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Petros Armenis, Malcolm Barker, Peter Christensen, Graham Harrington
The Canterbury Earthquake Sequence in September 2010 and February 2011 caused large areas of land to change by differing amounts throughout Christchurch, New Zealand. Land levels fell by more than 300 mm in some areas. This increased flood risk in the tidal reaches of the Avon River. Urgent repairs were completed with the objective to restore the tidal river defences to a crest level equivalent to a 1% AEP tide level. This work needed to be completed prior to impeding spring tides.
The levees will be required for up to 20 years and then probably be rebuilt on a new alignment. To better understand the risks associated with the ongoing reliance of the levees for flood protection in the interim, a risk assessment was undertaken using conventional Australian National Committee on Large Dams (ANCOLD) practices and levee design procedures. Careful consideration was made to the performance of the existing levees under seismic, flood and tidal loading from which the societal and individual risk profiles were derived. The work included the following:
- The identification of critical sections along both sides of the 11 km levee river alignment through consideration of the foundation and embankment construction
- Combining seismic events with tides and flood events with tides using levee lifetimes of 1, 5, 10 and 20 years
- Consideration of overtopping failure and piping through the levee embankment, foundation or tree roots and narrowed embankment sections owing to trees being blown over
- Application of the International Levee handbook (CIRIA 2013) and the “Piping Toolbox” (USACEet al 2008
- Evaluation of risk reduction with upgrade options
This paper will present the levee design and the process applied for the analysis of the levee and the upgrade options selection
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$15.00
2017 Papers
2017 – Application of Risk Assessment to an Emergency Levee Design in an Urban Environment
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Petros Armenis, Malcolm Barker, Peter Christensen, Graham Harrington
The Canterbury Earthquake Sequence in September 2010 and February 2011 caused large areas of land to change by differing amounts throughout Christchurch, New Zealand. Land levels fell by more than 300 mm in some areas. This increased flood risk in the tidal reaches of the Avon River. Urgent repairs were completed with the objective to restore the tidal river defences to a crest level equivalent to a 1% AEP tide level. This work needed to be completed prior to impeding spring tides.
The levees will be required for up to 20 years and then probably be rebuilt on a new alignment. To better understand the risks associated with the ongoing reliance of the levees for flood protection in the interim, a risk assessment was undertaken using conventional Australian National Committee on Large Dams (ANCOLD) practices and levee design procedures. Careful consideration was made to the performance of the existing levees under seismic, flood and tidal loading from which the societal and individual risk profiles were derived. The work included the following:
- The identification of critical sections along both sides of the 11 km levee river alignment through consideration of the foundation and embankment construction
- Combining seismic events with tides and flood events with tides using levee lifetimes of 1, 5, 10 and 20 years
- Consideration of overtopping failure and piping through the levee embankment, foundation or tree roots and narrowed embankment sections owing to trees being blown over
- Application of the International Levee handbook (CIRIA 2013) and the “Piping Toolbox” (USACEet al 2008
- Evaluation of risk reduction with upgrade options
This paper will present the levee design and the process applied for the analysis of the levee and the upgrade options selection
Learn more
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$15.00
2017 Papers
2017 – Sheet Piles: Driving a Solution to Piping Risk
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Tom Ridgway, Chris Topham, Aaron Brimfield
A significant number of dams across Australia are of earthen construction and may be susceptible to internal erosion of their earth core, also known as piping. In January of 2016, during an annual inspection of the Tarraleah No 1 Pond Levee it was found that the embankment was experiencing significant seepage at the toe. Further investigations found actively developing piping holes through the embankment. To better understand the condition of the dam, HydroTasmania’s remote monitoring trailer was deployed to provide telemetered seepage data to further understand the developing issue. It was found that the leakage was increasing dramatically, and carrying suspended core material, resulting in the need for prompt resolution to protect the embankment from further loss of material. A sheet piling wall was installed in the centre of the embankment to cut off the flow of water through the embankment. After the installation of the sheet piling wall, post works monitoring showed the seepage through the embankment reduced to virtually zero, only peaking in rainfall events. This paper outlines the investigation and management of the incident, and the mitigation measures put in place from the time of identification including the use of a sheet piling wall to mitigate a developing piping failure. The paper will conclude with the outcomes of the work and how a similar solution could be utilised for other dam owners in a piping event.
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