2nd International Seminar on Dam Protection against Overtopping

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https://hdl.handle.net/10217/201102

The 2nd International Seminar on Dam Protection against Overtopping, or Protections 2016, was held on September 7-9, 2016 at Colorado State University in Fort Collins, Colorado. With 48 participants from North America and Europe, Protections 2016 covered a wide range of topics related to physical and numerical modeling of embankment dam overtopping performance, case studies of prototype performance under extreme flood events, and the development of innovative systems for overtopping protection. The identification of potential failure modes and the use of risk to inform overtopping protection decisions was also discussed. The technical program concluded with a discussion of the special characteristics of levees and tailings dams with respect to overtopping. This digital collection includes papers given at the seminar.

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Open Access
ACB armoring potential failure modes at dam embankments and spillways
(Colorado State University. Libraries, 2016-09) Schweiger, Paul, author; Shaffer, Darin, author; Nadeau, Jim, author; Colorado State University. Department of Engineering, publisher
Over the past 26 years numerous embankment dams and earth-cut spillways in the United States have been armored using Articulating Concrete Blocks (ACBs) to provide erosion protection. Several dams and spillways armored with ACBs have been overtopped and performed satisfactorily with overtopping flow depths and velocities approaching 4 feet and 30 feet per second, respectively. Over the same period, some ACB overtopping applications have failed and others have experienced damage requiring maintenance to make the ACB system functional again. Much has been learned about what works and what does not work. Of the ACB installations that have failed or experienced damage, the underlying issues have been attributed to one of several potential failure modes that may not have been understood or adequately addressed during the design. The purpose of this paper is to share information on several recent ACB embankment armoring and spillway armoring failures, and to describe the specific failure modes associated with these incidents. Suggestions for incorporating design features to address these potential failure modes are also provided. This information is important for engineers to consider during their designs, and for regulators reviewing ACB armoring designs, so that future failures and unnecessary damage resulting in costly maintenance can be prevented.
Open Access
Overtopping performance of earthen dams during record flooding in Columbia, South Carolina
(Colorado State University. Libraries, 2016-09) Crookston, B., author; Hepler, T. E., author; Colorado State University. Department of Engineering, publisher
South Carolina experienced what has been described as a 1,000-year flood on October 4 and 5, 2015. Widespread rainfall from Hurricane Joaquin pounded the state's capital city, Columbia, with over 20 inches of rain recorded in many locations. As a result, over 70 miles of Interstate 95 had to be closed, in addition to local roads and bridges, and thousands of residents had to flee their homes. State-wide, 36 dams failed – 31 state-regulated, 1 federally-regulated (on Fort Jackson), and 4 unregulated. The South Carolina Department of Health and Environmental Control (DHEC) issued emergency orders on 75 additional dams in the state, with the vast majority of them privately-owned earthen dams. Sadly, there were 19 flood-related deaths, including a first responder whose work truck was swept away by the flood. Millions of dollars in property damages were incurred. This paper summarizes the historic storm and associated flooding of October 2015 in South Carolina, including the 74.5 mi2 Gills Creek Watershed in Richland County where 16 inches of rain was recorded in just 6 hours. It documents the overtopping performance of a number of earthen dams, including the overtopping failure and planned restoration of Gibson Pond Dam, as well as the satisfactory performance of Forest Lake Dam that had fabric-formed concrete overtopping protection on its crest and downstream slope. It is anticipated that the information presented in this paper would be of benefit and interest to those involved in dam safety.
Open Access
Insights from laboratory experiments on the failure of earthen embankments at bridge-waterway abutments
(Colorado State University. Libraries, 2016-09) Ettema, R., author; Ng, K. W., author; Colorado State University. Department of Engineering, publisher
Failure of compacted, earthfill embankments during breaching combines geotechnical and hydraulic processes that interact to erode the compacted earthfill. Our paper offers insights regarding these processes as observed during a series of laboratory flume experiments conducted to investigate the effect of soil strength on scour depth at abutments formed of erodible, compacted earthen approach embankment. The length scale of the model abutments was 1:30. We highlight the challenges in conducting laboratory experiments involving erodible model abutments. The challenges, or difficulties, include attaining scale-reduced shear strengths, controlling and verifying the soil compaction, and quantifying the in-situ shear strength of both non-cohesive and cohesive model soils. We addressed these difficulties through a sequence of soil tests designed to relate model soil strength to laboratory compaction, using hand-held devices to check soil strengths in the flume experiments. Our paper explains the successes and unresolved issues relating to the shear strength of model soils used in flume studies of embankment breaching. Additionally, our paper illustrates the importance of large-scale turbulence structures formed at the breach entrance in shaping the breach, and discusses the geotechnical manner whereby breaches widen.
