Krey Price, David Moore, John Palensky
Cold water pollution (CWP) occurs when dam releases draw from lower-temperature regions of a reservoir, potentially impacting fish survivability in downstream waterways. Declining fish populations along the Missouri River have prompted recent investigations into solutions for CWP prevention.
Fort Peck Dam is an 80-metre high, 7-kilometre long dam located along the Missouri River; completed in 1940, it is one of the world’s oldest and largest hydraulically filled earthen dams and is listed on the U.S. National Historic Register. Inflow temperatures to Fort Peck Reservoir are significantly warmer than the outflow temperatures through the dam during the months of March through August. A water temperature of 18°C has been identified as critical for spawning and recruitment of locally threatened fish species; however, downstream temperatures typically remain below 14°C during critical time periods. This difference is due to the current deep-water withdrawal from Fort Peck Reservoir.
Ten alternatives were proposed to increase the temperature of the discharge, and an options analysis narrowed the results to a single, preferred alternative that consisted of a flexible, submerged weir around the intake. This paper documents the design efforts undertaken for temperature control measures at Fort Peck Dam, including a description of the modelling methods, design criteria, and effectiveness of the submerged weir alternative.
The use of a submerged weir to increase discharge temperatures relies on the process of passing warmer water from the upper portion of the water column over the weir crest into the intake area, rather than drawing from the bottom of the reservoir. For reservoirs with fluctuating levels, such as those at Fort Peck Dam, a flexible curtain can be suspended a set distance from the water surface using a float system, with the bottom of the curtain anchored to the lake bottom with ballast and cables. The crest elevation is set relative to the thermocline; as the lake level fluctuates, the flexible curtain folds and unfolds in response.
The impacts of CWP are increasingly recognised as an environmental risk worldwide. This paper draws upon the results of similar, implemented projects around the world, including a comparison to cold water pollution prevention measures and costs that have been assessed by CSIRO for application to Australian reservoirs.
Keywords: Cold water pollution, reservoir stratification, thermocline, curtain, fish health
A.E. Bentley, P.I. Hill, S.M. Lang, M. Freund, A. Richardson
This paper describes the development of a detailed assessment approach using spatial data to estimate the consequences of dam failure across a portfolio of 18 dams in NSW. The assessment is made for potential loss of life; economic and financial losses and a qualitative assessment of environmental and social impacts. The approach is designed around the use and interrogation of spatial databases combined with outputs from hydraulic models. The assessment method is applicable to a wide range of dams in different valleys, each with different downstream characteristics. The paper provides discussion on the advantages of the approach and presents some insights into the effective application to a dam portfolio of significant size and scale.
Keywords: consequence assessment, spatial databases
David Hilyard, William Ziegler, Heather Middleton
New South Wales has a significant number of dams, including major water supply dams, located over or near mines. Mining near dams imposes dam safety risks including: mine subsidence, mine blast vibration, presence of mine personnel downstream, rapid changes in consequence during mining, and loss of stored waters. The NSW Dams Safety Committee(DSC) regulates mining near dams, using risk assessment to review applications to mine near dams. A structured approach allows rational, evidence-based decision making by stepping through a procedure involving: initial consultations, screening risk assessment, evaluation of technical arguments, risk assessment, and development of risk management strategies. The risk assessment for dam walls develops acceptance criteria, reviews 19 possible risks to dam walls, and site-specific hazards. For potential for loss of stored waters, four possible groups of flow paths from storage to underground mine are reviewed; flows are evaluated with Monte Carlo simulation in terms of tolerable loss. Risks are assessed from a dam engineering viewpoint, which may be more conservative than the perception of risk in the mining industry, considering both tolerable risks and operational time frames. Case studies include: a tailings dam 100 m upstream of an active open cut and underground portal was undermined by longwall mining, with about 1.5 m subsidence of parts of the embankment as each of four longwall panels was extracted; longwall mining beneath a major Sydney water reservoir, with no observed impact on the stored waters; and open cut mining immediately downstream of a mine water dam. Risk-based methodology has provided the DSC with increased confidence in reviewing applications to mine near dams.
Keywords: Mining, dams, risk assessment, New South Wales, Dam Safety Committee
M. Tooley, D. D’Angelo, B. Priggen, K. Sih, N. Vitharana, R. Mouveri
As the urban sprawl of residential and commercial businesses expand to meet rising population, consideration must be given to the frequency and intensity of storm events and changes in tidal levels, to mitigate the risk of flooding and damage associated with the failure of hydraulic structures.
This paper outlines the design method undertaken to ensure the ageing structure (founded on timber piles) meets modern dam safety criteria, extends the life of the 8 gates operating mechanisms and provides overall inherent reliability for the whole structure. The design method included updated hydrological assessment of the upstream catchment, geotechnical investigation, liquefaction review, consequence category and AFC assessment, hydraulic assessment and stability analysis.
These assessments are being undertaken to introduce inherent reliability in their operation in particular during king tide or storm water events, or a combination of the both, minimising leakage and breakdowns and ensuring the risks of flooding to low lying residential areas upstream of the structure and major airport are minimised. The Glenelg Gates structure is an integral part of a larger regulating system for the catchment.
The findings of the design upgrade would be useful to dam designers and owners faced with the upgrading of gated structures with flooding risks in residential areas.
Keywords: Gated Glenelg Gates structures, upgrade, dam design guidelines.
Graeme Mann, Michael Smith, Louise Thomas
Regular flooding around the coastal town of Busselton, south of Perth, led to the construction of large rural drains in the 1920s to divert two of the major rivers around the town. Hydrologic studies after major floods in 1997 and 1999 showed that the existing drains were providing much less than the desired 1 in 100 AEP flood protection, particularly as subdivisions were being developed along both sides of the Vasse River Diversion Drain (VDD).
Three compensating basins constructed in rural land south of Busselton provide a total storage capacity of 4.4 GL. The banks that form the three basins have a total length of 8.5 km, vary in height up to 6 m and are either zoned earthfill embankments, with a clay foundation cut-off through sandy soil horizons to a depth of 1 to 2 m below ground level or homogeneous earthfill embankments. The spillways are overflow sections on the embankments using concrete revetment mattresses. The outlet works are uncontrolled box culverts with a capacity of up to 14 m3/s. Peak outflows are typically about 30% of peak inflows to the basins.
The paper discusses the Busselton Flood Protection Project and associated diversion drains, including the design of long embankments for the compensating basins on very flat terrain that are required to survive their “first filling period” during each flood emergency.
Keywords: Earth embankments, flood mitigation, flood compensating basins, levee banks, diversion drains, Busselton, piping failures.
Tim Griggs and Richard Herweynen
The river diversion is an important aspect to be considered in the design of a dam. It generally consists of an upstream cofferdam, river diversion conduit and downstream cofferdam and allows the dam to be constructed in a dry section of river.
This paper reviews the diversion design adopted at three recent Australian roller compacted concrete (RCC) dams and comments on the effectiveness of the design in providing risk mitigation during the construction of each of these dams. The dams considered are Paradise Dam (2005), Meander Dam (2007) and Wyaralong Dam (2011).
Rather than selecting an arbitrary design flood for the diversion, a risk-based assessment was used that generally resulted in a relatively low design capacity. Even though there were cases where the diversion capacity was exceeded, it is considered that the risk based design process provided an economical diversion design for these recent Australian dams.
Keywords: Diversion, roller compacted concrete dam, RCC.