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.
Peter J Burgess, Delfa Sarabia, John Small, H. G. Poulos and Jayanta Sinha
The assessment of settlement behaviour of clay core rock fill dams has always been a challenge for dam designers and geotechnical engineers. The method of construction and the material properties of the clay and rock fill materials used in the dam construction have a significant influence on the inter-zonal interaction and the load transfer that occurs within the dam. At times this load transfer can lead to excessive differential and total settlements. The paper presents a case study of a major dam that experienced large settlements during and after construction. An elaborate analysis has been carried out by modelling the sequences of construction by using a finite element program (PLAXIS).
The paper describes the influence of the degree of compaction and moisture control on non-linear deformation characteristics of clay core. High vertical strains in the wet placed region of the core and low strains in the dry placed regions were analysed for possible shear development between the core and shell. The rock fill for the dam embankment consists of quartzite, metasiltstone and phyllite material. These materials have apparently undergone deformation with increasing height of the dam due to softening and crushing as saturation of the embankment took place. The effect of soil consolidation and strength gains have been considered in the analysis and are discussed. The settlement behaviour of the dam including these effects has been analysed, and compared with the historical post-construction settlements.
This paper is intended to provide valuable information for dam engineers handling clay core rock fill dams – especially where there is excessive settlement of the core.
The Koralpe hydropower scheme is a major development on the Feistritzbach tributary of the River Drau to utilize water in a 50 MW powerhouse located in the south-eastern Carinthia, Europe. The Soboth reservoir is situated 735 m higher in a narrow valley and is created by the 85 m high Feistritzbach dam which was constructed near the border of Austria and Slovenia between 1988 and 1990. This rockfill dam is the latest addition to KELAG’s more than 15 structures and is sealed by an asphaltic core. The excellent deformability and impermeability of the asphaltic core is able to follow the deformation of the compacted rock-fill material best during construction, initial filling and operation period without any seepage. The asphaltic core was placed in three 20 cm layers per day by a specially developed placing unit from a contractor. The upstream and downstream filter zone was placed at the same time with the same machine and compacted carefully by vibrating rollers. The dam is curved in plan with a radius of 650 m and contains about 1.6 million m³ rock fill material. The surface of the downstream side was built exceeding the environmental standards of the time.The most important indicator of the normal function of a dam is the behaviour of seepage. A monitoring system of seepage, piezometers, earth pressure cells and deformation has been installed. The seepage water is monitored online at seven points of the dam base and at the access tunnel to the bottom outlet valve. Geodetic measurements on and inside the dam are done once a year. Several additional pieces of surveillance equipment were installed to observe the behaviour of the asphaltic core. The paper concentrates on the design, construction and performance of the dam with the asphaltic core.
P Amos, N Logan, and J Walker
There are a number of geological faults in close proximity to Aviemore Power Station in the South Island of New Zealand, including a fault in the foundation of the 48m high earth dam component of the power station. Possible movement of the Waitangi Fault in the earth dam foundation is of particular concern for dam safety, and the effects on the dam of a fault rupture has been the subject of detailed investigation by the dam’s owner Meridian Energy Ltd. These investigations have concluded that the dam will withstand the anticipated fault displacement related to the Safety Evaluation Earthquake without catastrophic release of the reservoir.
The identification of damage to the dam following an earthquake and monitoring of the dam to identify the development of potential failure mechanisms are important for determining the post-earthquake safety of the power station. The first stage of the post-earthquake response plan is the quick identification of any foundation fault rupture and damage to the dam to enable immediate post-earthquake mitigation measures to be initiated, such as reservoir drawdown. Following initial response, the next stage of the post-earthquake monitoring programme for the embankment dam is longer term monitoring to identify a changing seepage condition due to damage to the dam that might lead to a piping incident. Such an incident may not occur immediately after an earthquake, and it can be some time before the piping process becomes evident.
This paper presents some key instrumentation installed at Aviemore Dam and included in the emergency response plan for the post-earthquake monitoring of the embankment dam.
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.
Joseph Matthews, Dr Mark Foster, Michael Phillips
Pykes Creek Dam is a 39m high earthfill dam with a central clay puddle core, first completed in 1911 and raised in 1930. A detailed risk assessment of the dam indicated that the risk did not satisfy ANCOLD societal risk criteria and that remedial works were necessary to address piping deficiencies and inadequate flood capacity. The risk assessment identified that piping at the embankment/spillway interface accounted for over 80% of the total risk. Therefore, interim risk reduction works were implemented in 2005 to address this risk issue while investigations and design studies were progressed for the second stage of works. Following the Stage 1 works, Pykes Creek Dam remains the highest risk in Southern Rural Water’s portfolio of dams and Stage 2 works are planned to commence in 2007 to reduce piping risks and increase flood capacity. The aim of the Stage 2 works is to reduce the risk below the Limit of Tolerability for Existing Dams (ANCOLD 2003) and to increase the flood capacity to a level more appropriate for an Extreme consequence category dam based on ALARP principles. The upgrade will stop short of meeting the PMF as there are other dams in Southern Rural Water’s portfolio requiring attention before an upgrade to this standard would be considered. The design of the works was complicated by the fact that the dam is bisected by a major freeway and has a complex spillway layout. This paper discusses the decision-making process and the methods used to analyse the dam from the initial risk assessment studies through to the design of the remedial works.