Kangaroo Creek Dam is a concrete face rockfill dam (CFRD) located on the Torrens River, approximately 22 km north east of Adelaide. The dam is currently undergoing a major upgrade to align it with updated safety guidelines set by the Australian National Committee on Large Dams (ANCOLD) to better withstand major flood events or earthquakes. As part of this upgrade, external omega-type waterstops have been installed on the vertical and perimetric joints to mitigate the impact of expected joint deformations due to seismic loading. Two profiles were selected for the external waterstops; one capable of extending 200 mm for the perimetric joint and the outer two vertical joints on each side, and one capable of extending 100 mm for the remaining vertical joints and the horizontal joint between the new face slab and the original face slab. Using the external omega-type waterstops as the second waterstop for the extended perimetric joint simplified construction, particularly with respect to reinforcement details adjacent to joints. It is understood that this is the first time in Australia that an omega-type waterstop is being fitted to a CFRD slab. This paper demonstrates the benefits of retrofitting waterstops to existing dam joints when required, provides general installation details, details for providing a continuous barrier with the existing waterstops by overlapping internal and external waterstops, and lessons learnt from the waterstop installation.
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Multiple-arch dam technology enjoyed a certain popularity between the fifties and seventies, but was later discontinued for practical reasons. The multiple-arch dam that is the subject of this paper is especially peculiar since it was built using prefabricated elements and a combination of several pre-stressed steel systems.
This dam consists of 17 buttressed arches with a maximum height of 35 m on a limestone and dolostone foundation. It has a crest length of 531 m and a 15 hm3 reservoir. After 55 years in operation, several apparent degradations have surfaced and a study on the safety of the dam is currently being carried out.
The main concern is the dam’s structural safety, which is apparently linked to the integrity of the post-stressed steel elements and the precast elements in the arches. This paper describes the approach chosen for the remediation study, the visual inspection, and the tests developed on the post-stressed steel and concrete, in order to feed a 3D numerical model of the structure.
There are many dams in Australia with appurtenant features such as spillway gates, large capacity outlet works, power stations and transfer tunnels. These features can play a significant role in how these dams are operated during flood events and allow for additional flexibility to implement flood mitigation activities such as pre-releases and surcharge depending on authorised operating procedures for the dam.
Typical practice in many dam flood hydrology studies has been to significantly simplify or even ignore the impacts of these features on the dam water level frequency curve. For example, it may have been assumed that spillway gates were either fully open or changed from fully closed to fully open in a uniform manner regardless of inflow rate. Whilst this approach significantly simplifies routing of floods through these storages, it may produce results which are inconsistent with the expected flood probability of the dam given its current operating procedures, especially for relatively frequent flood events. This is particularly critical for risk assessment where definition of the flood loading probabilities requires robust estimates of water level AEPs for all events.
In a number of recent studies, greater emphasis has been placed on detailed modelling of the effects of spillway gates and other outlet works on dam flood hydrology. This has required site-specific algorithms to be developed which incorporate the characteristics of the spillway gates or other features at each structure, as well as the flood operations procedures for the dam. This paper presents a number of case studies where explicit simulation of dam flood operations has had a significant impact on the resulting flood frequency curve and downstream flow rates and discusses the implications of that on dambreak modelling and risk assessment for those dams.
Extreme flood analyses are routinely used as inputs to dam risk assessments, spillway adequacy assessments and spillway designs. Estimation methods applied in Australia using rainfall-runoff models in combination with a Probable Maximum Precipitation (PMP) estimate are consistent with the current best practice applied around the world. The estimation methods can, however, result in substantial variability in peak flow estimates depending upon the practitioner and the methods used to quantify model parameters. Around the world, validation procedures are commonly applied to combat this variability, but no such techniques are routinely applied in Australia. A method is proposed for application across Australia which may variously be applied to validate and constrain extreme flood estimates and also provide quick estimates.
In 2018, DNRME released the latest revision of the Failure Impact Assessment (FIA) Guidelines and the first significant change since 2003. An FIA is the instrument for determining if a dam is referable and therefore regulated for dam safety purposes in Queensland.
The guidelines reflect upon changes in legislation and advances in methods and tools for assessing consequences of dam failure. The revised version tends to be less prescriptive and emphasises the responsibility of the engineer completing the assessment to develop appropriate and defensible methods.
The paper provides an overview of the FIA guidelines, key concepts, the steps to follow when preparing an FIA and a comparison to ANCOLD’s latest consequence assessment guideline.
Investigations into the core material of earth fill dams are undertaken reluctantly due to the potential to cause damage to the embankment. Where investigations are required, Cone Penetration Testing (CPT) is increasingly used to assist with the geotechnical assessment of dam embankments. The risk of hydraulic fracture within embankment core material is well known and procedures are typically adopted to minimise the risk of hydraulic fracture during remediation of the holes. Backfilling is typically done in stages allowing for an initial set of the cement/bentonite grout mixture prior to subsequent lifts.
While the risk of hydraulic fracture is well understood, the lesser known risk of pneumatic fracture is a possibility where certain conditions exist. This paper discusses CPT investigations at Fairbairn Dam, operated by Sunwater in Central Queensland, and the challenges faced in undertaking the remediation of the CPT holes. The potential for pneumatic fracture of the embankment core was highlighted during the investigations and details of alternative techniques adopted for reinstatement of the holes are presented. Recommendations are made to appropriately manage the risk of pneumatic fracture when undertaking CPT’s through embankment core.