M Gillon, T Logan, N Logan
The paper has been prepared to support the key questions selected for the ANCOLD Dam Instrumentation and Survey Seminar to be held in Sydney in November 2006 and to provide a New Zealand perspective. The paper is not a ‘state of dam monitoring practice in New Zealand’ dissertation but is rather a targeted summary of the authors’ experiences and observations from practicing in this area.
These experiences and observations on dam monitoring are grouped under the following headings, reflecting the key questions:
Now showing 1-12 of 59 2970:
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.
SunWater manages its portfolio of 29 major dams through 6 business centres each responsible for the Dam Safety Program for the dams under its management control.
The effectiveness of responses during an emergency depends on the amount of planning and training performed. Management must show its support for dam safety programs and the importance of emergency planning.
If management is not interested in community protection and in minimising property loss, little can be done to promote dam safety. It is therefore management’s responsibility to see that a program is instituted and that it is frequently reviewed and updated.
The input and support of all communities must be obtained to ensure an effective program. The emergency response plan should be developed locally and should be comprehensive enough to deal with all types of emergencies specific to that site.
SunWater is a responsible dam owner and has recently upgraded all its emergency action plans in consultation with emergency services of Queensland. This paper details the basic steps to handle emergencies of water infrastructure. These emergencies include inflow floods, rapid drawdown, earthquake, sunny day failure, changes in reservoir water quality and terrorist attacks including hoax.
This paper is intended to assist small dam owners that do not have dam safety programs in place. It is not intended as an all inclusive safety program but rather a provision of guidelines for planning for emergencies.
C Lake and J Walker
Meridian Energy is the owner and operator of a chain of hydro dams on the Waitaki River in the South Island of NZ. It operates a Dam Safety Assurance Programme which reflects current best practice; consequently it has focused primarily on managing civil dam assets. Advances in plant control technology have allowed de-manning of our power stations, dams and canals through centralised control. The safety of our hydraulic structures is increasingly reliant on the performance of Dam Safety Critical Plant (DSCP) – those items of plant (eg water level monitoring, gates, their power and control systems, and sump pumps) which are required to operate automatically, or under operator control, to assure safety of the hydraulic structures in all reasonably foreseeable circumstances.
Recent dam safety reviews have highlighted that the specification and testing of our DSCP is based on the application of ‘rules of thumb’ which have been established through engineering practice (eg. “monthly tests”, “third level of protection”, “backup power sources”, “triple voted floats”). The adequacy of these engineering practices is difficult to defend as they are not based on published criteria. The realisation that such rules may not be relevant to the increased demand on, and complexity of, DSCP led us to ask “Which belts and braces do we really need?”
The current NZSOLD (2000) and ANCOLD (2003) Dam Safety guidelines give little guidance regarding specific criteria for the design and operation of DSCP. Meridian has identified the use of Functional Safety standards (from the Process industry, defined in IEC 61511) as a tool which can be applied to the dams industry to review the risks to the hydraulic structures, the demands on the DSCP, and utilise corporate “tolerable risk” definitions to establish the reliability requirements (Safety Integrity Levels) of each protection, and determine lifecycle criteria for the design, operation, testing, maintenance, and review of those protections.
This paper outlines the background to identifying Functional Safety as a suitable tool for this purpose, and the practical application of Functional Safety Analysis to Meridian’s DSCP.
G. Hunter, R. Fell, S. McGrath
The main embankment at Tullaroop Reservoir is a 42m high zoned earth and rockfill dam that was constructed in the late 1950s. The constructed embankment has a very broad, well compacted clay earthfill zone with dumped rockfill on the mid to lower upstream and downstream shoulders.
Over a two week period in April 2004 a diagonal crack of 60mm width and greater than 2m depth developed on the downstream shoulder of the main embankment. The crack was located on the left abutment and extended from the crest to the toe of the embankment. The diagonal crack terminated at the downstream edge of the crest. A continuous longitudinal crack extended along the downstream edge of the crest from the diagonal crack almost to the left abutment. Since April 2004 no further widening of the diagonal crack has been observed.
This paper presents the findings of a series of site investigations and analysis to understand the mechanism for formation of the diagonal crack, and the risk assessment process that culminated in the eventual construction of a full height filter buttress on the left abutment of the main embankment. Factors that influenced the cracking included the change in slope in the foundation profile, the temporary diversion channel on the left abutment, residual stresses in the dam abutment due to differential settlement during construction, a complex foundation geology and presence of shear surfaces in a Tertiary alluvial sequence that formed due to valley formation, an historic dry period and a prolonged period of drawdown. The presence of the crack and its assessed mechanism of formation presented a dam safety risk of piping through the embankment. The risk evaluation process was worked through with URS, Goulburn-Murray Water (G-MW), and G-MW’s expert panel, and eventuated in construction of the localised filter buttress in February – March 2006 to address the dam safety deficiency.
Manuel G. de Membrillera, Ignacio Escuder, David Bowles, Eduardo Triana, Luis Altarejos
The work herein presented is an application of the risk assessment process to retroactively estimate the justification of an operating restriction implemented on a Spanish Dam. Since the risk approach is not yet an established practice in Spain, the main objective of this case study is to show, the utility that risk assessment can have as a decision support tool for decisions on dam safety risk reduction investments.
An operating restriction has been imposed at this dam since its first impoundment. All studies, analysis and documents related to the safety of the dam and reservoir have been completed, as required by the Technical Regulation on Dam and Reservoir Safety (Spanish legislation, 1996). In addition, the structural corrective actions recommended in these evaluations are being implemented, so it is expected that the operating restriction can be removed in the near future.
In this context, the problem that has been formulated and solved comprises an evaluation, after more than 30 years since construction, of the operating restriction justification in terms of risk mitigation. In order to achieve the objective of the work, ANCOLD guidelines on Risk Assessment (2003) have been followed in addition to tolerable risk guidelines from several other countries and organizations.