Malcolm Barker, Barry Vivian and David S. Bowles
Ross River Dam is located approximately 15 km upstream of Townsville and provides a dual role of water supply and flood mitigation. The dam comprises a 39.6m long concrete overflow spillway flanked by a central core rockfill embankment of 300 m in length with a 7,620 m long left bank earth fill embankment, which has inadequate internal filter zones for piping protection. Since completion, design rainfall predictions for the area have doubled, technical data has changed and so, too, have dam safety standards. Dam safety evaluations during 2000-2002 showed that the dam required upgrading in order to bring it up to international standards. As an interim measure, the spillway was cut down by 3.6m.
Upgrade design works were then completed using risk-based design criteria to validate the design, and construction is in progress. The upgrade works comprise spillway anchoring, installation of three radial gates on the spillway, stilling basin modifications, embankment filter protection, and dam crest raising.
This paper presents the options considered, the method of reliability analysis, and how the results influenced the spillway system design and overall risk evaluation for the upgrade design.
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For many years most emergency management agencies in Australia have used a framework called Prevention, Preparedness, Response and Recovery (PPRR). This approach has worked very well in the past and has been incorporated into the more recent framework of Emergency Risk Management.
While Emergency Management Agencies use practice sessions in the form of Desktop/Tabletop Exercises and Field Exercises as part of Preparedness (the 2nd P in PPRR) these activities can suffer from a lack of engagement with the community.
State Water Corporation, a dam owner in NSW, has installed warning systems to trigger plans written by the SES to warn affected residents of possible dam failure. Although the systems are maintained and tested regularly in a technical sense, the next logical step is to encourage the affected communities to understand their role in the event of evacuation.
A joint exercise involving the NSW State Emergency Service (SES), State Water Corporation and the community, was conducted in a town in the Namoi valley in 2005 and has provided an opportunity to explore this concept. State Water Corporation is now confident that not only will the technical side of the warning system work but that residents should be more aware of their role and that of the SES and State Water Corporation.
Other benefits from the exercise are: the opportunity for improving general flood awareness in the community; the SES identifying community representatives; fine tuning procedures between and within the SES and State Water Corporation; allaying fears within the community about what is required of them in a dam failure; and demonstrating the dam owner’s duty of care to affected residents.
N. Vitharana, G. McNally, C. Johnson, A. Thomas, K. Dart and P. Russell
Millbrook Reservoir is an offline storage with an earthen embankment dam containing a puddle clay core and a moderately sized upstream catchment. The dam is 31m high and has a capacity of 16.5 GL when the storage water level is at the Full SupplyLevel (FSL). The reservoir is 25km NE of Adelaide on Chain of Ponds Creek, a tributary of the River Torrens. The dam was constructed during the years 1914-1918. Earthworks were carried out only during summer as the five winters during the construction period were very wet.
Dam safety reviews and geotechnical investigations, undertaken between 2001 and 2004 by SKM, showed that these winter recesses would have created weak layers, increasing the potential for piping due to the lack of a filter. This was highlighted by the large deformations which occurred at the end of construction in 1918. The spillway was assessed as able to pass a flood event with AEP of 1:1,300,000. Given the location of the dam, ANCOLD(2000b) Guidelines suggest the dam should be able to safely pass the PMF flood event. Accordingly, the dam required upgrading to modern guidelines.
The 2005 detailed design of the upgrade included the construction of a 70m wide unlined spillway, construction of filters on the downstream face of the dam with a stabilisation (weighting) fill, installation of instrumentation and seismic protection of the outlet tower. The construction of these works is currently underway.
Karen Riddette, David Ho & Julie Edwards
Over the last five years in Australia, the use of computational fluid dynamics for the investigation of water flows through hydraulic structures has been steadily rising. This modelling technique has been successfully applied to a range of dam upgrade projects, helping to assess spillway discharge capacity and structural integrity, and giving insight into flow behaviours including orifice flow, shock wave formation and chute overtopping (Ho et al, 2006). Innovative and cost effective upgrade solutions have been implemented from numerical model studies including baffle plates (Maher and Rodd, 2005) and locking arrangements to protect radial gates from extreme floods.
This paper will begin with a review of recent dam engineering applications, including outlet flow through a fish screen, the performance of a fishway against hydraulic and environmental criteria and pipe flow in a large pumping station. Some of the difficulties and limitations of the modelling technique will be examined together with current research being conducted to address these issues and further validate the numerical results against published data. Some interesting results to date will be reported on elliptical crest discharge, boundary geometry, and model/prototype correlation.
With increasing computing power and software enhancements, the potential applications for numerical simulation in dam engineering continue to grow. This paper will also examine the future outlook and highlight some recent advances such as the thermal simulation of cold water pollution, air entraining flows and combined free-surface and pipe flow in a morning glory spillway.
Leonard A McDonald
Dam safety regulators look for evidence in support of the safety status of dams and to justify the need for safety improvements. Instrumentation and monitoring have a key role in providing the needed evidence.
In New South Wales, the Dams Safety Committee [the DSC] is the regulator of dam safety. The purposes of instrumentation and monitoring from the viewpoint of the DSC are set out, along with the current regulatory requirements in New South Wales. The relationship of instrumentation and monitoring to the tolerability of risk is discussed. There are remarks on some special considerations for a regulator and on the contemporary trend to remote sensing for the capture of information. Two case studies are described to show how instrumentation and monitoring has improved the understanding of dam behaviour. Some pitfalls to avoid are listed from DSC experience. Finally, there is an outline of matters that a regulator would see deserve attention if ANCOLD does undertake preparation of a guideline document on instrumentation and monitoring.
We can all learn by our mistakes and the experience of others. This paper seeks to look at three
incidents/accidents which recently occurred in the UK so that others can learn from them. The
paper then seeks to answer the question as to whether we are improving in looking after our dams
in the UK in respect of reservoir safety.