Kinchant Dam is a zoned earth and rockfill embankment situated on the north branch of Sandy Creek, approximately 30 km southwest of Mackay in central Queensland. Kinchant Dam was constructed in stages. The ‘Initial Development Stage’ which consisted of an embankment length of approximately 3.3 km and full supply level (FSL) of EL 49.21 m AHD was completed in 1977. Further development completed in 1986 (Stage I) increased the FSL to EL 57.21 m AHD with an embankment length of 5.5 km and a maximum embankment height of 22.3 m. The dam has a storage capacity of 62,800 Ml and a 60 m wide emergency spillway with a fixed crest level of EL 58.21 m AHD, one metre higher than the FSL.
A series of investigations have been carried out since its construction as a consequence of both regulatory safety reviews and observed excessive pore pressures within the foundation that have led to wet patches developing at the toe of the dam. In one area at the toe, pore pressures were such that artesian conditions developed. This paper outlines the history of various stages of construction of the dam, the foundation investigations since construction and the safety review and comprehensive risk assessment process that lead to the upgrade design and construction of remedial works. The remedial works include the extension of the downstream filter material adjacent to the clay core and the provision of additional pressure relief wells at the downstream toe of the dam.
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Nigel Connell, Karina Dahl, Steve Agnew and Brent Walton
The Waimakariri Irrigation scheme was initially built from 1997 to 2001 and irrigates approximately 18,000 hectares in North Canterbury with canals between the Waimakariri and Ashely Rivers. This was an enlargement from an existing stockwater scheme originally constructed in 1890. The owner and operator of the scheme, Waimakariri Irrigation Ltd, propose to construct a storage pond to supplement irrigation supply when take is restricted due to low flow in the Waimakariri River.
The footprint of the proposed pond is approximately 1 km x 1 km, with maximum dam height of 12 m and an 8.2 Mm3 maximum storage capacity. Accommodation for hydro-power development has been incorporated into the design of the irrigation storage ponds to provide multiple use of the reservoir contents.
The embankments are to be constructed from on-site granular material that forms the Canterbury Plains and lined with geomembrane. Careful consideration has been given in the seismic design for this High Potential Impact Classification (PIC) structure, which takes into account lessons from recent major earthquakes in the Canterbury Region. In addition, an understanding of the rapidly growing community downstream of the proposed dam has been crucial to ensuring that the potential risk of the dam is managed appropriately.
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.
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.
Bertrand Rochecouste Collet, Dawid van Wyk and Emmanuel Adanu
The preliminary design of the Kashimbila Multipurpose Dam on the Katsina-Ala River in the Taraba State, Nigeria was initially focussed solely on it functioning as a buffer dam in the case of failure of the natural embankment of Lake Nyos in Cameroon. The failure of Lake Nyos could generate an extreme flood endangering the population in south-eastern Nigeria. As the design process progressed with a more holistic and multipurpose approach, the capacity of the dam was increased to provide irrigation and potable water to the surrounding towns and villages, as well as the generation of hydropower. The dam is a composite structure consisting of a mass concrete gravity uncontrolled spillway, a clay-core rockfill embankment, a 40 MW hydropower station and an outlet works with twin 1.4 m diameter pipes feeding the irrigation pumpstation and water treatment works. This paper covers the design considerations of the Kashimbila Multipurpose Dam and Hydropower Station, with particular emphasis on hydrological challenges and related design solutions.
Upstream construction methodology has been used to raise tailings dams in Western Australia (WA) for more than three decades, and the tailings storage facilities (TSFs) built in this manner have performed satisfactorily so far. The maximum design earthquake (MDE) for most of the existing, upstream-raised TSFs in WA was that corresponding to a 1-in-1,000 year annual exceedance probability (1:1,000 AEP). However, the recommended MDE loading for the High/Extreme Failure Consequence Category in the 2012 ANCOLD Guidelines on Tailings Dams is that of a 1:10,000 AEP. This more stringent seismic design criterion may restrict the use of upstream TSF construction in some areas of WA and Australia in general.
To evaluate the viability of upstream construction for a new or existing TSF, the effects of the earthquake design ground motion (EDGM) on the liquefaction and deformation response of the structure must be understood. The results of such analyses are an essential component in determining whether upstream raising will be feasible, or whether more robust but much more costly centreline or downstream construction methods are required.
A parametric study was completed to investigate the liquefaction and deformation behaviour of a typical, upstream-raised tailings dam under different earthquake design ground motions with different response spectra. The study utilized two-dimensional finite difference code FLAC2D effective stress dynamic analysis, in which the UBCSAND constitutive soil model was incorporated. Twenty-eight earthquake ground motions (matched and unmatched to the target response spectrum) were used in the study and the liquefaction response of the tailings dam model under those ground motions was analysed.
The results of the study demonstrate the importance of appropriate ground motion and response spectrum selection in assessing the seismic performance of an upstream-raised TSF. Liquefaction response was shown to vary with different response spectra, even though the corresponding EDGMs had similar peak ground acceleration (PGA) values. The importance of earthquake frequency content and duration, which in turn are affected by earthquake magnitude, distance and ground motion response, is emphasized. Scaling and matching the earthquake input motion to the uniform hazard response spectrum (UHRS) may result in overly-conservative design. Thus, selection of the most representative EDGM is essential to evaluating expected seismic performance for an upstream-raised TSF, and scaling or matching the earthquake input motions must be done cautiously.