Dr Bradford Sherman, Dr Phillip Ford, Allison Mitchell, Gary Hancock
Recent reports from the World Commission on Dams have highlighted the relative lack of knowledge regarding the release of greenhouse gases (GHGs) from reservoirs. In order to be considered eligible to receive carbon credits in the future, hydropower facilities probably will be assessed using some sort of life cycle analysis of net GHG emissions.
Unfortunately, empirical data regarding GHG emissions is available only for a few reservoirs none of which are located in temperate or semi-arid climates.
We report preliminary observations on the vertical distributions of methane and carbon dioxide in Chaffey Reservoir (Tamworth, NSW) and Dartmouth Reservoir, two temperate zone reservoirs located in southeastern Australia. In Chaffey, the diffusive methane flux from the hypolimnion to the epilimnion (where it is oxidised by bacteria) was estimated to be 220-1760 mg-CH, m’ d’. Operation of a destratification system released 43 t of CH, to the atmosphere in 3 days. The carbon dioxide flux to the atmosphere via the surface of Dartmouth was 21-168 mg-CO, m’ d’, and 530 mg-CO, m° d’ through the turbine. The impact on GHG emissions of common reservoir management techniques such as destratification and hypolimnetic oxygenation is discussed.
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Neil Gillespie, Chris Hansen
With the introduction of the Resource Management Act in 1991, two significant changes have meant a complete review has been necessary of the planning provisions for hydro generation facilities in plans prepared under the new legislation.
Firstly, the Resource Management Act 1991 introduced an ‘effects’ based approach to planning, as opposed to an ‘activity’ based approach that existed under the previous Town & Country Planning Act 1977. Secondly, the planning mechanisms available to hydro generators to provide for their facilities changed.
Contact Energy Ltd (Contact) is a significant hydropower generator based in Central Otago. The new Regional and District Plans prepared under the Resource Management Act 1991 now contain provisions controlling activities previously provided for by way of a designation. Contact has invested considerable time and effort into the plan preparation process to ensure their activities are not unduly restricted by the new plans.
This conference paper provides an overview of the changes to the planning associated with hydropower generation facilities, and Contact’ s experience in the plan preparation process.
The regulatory environment for dams in Queensland will change when the new provisions of the Water Act 2000 are proclaimed in late 2001 or early 2002. The definition of a ‘referable dam’ has shifted from a simple height and storage criteria to one that requires a population at risk (PAR) before dams are considered referable. Additionally hazardous waste dams such as tailings dams will no longer be considered as referable dams and under the Act regulatory control will be transferred to the Environmental Protection Agency.
Referable water dams will be assigned a Failure Impact Category of 2 if they have a PAR greater than 100 and a Category of I if they have a PAR greater than or equal to 2 and less than 100. This has required the development of guidelines for the assessment of ‘population at risk’. These guidelines have been written to suit a wide variety of dam impact situations and a range of dam owner resources. The guidelines require certification of the failure impact assessment by a Registered Professional Engineer in the state of Queensland.
The Queensland Dam Safety Management Guidelines have also been re-written to make them more amenable for reference in dam safety conditions.
New dams will require development permits to be issued under the Integrated Planning Act and will have development permit conditions applied in accordance with their Failure Impact Category. There is a range of transitional provisions for existing dams.
This paper covers all of the above issues as well as providing an indication as to how these statutory guidelines relate to the various ANCOLD guidelines.
Peter Lilley, Kelly Deighton, Don Tate, Craig Scott
In recent years TrustPower has undergone a rapid transition from a part owner of three dams in the Kaimai ranges south of Tauranga and the Hinemaiaia and Wheao schemes near Taupo in 1998, to the present ownership situation. Today TrustPower owns 22 dams comprising a range of structure types, including arch, earthfill, rockfill, concrete gravity and a number of embankment canal systems. The dam classifications for the dam portfolio vary from small to large and the NZSOLD potential impact ratings vary from very low to high. The portfolio includes some of the largest dams in New Zealand, for example Matahina Dam a 70m high central core rock fill, Patea Dam an 80m high earthfill dam and Mahinerangi Dam a 40 m high concrete arch dam with concrete gravity abutments.
The dam structures vary significantly in terms of age, potential impact and risk to TrustPower . The Dam Safety Management Procedures (including monitoring and surveillance systems, inspections and reviews) that existed for each dam also showed considerable variation in comparison.
The approach adopted for dam safety management is described, and the interrelationship with commercial objectives and commonly accepted standard practices.
M.A. Foster, R. Fell, R. Davidson, C.F. Wan
The probability of failure of embankment dams by internal erosion and piping can be estimated using historic performance, and event tree methods. Event tree methods are preferred for all except preliminary assessments, because they can better model the characteristics of the dam. This paper provides guidance on how to estimate the conditional probabilities within the event tree based on an understanding of the process involved, the historic performance of dams, and experience in recent risk analyses. This includes methods for representing the reservoir water level; assessing the likelihood that piping initiates; assessing the likelihood that erosion will be controlled by the filters or transition zones; and assessing the likelihood of development of a pipe and breach. The paper will be useful for those carrying out risk analyses and will also have relevance to those who are assessing piping of dams using traditional methods.
P.A. Maisano, P.A. Miskell
Design and construction issues relating to Cadiangullong Dam were reported to ANCOLD at
the 1998 Conference on Dams.’ First filling of the dam occurred in July 1998. Monito
ring of installed thermocouples, piezometers, joint and crack meters, movement targets and
seepage measurement devices, has been regularly undertaken by the dam owner and
reviewed by the designer. Annual inspections over these first 3 years of service, with
condition/performance reporting by the designer, has been undertaken in terms of the
Piezometers revealed excessive foundation uplift pressures near the right abutment.
Pressure relief holes drilled into the foundation were subsequently shown to have been successful in lowering foundation uplift pressures. Stability analyses confirmed the dam to
be stable under the new uplift regime.
The paper presents the performance of the structure and the reservoir in meeting the
designer’s and owner’s expectations as an assured process water supply for the Cadia Hill
Gold Mine, one of Australia’ s largest gold mines.
As one of the first roller compacted concrete (RCC) dams to use grout enriched RCC as an
impermeable facing to the upstream face and a durable surfacing to the stepped spillway,
the paper will also provide a performance review of this material which has since been
adopted on a number of other RCC dams worldwide.