Zara Bostock, Helena Sutherland
Ewen Maddock Dam is located approximately 12.0 km west of Caloundra, in the Sunshine Coast area of Southern Queensland. The dam is a homogeneous earthfill embankment dam 10.5 m high and 724 m long. The dam was originally built between 1973 and 1976 and later upgraded in 1982 to raise the ogee spillway crest by 2.44 m to the current Full Supply Level (FSL) of 25.38 m AHD.
Seqwater is undertaking a staged upgrade of Ewen Maddock Dam to address deficiencies identified during the Acceptable Flood Capacity (AFC) Review (GHD, 2010). The consequence category assigned to Ewen Maddock Dam is ‘Extreme’ with a downstream Population at Risk greater than 1000.
Stage 1 construction was completed in 2012 to manage the seepage underneath the dam to reduce the risk of piping and improve embankment stability. Stage 2A involved retrofitting a filter in the existing embankment and raising the dam 1.61 m to 30.11 m AHD using a reinforced concrete parapet wall. Stage 2B involves spillway upgrade works and was split from 2A due to approval constraints.
Stage 2A construction was completed in April 2021, navigating various project and dam safety challenges. This paper presents some practical ways dam safety and risk was managed on the ground from the perspective of both the designer and owner.
— OR —
Now showing 1-12 of 37 3483:
Damien Bryan, John Sukkar, Erin Hughes, Michael Cawood
Alert triggers are a critical component of Dam Safety Emergency Management, aligning clearly defined adverse conditions with alert levels to initiate an appropriate emergency response. Early detection of these conditions allows for potential mitigation measures to be undertaken, early engagement of key stakeholders such as emergency agencies, and where necessary, the warning or evacuation of affected downstream communities. The Dam Safety Alert Trigger Framework provides WaterNSW with a consistent, repeatable, and defensible methodology for the determination of appropriate dam safety alert triggers. The framework was developed through the engagement of consultants, emergency and regulatory agencies (NSW SES & DSNSW), and several Australian large dam owners.
The determination of appropriate Dam Safety Alert Triggers is a challenge faced by all dam owners. Through the development and implementation of the Alert Trigger Framework, WaterNSW has achieved the ability to define defensible alert triggers through a consistent and repeatable methodology. This has resulted in an improved dam safety emergency response posture for WaterNSW, key emergency services partner the NSW SES, and greater protection for affected downstream communities. Concepts, processes and methodology covered in this paper could be used by other dam owners in addressing their own dam safety alert trigger challenges.
David Reid, Andy Fourie, Riccardo Fanni, Cristina Vulpe, Alexandra Halliday
Recent failures of a number of tailings storage facilities (TSFs) has highlighted the need for better
governance and operational management of these structures. One means to improve their safety is clearly better and more focussed monitoring. Significant efforts are underway in this area, with a number of technologies being deployed. In particular, the monitoring of deformations through a variety of means (direct, satellite inferred) is increasingly being applied. While deformation monitoring to warn against failure has a long history in geotechnical engineering, some aspects of the rapid triggering and resulting flow of some TSFs may not be amenable to deformation monitoring, in the sense that actionable warning of an impending failure is not assured.
To examine this issue, a series of numerical models of an idealised TSF are carried out. This idealised TSF is brought to failure by means of a rising phreatic surface – often referred to as the constant shear drained (CSD) stress path. Deformations of the outer slope and crest of the numerical model – i.e. those that could be monitored for a real TSF – are tracked and analyses for the models carried out. It is seen that under CSD loading distinct deformation patterns indicative of impending failure are not always clear. Rather, minimal deformations and indeed swelling of the crest is seen leading to failure. The importance of recognising the minimal pre-failure deformation patterns that may manifest with a rising phreatic surface is noted.
Sonel Reynolds, Alex Gower, Bob Wark
During the outlet works upgrade in 2017 it was found that the valve pit and stilling basin at Mundaring Weir were not founded on rock. Based on these observations and the arrangement of the spillway and outlet works, it was considered that during significant spillway overflow events, a high velocity jet could displace the stilling basin slabs, erode the underlying material, and progress to failure of the outlet pipe and valve pit. A comprehensive risk assessment was conducted to estimate the likelihood of stilling basin slab uplift, erosion of the underlying material, and failure of the outlet works. A geotechnical investigation was undertaken comprising drilling nine boreholes and a program of geophysical downhole logging. Computational Fluid Dynamic (CFD) modelling was used to determine the pressure fluctuations and turbulence intensity over the spillway slab which could lead to uplift. The erodibility of the rock mass material below the stilling basin slabs was assessed using the outcomes of the geotechnical investigations and CFD output, with analyses based on the Kirsten Index and eGSI. A net benefit analysis was conducted to assess whether preventative remedial works were justified. Through this process it was demonstrated that the business risk was low and risk reduction measures were not justified.
Christopher Dann, Chad Martin, Garry Fyfe, Nigel Rutherford
This paper presents a case study on remedial works that were undertaken at Lock and Weir One
along the River Murray, that to our knowledge are the first of their kind in Australia.
The weir structure’s left abutment is comprised of a stepped concrete structure founded on timber
piles, with timber sheet piles extending beneath the structure to cut off seepage through underlying
alluvium. A piping incident occurred at the left abutment in late 2014 and a filter blanket was
installed as an emergency response measure. A detailed review of historic construction documents
showed that there was a “missing” timber sheet pile upstream of the piping boil. Geotechnical
investigations, including piezometer installation confirmed the missing timber sheet pile was the
likely cause of the piping incident. A piping risk assessment showed the residual risk of further piping
was reasonably high.
A range of remedial works was considered as permanent risk reduction works. However, these
solutions required extensive temporary works to expose the missing timber sheet pile including a
cofferdam to access the defect and partial demolition of a recently constructed fishway structure.
An alternate Secant ‘Grout Column’ solution was developed that comprised targeted drilling and
backfill grouting to close the gap where the sheet pile was not installed and to grout an inferred void
under the abutment structure. This solution was successful at reducing seepage through the
abutment structure, as indicated by monitoring piezometers.
Ryan Cantrill, Petros Armenis & Angus Cannon
Large Australian dams span a range of ages and were designed and constructed to the prevailing
standards and practices of the day. Since that time, there has been a veritable explosion in monitoring and surveillance technologies available to dam owners to assist with risk management of their portfolio. Coupled with this has been the formalization and ongoing development of regulatory frameworks across the industry.
This paper endeavours to share Sunwater’s recent experience on this topic. Specifically, the following question is considered – how best to apply modern monitoring and surveillance technologies to manage dam safety risks associated with decades old structures, all while still meeting regulatory requirements? In answering this question, the authors necessarily had to consider several inputs including – physical condition of the existing assets; analysis of existing controls and mitigation measures; risk assessment and risk profile of the assets; and operational constraints. As always, outputs invariably required the prioritization of recommendations.
While dam owners must strive to comply with a standard and accepted way of managing their portfolio, it is vital they recognize and address the unique risks that each structure presents. It therefore follows that owners must be prepared to allow the time and provide the necessary resources when formulating a monitoring and surveillance program commensurate with the dam safety risk that their respective portfolio presents