Chi-fai WAN, Robin FELL
This paper presents the findings of experimental investigation of internal erosion by the process of suffusion within embankment dams and their foundations.
Suffusion is the process by which finer soil particles are moved through constrictions between larger soil particles by seepage forces. Soils susceptible to suffusion are usually described as internally unstable. Understanding of the suffusion process is important to the assessment of the risk of internal erosion in an embankment dam and its foundation. Suffusion results in a coarser soil structure, leading to increased seepage, progressive deterioration of the dam or its foundation, and a higher risk of toe instability. Suffusion within the protective filter of a dam may result in a coarser filter, rendering it ineffective in protecting the core materials from erosion.
Two types of suffusion tests, namely the downflow test and the upflow test, have been conducted at the University of New South Wales. The downflow test aims at identifying the types of soils that are susceptible to suffusion, whereas the upflow test aims at identifying the hydraulic gradient at which suffusion is initiated. This paper presents the initial findings of the downflow test. Eighteen downflow tests have been carried out on fourteen clay-silt-sand-gravel soils. The Kenney and Lau (1985, 86) method, which is commonly used for assessing the internal stability of coarse-grained soils, appears to be too conservative when used to predict the internal stability of silt-sand-gravel or clay-silt-sand- gravel soils, whereas the Burenkova (1993) method appears to provide better predictions. Further testing is required to define more accurate criteria for determining the internal stability of broadly-graded clay-silt-sand-gravel soils.
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Alan K Parkin
There is a widespread perception among dam engineers that tree root invasion occasions a very serious threat to embankment dams by virtue of its potential to initiate piping failure, with appropriate action invariably recommended. Remedial works can, on occasions, be extensive.
While the principle is ostensibly plausible and scarcely challenged, there has never been, to the Author’s knowledge, a satisfactory investigation to establish any credible scientific basis for it. One case that has attracted some attention in literature (by virtue of the extent of the investigation undertaken), viz a piping accident at Yan Yean Dam, is critically reviewed to show that the accepted view on the role of tree roots in this incident is less than satisfactory. In the course of this review, two physical Laws of Piping are proposed, and applied both to this case and to another nearby Melbourne Water dam that also has a history of piping.
Whilst the consequences of piping in a major dam are such that risk from this source must be kept to a very low level, it is concluded here that piping risk arising from tree root invasion has been considerably overstated and that a more balanced assessment is necessary before determining what, if any, action is required.
K. Chandler, D. Gill, B. Maher, S. Macnish and G. Roads
SEQWater is the major supplier of untreated water in bulk to Local Governments and industry in the South East Queensland region of Australia, through ownership of Wivenhoe, Somerset and North Pine Dams. Wivenhoe Dam (Lake Wivenhoe) is located on the Brisbane River in Esk Shire. The storage provides both flood mitigation and water supply storage to Brisbane and Ipswich. The water supply storage capacity at full supply level is 1,160 GL. An additional 1,450 GL of storage above full supply level is used for flood mitigation.
Changes to the estimation of extreme rainfall events has resulted in significant increases in the estimates of the PMF since the original design of Wivenhoe Dam. To upgrade the flood security of Wivenhoe Dam, SEQWater has formed an alliance with Leighton Contractors, Coffey Geosciences, MWH and the NSW Department of Commerce.
This paper details the alliance delivery method, the latest estimates of the PMF based on the GTSMR method and details of the two preferred options being finalised by the Alliance.
Hydro Tasmania has recently developed a Dam Safety Emergency Plan, which covers 54 referable dams throughout Tasmania. A major contribution was the development of the Pieman River flood warning system. The flood warning system is a computer-based model that forecasts the hydrological situation of the catchment up to 48 hours into the future and alarms the appropriate personnel when a flood event is imminent. The Pieman River catchment experiences some of the highest average annual rainfalls in Tasmania and contains dams in the High Hazard category. The flood warning system was developed using Hydstra Modelling™ (formerly TimeStudio), which links directly to the Hydstra TSM™ database. This package offers powerful automation tools that enable the Pieman River flood warning system to operate, alert personnel and display results on Hydro Tasmania’s internal website with no manual involvement. With its maintenance free operation and user-friendly interfaces, the Pieman River flood warning system is an effective contribution towards the overall risk management package of the Pieman River Power Development
Arthur Yapa, Tom Bowling and Peter Watt
Hydro Tasmania uses an electronic inclinometer to monitor the face deflections of nine of its CFRDs. The inclinometer is lowered down a steel pipe attached to the upstream face of each dam. The inclinometer was designed and constructed by the University of Tasmania and was first used on Cethana Dam when it was completed in 1972.
The success of its use on Cethana Dam lead to its use for the long term monitoring of eight subsequent CFRDs constructed by Hydro Tasmania.
After 25 years of successful operation some irregular readings of face deflection became apparent. This paper describes the investigation of the irregular readings that had been obtained, the assessment of other methods of observing concrete face deflection, and the refurbishment of the inclinometer using modern electronic components.
David Snape and Brian Simmons
Sydney Catchment Authority (SCA) has been progressively enhancing its asset management capability for dams and other headworks infrastructure since 1999. A key to the development of the integrated asset management system has been the application of asset condition assessment and Failure Modes, Effects and Criticality Analysis (FMECA) across the water supply mechanical and electrical assets. This has provided vital data necessary to:
Asset management features as a key result area within the SCA’s Corporate Business Plan. Integrated asset management is achieved by cascading corporate outcomes, strategies, objectives and responsibilities down through divisional and team work plans to individual staff members. This paper covers a range of issues that have a bearing on the day-to-day integrity of the infrastructure required to deliver bulk raw water to the SCA’s customers.
The management of maintenance at Warragamba Dam is used as an example to demonstrate the effectiveness and practicality of the application of the contemporary asset management system.