Steven L. Barfuss and Blake P. Tullis
An important aspect of improving the safety of dams is selecting designs that are both hydraulically efficient and cost-effective. A powerful tool that can be used as part of the hydraulic structure design process is a physical model study. To obtain maximum benefit from the model, it should be implemented as a part of the design process rather than as a post-design verification phase. A model study included early in the conceptual design phase can also provide increased flexibility to the designers.
Hydraulic model studies can often provide cost-effective answers to difficult problems. Some of the issues that can be efficiently resolved using model studies include optimizing spillway head-discharge relationships to increase reservoir storage while minimizing upstream flooding potential, controlling downstream scour, quantifying hydraulic uplift forces and/or overturning moments of dam structures, evaluating alternatives for structure retrofit or repair, and optimizing control gate sequencing during floods. Model studies also allow the engineer to simulate prototype performance (e.g., three-dimensional flow patterns, velocities, pressures, scour potential) over the full range of expected discharges. Quick and easy changes to the model can be made at minimal cost when evaluating the performance, safety and economic impact of various design alternatives.This hands-on model study approach to dam safety represents a tool that in some cases is underutilized.
Brief discussions of several physical model studies conducted at the Utah Water Research Laboratory, Utah State University in Logan, Utah, USA, are presented to illustrate key points of the paper. The primary objective of each of these model studies was to provide and/or improve the safety of the dam and the spillway while minimizing construction costs. This paper discusses the cost-effectiveness and hydraulic improvements that can be achieved through physical model studies.
Keywords: Physical models studies, design, hydraulic efficiency, dam safety, construction costs
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Mike Phillips and Karen Riddette
The use of Computational Fluid Dynamics (CFD) models in the dams industry has increased significantly in recent years and conversely the use of physical hydraulic models has decreased. Typical design approaches for an upgrade of similar magnitude to the Hinze Dam Stage 3 project would have allowed for considerable time to develop a preliminary spillway design before hydraulic modelling was introduced, potentially requiring only one type of model. So is there a need for both types of models?
Because of the complex hydraulics associated with the spillway required for the Hinze Dam Stage 3 raise and accelerated schedule, the utilisation of CFD and 1:50 Froude Scale physical hydraulic models was necessary. Both models were constructed independent of each other. Both models complemented each others strengths and weaknesses, and each provided critical information at the following different stages of design:
• Spillway selection and conceptual design stage – the CFD model results were highly valuable in steering the selection of spillway type and configuration, particularly with visual representations of the ranges of flow for each spillway option.
• Preliminary design – in a one week period, 90 to 95% of the final spillway layout was resolved with interactive modifications of the physical hydraulic model.
• Detailed design – both the physical hydraulic model and the CFD model were utilised to determine water pressures, velocities and water surfaces and evaluate cavitation potential as input to detailed design.
In the case of the Hinze Dam Stage 3 project, it was highly advantageous to utilise a CFD and physical hydraulic model to achieve the design outcomes at each phase of the design. The dual-model study approach also provided advantages for project management of the design and stakeholder involvements.
Keywords: Computational fluid dynamics, CFD, physical hydraulic model, spillway, hydraulics
Dörte Jakob, Robert Smalley, Jeanette Meighen, Brian Taylor and Karin Xuereb
Probable Maximum Precipitation (PMP) is one of the required inputs for estimating the PMP design flood. In estimating the PMP, currently no allowance is made for long-term climatic trends. A 2-year project funded jointly by the Australian Greenhouse Office and the Queensland Department for Natural Resources and Water, and with in-kind contributions by the Bureau of Meteorology began in May 2006. This study aims to assess how climate change might affect estimates of PMP. Preliminary results from this work will be presented.
Changes in factors used in PMP estimation, such as storm type and depth-duration-area curves, were assessed using a storm database covering the period 1893 to 2001 (Beesley et al. 2004). Based on the last 50 years, there is little evidence to support the notion that tropical cyclones (connected to major rainfall events) are penetrating further south or have become more frequent. A recent event that led to widespread flooding (Gold Coast, June 2005) was found to have very high storm efficiency. Changes in observed and projected moisture availability were assessed on the basis of a high-quality dataset of surface dewpoint temperatures and climate model output.
It is assumed that PMP received by a catchment is not uniformly distributed over a catchment but rather follows a typical spatial pattern. A pilot study to revise design rainfall estimates is currently under way at the Bureau of Meteorology. The methods developed in the pilot study were used to assess whether the spatial distribution of design rainfall estimates might be changing under a changing climate.
