USACE Dam Risk Assessment Program Overview and How ......Data compilation and review, site visit,...
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217 217 217 200 200 200 255 255 255 0 0 0 163 163 163 131 132 122 239 65 53 110 135 120 112 92 56 62 102 130 102 56 48 130 120 111 237 237 237 80 119 27 252 174 .59 Todd N. Loar, PG, CEG Senior Geological Engineer Risk Management Center Lakewood, CO 14 September 2017 USACE DAM RISK ASSESSMENT PROGRAM OVERVIEW AND HOW ENGINEERING GEOLOGY CONTRIBUTES TO THE LEVEL OF CONFIDENCE AND RESULTS 1 File Name Association of Engineering Geologists Colorado Springs, CO September, 2017 Hurricane Katrina, 2005 inundation map
USACE Dam Risk Assessment Program Overview and How ......Data compilation and review, site visit, brainstorming PFM’s and first cut at assigning risk and estimating uncertaintie\
Todd N. Loar, PG, CEGSenior Geological EngineerRisk Management CenterLakewood, CO14 September 2017
USACE DAM RISK ASSESSMENT PROGRAM OVERVIEW AND HOW ENGINEERING GEOLOGY CONTRIBUTES TO THE LEVEL OF CONFIDENCE AND RESULTS
1
File Name
Association of Engineering Geologists
Colorado Springs, CO
September, 2017
Hurricane Katrina, 2005 inundation map
Presenter
Presentation Notes
Worked in private sector consulting primarily for dams. Participated in a number of FERC Part 12 and PFMA evaluations over that time period. Now work for the USACE RMC for 3 years where we manage the entire dam and levee safety portfolio using a risk informed decision making process rather than standards-based process. While many specific private sector practitioners know and understand the USACE RIDM process (are utilized as external reviewers), many people from outside the Corps or Reclamation are generally unfamiliar with the specifics of the risk analysis process (beyond PFMA) that is used for evaluating dam safety at USACE and USBR. This RIDM process allows for prioritizing modifications/actions and equitable comparison of the relative risk posed to society by each project throughout the entire inventory across the entire country.
USACE INVENTORY OVERVIEW
Dams: 710 structures (at 556 different flood management projects) Levees: 15,000 mi of federally authorized levees (USACE and other stakeholders) Navigation Systems
Presenter
Presentation Notes
USACE responsible for more dams than any other dam owner in the US and worldwide (China is unknown how their DS and infrastructure management works). Increased knowledge/understanding of the magnitude and frequency of loading events Aging infrastructure Increased downstream population & development; increasing societal aversion to risk; high expectations for protection from natural / anthropogenic events Flood protection is a critical mission for USACE Many USACE dams have never been fully loaded so may experience a first filling in the upper portion for the first time decades after construction.
USACE INVENTORY OVERVIEW
Presenter
Presentation Notes
USACE responsible for more dams than any other dam owner in the US and worldwide (China is unknown how their DS and infrastructure management works). Increased knowledge/understanding of the magnitude and frequency of loading events Aging infrastructure Increased downstream population & development; increasing societal aversion to risk; high expectations for protection from natural / anthropogenic events Flood protection is a critical mission for USACE Many USACE dams have never been fully loaded so may experience a first filling in the upper portion for the first time decades after construction.
Part of USACE HQ (Institute for Water Resources, IWR). Lead risk management for centrally-located dam/levee
safety program: Program management Risk analysis and assessments Review and support Establish project prioritization, plan studies, and modification
activities Data management / compilation Develop technical competency (training)
The Risk Management Center: Centrally managed is the key to improve dam safety RA is performed by risk cadre teams from districts outside the project with input / oversight /guidance from District and RMC advisors. risk assessment team are multi-disciplined lead by a trained facilitator that has prior RA experience (engineers, geotechs, H&H, eng. geologists, mechanical, structural, economist, and sometimes environmental and social fields) Have trained hundreds of technical personnel from throughout the Corps Many other Federal agencies are incorporating RIDM concepts and methods into their dam safety regulatory programs and it appears that the State of CO is starting to explore how to incorporate RIDM into their programs. Spain and Netherlands are also transitioning to RIDM for dams/levee safety. USACE (RMC) has assisted other Fed Agencies in performing risk assessments (TVA) and conducts RA training for other Fed agencies and in development of other Fed RA Guidelines. In my view there appears to be an opportunity for engineering geologists to position (and educate) yourself in RA for dam safety of the future.
