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West Chester, PA, United States

McCann M.W.,Stanford University | Paxson G.,Schnabel Engineering
Association of State Dam Safety Officials, Dam Safety 2015 | Year: 2015

In water resources planning studies and dam safety risk analyses it is common to use best estimates of the probability of floods, best estimates of peak flood levels and best estimates of damage to estimate the "expected" value of economic consequences or fatalities from flood events or the uncontrolled release of a reservoir resulting from a dam breach. Typical practice does not consider the uncertainties (aleatory and epistemic) in various elements of the risk analysis, In risk analysis for dams, the failure to address uncertainties in the elements of the risk analysis can have important implications to; 1) understanding the distribution of consequences that can result from a dam breach, 2) level of confidence in the risk results, 3) potential area of inundation, the residences, infrastructure, and the population-at-risk, and 4) deriving a Bayesian estimate of the expected-value of losses from a dam breach. This paper looks at two aspects of risk analysis studies for dams; alternative approaches for calculating risk and the effect of uncertainties in the dam breach and inundation analysis and in the flood damage relationships on the estimate of flood damages. In the example presented, a seismic risk analysis for an earth embankment is presented in which the economic consequences of uncontrolled release of the reservoir is evaluated. The aleatory and epistemic uncertainties in the frequency of dam failure, the dam breach and inundation analysis and in the flood damage assessment are explicitly propagated through the estimates of the frequency distribution on economic consequences. © Copyright 2015 Association of State Dam Safety Officials, Inc. All Rights Reserved.

Hepler T.E.,Schnabel Engineering
Dam Protections against Overtopping and Accidental Leakage - Proceedings of the 1st International Seminar on Dam Protections Against Overtopping and Accidental Leakage | Year: 2015

This paper provides an overview of Technical Manual: Overtopping Protection for Dams, which was recently released by the Federal Emergency Management Agency (FEMA) of the United States, to be included in the Proceedings of International Seminar on Dam Protection against Overtopping and Accidental Leakage. U.S. customary units have been converted to S.I. metric units for purposes of this international seminar. © 2015 Taylor & Francis Group, London.

Cadden A.,Schnabel Engineering
Geotechnical Special Publication | Year: 2012

A Discussion Board was started on the professional networking site Linkedin. Its goal was to review the state of practice of Limited Mobility Grouting in karstic environments for foundation support. The discussion focused mostly on hole layout and grout depth relative to foundation stress or size, grouting procedures and refusal criteria, verification, quality control and quality assurance procedures. This paper summarizes the interesting ideas generated within the Discussion Board, and reviews recent publications on the subject. It also contains the author's experiences in the use of LMG for foundation applications in karst. © 2012 American Society of Civil Engineers.

Fitzgerald T.J.,Schnabel Engineering
Association of State Dam Safety Officials Annual Conference 2014, Dam Safety 2014 | Year: 2014

The use of Roller-Compacted Concrete (RCC) placed on the downstream slope of embankment dams to provide erosion resistance during overtopping was started 30 years ago. Since that time, about 120 such projects have been completed in the United States to increase spillway capacity for infrequent overtopping flows. Because most of these improvements were designed to accommodate rare flooding events, little information is available on the performance of such spillways when overtopped. However, recent extreme rainfall events caused several RCC spillways to be activated. Also, there have been some spillways designed for fairly routine storm events that have been subjected to full scale testing. This paper will focus on the lessons learned and/or re-learned in the past ten years regarding the performance of RCC overtopping protection and spillways when subjected to flows from extreme flooding events, including flows carrying large amounts of gravel and rock. In addition, the paper will evaluate the performance of several RCC mixtures due to weathering effects-mainly freeze-thaw (F/T) cycles in variable climates around the country. Some of the new topics covered include: • The performance of two dams with RCC overtopping protection that were subjected to the 2013 flooding in Colorado. • The performance of an RCC faced inlet structure in Las Vegas that was subjected to an extreme rainfall event on August 25, 2013. The six hour storm event was nearly twice the annual average rainfall in Las Vegas and the resulting flows included large amounts of erosive debris. • The effect of aggregate gradation on the compressive strength of the RCC and the associated durability of the exposed RCC. • Various covers for RCC to limit F/T damage and a discussion on the use of air-entrained RCC. Based on these and other case studies, Conclusions and Recommendations are presented to improve the state of the practice for RCC overtopping protection and spillway design.

Paxson G.,Schnabel Engineering | Laugier F.,Electricite de France
Association of State Dam Safety Officials Annual Conference 2014, Dam Safety 2014 | Year: 2014

In the United States, the labyrinth spillway, a "folded" weir, has become a relatively common approach to upgrade dams with inadequate spillway capacity. The Piano Key Weir (PKW) is a variation of the labyrinth concept. The PKW has a smaller upstream to downstream footprint than a labyrinth weir, due to a cantilevered apex geometry, making the weir a more practical alternative for applications where the footprint is limited (e.g. the crest of gravity dams). Each of these passive spillways provides significant discharge capacity within a given spillway width, often comparable to that of gated spillways. It is interesting to note that while the labyrinth concept has become relatively commonplace for dam construction and rehabilitation in the United States, the PKW has not yet gained popularity. By contrast, the PKW is being widely used in France, while there are few labyrinth spillways. The vast majority of the labyrinth spillways have been constructed for earth embankment dams while PKW spillways are more common for concrete gravity dams. This paper includes a discussion of the similarities and the differences between these unique spillways and draws upon the authors' experience with numerous labyrinth spillways in the United States and several PKW projects in France. This discussion includes key geometric parameters, hydraulic modeling and performance, additional beneficial research and lessons learned in design and construction.

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