Mark Locke and Scott Kindred
The Bulk Water Alliance (BWA) consisting of ACTEW and ACTEW-AGL, GHD, and John Holland / Abigroup, are delivering the Enlarged Cotter Dam project in Canberra, ACT. The greatly enlarged reservoir will require two central core rockfill saddle dams on a ridge adjacent to the main dam site. Construction of these two dams was completed in early 2011. The challenges of the site and the Alliance delivery model have provided opportunities for innovation in both use of materials and construction.
The dam foundations were variably weathered and fractured with some highly weathered seams extending below the cutoff trench foundation. The foundation was grouted effectively using GIN grouting and the entire cutoff trench was shotcreted to reduce the risk of piping of the dispersive core material.
The steep topography provided very limited sources of material suitable for a dam core. Potential contingency plans considered included bentonite enrichment of the low plasticity materials or a change to a concrete faced rockfill dam. The high cost of these options drove the decision to use the available residual soils from small gullies by selectively winning material with a higher fines content for use below full supply level. The lack of room on the ridge for stockpiling and conditioning of clays lead to trialling of a continuous mixer for mixing and conditioning the core which was found to be highly successful.
Filter materials were crushed sands and gravels produced from nearby commercial quarries. The materials and grading were generally high quality, with some challenges producing coarser filter materials by blending available aggregate products. A range of options were effectively adopted for placement of the filters including loader placement, trench boxes and spreading from a modified ejector dump truck.
Enlarged Cotter Dam Saddle Dams – Materials and Construction
John Grimston, Robin Dawson
The Ambuklao and Binga Hydro-Electric Power Projects are located in Luzon, Philippines and were privatised in early 2008 after public bidding. Ambuklao dam forms an impoundment on the Agno River. The nearest city, Baguio, is approximately 45km or 1.5hrs drive away. The key headworks feature is an embankment central core rockfill dam and reaches a maximum height of some 129 m above the bed of the Agno River. A gated spillway is located at the left abutment, with a steep chute and flip bucket. Binga dam forms an impoundment approximately 20 km downstream of the Ambuklao dam. The rockfill embankment with an inclined clay core reaches a height of about 107 m above the bed of the Agno River. The spillway is located at the left abutment.
Heavy tropical rains and typhoons can cause very high flows in the rivers leading into the Ambuklao and Binga reservoirs. PMF peak flow is 11,600 cumecs. Due to the steep slopes surrounding the reservoir and along the access roads to the Binga Dam, landslides can create a hazard in the reservoir or for emergency access to the dam. There are numerous active faults in the area, including the Abra, Digdig and Philippines Faults (the latter being one of the most active faults around the Philippines). The region around the dams is capable of and has experienced earthquakes with a magnitude of 7.8 on the Richter Scale. This was demonstrated by the 1990 earthquake (7.8 magnitude) and caused minor damage to the dam structures.
The Project owner commenced rehabilitation implementation planning immediately after purchasing the facilities aimed at reactivating the Ambuklao plant’s 75MW capacity (inoperable since 1999 due to reservoir siltation issues triggered by the 1990 earthquake) and increasing it to 105MW. Rehabilitation at the Binga plant will increase capacity from it’s current 100MW to 120MW. The overall rehabilitation works include plant, intakes, associated tunnels, etc. This paper will focus primarily on the dam and spillway related rehabilitation, studies and design including review of the PMF and spillway capacity for both dams, Ambuklao innovative upstream face rehabilitation, Ambuklao spillway studies and rehabilitation and Binga spillway works and reservoir sedimentation studies.
2011 – Refurbishment of Ambuklao and Binga Hydro Power Dams and Appurtenant Works
Amanda Ament, Jon Williams, Malcolm Barker
Aplins Weir is located on the Ross River in Townsville, downstream from the Ross River Dam. Previous work had identified Aplins Weir as exhibiting factors of safety below 1.0 under normal operating conditions, with over 1000 persons at risk today in the event of failure. Originally constructed in the early 1920s, Aplins Weir has been upgraded and repaired following various failures on a number of occasions. The end result is a complex reinforced concrete and steel sheet pile composite structure reliant for stability on a number of unreliable components. This paper presents the historical data describing the current configuration of the weir, and the analyses required to evaluate the extisting structure, leading to the design of the proposed upgrade works. The final design involves a retrofit of large diameter cast-in-place lined piles and a heavily reinforced base overlay slab designed to completely bypass all existing vulnerable substructure elements.