Open Access
A model for the analysis of the structural failure of the clay core in rockfill dams due to overtopping
(Colorado State University. Libraries, 2016-09) Ricoy, L. F., author; Toledo, M. Á., author; Morán, R., author; Colorado State University. Department of Engineering, publisher
In 2014 the Dam Safety Research Group (SERPA) of the Technical University of Madrid performed several tests to assess the behavior of rockfill dams in overtopping scenarios. A structural failure pattern of the clay core was observed, as expected. Hence, it was concluded that a model to simulate the observed failure mechanisms was needed. The model described herein provides the first results on assessment of the clay core stability following failure of the downstream shell. The failure process may result in one or more brittle and abrupt breakage phases of the core, herein classified as structural breakages, as opposed to the progressive failure caused by the erosion of the cohesive material. Thus, total or partial failure of the clay core occurs when the acting forces reach one of the instability conditions: overturning or sliding. The model was utilized to retroactively analyze two experiments carried out in the laboratory; the results obtained were consistent with the experimental measurements. The model is based on simple mechanical principles, but represents a paradigm shift in the interpretation and evaluation of the overtopping failure processes, especially since it results in a failure hydrograph different from those typically adopted, and therefore, has repercussions in the development of emergency plans.
Open Access
Root causes of tailings dam overtopping: the economics of risk & consequence
(Colorado State University. Libraries, 2016-09) Bowker, Lindsay Newland, author; Chambers, David M., author; Colorado State University. Department of Engineering, publisher
This paper examines overtopping failures of embankments at tailings impoundments from 1915-2015 and compares the severity of consequence for overtopping failures to that of other causes of failure. We find that the distribution by severity of consequence for overtopping at active mines is not significantly different from any of the other established "causes of failure." Further we find that the distribution by severity within and across all active TSF recorded failure causes (N=125) is also reflected in the mean distribution of severity for all of our recorded TSF failures (N=267) suggesting that a common root cause, rather than the individual causes of failure, may determine the severity of failure. We look here at the demonstrated link between severity of consequence of failure and the economic dynamics of the "Mining Metric" over 100 years (Bowker and Chambers 2015) as it applies to overtopping. We offer what is available from authoritative sources on the economics backstory of known overtopping failures and crises. We conclude that the deviations from best available technology and best applicable practices at the mine level are conscious choices driven by economics and that without a reframing of the professional, regulatory, and legal frameworks for mining these choices will continue to be made even where proven technology and new promising technology are available and better suited to a given mining asset. Solutions that will prevent mine failure require not only the work of evolving consensus on best available technology/best applicable practices, but also the recognition of root causes which build to catastrophic failure. A complete solution cannot be attained without accountability to best knowledge, best practice, best effective technology in mining law and regulation, as permit standards, as standards for oversight for life-of-mine and of life-of-tailings storage facilities.
