Earthquake design of a dam and associated appurtenant structures is a key aspect of dam design in the modern era. This paper outlines the design process undertaken to address potential earthquake loading for the 32m high outlet tower to be constructed as part of the new Eurobodalla Southern Storage project on the NSW South Coast. The driver for the project is to provide increased water supply security to communities on the South Coast, an area that is currently serviced by a single reservoir and is subject to frequent water restrictions. Construction is planned to commence for the project in early 2021.
This paper presents the design methodology undertaken to meet the requirements for earthquake design and presents a novel defensive design solution to improve the reliability of the outlet works for post-earthquake operation. The Authors contend that utilising this approach in design of future outlet towers will provide a greater level of confidence in the ability to undertake intervening measures following a severe earthquake. Moreover, the technology has the potential to serve as a relatively inexpensive interim upgrade measure for existing outlet towers expected to sustain an unacceptable degree of damage under earthquake loading.
Auckland Council (Council) is developing a dam safety management system with an overall objective to protect people, property, infrastructure, and the environment, from the harmful effects of a dam failure.
Council has responsibilities as an owner and operator of approximately 600 stormwater ponds and wetlands, many associated with dams. Council also has wider responsibilities for safety in the Auckland region, which may be affected by dams owned by others and even by inadvertent dams, such as road or rail embankments across streams that have the unintended but potential function of diverting, storing or holding back water. Three categories of dams have been distinguished, associated with Council’s different types of responsibility. Each category of dam is managed differently in the dam safety management system.
Given the large number of structures, which are not always obviously dams, a key activity has been the initial identification of dams across the Auckland region. Prioritisation has also been a necessary tool to direct resources and programme. Once dams have been identified, the consequences and risk of dam failure have been assessed, and commensurate measures have been established to manage those risks. There is limited guidance for some of these activities, and new procedures and tools have been developed.
This paper describes the process and the challenges encountered, for consideration by other councils when developing their own systems, and for consideration by the wider dams’ community.
The purpose of this paper is to document a limited review of the existing concrete chute spillways in the United States Army Corps of Engineers (USACE) portfolio of dams. This internal review was undertaken in response to the partial spillway failure of the Oroville Dam concrete chute spillway in February 2017, the partial spillway failure of the Guajataca Dam concrete chute spillway as a result of Hurricane Maria in September 2017, and to address the request by the United States Congress for USACE, United States Bureau of Reclamation (USBR), and the Federal Energy and Regulatory Commission (FERC) to review their respective portfolios for similar spillway vulnerabilities as Oroville Dam. The intent was to screen for existing concrete chute spillways within the USACE portfolio that may be susceptible to damage/failure during operation.
Computational Fluid Dynamics (CFD) is the science of predicting momentum, mass and heat transport, and can aid in design and safety issues for dam resilience in modern settings. Applications of CFD have historically been in the aerospace, automotive and chemical process industries with limited application in the hydraulic engineering field; possibly due to the associated computational intensity that is typically required. However, over the past two decades the cost of computing power has decreased substantially while the processing speed has increased exponentially. These developments have now made the application of CFD in the commercial environment feasible. CFD is particularly valuable in complex flow situations where the outputs required cannot be provided by a traditional hydraulic assessment approach and where there are stakeholder drivers such as service life, insurance cover and safety implications of infrastructure. The need for CFD when these drivers and complex flow situations arise, are demonstrated by means of a case study.
In the case study, CFD was used to investigate the flow patterns and the predicted performance of the outlet pipework from Massingir Dam in Mozambique. Three flow scenarios with appropriate pressure and flow boundary conditions were analysed for the outlet pipework, which included bifurcations for power generation from the main discharge conduits. Specific concerns addressed were, firstly, the possible excessive negative pressure in the region of the offtake for power generation and the potential for cavitation effects and, secondly, unacceptable velocity gradients in the power offtake pipework. Results showed that although some negative pressures were possible in one flow scenario, mitigation measures based on the CFD outputs could be considered and designed before construction.
The implementation of CFD in the above case study displays how risk in design can be reduced to ensure safety issues are addressed effectively.
There are currently around four new flood detention reservoirs (retarding basins) built each year in UK, which although only being modest structures with median height of 4m and reservoir capacity of 300,000m3 pose a significant risk to the community as they are located immediately upstream of the community they are protecting. These communities range from around five to several thousand households.
The cost and therefore viability of these structures can vary depending on the number of defensive features built into the design, which raises interesting conflicting issues of public safety contrasted to vulnerability to property inundation in operational (say, 1 in 100 chance) floods.
The authors have designed and supervised over 30 flood detention reservoirs in the UK in the last 20 years. This paper describes the engineering decisions which need to be made regarding defensive measures and the resilience of these structures to withstand flood loading on demand. Examples of measures to include resilience are described, with discussion of when selection of the options to increase resilience against a particular failure mode should be mandatory, and when it may be more appropriate to consider it on a case by case risk-based approach. The paper will also discuss more strategic issues of how to balance making flood detention reservoirs affordable, while at the same time maintaining high standards of public safety and compares Australian and UK approaches.
This paper discusses the current regulatory requirements and guidelines, which address to varying degrees the need for recovery controls and the engagement of Owners with Impacted Communities (ICs) within a Dam Safety Emergency Response Plan. The planning and application of appropriate recovery controls, which are applicable from the moment of failure, help to build resilience and reduce the ultimate consequence of TSF failure. The application of such controls, developed with close engagement with impacted communities has a strong precedent, being recommended as a result of the International Council on Mining and Metals (ICMM) review of good practice for emergency preparedness (Emery, 2005).
This paper presents a simple method to assess various recovery controls, with risk minimisation as its basis, and the use of existing risk assessment techniques such as bow-tie diagrams or the inclusion of recovery controls to other qualitative assessment methods. This will be illustrated through application to some relevant historical TSF failures.