RISK MANAGEMENT CENTER (RMC)
Presenter
Presentation Notes
The Risk Management Center: Centrally managed is the key to improve dam safety RA is performed by risk cadre teams from districts outside the project with input / oversight /guidance from District and RMC advisors. risk assessment team are multi-disciplined lead by a trained facilitator that has prior RA experience (engineers, geotechs, H&H, eng. geologists, mechanical, structural, economist, and sometimes environmental and social fields) Have trained hundreds of technical personnel from throughout the Corps Many other Federal agencies are incorporating RIDM concepts and methods into their dam safety regulatory programs and it appears that the State of CO is starting to explore how to incorporate RIDM into their programs. Spain and Netherlands are also transitioning to RIDM for dams/levee safety. USACE (RMC) has assisted other Fed Agencies in performing risk assessments (TVA) and conducts RA training for other Fed agencies and in development of other Fed RA Guidelines. In my view there appears to be an opportunity for engineering geologists to position (and educate) yourself in RA for dam safety of the future.
We live in a world filled with risk and its in our nature to continually evaluate our actions, environment & decisions relative to the potential consequences and/or benefits.
Presenter
Presentation Notes
It is in our nature as humans to perform risk assessments (since the beginning of time) in our decision making process on a daily basis. While in engineering many are comfortable with a Standards Based decision making and Factor of Safety values, we still perform Risk Assessment during design of a project to make decisions based on the results from the Standards based analysis. However, standards based analysis are included in the RA process If Standards are used as the basis for repairing aging infrastructure we would be out fixing every single dam, bridge, pipeline, airport etc… and perhaps focusing on or investing in the wrong projects.
RISK AND RISK ASSESSMENTS
The risk assessment process attempts to answer the following questions:
Incremental Risk=�� Probabilityof the Loading� �
Probability of FailureGiven the Loading � �Consequences
Given Failure� X X
Consequences include: life, economic, and environment and other non-monetary impacts.
Life safety is paramount.
Failure Likelihood(loading & system response)
Includes statistical & subjective probability
Consequence Level
Presenter
Presentation Notes
Risk Informed Decision-Making (RIDM): A method of dam safety evaluation and management that uses the likelihood of loading, dam fragility, and consequences of failure to estimate risk and equitably compare projects across inventory. This risk estimate is used along with standards- based analyses to decide if dam safety investments are justified or warranted. This approach has many benefits including a greatly improved understanding of the safety of the dam and identifying dam safety vulnerabilities that have not been identified using standards-based evaluation techniques. There is uncertainty associated with all 3 parts and this uncertainty must be understood, characterized, communicated, and explicitly accounted for. If we used standards we’d be out fixing all the dams for the PMF or some M9 seismic event. Does it make sense to start modifying ALL dams to pass the PMF if the probability of that loading condition is 1/1,000,000 in some cases? Why focus on dams with no downstream consequences if there are others in the inventory with 1,000’s of people downstream?
TOLERABLE RISK GUIDELINES (TRG’S)
Decisions are risk INFORMED:
Emphasis is on the decision, NOT the number or the model
Numbers are NOT decisions
Risks that society is willing to live with so as to secure certain benefits.
Risks society does not regard as negligible.
Risks that society is confident are being properly managedby the owner.
Risks that the owner keeps under review and reduces still further as practicable.
