2013-03-25 – NRC – Jocassee Dam – Oconee slides on flood hazard report – ML16237A004

2013-03-25-nrc-jocassee-dam-oconee-slides-on-flood-hazard-report-ml16237a004

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Boska, John
From:
Sent:
To:
Subject:
Attachments:
Attached are the slides.
John Boska
Boska. John
Monday, March 25, 2013 8:09AM
Connor, Eric
RE: march 25 oconee meeting
2013-03-25 Oconee slides on flood hazard report.pdf
Oconee Project Manager. NRR/DORL
U.S. Nuclear Regulatory Commission
301-415-2901
email: [email protected]
From: Boska, John
Sent: Thursday, March 21, 2013 12:11 PM
To: ‘Connor, Eric’
Subject: RE: march 25 oconee meeting
It is part of the Fukushima response. Our letter requesting the information is available publicly from our web
site, www.nrc.gov, under ADAMS accession# ML 12053A340. You can enter accession numbers in the search
box in the upper right of the home page. In section 2.1 on flooding, we requested a flooding hazard
reevaluation report from all power reactor licensees.
John Boska
Oconee Project Manager, NRR/DORL
U.S. Nuclear Regulatory Commission
301-415-2901
email: [email protected]
From: Connor, Eric [mailto:[email protected]]
Sent: Thursday, March 21, 2013 11:43 AM
To: Boska, John
Subject: RE: march 25 oconee meeting
Thanks, John. Is this re-evaluation report specifically related to requests pre-Fukushima about the Jocassee Dam issue.
Or is this part of a larger Fukushima response?
Eric Connor
The Greenville News
GreenvilleOnline.com
~~L.ULL.L…:%l..I.>..L:r..,'( 0 ~
c)
From: Boska, John [mailto:[email protected]]
Sent: Thursday, March 21, 2013 11:38 AM
To: Connor, Eric
Cc: Hannah, Roger; Ledford, Joey
Subject: RE: march 25 oconee meeting
..
Duke Energy did submit a flooding hazard reevaluation report to the NRC dated 3/12/13, but it is a non-public
document. At the meeting we will discuss sections of the report that can be discussed publicly. Duke may
provide public slides. For example, Duke did an analysis of the consequences of a failure of the Jocassee
Dam. I expect the NRC staff will discuss the analysis method they used. and ask questions about how the
parameters were selected (for example, how large was the assumed failure and what were the flow rates out of
Lake Jocassee). The NRC will not be making any decisions at this meeting, but rather just gather information
to help us reach a decision on the validity of the methods used in the analysis.
John Boska
Oconee Project Manager, NRR/DORL
U.S. Nuclear Regulatory Commission
301-415-2901
email: [email protected]
From: Connor, Eric [mailto:[email protected]]
Sent: Thursday, March 21, 2013 11:03 AM
To: Boska, John
Subject: march 25 oconee meeting
Hi, John. I’d like to get the info on the meeting re: Jocassee Dam flooding issues on Monday.
Is there any material to review beforehand?
I’m curious what exactly the meeting will address and what is expected to come out of it.
Thanks
-Eric
Eric Connor
The Greenville News
Greenville Online. com
4.298.4304 (o)
·. (b}(6} kc’
itter @econnorgvnews
2
Boska, John
From:
Sent:
To:
Subject:
Attachments:
Attached are the slides.
John Boska
Boska. John
Monday, March 25, 2013 8:11 AM
Smith, James D
RE: Oconee meeting – flooding hazard
2013-03-25 Oconee slides on flood hazard report.pdf
Oconee Project Manager, NRR/DORL
U.S. Nuclear Regulatory Commission
301-415-2901
email: [email protected]
From: Boska, John
Sent: Thursday, March 21, 2013 7:36AM
To: ‘Smith, James D’
Subject: RE: Oconee meeting- flooding hazard
At 2 pm on 3/25/13. call888-469-5869. enter cod nd press the# button. During the meeting we ask
that you don’t allow your background noise on tot e p one line, which is shared by everyone who is calling in.
If your phone has a mute button you can use that. Otherwise, use the built in mute feature of our phone
system. Press •a to mute your phone, and *6 again to unmute if you decide to ask a question during the public
question period. If your phone system plays music when you put a call on hold, please do not put this call on
hold.
John Boska
Oconee Project Manager, NRR/DORL
U.S. Nuclear Regulatory Commission
301-415-2901
email: [email protected]
From: Smith, James D [mailto:[email protected]]
Sent: Wednesday, March 20, 2013 3:54PM
To: Boska, John
Subject: Oconee meeting- flooding hazard
Please provide telephone number and pass code for the subject meeting.
