment tracing techniques have been used to help confirm the sources of sediment in the catchment, and the paper describes these, and the broad range of results and how they have helped direct the work on catchment management.
Keywords: Sediment, monitoring, catchment management, Lake Argyle, Ord River
Barton Maher, Michel Raymond, Mike Philips
The Queensland Bulk Water Supply Authority (trading as Seqwater) owns and operates North Pine Dam, situated on the North Pine River in the Northern Suburbs of Brisbane. North Pine Dam is an Extreme Hazard Dam consisting of a concrete gravity dam with earthfill embankments at both abutments and three earthfill saddle dams. The spillway consists of five radial gates which are manually operated. Flood operations at the dam are controlled in real time by the Seqwater Flood Operations Centre.
In January 2011, North Pine Dam experienced the flood of record at the dam site with a peak inflow of approximately 3,500 m3/s and a corresponding outflow of approximately 2,850 m3/s. This inflow was more than double the previously recorded flood of record. The inflow was generated by high intensity rainfall both at the dam and in the upper catchment resulting in a rapid rise of the storage. The system which caused this rainfall was also contributing to the major flooding occurring in the adjacent Wivenhoe – Somerset catchment, also being managed by the Seqwater Flood Operations Centre. The rapid rise and fall of the storage presented difficulties for both the Seqwater Flood Operations Centre and the operators at the dam site.
Following the flood event, an analysis of the rainfall and the resulting inflows indicated a significant difference between the Annual Exceedance Probability (AEP) of the rainfall in the catchment and the estimated AEP of the inflow and peak water levels from previous hydrology studies. A detailed review of the flood event was commissioned by Seqwater and undertaken by URS Australia Pty Ltd.
This paper presents details of the flood event, lessons learned for the operation of the dam, upgrade works undertaken to date, results of the hydrology review and the conclusions of the Acceptable Flood Capacity (AFC) study. A key implication for dam owners was the increase in the estimate of the Probable Maximum Flood (PMF) by over 30% due to changes in calibration of the hydrologic model for the catchment.
Keywords: Probable Maximum Flood, Flood Operations, North Pine Dam, Flood Estimation
M C N Taylor, Dr H E Cherrill, S F Croft, S F Eldridge
The Stuart Macaskill Lakes are two raw water storage lakes with a combined storage of approximately 3280 ML supplying Wellington City, New Zealand. The lakes are High Potential Impact Category (PIC) earth embankment dams constructed on terrace gravel deposits adjacent to the Hutt River and located within approximately 20 to 50 metres of the Wellington Fault Deformation Zone. Construction of the lakes began in 1982 and they were commissioned in 1985.
In early 2008, the lake’s owner Greater Wellington Regional Council (GWRC), embarked on a programme to supplement Wellington City’s water supply storage. Whilst that study is ongoing, GWRC engaged Tonkin & Taylor (T&T) to investigate the feasibility of increasing the Stuart Macaskill Lakes capacity as an interim measure.
The feasibility study concluded in late 2009 that the lake dam embankments could be raised by up to 1.3 metres in height to gain an approximate additional 450 ML of water storage. An important finding of that feasibility study has been that the seismic requirements have increased significantly since the construction of the lakes. To address this issue GWRC is currently constructing Stage Two of a two stage construction programme to both raise the lakes and to incorporate seismic resistant features into the lakes.
The primary design features are downstream rock buttressing in the critical areas of the lakes and synthetic lining the inside of the lake embankments. The buttressing works were completed in early 2011 and the lining and crest raising works are due for completion in 2013.
This paper summarises the design, laboratory testing and construction to enhance the lakes performance during very strong seismic accelerations (Peak Ground Accelerations of up to 1.08g) expected during a maximum design earthquake originating from the Wellington Fault.
Keywords: Water Reservoir, Seismic Design, Geomembrane, Rock Buttressing, Seismic Risk Assessment, Wellington Fault
M. Tooley, D. D’Angelo, B. Priggen, K. Sih, N. Vitharana, R. Mouveri
As the urban sprawl of residential and commercial businesses expand to meet rising population, consideration must be given to the frequency and intensity of storm events and changes in tidal levels, to mitigate the risk of flooding and damage associated with the failure of hydraulic structures.
This paper outlines the design method undertaken to ensure the ageing structure (founded on timber piles) meets modern dam safety criteria, extends the life of the 8 gates operating mechanisms and provides overall inherent reliability for the whole structure. The design method included updated hydrological assessment of the upstream catchment, geotechnical investigation, liquefaction review, consequence category and AFC assessment, hydraulic assessment and stability analysis.
These assessments are being undertaken to introduce inherent reliability in their operation in particular during king tide or storm water events, or a combination of the both, minimising leakage and breakdowns and ensuring the risks of flooding to low lying residential areas upstream of the structure and major airport are minimised. The Glenelg Gates structure is an integral part of a larger regulating system for the catchment.
The findings of the design upgrade would be useful to dam designers and owners faced with the upgrading of gated structures with flooding risks in residential areas.
Keywords: Gated Glenelg Gates structures, upgrade, dam design guidelines.
Nicole Anderson, M. Tooley, N. Vitharana, D. Moore
There is a significant stock of aging concrete dams in Australia which do not meet the requirements of modern dam safety practices. Where no site-specific information exists, current practice requires unduly simplified, conservative assumptions to be made. In some cases, this results in theoretical dam failure for load conditions which the dam has already experienced and safely withstood.
This paper outlines a range of site-specific field and laboratory investigations undertaken to reduce uncertainties in the assessment of two concrete gravity dams. For one dam, a suite of lab tests was undertaken to determine the residual reactivity so that potential future Alkaline-Aggregate Reaction induced expansion can be incorporated into any upgrade design.
The main purpose of the investigations was to reduce inherent uncertainties surrounding the design assumptions for strength and uplift pressures. This in turn reduced uncertainties relating to the risk profile of the dams.
The findings of this investigation will be of interest to dam designers and owners faced with upgrading concrete dams where a single traditional assumption can result in the difference between no upgrade or an upgrade worth several million dollars.
Keywords: Concrete gravity dams, testing, upgrade, Alkali Aggregate Reaction, dam design guidelines.
John Grimston, David Leong, Robin Dawson
The Angat Multipurpose Project, originally constructed in the 1960’s, is located 60 km north-east of Manila, and provides power, irrigation and domestic water supply and flood mitigation. The major water-retaining structures of the scheme are a 131 m high main rockfill dam and a 55 m high rockfill saddle dam.
Previous seismology studies have identified the presence of a possible branch of the West Valley Fault crossing under the saddle dam. If the fault dislocated, the branch under the saddle dam could produce horizontal and vertical shear displacements. Further, earthquake shaking poses a risk outside the fault zone. If the main dam/saddle dam were to fail in such an event, there would be major consequences in respect to both the water supply (serves a population of approximately 10 million) and the large population living below the dams. The dams are thus in the highest hazard category under any internationally accepted standard.
A study to investigate the dam safety aspects and identify remediation works which would bring the seismic performance of the main dam/saddle dam system up to an acceptable level was undertaken and included:
The main conclusions were:
Keywords: Dam, Remedial, Seismic, Fault, Spillway.