Presenter
Presentation Notes
Tolerable Risk Guidelines (TRG): Risks that society is willing to live with so as to secure certain benefits. Risks society does not regard as negligible or something it might ignore. Risks that society is confident are being properly managed by the owner. Risks that the owner keeps under review and reduces still further if and as practicable. Emphasis is on the Decision, Not the Number or the Model Numbers are NOT Decisions Need people involved “No Verdict” is a decision Consistency in data, methods, people, and decisions
LEVELS OF A RISK ASSESSMENT1. Periodic Assessments (PA) and Semi-
Quantitative Risk Assessment (SQRA)
2. Issue Evaluation Studies (IES)
3. Dam Safety Modification Study (DSMS)
4. Post-Implementation Evaluation (PIE)
Each “Level” involves an increasing amount of data compilation, review, evaluation, site characterization, and engineering analysis
Presenter
Presentation Notes
Risk assessments vary in purpose and therefore in the data required, detail and robustness of analysis, and in uncertainty and confidence in the results. There are a number of RA “Levels” performed PA / SQRA first level of effort, routine (10 yr interval). Data compilation and review, site visit, brainstorming PFM’s and first cut at assigning risk and estimating uncertainties. Approx 5-10 day PFMA and RA meetings, total of a few months to perform from beginning to report and presentation to decision makers. IES – more advanced, involved additional data collection and advanced engineering analysis and more quantitative risk analysis and identification of the primary risk drivers. Can take many months to about a year depending on the PFM’s. DSMS- A risk driver poses a significant risk and needs to be studied further to evaluate alternatives to mitigate that risk. Takes years and designs of various alternatives, cost evaluations and RA for the different alternatives. PIE – after construction of the mitigation alternative an as-built completion risk assessment is performed as the new basis for evaluating the project within the context of the entire portfolio and it enters the routine PI and PA process again.
Incremental Risk=�� Probabilityof the Loading� �
Probability of FailureGiven the Loading � �Consequences
Deterministic & probabilistic earthquake loadings for dam stability analyses
Potential for and geometry of surface fault rupture
Presenter
Presentation Notes
RA Team should ALWAYS include an ENGINEERING geologist. Geologist and/or geotechnical engineers can develop the seismic loading but Eng Geo should be responsible for identifying potential fault rupture. The loading are generally easy to estimate as there are hydrologic and seismic data / methods / procedures and tools available to make these assessments.
Incremental Risk=�� Probabilityof the Loading� �
Probability of FailureGiven the Loading � �Consequences
Hydrologic Loading: Constrain hydro-loading using long-term flood records:
Geomorphic indicators and investigations of paleo-flood stage
Geomorphic indicators of stage non-exceedance (upper bound)
Age-dating to define frequency of extreme loading
House et al. (2002) AGU Paleoflood
Paleo-flood point
Presenter
Presentation Notes
Many USACE dams (75%) have NEVER been fully hydrologically loaded – so we may have a First Filling Event of the upper portion decades after construction Paleo-flood studies find physical range of floods that have not been exceeded or floods that have been at least so large in certain time range. Use 2-D flow analysis to calibrate and estimate valley discharge volume at that location.
Incremental Risk=�� Probabilityof the Loading� �
Probability of FailureGiven the Loading � �Consequences
This is where engineering geology contributes the most to the RA Process
Consequence analysis for various loading, breach & non-breach
scenarios are developed by the MMC
Presenter
Presentation Notes
Consequences: Performed by an Economist on the RA Team Not necessarily intuitive (you can’t just google it) Not many people have the background or training for it Uniquely site-specific As important as probability of failure Standard MMC Modeling Scenarios 5 Hydrologic Loading Conditions 10 Scenarios (Fail and No-Fail for each condition) The Engineering geologist can contribute the most to the risk assessment at this part of the Risk Function.
DAM FAILURES IN THE 20TH CENTURY
~1/3 of all dams failed by overtopping
~1/3 failed by seepage and piping through the dam or into the foundation
~1/3 failed due to foundation and miscellaneous causes
~55% of all concrete dam failures attributed to foundationissues (ICOLD, 1995)
Approx. 70% of failures can be attributed to geologic and/or geotechnical issues
Quail CreekSt. Francis
Fontenelle
Bayless
Presenter
Presentation Notes
Approximately 70 percent of dam failures (gravity and arch) can be attributed to geological or geotechnical problems. ICOLD, 1995
Example: The PFM needs to be well developed and written and follow logical and previously established failure modes (to some degree – each project/condition might be slightly different). Lack of well written PFM’s is a major complaint of reviewers. Need to develop good graphics and present information that clearly communicates the technical conditions, geologic reasoning/justification, and pertinate information within the PFM sequencing.