Keywords: Probable Maximum Precipitation, climate change, moisture availability, storm efficiency
Russell Paton and David Murray
The South-East Queensland Regional Water Supply Strategy is securing future water supplies, which includes a regional water grid and new water storages. The Queensland Government’s contribution to future water supplies includes Traveston Crossing Dam on the Mary River, Wyaralong Dam on the Teviot Brook, and Bromelton Offstream Storage and Cedar Grove Weir on the Logan River.
Queensland Water Infrastructure (QWI) was established by the Queensland Government in June 2006 to progress feasibility studies, design and construction of this new water infrastructure. QWI commissioned SunWater to investigate much of this infrastructure to preliminary design level for the impact assessment process and as supporting information for potential alliance partners for the delivery of the projects. The work undertaken included extensive geotechnical investigations, hydraulic modelling, hydrologic modelling and design activities. This paper outlines the investigations associated with the preliminary design of this infrastructure and process of risk and opportunity identification to establish the program and budgets for these projects.
Stage 1 of Traveston Crossing Dam is to be constructed by the end of 2011, with a storage capacity of 153,000 ML providing a yield of 70,000 ML each year. The design adopted for the dam consists of a roller compacted concrete structure across the valley floor with an earth embankment section on the left abutment. In order to limit inundation upstream and mitigate flooding in Gympie, a gated spillway on the right abutment has been adopted. The Traveston Crossing Dam has an estimated project cost of $1,700 million.
The design developed for the Wyaralong damsite provides a reservoir with storage capacity of 103,000 ML and a yield of 21,000 ML each year when operated in conjunction with Cedar Grove Weir. Preliminary designs have been prepared for three types of dam, which are all considered technically feasible for the site. They are a roller compacted concrete dam, an earth and rockfill dam and a concrete faced rockfill dam. The Wyaralong Dam has an estimated project cost of $500 million.
The Bromelton Offstream Storage, of earthfill construction, provides a storage capacity of 8,000 ML and Cedar Grove Weir, a sheet pile structure, provides a storage capacity of 1,000 ML and both are to be constructed by the end of 2007.
Keywords: Planning, Traveston Crossing Dam, Wyaralong Dam, Bromelton Offstream Storage, Cedar Grove Weir, Queensland, risk.
Ken Ho, Robert Davey and Jim Walker
The Aviemore Dam appurtenant structures were upgraded for seismic performance in 2006. A comprehensive dam safety review programme conducted by Meridian Energy evaluated the performance of the dam and appurtenant works under extreme ground movements and rupture displacements of the Waitangi Fault, which passes through the embankment dam foundation. The spillway and sluice gates are key elements of the dam safety critical plant for the passage of floods to prevent overtopping or emergency dewatering of the reservoir after a major seismic event if there are concerns about damage to the dam. This paper outlines the assessment undertaken for the spillway and sluice gates for seismic performance and the upgrade necessary to safeguard their integrity for operation after the event.
The spillway and sluice gates are large steel radial gates operated by electrically powered wire rope winches and hydraulic actuation, respectively. Combined hydrostatic and the Safety Evaluation Earthquake (SEE) induced hydrodynamic loads would be expected to stress the gate structures beyond their yield capacity. The yield would be downstream only due to the influence of the hydrostatic load under the earthquake response cycle. The resulting deformations were predicted to fracture connecting bolts in the spillway gate arms and cause severe leakages past the top leaf of the sluice gates. The solutions developed for the spillway gates to reduce connection bolt damage and the strengthening of the sluice gates will ensure their post-earthquake operation.
Keywords: Aviemore Dam, spillway, sluice, radial gate, seismic performance, post-earthquake operation.
Appurtenant structures associated with a dam play and important part to the dam’s operation. For these structures it may be important that their functional and structural integrity is retained in the event of a notable earthquake, particularly when they are required to release water from the reservoir in a controlled manner to lower the storage following an earthquake. Research has been conducted into the current state of practice for the seismic design and analysis of these structures, including review of the main issues for seismic effects, documentation of case histories and review of current research, international guidelines and standards. The general assessment philosophy was found to be relatively consistent internationally, however, the adopted assessment procedures were found to vary. The status of the current ANCOLD earthquake guidelines has been provided in relation to the current international state of practice for various types of appurtenant structures.
Keywords: Appurtenant structures, performance criteria, seismic performance, seismic analysis.