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Many dam structures in Australia were designed and built in the 1950s and 60s with limited hydrological information. As a result existing spillway structures are under-sized for today’s revised probable maximum floods (PMF). Potential problems such as the generation of excessive negative pressure over spillway crest under increased flood condition could be encountered. This may cause instability or cavitation damage to the spillway. The raised flow profile may also have adverse impacts on crest bridges and gate structures.

Historically, physical models have been constructed in hydraulic laboratories to study these behaviours, but they are expensive, time-consuming and there are many difficulties associated with scaling effects. Today, with the use of high-performance computers and more efficient computational fluid dynamics (CFD) codes, the behaviour of hydraulic structures can be investigated numerically in reasonable time and expense.

This paper describes the two- and three-dimensional CFD modelling of spillway behaviour under rising flood levels. The results have been validated against published data and good agreement was obtained. The technique has been applied to investigate several spillway structures in Australia.

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2003 Papers

2003 – NUMERICAL FLOW ANALYSIS FOR SPILLWAYS
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Many dam structures in Australia were designed and built in the 1950s and 60s with limited hydrological information. As a result existing spillway structures are under-sized for today’s revised probable maximum floods (PMF). Potential problems such as the generation of excessive negative pressure over spillway crest under increased flood condition could be encountered. This may cause instability or cavitation damage to the spillway. The raised flow profile may also have adverse impacts on crest bridges and gate structures.

Historically, physical models have been constructed in hydraulic laboratories to study these behaviours, but they are expensive, time-consuming and there are many difficulties associated with scaling effects. Today, with the use of high-performance computers and more efficient computational fluid dynamics (CFD) codes, the behaviour of hydraulic structures can be investigated numerically in reasonable time and expense.

This paper describes the two- and three-dimensional CFD modelling of spillway behaviour under rising flood levels. The results have been validated against published data and good agreement was obtained. The technique has been applied to investigate several spillway structures in Australia.
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$15.00

2003 Papers

2003 – Numerical Flow Analysis for Spillways
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David Ho, Karen Boyes, Shane Donohoo and Brian Cooper

Many dam structures in Australia were designed and built in the 1950s and 60s with limited hydrological information. As a result existing spillway structures are under-sized for today’s revised probable maximum floods (PMF). Potential problems such as the generation of excessive negative pressure over spillway crest under increased flood condition could be encountered. This may cause instability or cavitation damage to the spillway. The raised flow profile may also have adverse impacts on crest bridges and gate structures.

Historically, physical models have been constructed in hydraulic laboratories to study these behaviours, but they are expensive, time-consuming and there are many difficulties associated with scaling effects. Today, with the use of high-performance computers and more efficient computational fluid dynamics (CFD) codes, the behaviour of hydraulic structures can be investigated numerically in reasonable time and expense.

This paper describes the two- and three-dimensional CFD modelling of spillway behaviour under rising flood levels. The results have been validated against published data and good agreement was obtained. The technique has been applied to investigate several spillway structures in Australia.
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2005 Papers

2005 – Blowering Dam – Spillway Hydraulic Modelling
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David Ho, Karen Riddette, Michael Hogg, Jayanta Sinha and John Roberts

Blowering Dam was constructed in 1968 by the Snowy Mountains Hydro-Electric Authority, on behalf of the Water Conservation and Irrigation Commission. It is a large earth and rockfill embankment dam, approximately 112m high and 808m long, with a concrete chute spillway at the right abutment. The reservoir holds about 1,628GL of water that is mainly for irrigation and supplying an 80MW hydro-electric power station. The dam is owned and operated by State Water Corporation, NSW.

Revisions to the design flood estimate have highlighted the dam requiring an upgrade to cope with increased discharge rates. The NSW Department of Commerce has carried out feasibility studies of different upgrade options. The need to evaluate the hydraulic performance of the existing un-gated spillway was identified. Flow overtopping the chute walls can potentially erode the backfill behind the walls, and, the rockfill on the downstream toe of the embankment. Consequently, this may lead to significant damage of the spillway and may risk the safety of the dam.

Hydraulic analysis of the spillway using a 3-D computational fluid dynamics model was performed for
various flood levels to determine the discharge coefficients and the discharge rating curve. It was also required to identify whether the chute walls need raising to contain the increased discharges. These results were compared with those calculated by other “standard” methods. Such verification provided a level of confidence in the analysis results which were then used in the studies to assess available upgrade options.