Example: The PFM needs to be well developed and written and follow logical and previously established failure modes (to some degree – each project/condition might be slightly different). Lack of well written PFM’s is a major complaint of reviewers. Need to develop good graphics and present information that clearly communicates the technical conditions, geologic reasoning/justification, and pertinate information within the PFM sequencing.
1) Reservoir Loading
Flaw: Open Rock
Discontinuities
Flaw: Ineffective Treatment
Initiation
Continuation
Probability that the surface treatment / grouting in the core trench fails to cut off
the seepage path
Probability that gradients and velocity are sufficient to
initiate scour?
Probability an unfiltered exit
exists downstream?
Probability that the embankment
materials are unable to self-heal or clog
the failure paths and a stope forms?
Probability that intervention is unsuccessful?
UnsuccessfulIntervention
Probability the stope enlarges to collapse the crest of the dam leading to breach by
overtopping?
1
2
3
4
5
6
7
Breach
Progression:Clogging
Probability that rock defects exist & are open/continuous
enough to transport embankment
materials
Geologic / Geotech / Hydrogeologic Uncertainties:
Open/continuous network of discontinuities downstream of
core/curtain within the SS/LS unit allowing embankment material to
migrate/erode
Evaluate foundation treatment and effectiveness.
Obtain information to understand the gradients across the core trench and between the core
material and downstream rock
Potential Targets for Field Studies(mapping, drilling, testing, instrumentation)
Example Geological PFM: Event Tree
Presenter
Presentation Notes
Certain events (say seismic or hydrologic loadings) have event trees that are broken down first by probability of the loading (less than 100 year; 100-1000, etc.) then each node is multiplied, then each branch added to get the overall risk for that PFM We use the event tree to focus geologic data collection and analysis to target the specific nodes. If the geologic studies or analysis don’t target PFM event tree nodes they do not really contribute to evaluation of the failure mode because key questions were not answered to help characterize the risk. Event Tree: Series of nodes and branches. Each node represents an uncertain event in sequence, and each branch represents a possible outcome Well defined failure mode is easily decomposed into a sequence of necessary events or potential states of nature All events in the sequence must take place to allow an uncontrolled reservoir release Event trees are flexible and can be adapted to portray most any potential failure mode Loads partitioned into ranges which cover the possibility of loading Probability for each outcome at each subsequent node is estimated assuming the previous branch has already occurred Branch probabilities for a given node must sum up to 1.0 Branch probabilities are multiplied through the tree from left to right Each branch probability which leads to a failure are summed for annual failure probability.
MORE LIKELY / LESS LIKELY FACTORS
High confidence – we are unlikely to revise our estimate with more information.
Moderate confidence – we are unsure about the potential to change the estimate with more information
Low confidence – likely to revise estimate with more information.
Example Geological PFM: Characterizing the Uncertainty at Each PFM Node
Geomechanicalmapping, drilling angled borings, packer testing, down-hole televiewer survey, additional piezometers might improve our confidence and reduce uncertainty with this node of the PFM
Presenter
Presentation Notes
Compile supporting observations & interpretations that make the conditions for failure either more likely to be present or less likely to be present. This exercise performed for each failure mode helps to identify and communicate knowledge gaps and uncertainty Rank the confidence of the PFM likelihood: High, Moderate, and Low based on the likely vs less likely factor table Uncertainty – result of imperfect knowledge concerning present or future state of a system, event, situation, or population under consideration. The level of uncertainty governs the confidence in predictions, inferences, or conclusions. Epistemic – “knowledge uncertainty that is possible to reduce with additional data and study. Aleatory – natural variability reflects a process that is random but uncertainty in its magnitude and value might not be; reduced with additional data and study.
SUCCESSFUL ENG. GEO. IN RIDM Has experience / background in dam & levee design and construction
Basic understanding of geotechnical, civil, hydrologic, and structural engineering disciplines
Knowledge of different PFM’s and how geologic conditions influence the PMF mechanics.
Understands probability estimates/analysis for various nodes in the event tree.
Familiar with past precedents, incidents, and failure case histories.
Ability to sort, query, analyze, compile, and portray different types of geologic/geotechnical spatial data and create plots, figures and drawings that communicate the spatial geological conditions related to the PFM’s.
Must know what data is IMPORTANT and NECESSARY to evaluate foundations and solve engineering problems related to the PFM.
