Hydrologic Issues for Dams - Association of State Dam Safety Officials

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y BOSS International has an option for considering mud-wave propagation usingBingham Plastic Flow Theory, but it does not appear to work satisfactorily. Sincewe are building tailings dams higher and higher, we must have the necessaryanalytical tools that enable us to address the safety issues related to this type ofdam, particularly how they could affect the downstream community andinhabitants when they fail. (Bechtel has recently completed, in high ChileanAndes, a 120-m high tailings starter dam, which will be built-out to an ultimateheight of 175 m high in 8 years, and retain more than 60 million cubic meters oftailings consisting of fine soil particles and slime.)The development of such computer codes is, by no means, an easy undertaking.It will involve hydrologic and hydraulic engineers, geotechnical engineers as wellas mining process engineers. But it is a task we must do in order to improve ourstate-of-the-art knowledge in dam safety analysis.Closing RemarksI have stated, from my own perspective as a practitioner from the industrial sector, theapplied and fundamental research needs for hydrology in dam safety analysis. They are:•••the compilation and publication of regional basin runoff models and parametersthe provision of guidance in incorporating confidence limits in flood frequencyanalysisthe development of computer codes for the simulation of dam break mud-wavepropagation in river channel resulting from breaching of tailings damsI hope that we can give these topics serious considerations and include them in the list ofresearch needs for dam safety analysis to be formulated by this Workshop.Paper 10 - Hui 48
Hydrologic Analyses Related to Dam SafetyByAnand Prakash, Ph. D., P. E. 1AbstractHydrologic design of dams involves consideration of risks and costs associated with damfailure due to hydrologic factors. This paper presents a procedure to characterize damson the basis of hydrologic risk associated with potential failure. Methods are presented toestimate economic risks associated with different design-basis floods lower than theprobable maximum flood (PMF). Practical difficulties in estimating appropriateparameters to be used for the determination of the PMF and to assess the appropriatenessof the estimated PMF are described. A fuzzy set approach is presented, which includescon sideration of both tangible and intangible risk factors in determining risk-based designbasis flood for a dam. Research needs related to risk analysis for hydrologic safety ofdams are identified.IntroductionIn most cases, hydrologic safety of dams is assessed in terms of their capability to safelypass the probable maximum flood (PMF) or a fraction thereof depending on the size andhazard potential of the dam. The PMF is defined as a hypothetical flood that can beexpected from the most severe combination of critical meteorologic and hydrologicconditions that are reasonably possible in a region. It is derived from the probablemaximum precipitation (PMP) using an event-based rainfall-runoff model. The PMP is,theoretically, the greatest depth of precipitation for a given duration that is physicallypossible over a given size storm area at a particular geographic location at a certain timeof the year.Hydrologic Categorization of DamsFrom the standpoint of hydrologic safety and risk analysis, dams may be divided intothree categories (ASCE, 1988).(i)(ii)Category 1 includes dams where potential loss of life, economic loss, and socialand environmental damages resulting from failure are unacceptable. For thesedams, PMF is the design-basis flood (DBF) and a detailed risk analysis, otherthan hydrologic analysis to estimate the PMF, may not be necessary. Of course,the potential for overtopping and severe scour or erosion due to a long-term PMFevent or more than one successive storm events less severe than the PMP must beevaluated as part of the hydrologic analysis.Category 2 includes dams where the DBF is PMF unless it can be demonstratedthat a smaller DBF results in total costs (including failure consequences) lower1URS Corporation, One Continental Towers, 1701 Golf Rd., Suite 1000Rolling Meadows, Illinois, 6000849Paper 11- Prakash
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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....
Page 7 and 8: NEW DEVELOPMENTS AND NEEDS IN SITE-
Page 9 and 10: FOREWORDThe Federal Emergency Manag
Page 11 and 12: The PMF represents an estimated upp
Page 13 and 14: RESEARCH AREASResearch needs were b
Page 15 and 16: Lack of Historical Data for Extreme
Page 17 and 18: should be developed that will allow
Page 19 and 20: • Storms used in HMR 55A and in t
Page 21 and 22: last 20,000 year s in submitting th
Page 23 and 24: d. USBR Guidelines Publication, Dam
Page 25 and 26: was severe. There was a potential,
Page 27 and 28: Thirdly, we must develop better way
Page 29 and 30: For most projects, the first step f
Page 31 and 32: Instead of lumping the loss rates t
Page 33 and 34: adjust the rating curve for when th
Page 35 and 36: In response to this situation, TVA
Page 37 and 38: TVA established a Regional Resource
Page 39 and 40: The Utah Hydrological ExperienceByM
Page 41 and 42: The Utah Hydrological ExperienceByM
Page 43 and 44: Late SpringRain on snow eventModel
Page 45 and 46: State of GeorgiaFEMA Workshop on Hy
Page 47 and 48: 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: Looking at the four test cases give
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 and 100: Decision BasisThe third feature of
Page 101 and 102: However, should it be revealed that
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
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well, and usually do include subjec
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Against this background, there is n
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Howson, Colin., and Peter. Urbach.
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Procedures and Analysis Technologie
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Currently transposition limits for
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pro cedures are used to allow the h
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Use of Atmospheric Models in Rainfa
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mountain watersheds in response to
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18. Schaefer MG, Stochastic Modelin
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dams which could be used to save li
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Hydrodynamic modelMIKE 21 BACKGROUN
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A FRAMEWORK FOR CHARACTERIZATION OF
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c) Decision Level Risk Assessment:
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credible estimates of extreme flood
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Fitting a distribution to data sets
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unoff volumes. Examples of this typ
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used to estimate frequency distribu
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Hosking, J.R.M., and J.R. Wallis, 1
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in west central Arizona. The draina
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Trial and error reservoir routings
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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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