Jim Smith
licensing Project Manager
Plant licensing
Westinghouse Electric Company
Phone: +1 423·290-5223
Email: [email protected]
Home Page: www.westinghousenuclear.com
C-3
Boska, John
From:
Sent:
To:
Cc:
Subject:
Attachments:
I \ ~ ‘J f -!
Boska, John 1 1 ~ · \J’·
Monday, March 25, 2013 7:35 AM
Dick Mangrum
Hannah, Roger; Ledford, Joey
RE: Today’s Duke-MRC meet
2013-03-25 Oconee slides on flood hazard report.pdf
At 2 pm on 3/25/13, call 888-469-5869, enter cod nd press the # button. During the meeting we ask
that you don’t allow your background noise on to p line, which is shared by everyone who is calling in.
If your phone has a mute button you can use that. Otherwise, use the built in mute feature of our phone
system. Press *6 to mute your phone, and *6 again to unmute if you decide to ask a question. If your phone
system plays music when you put a call on hold, please do not put this call on hold. Attached are the slides for
the meeting.
John Boska
Oconee Project Manager, NRR/DORL
U.S. Nuclear Regulatory Commission
301-415-2901
email: [email protected]
From: Dick Mangrum [mailto:[email protected] .com]
sent: Monday, March 25, 2013 6:55AM
To: Boska, John
Subject: Today’s Duke-MRC meet
John,
Please let me have phone number and pass code for today’s 2 p-m flood hazard re-evaluation meeting.
Sincerely,
Dick Mangrum
News Director, WGOG
Walhalla, SC
1
c __ -Lf
Boska, John
From:
Sent:
To:
Subject:
Attachments:
See attached.
John Boska
Boska, John
Monday, March 25, 2013 8:06 AM
Riccio, Jim
Slides for Oconee public meeting on 3/25/13 at 2pm
2013-03-25 Oconee slides on flood hazard report.pdf
Oconee Project Manager, NRR/DORL
U.S. Nuclear Regulatory Commission
301-415-2901
email: [email protected]
—–Original Message—–
From: Boska, John
To: Colleen Payne ; Pascarelli, Robert
Sent: Mon, Mar 25, 2013 8:04 am
Subject: RE: Duke Energy meeting
Colleen, we receive such a high volume of requests that we do not have the time to communicate with
individuals on these items. We have established an email listserver for each of the power reactors, and if you
sign up for the listserver, you will be emailed a copy of all the public documents we issue for Oconee Nuclear
Station. The listserver is automated, I cannot add people or remove them or even see who is on the list. If you
want to sign up, please go to
http://www.nrc.gov/public-involve/listserver/plants-by-region.html
and sign up for Oconee. The meeting notice for 3/25/13 was issued on the listserver on 3/18/13 and was
placed on the NRC web site on 3/19/13.
I will add your name to the security list for today’s meeting (although it is not a requirement, any member of the
public can attend, they just have to register with security when they get here). Attached are the slides for
today’s meeting. Copies will be available at the meeting. Please call my cell phone, 301-661-6969, after you
pass through security and I will ensure an escort brings you to the meeting room.
John Boska
Oconee Project Manager, NRR/DORL
U.S. Nuclear Regulatory Commission
301-415-2901
email: [email protected]
From: Colleen Payne [mailto:[email protected]]
Sent: Saturday, March 23, 2013 10:05 AM
To: Pascarelli, Robert; Boska, John
Subject: Re: Duke Energy meeting
John and Robert,
Could you please keep me informed, I thought from last meetings, correspondence and my request that I was clear on
receiving all current, future meetings re: Lake Jocasse/Oconee/Duke Energy & NRC. I receive daily updates and
continually monitor NRC site, however, somehow I missed the upcoming 3/25 meeting re flooding issues/Duke/NRC.
Thank you, Colleen Payne
—–Original Message—–
From: Colleen Payne To: robert.pascarelli ; john.boska
Sent: Sat, Mar 23, 2013 9:56 am
Subject: Re: Duke Energy meeting
Good morning John and Robert,
Is Monday’s, 3/25 meeting re: “to discuss the licensee’s flooding hazard reevaluation report for the three Oconee units…” a
rescheduled or new meeting? I was not made aware nor was this posted until just recently – within past few days.
I will be attending this meeting, please add my name to security list.
Thank you, Colleen Payne
703/786-2247
—–Original Message—–
From: Colleen Payne To: Robert.Pascarelli
Sent: Mon, Mar 11, 2013 2:36 pm
Subject: Re: Duke Energy meeting
Bob,
Yes, that is correct. Thank you.
