The U.S. Army Corps of Engineers (USACE) has a robust Dam Safety Program (DSP) that utilizes risk- informed decision-making to prioritize its portfolio of dams in need of further study and modifications. USACE also utilizes a two-tiered governance structure in which one body makes portfolio recommendations around risk management while the other body oversees the execution of the agency’s routine DSP and makes policy recommendations. The routine program consists of the activities required for interim risk reduction measures, inspections, instrumentation, monitoring, assessments, operations and maintenance, emergency action planning, training, and other dam safety activities. An internal program management tool exists to monitor and track all these activities and generate metrics around execution of the routine DSP, however, it does not include metrics around other aspects of the DSP like governance, asset management, public safety and security, flow controls, or audits/reviews. USACE hopes to identify gaps in its DSP that can be used to correct shortcomings, continuously improve, and to increase the resilience of its DSP, which will enable each project to deliver benefits to the Nation. The Centre for Energy Advancement through Technological Innovation (CEATI), through its Dam Safety Interest Group (DSIG), collaboratively developed a spreadsheet tool known as the Dam Safety Maturity Matrix (DSMM). The DSMM is a facilitated exercise used to help evaluate how well-developed a program is across 12 elements considered to be typical and important of most dam safety programs. Each of the elements is then deaggregated into sub-elements, each of which can be evaluated by the team. The maturity ranges across 5 levels from Needing Improvement to Leading Edge. After all sub-elements are evaluated, an aggregate maturity level is computed that gives an estimation of the overall maturity level of the program. USACE will present the results of its pilot project using the DSMM and share lessons learned regarding its implementation. The short-term goal is to identify program strengths and areas for improvement, while the long-term goal of USACE using the DSMM is to participate in bench- marking across multiple agencies and international dam owners regarding their dam safety programs, for which has never been done to the knowledge of this author.
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.
Vertical gates and their operating plant are an essential part of dam safety at many dam sites. Apportioning appropriate levels of resilience during the design phase requires a thorough understanding of a gate system as a whole, not only of a single component in isolation.
This paper offers a designer’s perspective on modern engineering design features, materials and practices which can improve gate resilience during onerous operating conditions. This is of particular relevance to gates that are seldom used. Design aspects relating to the capability and limitations of the gate, hoist type, power supply arrangement and control system equipment to work together as a complete system are paramount design considerations in ensuring overall system resilience.
A discussion of the role and duty a hydraulic gate has in a dam safety context is presented. Supporting commentary is offered on appropriate levels of reliability, redundancy and diversity, including a comparison of different gate, bearing and hoist types. The authors draw on their own experience regarding gate design, fabrication and operation from completed and ongoing projects both locally and internationally.
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.
It is inevitable that, sooner or later, most dams will fill with sediment. It is simply a matter of time.
When the sediment reaches the power intakes of a hydro dam, there is a risk of the turbines being destroyed and the power station being abandoned. If this happens the spillway will need to operate continuously and this may lead to spillway failure possibly followed by failure of the dam.
Spillways are likely to fail because they are not designed for continuously discharging large amounts of sediment. The concrete and fixed parts will soon be damaged and need to be repaired. Repair is possible only if the spillway is segregated into two or more chutes so that one chute can be isolated and the flow passed down the other chute(s).
Reservoir sedimentation is a serious long-term problem that threatens the long-term viability of storage hydropower schemes. In 2010 global storage capacity was estimated at 6,000,000 km³ but it is projected that 4,000,000 km³ will be lost to sedimentation by 2050.1 Storage loss occurs worldwide at a rate of about 0.8 percent per year, but the sedimentation rate in many regions such as Asia is much higher.
Many reservoirs will fill with sediment within the next 100 years or so but some will fill up in a much
shorter timeframe. The sediment builds up at the head of the lake and a wall of sediment moves slowly down the lake until it reaches the dam and, eventually, the power intakes.
This paper is intended to draw attention to the problem and to emphasise the need to mitigate or solve the problem by providing a scour intake beneath the turbine intakes.
The major problem is designing the upstream gate to operate reliably when finally needed after, possibly, many years with little or no maintenance. A solution is suggested but it is recognised that better ones may be found: the objective of this paper is to encourage designers and developers to consider a wide range of solutions and to examine the potential of modern materials to help solve this very serious problem.
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