In order to have further confidence in the analysis, the computed results were validated against physical test data and some limited information from an actual discharge. Further verification against established theory was conducted by modelling a supercritical flow through a contraction in an open-channel in order to see if the computation could predict the shock wave effect that was observed in physical models as well as full scale channels. A reasonably good correlation was obtained from all validating tests.

This paper presents some background of the proposed dam upgrade, potential upgrade options considered and details of the hydraulic modelling of the spillway. Some interesting flow behaviour caused by the shock wave will be highlighted.
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2005 Papers

2005 – BLOWERING DAM – SPILLWAY HYDRAULIC MODELLING
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Blowering Dam was constructed in 1968 by the Snowy Mountains Hydro-Electric Authority, on behalf of the Water Conservation and Irrigation Commission. It is a large earth and rockfill embankment dam, approximately 112m high and 808m long, with a concrete chute spillway at the right abutment. The reservoir holds about 1,628GL of water that is mainly for irrigation and supplying an 80MW hydro-electric power station. The dam is owned and operated by State Water Corporation, NSW.

Revisions to the design flood estimate have highlighted the dam requiring an upgrade to cope with increased discharge rates. The NSW Department of Commerce has carried out feasibility studies of different upgrade options. The need to evaluate the hydraulic performance of the existing un-gated spillway was identified. Flow overtopping the chute walls can potentially erode the backfill behind the walls, and, the rockfill on the downstream toe of the embankment. Consequently, this may lead to significant damage of the spillway and may risk the safety of the dam.

Hydraulic analysis of the spillway using a 3-D computational fluid dynamics model was performed for various flood levels to determine the discharge coefficients and the discharge rating curve. It was also required to identify whether the chute walls need raising to contain the increased discharges. These results were compared with those calculated by other “standard” methods. Such verification provided a level of onfidence in the analysis results which were then used in the studies to assess available upgrade options.
In order to have further confidence in the analysis, the computed results were validated against physical test data and some limited information from an actual discharge. Further verification against established theory was conducted by modelling a supercritical flow through a contraction in an open-channel in order to see if the computation could predict the shock wave effect that was observed in physical models as well as full scale channels. A reasonably good correlation was obtained from all validating tests.
This paper presents some background of the proposed dam upgrade, potential upgrade options considered and details of the hydraulic modelling of the spillway. Some interesting flow behaviour caused by the shock wave will be highlighted.
Learn more
$15.00

2006 Papers

2006 – Hydraulic Flow Simulation – Five Years On: Lessons Learned and Future Challenges
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Karen Riddette, David Ho & Julie Edwards

Over the last five years in Australia, the use of computational fluid dynamics for the investigation of water flows through hydraulic structures has been steadily rising. This modelling technique has been successfully applied to a range of dam upgrade projects, helping to assess spillway discharge capacity and structural integrity, and giving insight into flow behaviours including orifice flow, shock wave formation and chute overtopping (Ho et al, 2006). Innovative and cost effective upgrade solutions have been implemented from numerical model studies including baffle plates (Maher and Rodd, 2005) and locking arrangements to protect radial gates from extreme floods.

This paper will begin with a review of recent dam engineering applications, including outlet flow through a fish screen, the performance of a fishway against hydraulic and environmental criteria and pipe flow in a large pumping station. Some of the difficulties and limitations of the modelling technique will be examined together with current research being conducted to address these issues and further validate the numerical results against published data. Some interesting results to date will be reported on elliptical crest discharge, boundary geometry, and model/prototype correlation.

With increasing computing power and software enhancements, the potential applications for numerical simulation in dam engineering continue to grow. This paper will also examine the future outlook and highlight some recent advances such as the thermal simulation of cold water pollution, air entraining flows and combined free-surface and pipe flow in a morning glory spillway.
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2006 Papers

2006 – Hydraulic flow simulation – five years on: lessons learned and future challenges
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Karen Riddette, David Ho & Julie Edwards

