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Christopher Bennett, Helena Sutherland, Graham Irvine
The development of geological, engineering geological and geotechnical models is essential for all dams. These models provide the basis for understanding the engineering characteristics of foundation materials and geological structures that are critical to the safe design, construction and operation of the dam.
The use of digital three dimensional (3D) engineering geological modelling techniques is becoming more common for civil infrastructure projects. In addition to established design applications, 3D engineering geological models can be utilised by dam owners, operators and stakeholders for ongoing management of the dam.
The recent option studies at North Pine Dam in Brisbane, Australia, provides an example of collaboration between the owner (Seqwater) and the designer (GHD) to maximise the use of existing information and to enable future information to be efficiently integrated and utilised.
The initial North Pine Dam 3D engineering geological model was developed using historical records dating from the design and construction of the dam in the 1950’s and 1960’s. These records had been carefully stored, collated and digitised by the owner, so that they could be easily georeferenced and incorporated into the 3D engineering geological model.
The initial model was interrogated to identify data gaps and to plan targeted and cost-effective investigations that addressed critical geotechnical issues. The 3D engineering geological model was further refined using the newly acquired data, to develop a comprehensive “3D database” that can be used to visualise and interrogate all existing records as high- resolution georeferenced images and embedded data.
This provides an asset for the dam owner to maximise the use of existing information and reduce the cost of future safety reviews or design.Learn more
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.Learn more
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
After a period of drought for many years, inflows during May and June 2009 resulted in releases from North Pine Dam. These releases resulted in deaths of fish downstream of the dam wall including lungfish. The Australian Lungfish is a protected species under the Environmental Protection and Biodiversity Conservation Act 1999 (Australian Government). The events of 2009 have shown, however, that a proactive response supported by sound knowledge is required to minimise lungfish losses from flood events and other dam operations activities. A framework has been developed for the management of lungfish populations in Seqwater storages. The framework centres on a Seqwater Fish Management Policy, and four broad strategies that are considered necessary for addressing fish management in Seqwater storages: Fish Management, Storage Operations, Communication, and Research. These strategies are being used as a basis for identifying, planning and managing a range of actions designed to ensure that impacts to lungfish are minimised. Seqwater intends to develop the framework further to include long term management initiatives such as implementing viable technologies for preventing lungfish strandings, habitat protection and restoration activities that support viable lungfish populations, as well as establishing priorities for managing risks to other aquatic vertebrates in Seqwater storages, including other protected species, recreationally and commercially important species; e.g. turtles , carp, mullet, etc.Learn more