Open Access
Field trial for air entrained grout enriched roller compacted concrete
(Colorado State University. Libraries, 2016-09) Musselman, E. S., author; Zimmer, G. J., author; Young, J. R., author; Colorado State University. Department of Engineering, publisher
Roller compacted concrete (RCC) is frequently used to armor earthen embankments for passing extreme floods and to construct gravity dams and stepped spillways. Early experience on RCC dam applications in the 1980s showed a tendency for seepage to develop along the lift lines. Therefore, RCC dam designers started including an upstream facing system as a watertight barrier. An alternative facing material that has been used extensively overseas and is starting to gain more widespread acceptance in the United States is Grout Enriched RCC (GERCC). The grout enriched method of face construction has been shown to be less expensive than other facing options, particularly on larger dam projects, and has also been used on exposed RCC embankment overtopping projects. However, in the United States, the use of GERCC technology has been fairly limited, primarily due to concern over the material's freeze-thaw resistance. The objective of this project is to develop a grout formulation and construction technique that allows the production of air entrained GERCC. The study includes four phases to systemically achieve this objective: (1) optimizing grout formulation, (2 and 3) evaluation of small scale laboratory samples of GERCC, and (4) conducting a field trial. This paper focuses on the final phase, a field trial conducted with ASI contractors at the Duck River Dam site located in Alabama. The results show that the adequate freeze thaw resistance can be attained by air entraining GERCC, but the results are very sensitive to the distribution of the grout through the RCC and adequate performance requires significant internal vibration.
Open Access
Proposed USACE EM 1110-2-1913 erosion analysis guidance
(Colorado State University. Libraries, 2016-09) Shewbridge, S. E., author; Colorado State University. Department of Engineering, publisher
The U.S. Army Corps of Engineers is updating EM 1110-2-1913, Design, Construction and Evaluation of Levees, including new guidance on how to conduct erosion analysis. This paper presents the two erosion models considered: erosion rate as a function of shear stress and an empirical relationship relating wave overtopping flow rate to erosion rate. The paper also suggests the current state-of-the-practice regarding factors to be considered when selecting erosion model parameters. Erosion design will be conducted in a risk-informed framework, using potential failure modes analysis and when possible, probabilistic limit state analyses to assess design reliability. Required design reliability will be selected based on levels necessary to achieve various life-safety, economic and other unspecified objectives, as appropriate for each flood risk mitigation system.
Open Access
Wedge-shaped blocks: a historical review
(Colorado State University. Libraries, 2016-09) Morán, R., author; Colorado State University. Department of Engineering, publisher
The article aims to be an introduction to the history of the wedge-shaped blocks technology. As it is well known, the WSBs protection system was born in the middle of 20th century in the former Soviet Union. Even though its basis of operation remains, relevant studies have been yielded in order to apply this kind of protection in real cases. Besides, direct application in several case studies has shed some light on practical difficulties and the need of new technical criteria to overcome them. Thus, applied research has been developed in countries such United Kingdom, USA, Portugal, and Spain, among others. The article consists of three parts. It commences with a brief summary of some relevant research and development studies. Afterwards, a description group of case studies of stepped block spillways is included. Finally, the article ends with a short compilation of the state of the art of the current design criteria.
Open Access
Advances in the understanding of the hydraulic behavior of wedge-shape block spillways
(Colorado State University. Libraries, 2016-09) Caballero, F. J., author; Toledo, M. Á., author; Morán, R., author; San Mauro, J., author; Salazar, F., author; Colorado State University. Department of Engineering, publisher
The technology of wedge shaped blocks (WSB) for spillways has had a rising development through the last forty years, and has proved its reliability for practical applications with spillways executed during the last decade. Ongoing additional research aims to complete the understanding of the hydraulic behavior, improve current design criteria and make this technology available to practitioners, in order to consider this type of spillway together with the conventional alternatives when designing an embankment dam spillway. A summary is here shown of recent research performed by the consortium formed by the research organizations: Research Group in Dam Safety (SERPA) of the Technical University of Madrid (UPM) and the International Center for Numerical Methods in Engineering (CIMNE) and the company PREHORQUISA. Even though the experimental campaign has not been completed, some preliminary conclusions can be addressed about the developed pressures along the block tread and the leakage flow from the joints among blocks and the drainage holes.
Open Access
Lessons learned from articulating concrete block (ACB) field installations
(Colorado State University. Libraries, 2016-09) Nadeau, J. A., author; Colorado State University. Department of Engineering, publisher
Articulating Concrete Blocks (ACBs) have been a popular choice for high performance erosion control applications and shoreline revetments for well over 35 years and continue to grow in popularity. Estimates point to over 200 dam embankments and emergency spillways having been armored with ACBs in the past 30 years. As a result of these applications, as well as the thousands of other projects not specific to dams, much has been learned from a theoretical as well as practical application standpoint of properly utilizing ACBs in the field. This presentation will provide information concerning ACB Factor of Safety (FOS) determination, briefly review the ACB testing protocols and data analysis, and discuss the practical uses and limitations of ACB applications. New installation techniques that show promise for improving ACB performance will be discussed. ACBs are a proven cost effective erosion countermeasure, however experience and attention to detail during the design and installation of systems is of paramount importance for expected performance.
