Hydrologic Issues for Dams - Association of State Dam Safety Officials

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UNACCEPTABLEregion: risks onlyjustified underextraordinarycircumstancestyAssociated UncertainTOLERABLE region: riskcontrol measures must beintroduced to drive the residualrisk towards the broadlyacceptable region.Mean ValueBROADLY ACCEPTABLEregion: residual riskinsignificantFigure 4. Tolerability of Risk (HSE, 2001)A Basis for Determining Research Needs in Dam Safety AnalysisIt is possible to determine the research needs by examining how well the inputs to andoutputs from the decision process meet requirements for quality, scientific validity,verifiability and legal defensibility. The quality and validity of the risk estimates asillustrated in Figure 3 and the reliability and legal defensibility of the decisions based onthese estimates as utilized in the decision process of Figures 2 and 4 are dependent on thequa lity and robustness of the procedures used to generate the risk information illustratedin Figure 3.The determination of the quality and reliability of the risk estimates can be determinedthrough analysis of the underlying procedures and the process used to integrate theoutputs of the individual procedures. This entails decomposing the risk measure,including associated uncertainties into its fundamental parts and examining therobustness of each of the constituent procedures and the robustness of the integrationprocess. Clearly, if each constituent procedure and the method of integration are robustand meet the accepted norms of broad professional acceptability established in terms ofthe time tested approach of open challenge, and have not been overtaken by modernscientific advances (cannot be improved upon at the moment) little in the way of researchcan be justified.Paper 14 – Hartford 92
However, should it be revealed that the capability of characterizing the risk in ascientifically valid and legally defensible way, is somewhat questionable, or that recentscientific advances permit a marked improvement in the quality and economic efficiencyof the dam safety assurance process while not reducing safety standards, then a basis forjustifying research projects exists.While risk analysis may be based on past experience, with an implicit assumption that thepast is a good predictor of the future, the relatively small number of dam failures in thehistoric record together with the lack of homogeneity across the population of damfailures mean that statistical methods cannot be relied on as a basis for assessing the risksposed by individual dams. Therefore, the risk analysis process involves constructing adescription of how events may develop from a given initial state. This description istermed a model of the behavior of the different elements of the system under the variousconditions that can exist. Usually this modelling endeavor will require the constructionof a number of sub-models for the different sub-systems and elements. Linking all of thesub-models together constitutes part of the overall analysis process.One possible “process” model is illustrated in Figure 5 (Hartford et al. 2001).1Pseudo P f0QQ IFFQ PMF10 -1 Characteristics of IFFF)Annual Exceedance Frequency (AE10 -210 -310 -4Characteristics of PMF10 -510 -6UNACCEPTABLEREGIONTOLERABLEREGIONFigure 5. Process model for analyzing risk93Paper 14 - Hartford
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The National DamSafety ProgramResea
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collaboration and expertise, and th
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TABLE OF CONTENTSPage #FOREWORD....
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NEW DEVELOPMENTS AND NEEDS IN SITE-
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FOREWORDThe Federal Emergency Manag
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The PMF represents an estimated upp
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RESEARCH AREASResearch needs were b
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Lack of Historical Data for Extreme
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should be developed that will allow
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• Storms used in HMR 55A and in t
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last 20,000 year s in submitting th
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d. USBR Guidelines Publication, Dam
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was severe. There was a potential,
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Thirdly, we must develop better way
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For most projects, the first step f
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Instead of lumping the loss rates t
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adjust the rating curve for when th
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In response to this situation, TVA
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TVA established a Regional Resource
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The Utah Hydrological ExperienceByM
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The Utah Hydrological ExperienceByM
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Late SpringRain on snow eventModel
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State of GeorgiaFEMA Workshop on Hy
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a. HEC1• DOS based program - glit
Page 49 and 50: Long te rm hydrologic needs include
Page 51 and 52: Current State and County PracticesA
Page 53 and 54: present standards and, as such, are
Page 55 and 56: Research Needs in Dam Safety Analys
Page 57 and 58: Looking at the four test cases give
Page 59 and 60: Hydrologic Analyses Related to Dam
Page 61 and 62: (iii) Modified Expected Cost Approa
Page 63 and 64: Parameter Estimation Based on Joint
Page 65 and 66: estimation of lag times and loss ra
Page 67 and 68: Hydrology for Dam Safety - Private
Page 69 and 70: Probable Maximum PrecipitationAll o
Page 71 and 72: The most common synthetic methods a
Page 73 and 74: the standard would be very conserva
Page 75 and 76: 65Paper 12 - Cecilio
Page 81 and 82: REFERENCES1. U. S. Army Corps of En
Page 83 and 84: Overview of Flood Estimation Proced
Page 85 and 86: Extreme FloodsExtreme floods, the t
Page 87 and 88: Temporal patterns used to distribut
Page 89 and 90: Preliminary Estimates of Rainfall a
Page 91 and 92: 24 to 72 hours). CRC Research Repor
Page 93 and 94: CURRENT AND FUTURE HYDROLOGIC RESEA
Page 95 and 96: ecause existing procedures are inad
Page 97 and 98: REGULATORY INVOLVEMENT AND COMMUNIC
Page 99: Decision BasisThe third feature of
Page 103 and 104: supporting sub-processes. Therefore
Page 105 and 106: Probability ofFailure P f1Probabili
Page 107 and 108: Since any rigorous analysis is an i
Page 109 and 110: well, and usually do include subjec
Page 111 and 112: Against this background, there is n
Page 113 and 114: Howson, Colin., and Peter. Urbach.
Page 115 and 116: Procedures and Analysis Technologie
Page 117 and 118: Currently transposition limits for
Page 119 and 120: pro cedures are used to allow the h
Page 121 and 122: Use of Atmospheric Models in Rainfa
Page 123 and 124: mountain watersheds in response to
Page 125 and 126: 18. Schaefer MG, Stochastic Modelin
Page 127 and 128: dams which could be used to save li
Page 129 and 130: Hydrodynamic modelMIKE 21 BACKGROUN
Page 131 and 132: A FRAMEWORK FOR CHARACTERIZATION OF
Page 133 and 134: c) Decision Level Risk Assessment:
Page 135 and 136: credible estimates of extreme flood
Page 137 and 138: Fitting a distribution to data sets
Page 139 and 140: unoff volumes. Examples of this typ
Page 141 and 142: used to estimate frequency distribu
Page 143 and 144: Hosking, J.R.M., and J.R. Wallis, 1
Page 145 and 146: in west central Arizona. The draina
Page 147 and 148: Trial and error reservoir routings
Page 149 and 150: Figure 1 Alamo DamAlamo Dam and Spi
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Paper 19 - Chieh and Evelyn 146
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esources are made to mitigate flood
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implementing a risk-assessment meth
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Typically, the elevation of the top
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similar to that of the high-gradien
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and provides a cost-effective frame
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10000E. Colorado
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10000x Peak Discharge95% confidence
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An integrated science approach will
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ReferencesBaker, V.R., Kochel, R.C.
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Partnerships, Proceeding of the 200
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Flood HydrographThe flood hydrograp
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A variety of data including informa
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Improved Flood Frequency Extrapolat
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RESEARCH NEEDS SUMMARYJerry Webb, H
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o Unsteady flow computer models for
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• Upd ate “Generalized Snowmelt
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DISCUSSION1. Genera l - After the p
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participant was asked to pick what
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RISK ANALYSIS100Relative Comparison
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WORKSHOPONHYDROLGIC RESEARCH NEEDSF
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JOE SKUPIENPrincipal Hydraulic Engi
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Hydrologic Issues for Dams - Association of State Dam Safety Officials

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