Over the last five years in Australia, the use of computational fluid dynamics for the investigation of waterflows through hydraulic structures has been steadily rising. This modelling technique has been successfully applied to a range of dam upgrade projects, helping to assess spillway discharge capacity and structural integrity, and giving insight into flow behaviours including orifice flow, shock wave formation and chute overtopping (Ho et al, 2006). Innovative and cost effective upgrade solutions have been implemented from numerical model studies including baffle plates (Maher and Rodd, 2005) and locking arrangements to protect radial gates from extreme floods.
This paper will begin with a review of recent dam engineering applications, including outlet flow through a fish screen, the performance of a fishway against hydraulic and environmental criteria and pipe flow in a large pumping station. Some of the difficulties and limitations of the modelling technique will be examined together with current research being conducted to address these issues and further validate the numerical results against published data. Some interesting results to date will be reported on elliptical crest discharge, boundary geometry, and model/prototype correlation.
With increasing computing power and software enhancements, the potential applications for numerical simulation in dam engineering continue to grow. This paper will also examine the future outlook and highlight some recent advances such as the thermal simulation of cold water pollution, air entraining flows and combined free-surface and pipe flow in a morning glory spillway.
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$15.00

2007 Papers

2007 – Safety assessment of mining subsidence impact on Upper Cordeaux Number 2 Dam
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David Ho, Chee Wei Tan and Glen Dominish

Upper Cordeaux Number 2 Dam is founded on an igneous intrusion rock mass which overlays sedimentary rock layers above the Wongawilli Coal seam. The coal mining company, BHP Billiton Illawarra Coal, planned to extract coal close to the dam. Although the dam is classified as a low hazard dam, its importance, both as part of the Sydney Catchment Authority’s water supply system and for its significant heritage value, mean that the proposed mining should not have undesirable impact on the structure. This paper describes how the mining impact on the dam was assessed using a nonlinear 3D finite element model. The model considered the pre-existing cracks in the dam wall, uplift water pressure along the dam/foundation interface and the hydrostatic pressure at full supply level. Mining-induced movement such as valley opening, closure and upsidence were applied to the model. Stability and strength assessments were made against a set of acceptance criteria developed for mining impact. The development of different stabilising mechanisms was examined. From the numerical investigation, WorleyParsons was able to provide technical advice to the mining company, the dam owner and the NSW Dam Safety Committee to facilitate the mining application and to satisfy dam safety requirements.

Keywords: Mining subsidence, Arch/gravity dam, Nonlinear numerical analysis, Safety assessment
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2012 Papers

2012 – Investigation of stilling basin slab stability for Waipapa Dam Spillway, NZ
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Karen Riddette, Chee Wei Tan, Alan Collins, David Ho

Due to a number of historical stilling basin slab failures around the world, modern basin slab stability assessment approaches now require allowance for hydrodynamic pressure fluctuations. Extreme fluctuations in uplift pressures have been found to occur in hydraulic jumps and plunge pools resulting in high-pressure pulses being transmitted via joints and drainage openings to the underside of the slab. If, peak uplift forces beneath the slab coincide with minimum pressure fluctuations on the top of the slab, the resulting pressure differential can be sufficient to lift a slab. As a result, simple static design based on tailwater depth and mean floor pressures is now considered highly non-conservative.

Through a case study on the Waipapa Dam spillway stilling basin, this paper examines the use of CFD modelling to compute mean hydrodynamic slab pressures taking into account the location of the hydraulic jump and the effect of the impact blocks on the pressure distribution over the slab. By combining the CFD results with empirically-derived pressure fluctuations, uplift scenarios are applied in a FEA model to compute the maximum load in the slab anchors and examine the sensitivity of the stilling basin slabs to uplift failure.
Keywords: Stilling basin, hydrodynamic modelling, CFD, pressure fluctuation, slab stability.

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2008 Papers

2008 – Modelling extreme flows over a stepped spillway
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Karen Riddette, David Ho, Mike Phillips

Abstract: Stepped spillways have seen a resurgence in popularity in recent years as new research has better described flow conditions and quantified the energy dissipation capacity of this type of spillway.

While carrying out hydraulic modelling for the Hinze Dam Stage 3 upgrade project using Computational Fluid Dynamics (CFD) analysis, extensive numerical testing and validation of the CFD model for the proposed 0.8H:1V stepped spillway design was undertaken. It was found that for the expected Probable Maximum Flood (PMF) discharge, the high flow depth would result in a non-aerated, non-uniform flow, typically seen in the developing flow region just beyond the spillway crest, occurring over the entire length of the stepped spillway. To date, only limited laboratory studies have been published concerning energy losses in this particular flow regime.

This paper examines the ability of CFD modelling to compute energy dissipation and air entrainment effects in stepped spillways under extreme flow conditions. Where possible, the computed results were validated against limited published data. Some new data obtained by the CFD model is presented for energy loss in the developing flow region that has not been established before.

Keywords: stepped spillway, CFD, energy loss, developing flow.
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