Open Access
Overflow for the complete failure of the downstream shell of a rockfill dam
(Colorado State University. Libraries, 2016-09) Alves, R. M., author; Toledo, M. Á., author; Morán, R., author; Colorado State University. Department of Engineering, publisher
This paper presents the results of experimental research using physical models regarding the failure of the downstream shoulder of rockfill dams caused by overtopping. The aim of this investigation is to analyze how different parameters such as the rockfill permeability, the main geometric dimensions of the dam, or the impervious element type affect the flow that initiates failure and also the ultimate flow needed to break the downstream shell of the dam. The primary objective of this study is to develop predictive models for both discharge flows. For this purpose, tests with stepwise flow increments were performed by varying the rockfill size, the height and width of the dam, the downstream slope and the type of impervious element. The regression analysis was based on results from 61 experimental tests: 50 tests were used to calibrate the formulas and 11 were used for validation. The analysis shows that, for a given dam height, the failure and the initiation discharges depend essentially on the rockfill permeability and, to a lesser extent, on the slope of the downstream shell. The type of impervious element, central core, upstream face or the absence of this element, seems to have no significant effect.
Open Access
Soil-cement for high-velocity spillway flow applications
(Colorado State University. Libraries, 2016-09) Kadrmas, Korey J., author; Huzjak, Robert J., author; Colorado State University. Department of Engineering, publisher
Although soil-cement has been used on many dams for slope erosion protection for over 50 years, soil-cement has had limited use as an overtopping liner protection for spillways. The application of soil-cement for a spillway liner was researched and modeled to establish performance criteria to support design of an auxiliary spillway for a new large, high hazard dam in Colorado. Case studies were researched and hydraulic performance tests were conducted at the Hydraulics Laboratory at the Engineering Research Center of Colorado State University (CSU) to establish design criteria for soil-cement lined spillways subject to high-velocity flows. The purpose of this paper is to supplement the existing base of research regarding the suitability of soil-cement for hard protection channel lining applications subject to high-velocity flow. Information in this paper was developed from a special application testing program developed for an emergency spillway for a dam in Colorado. The paper will include the methods and procedures of batching and placing the soil-cement specimens, a summary of data collected, results, and conclusions for the soil-cement performance testing program.
Open Access
Performance of Type III stilling basins for stepped spillways
(Colorado State University. Libraries, 2016-09) Frizell, K. W., author; Svoboda, C., author; Matos, J., author; Colorado State University. Department of Engineering, publisher
Energy dissipation within hydraulic structures continues to be one of the major issues facing the designer of new or rehabilitated facilities, such as for overtopping protection of embankment dams. The energy dissipation characteristics of stepped spillways have been well documented, both for low- and high-head dams. Interestingly, much of the generalized research on stepped channels and spillways over the past few decades, while concerned with the amount of energy dissipated on the steps themselves, has contributed very little to generalized design criteria for terminal dissipation structures/stilling basins. Many site specific studies have included work on modifications to stilling basins to account for the increased energy dissipation on the steps, typically resulting in a shortening of the basin length. Others have included some stilling basin parameters within their studies. A few studies have attempted to provide generalized design guidance for the use of specific types of stilling basins with stepped chutes and spillways. This paper will focus on recent studies at the Reclamation laboratory that evaluated the application of smooth channel design criteria for Type III stilling basins to a variety of stepped spillway slopes. While there is a lack of specific generalized studies for stilling basin performance over the range of all types of stepped spillways that exist, there appears to be adequate data available to allow the designer to select and size an appropriate stilling basin for most types of stepped spillways currently in use, including RCC overtopping protection systems.