Presenter
Presentation Notes
An engineering geologist working in RA needs to know as many of the specifics/details of case histories that involve geologic conditions that contribute/influence the failure. They need to know the steps through the PFM sequence (initiation, continuation, progression – each node of the event tree may have geologic). (collaboration and communication is essential). Need to develop conceptual, realistic model of the site conditions including depositional environments, continuity of deposits (e.g., “open work gravels”), fracture networks (continuity, infilling and aperture), erosion/scour mechanics and evaluation tools. Eng Geo should have familiarity with the other RA disciplines that are involved with the failure (hydrology, geotech, structural) and also fundamentals of statistical analysis and how to apply it to geological systems/conditions. Must come to the meeting prepared and knowledgeable and able to lead everyone to a solid understanding of the most important data, and the significant unknowns, and use imagination to guide the possibliity of unknown unknowns or oddballs, or minor details not always seen. Do add something about responsibility to present a valid summary of it all to the team at the start. I see too many geologists show up unprepared.
Reviews, understands, summarizes, & prioritizes existing data prior to the RA
Understands what the instrumentation data is telling the RA team in the context of the geology and PFM’s (data tabulation is not interpretation)
Thinks about PFM’s and uses all geologic “tools” to most accurately reflect the subsurface and make realistic estimate of depositional environments, spatial extents and infer the most realistic behavior given the PFM
Creates detailed plans and section drawings to display, summarize, and communicate material properties and instrumentation data
Has genuine enthusiasm to solve specific technical geologic problems (be a problem-solving detective).
SUCCESSFUL ENG. GEO. IN RIDM
Presenter
Presentation Notes
I would try to take some of this and expand it for AEG members. How do they know what failure modes to be concerned with when they are developing data prior to any risk meeting (experience, network with experienced facilitators, can assume seepage failure modes are important for nearly all emb. Dams, etc) Say something about not just creating the needed drawings, but understanding all the most important data on them. USACE is now using GIS as a big copy machine and I see a lot of data that is of little use being developed. If someone pulls all the data together into drawings, they need to understand it all, have it focused on the failure modes, and be in the dam(n) meeting. The data bases I see being developed are not turning data into knowledge, they are only throwing all the data into one pile for others to figure out. That is not what we want or need geologists to be doing.
LESSONS LEARNED PFMA is starting point for RA
Training of facilitators, technical team members, and participants is essential
Engineering geologists are fully capable to lead / facilitate risk assessment teams
Select realistic engineering properties and ranges (avoid conservatism in RA)
PFM must be well developed and presented to characterize the failure modes and answer specific questions associated with the event tree nodes
There is no clear line between geotechnical engineering and engineering geology
Archived data or previous findings must be identified early as it can significantly alter the risk estimates
Reports and geologic evaluation must be focused on the PFM and point to specific evidence supporting & justifying the conclusions and interpretations
Presenter
Presentation Notes
Your goal should be to show AEG how much good can come out of this process if there are experienced participants focused on the real and imagined vulnerabilities. What would it have taken to understand the design deficiencies at oroville dam? Concrete was very thin, dowel anchors were not in decent rock, cracks allowed water to enter, signs of high foundation pressures seemed to have been ignored, spillway foundation left weak materials in place. Could we have caught all of this if we did a risk assessment a few years ago? Totally depends on the team and their dilligence and experience. Big lessons The majority of USACE reports have dozens of reports included in the appendices, but very poor references to the critical information. Often it has not even been read by the report writer. The reports need to serve as a “road map” pointing the reader to all the essential data supporting the conclusions. The most important information should be included in the report or easily-located in appendices. Old drawings and photos key to making the dam safety case need to be re-published in the report. Readers should not have to hunt down any critical data. analyze it, but in FAILURE MODE and RISK DRIVEN MANNER
Life Safety is Paramount
Protecting People, Not Infrastructure
Presenter
Presentation Notes
Overall point 1: Focus is on protecting people, not levees or dams
![[USACE] Risk Assessment Handbook, Volume II - Z - A-d](https://img.dokumen.tips/doc/110x75/577d22c61a28ab4e1e98323e/usace-risk-assessment-handbook-volume-ii-z-a-d.jpg)