2011 – Where is our Weir going – an Unusual Upgrade!
Robert Keogh RPEQ, CE Civil (Hon), Mal Halwala, Peter Boettcher, Renee Butterfield
SunWater is a Government Owned Corporation (GOC), operating in a competitive market on an equal commercial footing with the private sector. SunWater owns 23 referable dams. Over the last fifty years there has been significant development of the methodologies used to estimate extreme rainfall events. These have resulted in substantial increases in probable maximum flood (PMF) estimates for most of SunWater’s dams.
SunWater has undertaken a Comprehensive Risk Assessment program across its portfolio. SunWater now has a good understanding of the deficiencies and available risk reduction options for each dam under all load conditions. The total cost to rectify all deficiencies is several hundred million dollars and well beyond the financial capacity of the organisation in the short term.
ANCOLD and Regulators have different published opinions on decision making criteria for dam safety upgrades. Once the conditions for the tolerability of Societal and Individual Risk are satisfied the onus remains with the dam owner to meet the ALARP principle. The decision making process is complicated by uncertainties in inputs to risk assessments. The authors have considered these uncertainties as well as the legal implications, differing ANCOLD and Regulator requirements, and business and economic loss, in formulating the decision making process. The methodology is simplified but effective. If the process is followed the dam owner’s investments will meet ANCOLD, Regulatory, legal and business requirements.
This Paper details a logical decision making process designed to allow a non technical Board to balance social, legal and financial objectives. The process considers overall risk, tolerability, the ALARP principle, and project prioritisation. The process is being used by SunWater to determine the Acceptable Flood Capacity of each dam, which dams will be upgraded, priorities and scheduling of each upgrade.
How SunWater, as a commercial dam owner makes investment decisions for dam safety upgrades
Lesa Delaere, Ivor Stuart, Thomas Ewing, David Marsh
As part of Wide Bay Water’s commitment to minimising environmental impacts of its water supply weirs, a “Nature Like” Fishway is under development for the Burrum No 1 Weir. This project is a fishway offset provision for the raising of Lenthalls Dam in the upper reaches of the Burrum River in Hervey Bay. The Burrum No 1 weir forms the primary pumping pool for the Hervey Bay water supply and is located at the tidal limit of the Burrum River. Understanding fish biology and behaviour is critical to the effectiveness of the design of a fishway as much as the balance between the goals of maximising fish passage versus cost, construction and operational difficulties that a fish passage solution may present.
This paper presents the aquatic ecology of the project and the inter-relationship of fish biology and river flow frequency. It discusses the fish species of the Burrum River, their behaviour, seasonal migration and criteria for successful passage. It presents the analysis of river flows with respect to frequency and headwater/tailwater relationships to weir drownout, which was complicated by the tidal flow regimes downstream of the weir. These aspects were also applied in consideration of river behaviour; low flow characteristics for fishway operation during dry seasons and drought, and high flow characteristics during the wet season and floods.
The biological needs for successful fish passage for two very different river flow characteristics were analysed. This allowed targeted design criteria and fishway solution to be developed to provide maximum benefit without causing undue cost to the project.
Burrum Weir Fishway – Fish Biology and River Flows: Two Faces
T. Mortimer, J. McNicol, P. Keefer, W. Ludlow
CS Energy’s Kogan Creek Coal Mine located in the Surat Basin in Queensland, services the 750MW coal fired, Kogan Creek Power Station. Strip mining generates large volumes of mine waste which is typically used to construct waste dumps. Recent work at the mine has focused on using mine waste to construct an ash storage facility to store ash that is piped over 5 km from the power station as a dense phase slurry. The use of mine waste to construct the ash storage facility provides significant cost and time savings, however a range of design, construction and operation issues needed to be addressed to operate a facility of this type.
This paper describes some of the key design, construction and operation considerations for the ash storage facility. Design considerations include pipeline transport through environmentally sensitive areas, addressing the stability of the embankment and the use of a partial LLDPE geomembrane lining system to reduce the risk of seepage from the storage. Construction considerations include post construction (pre ash deposition) floor treatment to reduce potential settlement. Operational considerations include ash slurry deposition, water management of the decant pond and progressive rehabilitation of the final landform.
2011 – Design, Construction and Operation of a Partially Lined, Ash Storage Facility Constructed from Mine Waste