The disused Stapylton quarry is located in the suburbs of the Queensland Gold Coast. Gold Coast City Council, as part of the Northern Wastewater Strategy, has included the use of the quarry for storage and re-distribution of reclaimed water from the Beenleigh Water Reclamation Facility (WRF) to the downstream cane farmlands. A comprehensive EIS has been produced, which has strict water quality requirements for the quarry environs as well as the reservoir and outflow. This paper presents the background to the Northern Wastewater Strategy, the requirements for the Stapylton reservoir and the analysis performed for the detailed design of the embankment dam and the inlet bubble plume destratification system. The modelling of the destratification system was undertaken using the programme DYnamic REservoir Simulation Model (DYRESM) coupled with Computational Aquatic Ecosystems DYnamics Model (CAEDYM). The outcomes and implications of the modelling for the design and system operation including environmental monitoring are discussed.
P Maisano, M Taylor , M Barker and A Parsons
South Para Dam, completed in 1958, is located on the South Para River, 38 km north of Adelaide. The embankment is 45 m high and comprises compacted crushed phyllite with rockfill toes. The 13 m high rock fill toes are protected with three-stage filters but the remaining 32 m of embankment height has no downstream filter protection.
The South Australian Water Corporation (SA Water), the owner and operator of the dam, is considering modifications to the dam, to augment its flood mitigation role. The proposed works, while not affecting the full supply level, involve a modification to the spillway crest and raising of the embankment crest to accommodate increased flood levels. SA Water therefore commissioned a dam safety review to assess the need for any piping or overtopping protection that may be required. This was followed by concept designs to ensure that flood mitigation work is compatible with any required dam safety upgrade work.
The results of a detailed dam failure risk analysis using event trees showed that the Societal Risk for the existing dam needed to be reduced, and that the proposed spillway modifications increased the Societal Risk due to the increased risk of piping failure with higher flood levels.
The risk analysis showed that eliminating the overtopping modes of failure by raising the dam crest is not sufficient in itself to achieve the required reduction in risk. The provision of filter protection to reduce the risk of piping failure is required, but it was shown that it is not necessary to provide full height filters as the provision of filters only above full supply level would be sufficient to achieve the required reduction in risk.
The recommended upgrade works, in addition to the proposed spillway modification for flood mitigation purposes, consist of filter protection and a weighting fill above the top berm (4.4 m below FSL) to facilitate connection to a possible full height filter in the future, and a parapet wall to provide overtopping protection.The resulting cost saving compared with the installation of full height filters is in excess of $2 Million.
Since the research and development work carried out by the (then) Metropolitan Water Sewerage and Drainage Board for the strengthening of Manly Dam in 1979/80, there has been over twenty years of continuous improvement in the application of advanced post-tensioned anchors for gravity dam rehabilitation.
Up until the Manly Dam remedial works, concerns had been increasing as to the long-term viability of available anchors. Sophisticated monitorable and restressable anchors, with superior corrosion protection afforded by greased and sheathed strands, were developed initially in test-bed conditions. This style of anchor has subsequently been used extensively throughout Australia on dam upgrades.
This paper compares the claims made by the designers with the demonstrated outcomes of installations that have been achieved, with particular emphasis on dams now owned by the Sydney Catchment Authority and Sydney Water Corporation. The original commitments to economy, aesthetics and rapidity of construction have been borne out by experience, with additional environmental advantages also being achieved. With the confidence built up from many successes in the strengthening of older dams, the time appears right to revisit the construction of new dams using the same style of post-tensioned anchors as the primary stabilising force.
Stefan Hoppe, Vicent J. Espert-Canet
Monitoring data has to be transformed into useful knowledge to provide owners and operators with valuable information about the safety status of their dams. This information should be up-to-date and easily accessible for all technicians and engineers involved inthe safety program,and directly linked to operation and emergency preparedness procedures.This article describes the main functions of a web-based software for the acquisition, processing,and evaluation of monitoring data. It runs on conventional internet browsers,and does not require the installation of any additional software. It provides appropriate tools for monitoring the safety status of dams and analysing dam behaviour.This article uses a case study to outline the experience gained from implementing and operating the software for 8 years to control more than 50 Spanish public dams owned by a river basin authority. The implementation involved completely revisingthe installed monitoring systems and recompiling all available information. This was used as a basis for an updated,goal-oriented definition of necessary variables, configuration of charts, SCADA views and threshold values. A key aspect of the software ́s successful implementation was the theoretical and practical training of all stakeholders.As a result of the software ́s implementation, the dam owner was able to use the data from their monitoring system more efficiently. The development of safety reviews and dam safety status evaluations were also considerably improved.
Monique de Moel, A/Professor Jayantha Kodikara, Dr Gamini Adikari
All embankment dams have some seepage as the impounded water seeks paths of least resistance through the dam and its foundation. Seepage must, however, be controlled to prevent internal erosion of the embankment or foundation and avoid damage to surrounding structures. Embankment dams are designed to operate under controlled steady state seepage, which over time may change due to movement in the foundation and the dam, chemical actions and other forms of deterioration. Effective monitoring of seepage within embankment dams is therefore essential in regards to management of dam safety and prevention of failure.
Traditional methods of seepage monitoring have involved measurement or visual monitoring on the downstream side of the dam after the seepage has occurred. Effective, early detection of seepage in embankment dams has been difficult as it originates and develops in the subsurface. Infrared Thermal Imaging is such a technique that is non-contact, non-intrusive, simple and flexible. The analysis draws on the temperature behaviour and the heat capacity of materials within the body of the dam and consequently allows the user to identify and isolate temperature variations along the surface of interest. This paper describes the method, application and feasibility of infrared thermal imaging for the detection of seepage in earth and rockfill embankment dams. The value of this technique as an additional tool in the surveillance of dams is discussed.
Infrared thermal imaging has been in use in other fields of engineering for condition monitoring and defect detection of structures. It has shown great potential in identifying variations in surface characteristics, which may not be evident through visual inspection alone. In this paper, reliability of this technique for seepage detection in embankment dams has been analysed using 8 case studies in order to arrive at a fair understanding of the best conditions under which Infrared Thermal Imaging field inspections should be carried out. The results of field investigations undertaken at these dams suggest that Infrared Thermal Imaging is a useful and effective tool for detection of seepage and an aid in identifying seepage behaviour.
Keywords: Seepage Detection, Infrared Thermal Imaging, Dam Surveillance, Monitoring