P Maisano, M Taylor , M Barker and A Parsons
South Para Dam, completed in 1958, is located on the South Para River, 38 km north of Adelaide. The embankment is 45 m high and comprises compacted crushed phyllite with rockfill toes. The 13 m high rock fill toes are protected with three-stage filters but the remaining 32 m of embankment height has no downstream filter protection.
The South Australian Water Corporation (SA Water), the owner and operator of the dam, is considering modifications to the dam, to augment its flood mitigation role. The proposed works, while not affecting the full supply level, involve a modification to the spillway crest and raising of the embankment crest to accommodate increased flood levels. SA Water therefore commissioned a dam safety review to assess the need for any piping or overtopping protection that may be required. This was followed by concept designs to ensure that flood mitigation work is compatible with any required dam safety upgrade work.
The results of a detailed dam failure risk analysis using event trees showed that the Societal Risk for the existing dam needed to be reduced, and that the proposed spillway modifications increased the Societal Risk due to the increased risk of piping failure with higher flood levels.
The risk analysis showed that eliminating the overtopping modes of failure by raising the dam crest is not sufficient in itself to achieve the required reduction in risk. The provision of filter protection to reduce the risk of piping failure is required, but it was shown that it is not necessary to provide full height filters as the provision of filters only above full supply level would be sufficient to achieve the required reduction in risk.
The recommended upgrade works, in addition to the proposed spillway modification for flood mitigation purposes, consist of filter protection and a weighting fill above the top berm (4.4 m below FSL) to facilitate connection to a possible full height filter in the future, and a parapet wall to provide overtopping protection.The resulting cost saving compared with the installation of full height filters is in excess of $2 Million.
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Stuart Macnish, Natarsha Woods, Michael Dixon
What happens when the people that undertake early environmental investigation stay on as part of the delivery team throughout the design and construction phases of a major project such as the Wivenhoe Alliance?
Often, the early investigation for projects, particularly in the case of environmental impact assessments and approvals processes, is carried out independently of the construction team. In the case of the Wivenhoe Alliance, these issues were set out in the scope of the project itself and delivered by the same team during construction.
The benefits and outcomes have been impressive not only for the project, but for SEQWater and the local community into the future. Improved biodiversity values, increased water quality protection, safety improvements, and value for money are only some of the key benefits experienced.
Individuals within the team also benefit. Environmental professionals are able to implement their
knowledge ‘on-ground’ and progressively improve practices in an area of constant change due to
construction initiatives and timeframes.
This paper explores the specific areas in which the involvement of environmental professionals throughout early investigation and planning, design and construction have benefited the Wivenhoe Alliance and the outcomes that have resulted from this innovative approach.
Howard and Opper
Dam safety planning is a team game. There are many players involved and there is a need for information to be shared and actions to be properly coordinated. The State Emergency Service is the legislated combat agency for flooding in New South Wales and is responsible for planning for and conducting the warning and evacuation of communities at risk from floods, including floods affected by dams. The successful execution of these responsibilities is dependent upon the continuing development of a strong, cooperative relationship between the dam owners and managers, dam regulators and emergency managers and the effective incorporation of community expectations in dam safety planning.
This paper explores some of the ways that this relationship can help to meet well accepted community expectations in respect of risk to life and property and outlines progress made in dam safety planning to date. The emergency response aspect of dam failure planning is still a relatively immature field in Australia, and it follows that there are lessons to be learned as we proceed. In that context, the paper also describes some of the difficulties the State Emergency Service has encountered in its role as the response planning agency and suggests some guiding principles to enhance future interactions between the key stakeholders.
This paper presents a number of innovative hydrologic investigations undertaken for the recent
detailed design of upgrades for Ross River Dam in North Queensland. A key issue for estimating
extreme floods in the tropics is the estimation of flood events of long critical durations. The
implication is that there is an increased focus on estimating the correct volume (not only the peak
flow). This paper describes the regional analysis of flow volumes that was used to validate the
estimated flood volumes.
Another issue of considerable importance is the assumed relationship between inflows and initial
reservoir level. The analyses described in this paper showed that inflows are independent of reservoir levels for the more frequent events but for more extreme events they are correlated. This has important implication on how the initial reservoir level is incorporated in the hydrologic analysis. The final aspect covered by the paper is the derivation of seasonal flood frequency curves. This is particularly important given the highly seasonal nature of rainfalls in the tropics and the results are important for assessing risks during construction and scheduling the upgrade works.
Brett Jones, Brian Mayhew
In preparation for the Corporatisation of the former Snowy Mountains Hydro-electric Authority, an
enquiry was held into the health of the Snowy River below Jindabyne Dam. This enquiry has led to a
range of environmental release requirements being placed on the new entity Snowy Hydro, including
requirements for variable release patterns (daily base flows and periodic flushing flows) and water
Construction works are currently underway to modify the existing Jindabyne Dam structures so that
these releases can be provided. The works include a new intake channel and control structure, a new environmental release tunnel and modifications to the existing spillway, including a concrete lined chute and plunge pool. Provision is also being made for a future mini-hydro power station, which would generate using waters released to provide environmental flows.
This paper discusses the history and background of Jindabyne Dam including the Snowy River
inquiry, details of the environmental flow requirements; design to meet the required capabilities and
the current status of the project.
Joseph Thomas, Peter Thomson, John Grimston, Sally Marx
The Waimea Basin is located in the South Island of New Zealand. The area has an acute water shortage with recent studies showing the water resources to be over-allocated by 22% for a 1 in 10 year drought security. The current area irrigated is about 3,700 ha and there is additional productive land that could potentially be irrigated if more water were available. Water users have suffered severe restrictions on their water use over recent years through drought management measures imposed to meet critical environmental flow requirements and coastal salinity buffering. This has caused significant production cutbacks for irrigated crops resulting in regional economic loss, affected major urban water supplies resulting in water supply cut-backs affecting domestic and industrial users and also affecting the important environmental values of the Wairoa/Waimea Rivers and the coastal springs that are highly valued by the community and local iwi (Maori).
The principal objective of this project is to carry out a study into the feasibility of water storage in the upper parts of the catchment for enhancing water availability for both consumptive and environmental/community/ aesthetic benefits downstream. The outcome from this feasibility study will provide the community with the necessary information to make an informed decision on proceeding with potential storage options. The Waimea Water Augmentation Committee is overseeing this feasibility study. The study will be completed byJune 2007.
The Waimea Plains area is also quite unique as to the interest and values relating to the water resource as it has multi stakeholder interest. Being close to urban centres, the water resource not only caters for irrigation use but also public water supplies as well as recreational, community interest and cultural values.
This paper sets out the project’s aim, general methodology being followed, and summarises the progress to June 2005.