Open Access
Applications of numerical methods in design and evaluation of overtopping protection systems
(Colorado State University. Libraries, 2016-09) Salazar, F., author; San Mauro, J., author; Larese, A., author; Irazábal, J., author; Morán, R., author; Oñate, E., author; Toledo, M. Á., author; Colorado State University. Department of Engineering, publisher
The development of overtopping protection systems often requires detailed analyses of complex physical phenomena. This hinders the comprehensive knowledge of their behavior, and therefore the development of suitable design criteria. In recent years, the authors have developed and validated different methods, combining continuous, particle and discrete numerical techniques, to obtain accurate and reliable solutions of different numerical problems involving fluid-soil-structure interaction. In this contribution, some applications of these methods to the study of dam protection against overtopping are presented. The main advantages of this approach include the ability to extract results of the governing variables (pressure, velocity) at any location of the domain, and the possibility to consider scenarios without the restrictions of the experimental facilities (flow rates, size, scale effects). In particular, the contribution gathers examples of application of numerical methods in a) analysis of rockfill dam stability against overtopping, including seepage evolution and deformation of the downstream shoulder, and b) stability analysis of wedge-shaped-blocks subjected to vandalism.
Open Access
Updating PMP to provide better dam and spillway design
(Colorado State University. Libraries, 2016-09) Kappel, W. D., author; Hulstrand, D. M., author; Muhlestein, G. A., author; Colorado State University. Department of Engineering, publisher
Probable Maximum Precipitation (PMP) is used as input to derive the Probable Maximum Flood (PMF) for high hazard dams across the United States. The PMF is used to design high hazard dams to ensure they do not overtop and fail during a PMP/PMF event. PMP values were developed for most of the United States by the National Weather Service (NWS) in a series of Hydrometeorological Reports (HMRs) starting in 1940 and continuing through 1999. However, the NWS stopped updating the HMRs and the storms used to derive the PMP values. Since that time the meteorological understanding of extreme rainfall has advanced significantly and numerous large rainfall events have occurred which affect PMP. Because the dam safety community required updated PMP values which incorporated these updated data and meteorological understanding to ensure proper design and rehab of dams, Applied Weather Associates (AWA) has been performing site-specific, statewide, and regional PMP studies to update these data and advance the science regarding PMP. Beginning in the 1990's, AWA has completed more than 100 PMP studies, which have been accepted by state and Federal dam safety regulators. Each of these provide updated PMP values which replace those from the HMRs. In this process, AWA has analyzed hundreds of the most extreme rainfall events, which are required for proper PMP development. This presentation will detail the history of PMP development in the United States, provide an understanding of current PMP development, discuss the storm analysis process, and detail future improvements that are needed for dam safety.
Open Access
Pressure and velocity distributions in plunge pools
(Colorado State University. Libraries, 2016-09) Castillo, Luis G., author; Carrillo, José M., author; Colorado State University. Department of Engineering, publisher
When dam overtopping produces rectangular free jets that discharge into plunge pool basins below the dam, the pressure and velocity distributions of the flow in the plunge pool must be estimated to evaluate potential scour that might destabilize the dam. The high turbulence and aeration phenomena that appear in falling jets and dissipation basins make it difficult to carry out studies based only on classical methodologies. This work addresses plunge pool flows, and compares numerical results against our own experiments. Instantaneous pressures, velocities and air entrainment were obtained with the use of piezoresistive transducers, Acoustic Doppler Velocimeter and optical fiber, respectively. Mean velocity field and turbulence kinetic energy profiles were determined. To identify the level of reliability of models, numerical simulations were carried out by using the "homogeneous" model of ANSYS CFX, together with different turbulence closures. The numerical results fall fairly close to the values measured in the laboratory, and with expressions for submerged hydraulic jumps and horizontal wall jets. The observations can be well predicted for horizontal velocities greater than 40% of the maximum velocity in each profile, and when the ratio of the water cushion depth to the jet thickness is lower than 20.
