Iain Lonie, Malcolm Barker and Colin Thompson
Consideration of flood mitigation benefits, water supply, irrigation and recreational usage played an instrumental role in developing the proposed upgrade for Maroon Dam to meet dam safety and flood capacity requirements. Maroon Dam is a 47.4 m high zoned earthfill dam completed in 1974. The dam is a multi-purpose reservoir which is now owned and operated by Seqwater and plays an important role in the local community. Key drivers for the proposed upgrade design included embankment stability, foundation concerns, piping, spillway capacity and erosion of the embankment toe.
Six options were reduced to three through a high level screening exercise. A more detailed assessment of the remaining options was undertaken using a Multi Criteria Analysis and a detailed risk assessment. Consideration of the competing uses of the reservoir was critical in the development and assessment of the preferred option. This paper will present the details of the analytical methods used as input for the Multi Criteria Analysis and the detailed risk assessment for the final proposed design option that will meet the requirements of dam safety and flood capacity without impacting on water supply, irrigation and recreational usage.
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Alan Collins and Michelle Archer
The Waikato River is the longest river in New Zealand. Mighty River Power operates nine dams on the river with a combined net head of 335 m. The reservoirs have limited storage capacity so that the Waikato Hydro System is effectively a continuous run of the river scheme, providing constant generation for the New Zealand electricity grid. The river is also the habitat of the New Zealand Longfin and Shortfin Eel. Before the dams were constructed, eels naturally migrated as small elvers and lived as far upstream as the Arapuni gorge, where a waterfall prevented them from travelling further upstream. The commissioning of the Karapiro dam in 1947 reduced the natural habitat of the eels. In recent years, the eel population has been declining through a variety of anthropogenic factors and protective status is being called for. An elver catch and release program commenced at Karapiro Dam in 1992. This transferred elvers as far upstream as Lake Ohakuri and significantly increased the available habitat for the elvers to grow into adult eels. Spawning adults migrate downstream and back out to sea and as a result most of these eels are killed by turbines at the hydro stations. While consent conditions don’t stipulate it, Mighty River Power is committed to being an environmentally responsible custodian of the Waikato River and is dedicated in efforts to preserve the eel fishery. Mighty River Power recognises the importance of eel to local iwi; particularly highlighted by the emphasis on eel in the Waikato River Independent Scoping Study. The Karapiro eel bypass project, started in 2010, sought to investigate and research means to assist downstream eel migration. Research was gathered into eel searching patterns, timing of eel migration, durability in high velocities and other survival factors. This information was used to design, construct, and test a prototype downstream eel bypass at the Karapiro dam, something that had not been built on a dam this size before. In the 2013 migration season, three eels safely used the bypass. Plans are in place to improve the performance of the bypass in the coming seasons. Mighty River Power wishes to share the lessons learnt from this project with other dam operators for the conservation of this important species.
Joseph Camuso, Bruce Howse, Vaughan Martin and Don Tate
The proposed Kotuku Flood Detention Dam has been designed to reduce flooding within Whangarei City. This paper describes the potential benefits and the impact of the project on the community and the environment. It also covers the engineering challenges encountered during the design phase of the project. In particular, the dam site is located within a complex geological area, including a basalt lava flow on the left abutment, and site constraints required a twin emergency spillway design. If the risks associated with the dam are managed effectively, the proposed dam will provide a valuable asset to the community.
Peter Buchanan, Damian Nott, Martin Weir and John Dymke
The Bulk Water Alliance (BWA) consisting of ACTEW and ACTEW-AGL, GHD, and John
Holland/Abigroup, was formed to deliver the Enlarged Cotter Dam project in Canberra,
ACT. This project consisted of the construction of an 87 m high RCC dam and two
saddle dams, 15 m and 20 m high, to provide additional capacity to the ACT‘s water
supply system. The project is scheduled to be completed in September 2013.
During construction, the dam site was subject to three significant flood events which
affected the construction program. The March 2012 flood, the largest of the three, also
indirectly caused the formation of longitudinal cracks at the top surface of the RCC, when
the dam had reached about 45 m in height.
This paper first looks at the consequence of the flooding on both the design and
construction of the dam; in particular the modification of the diversion strategy and the
impacts on the final dam arrangement. The risk mitigation strategies put in place,
including the construction of a significantly larger diversion conduit through the partially
completed dam, are also discussed. The paper then focusses on the formation of
longitudinal cracks in the dam; the cause of cracking, analysis of the likely extent of
cracking, and the treatment of the cracks to minimise the risk of any significant long-term
impacts on the safety of the dam.
Finally the paper will discuss lessons learned from constructing the Enlarged Cotter Dam
during a period of above average rainfall.
As the Panama Canal is upgraded to accommodate larger vessels, hydrological and ecological elements of the project are being closely monitored, along with the effects of the increased usage that is projected to accompany the upgrade when it opens to traffic in 2015. Each of the 14,000 ships that annually pass through the Panama Canal requires 200 ML of fresh water – drawn from Gatun Lake and other Chagres River reservoirs – to navigate through the locks. The reliability of a sustainable water supply is thus vital to the canal’s operation and, by extension, to the world’s economy.
Hydrologic, hydraulic, and sedimentation studies are providing baseline data for comparison with projected operational scenarios. Several projects are currently being undertaken to restore and protect the widely recognised and highly valued biodiversity within Gatun Lake’s catchment area. Efforts to promote biodiversity conservation during the construction and operation of the expansion project are being coordinated with the concurrent efforts of a variety of academic, scientific, and private institutions, including the Smithsonian Tropical Research Institute, which is located on the largest island in Gatun Lake.
This paper examines the implications of growth and expansion on Gatun Dam and Lake. Current studies are assessing the impacts of deforestation on sedimentation and temporal flow distribution into Gatun Lake. Methodologies and results are presented for the USAID-funded Panama Canal Watershed Biodiversity Conservation Project, an undertaking that engages public and private sector partners in an effort to improve the management and conservation of critical areas through the implementation of sustainable practices and engagement of local stakeholders.
Lyndon Johnson, Alan White and Chris Topham
The integrity of foundation drainage systems is a key factor in minimising uplift pressures under concrete gravity dams. Contemporary industry practice for foundation drainage systems (and modern criteria presented in the imminent release of the concrete gravity dam guidelines) will lead owners with older concrete dams to consider enlarging foundation drainage systems via borehole drilling in the foundation. This paper presents the cautionary tale of a dam owner that undertook foundation drilling works in the gallery of a 67-m high concrete gravity arch dam and experienced borehole “blowout” in one of the drilled holes. Water under 90% of full reservoir head issued from the borehole and needed to be controlled. The context of the works is presented, followed by a description of the blowout, the risk mitigation measures that were planned prior to the work, and which ultimately had to be initiated. Management of the incident is discussed, including the use of blowout protection collars and valves, subsequent investigatory drilling, and pressure grouting programme. Dam safety concerns associated with the incident and their management are presented. The paper concludes with some recommendations to manage these risks for other owners considering a drilling programme in a concrete dam foundation.