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.
Australasian and global need and demand for water resilience often changes reservoir use from single purpose to multipurpose. These changes are affecting existing dam and reservoir structures and operations, as well as those planned or under construction. The International Commission on Large Dams (ICOLD) recognised this issue and established a working group to investigate and prepare Bulletin 171 titled Multipurpose Water Storage “Essential Elements and Emerging Trends”, which is now and available on the ICOLD website.
The Bulletin’s scope was to provide a global view on the dynamics of multipurpose water schemes (MPWS) by presenting essential elements and emerging trends for planning and managing reservoir and dam infrastructure, with source data collected from 52 global case studies including five from New Zealand and two from Australia.
Water storage design and implementation has evolved significantly in recent decades, and further
development is expected as innovative approaches emerge in search of optimal sustainable solutions. The focus of Bulletin 171 is therefore not on what should be done, but rather what is being done, how, and by whom. Essential elements represent a recommended checklist for implementing MPWS storage, while emerging trends is a snapshot of the current state-of-the-art for MPWS projects.
This paper presents a summary of Bulletin 171 and its findings, and a brief overview of the new and
complementary ICOLD Committee ‘T’ which is assessing emerging challenges and needs for dams in the 21st century.
Fault displacement can occur due to primary faulting on a main fault intersecting a dam foundation or rim, as well as by secondary faulting. This secondary faulting may be triggered locally by the occurrence of primary faulting on a main fault; its occurrence is conditional on the occurrence of an earthquake on the main fault. A probabilistic approach is most viable for fault displacement hazard analysis. Unlike the case of probabilistic ground motion hazard, which is nonzero even for short return periods due to the occurrence of a broad range of earthquake magnitudes in a wide region around the site, probabilistic fault displacement hazard is zero for return periods less than the recurrence interval of surface faulting earthquakes on the fault. In Australia, these recurrence intervals typically lie in the range of 10,000 to 100,000 years.
Consequently, the fault displacement hazard due to primary faulting may be zero or negligible for return periods shorter than 10,000 or 100,000 years. For longer return periods, the hazard is best evaluated using a risk-based approach, as recommended by ANCOLD (2018); the alternative of using a deterministic approach, which disregards return period, could potentially yield a large fault displacement. The probability of triggered secondary faulting, conditional on the occurrence of a large earthquake on the main fault, is typically one or two orders of magnitude lower than that on the main fault, and so is even more likely to be zero or negligible for return periods shorter than 10,000 to 100,000 years
Estimating the likely extent, depth and velocity of flooding should a dam fail – and planning to both prevent and respond to such a failure – are important parts of managing risk from dams and ensuring community resilience. This paper compares and contrasts current standards and practices for dambreak analyses and flood routing in New Zealand, Australia, the US, and the UK. Comparisons highlight consistent and evolving practices and consider how dambreak modelling supports robust dam safety decision making. In addition, the paper offers opinions regarding selected areas for future research, and insights into the benefits and limitations of increasing complexity in breach modelling.
Design floods for most dams and levees typically have an annual exceedance probability (AEP) of 1:100 (1E-2) or less frequent. In the U.S., high hazard dams are designed to pass the Probable Maximum Flood (PMF), which typically has an AEP of 1:10,000 (1E-4) or less frequent. In order to reduce epistemic uncertainties in the estimated AEP for extreme floods, such as the PMF, it is important to incorporate as much hydrologic information into the frequency analysis as reasonably possible. This paper presents a Bayesian analysis framework, originally profiled by Viglione et al. (2013), for combining at-site flood data with temporal information on historic and paleofloods, spatial information on precipitation-frequency, and causal information on the flood processes. This framework is used to evaluate the flood hazard for Lookout Point Dam, which is a high priority dam located in the Willamette River Basin, upstream of Portland, Oregon. Flood frequency results are compared with those from the Expected Moments Algorithm (EMA). Both analysis methods produce similar results for typical censored data, such as historical floods; however, unlike the Bayesian analysis framework, EMA is not capable of incorporating the causal rainfall-runoff information in a formal, probabilistic manner. Consequently, the Bayesian method considered herein provides higher confidence in the fitted flood frequency curves and resulting reservoir stage-frequency curves to be used in dam and levee safety risk assessments.
Estimation of the potential economic consequences of dam failure is becoming an issue of increasing importance in the Australian dams industry. As a result of the ongoing investment in dam safety upgrades, societal risk profiles for many dams are generally reducing. Additionally, there is evidence of the potential magnitude of economic and financial costs from recent overseas dam incidents. Whilst there is a well established framework for estimation of economic consequences, based on concepts of direct/indirect and tangible/intangible damages, there is a dearth of recent literature on the application of modern unit cost rates for various asset classes. This is particularly important in cases where direct, tangible damages are an important component of economic consequences.
Currently, unit cost rates used to estimate direct tangible economic consequences in Australia are typically taken from older sources such as the floodplain Rapid Assessment Method (RAM). The appropriate cost rates are then factored by CPI to represent ‘current day’ estimates of these costs. However, since the time when the RAM was first developed, there have been changes to the categorisations used to identify economic assets such as businesses in common databases such as the census. Additionally, there have been a number of large, recent flood events in Australia which provide very useful data to assist in deriving updated unit cost estimates.
This paper presents proposed unit rates for damaged and destroyed residential and commercial structures (including stage-damage curves) consistent with the Australian Bureau of Statistics categorisations used in the census data, agricultural land and assets such as roads. These rates have been derived based on a range of sources. The purpose of producing these unit rates is to promote ease-of-use and consistency, especially for large consequence assessment studies where numerous assets are impacted. A case study is presented showing the application of these unit cost rates and highlighting the variability in direct, tangible damages in different circumstances