Open Access
Performance of RCC used for overtopping protection and spillways
(Colorado State University. Libraries, 2016-09) Hansen, Kenneth D., author; Fitzgerald, Thomas J., author; Colorado State University. Department of Engineering, publisher
Roller-compacted concrete (RCC) has become the most widely accepted method for providing safe overtopping protection for embankment dams in the United States. The concept consists of placing horizontal layers of erosion resistant RCC on the downstream slope of existing dams to increase spillway capacity during extreme rainfall events. Since the first earth dam with an RCC overlay was constructed in 1984, more than 130 such projects have been put in service. Because most of these hydraulic upgrades were designed to accommodate rare flow events, there was little information initially available of their actual performance when overtopped. With more RCC overtopping protection in service, there are now more examples of floods in excess of the 1 in 100 year event overtopping RCC protected dams. This paper will present data on the performance of RCC overlay projects when overtopped and lessons learned from these actual examples.
Open Access
Cost-effective numerical modeling for evaluation of overtopping protection systems
(Colorado State University. Libraries, 2016-09) Dababneh, Ahmed "Jemie" A., author; Schwartz, Mark A., author; Tastan, Erdem Onur, author; Edwards, Tom, author; Colorado State University. Department of Engineering, publisher
Case studies that focus on exceedance of the design flood event and the resulting overtopping conditions may be used to provide cost-effective analysis of overtopping protection systems. For this case study, conditions of levee overtopping are evaluated for the Probable Maximum Flood (PMF), with a two dimensional flow model (FLO-2D) used to represent the flood event in a relatively flat area susceptible to flash flooding. The model calculates the duration of overtopping and the resulting flood depths and velocities. The model outputs are utilized to evaluate the effectiveness of riprap as potential overtopping protection.
Open Access
Embankment overtopping protection by riprap considering interstitial flow
(Colorado State University. Libraries, 2016-09) Wahl, Tony L., author; Colorado State University. Department of Engineering, publisher
Riprap is commonly provided to protect embankment slopes from localized erosion caused by surface runoff during rainfall events, but it can also provide erosion protection during small overtopping events. When flow rates are small, most water may flow interstitially through the riprap layer, then gradually above the riprap layer as flow rates increase. On relatively steep slopes, interstitial flow may still be a significant proportion of the total flow—even 100% of the flow—when the failure discharge is reached. In the late 1990s the Bureau of Reclamation sponsored tests on 2H:1V (50%) embankment slopes to determine allowable rates of overtopping flow for large riprap with median stone sizes up to 26-inch diameter. These tests included measurements of interstitial flow, and Mishra (1998) and Frizell et al. (1998) used the collected data to develop a design procedure for riprap on steep slopes accounting for interstitial flow. Unlike other riprap design equations that relate allowable discharge or stone size to independent variables through simple closed-form equations, the method incorporates interstitial flow in a mechanistic way through iterative calculations that add complexity to the solution process. This paper illustrates the Mishra/Frizell design method through example calculations and highlights key aspects of the solution process. Important conclusions are drawn related to the use of riprap for overtopping flow protection on typical embankment dam slopes.
Open Access
Hydraulic and stability analysis of the supporting layer of wedge-shaped blocks
(Colorado State University. Libraries, 2016-09) San Mauro, J., author; Larese, A., author; Salazar, F., author; Irazábal, J., author; Morán, R., author; Toledo, M. Á., author; Colorado State University. Department of Engineering, publisher
Wedge shaped blocks (WSB) are attracting increasing attention as protection against overtopping for earth and rock-fill dams. However, there are limited examples of application and some aspects of the technology merit additional research and improvement. One key issue is the design of drainage and supporting layer for WSB protections. During overtopping, part of the overflow leaks through the joints between blocks, hence circulating through the granular material. The permeability and thickness of the supporting layer must be sufficient to prevent the flow from generating pressure on the bottom side of the blocks, which contributes to its destabilization. However, it must also be structurally stable to avoid undesirable deformations on the downstream face. Both the material permeability and the layer thickness determine the hydraulic behavior of this element. These, together with the weight of the blocks and the slope of the downstream face, directly influence mass and block stability. These aspects should be taken into account for the numerical modeling of seepage through the supporting layer. To this end, an application of the open source software Kratos Multi-physics was employed. A parametric study was conducted to quantify the influence of each design variable in the safety factor against mass sliding of the supporting and drainage layer.

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