I just received notice from John Boska, 3/19 meeting has been rescheduled to 4/9.
Colleen
—–Original Message—–
From: Pascarelli, Robert
To: Colleen Payne Sent: Mon, Mar 11, 2013 1:40 pm
Subject: RE: Duke Energy meeting
Colleen,
I believe that you are referring to the April 16-18 industry meeting in Columbia, SC. It is an industry-sponsored meeting
that the Office of New Reactors (NRO) has been invited to speak at for the last few years. Due to budget restrictions,
NRO is not planning to attend this year.
Bob Pascarelli
From: Colleen Payne [mailto:[email protected]]
Sent: Thursday, March 07, 2013 4:43 PM
To: Pascarelli, Robert
Subject: Re: Duke Energy meeting
Bob,
Do you know who will be speaking at the SMR Conference April 16-17? I was registered for that event, but will not be
able to attend.
Thank you, Colleen
—–Original Message—–
From: Pascarelli, Robert
To: Colleen Payne Sent: Thu, Mar 7, 2013 2:29 pm
Subject: RE: Duke Energy meeting
Colleen,
It’s possible that the meeting could occur as late as May. We coordinate resources with our Region II office to ensure that
we can conduct all of the site meetings within a few months following the issuance of the annual assessment letters. I’ll
let you know as soon as we have a tentative date. Have a nice day.
Bob
From: Colleen Payne [mailto:[email protected]]
Sent: Thursday, March 07, 2013 2:14 PM
To: Pascarelli, Robert
Subject: Re: Duke Energy meeting
Bob
Thank you for this information. Any chance of scheduling assessment meeting in May? I would like to attend and mid-
May would work for me. (smile, I am joking – but doesn’t hurt to ask)
Colleen
—–Original Message—–
From: Pascarelli, Robert
To: Colleen Payne Sent: Thu, Mar 7, 2013 10:35 am
Subject: RE: Duke Energy meeting
Ms. Payne,
It was a pleasure to speak with you on Tuesday afternoon and I look forward to seeing you on March 19th. Another
meeting that you may be interested in is the annual end-of-cycle assessment meeting that is held in the Oconee visitor’s
center. Although we have not finalized a date, our annual meeting will most likely occur in the early April timeframe. I
encourage you to consider attending if you are in the area. Additionally, please feel free to contact myself or John Boska if
you have any questions or concerns. Have a great day!
Bob Pascarelli, Chief
Plant Licensing Branch II-1
Division of Operating Reactor Licensing
Office of Nuclear Reactor Regulation
From: Colleen Payne [mailto:[email protected]]
Sent: Thursday, March 07, 2013 9:52 AM
To: Pascarelli, Robert
Subject: Duke Energy meeting
Bob,
Just a quick note to thank your for your time on Tuesday, March 5 during and after Duke meeting.
I appreciate you taking the time to discuss some of the concerns regarding NRC’s position regarding Oconee site.
I look forward to seeing you on the 19th – or rescheduled date.
Have a good rest of week,
Colleen
Duke
nergy
———~-~·_:.’J~~··:’\-
For Information On~
Fukushima·
Flooding Hazard Reevaluation
Upstream Dam Failure Analysis
NCR
Technical
Presentation
NRC Headquarters
One White Flint North
Rockville, MD
March 25, 2013
Dave Baxter, VP, Regulatory Project Completion
Dean Hubbard, Oconee External Flood Licensing Manager
Ray McCoy, Principal Engineer, ONS Civil Design
Chris Ey, Civil Engineering Manager, HDR
Daria Jones, Oconee Fukushima Engineering Supervisor
Joe Ehasz, VP, URS Program Manager- Water Resources
2
For Information Only
Agenda
·:· Current Dam Failure Analysis • January 28, 2011
~ Breach Analysis Summary
~ Model Development
·:· Updated Dam Failure Evaluation -submitted March 12, 2013
~ Models Considered
} Selection of Xu & Zhang
~ Update Breach Parameters
~ Sensitivity Analysis
~ Independent Review
~ Comparative Analysis • Large Modern Dam Failures
•!• Modifications Scope
For Information Only
3
2011 Breach Analysis Summary
·:· Breach parameters developed using regression methodology and
technical papers:
~ Froehlich 2008
~ Walder & O’Connor
~ MacDonald & Langridge-Monopolis
·:· Breach analysis focused on maximizing flooding levels to provide a
very conservative and bounding analysis:
~ Breach dimensions maximized to assume loss of most of the dam
embankment.
~ Froehlich breach time of 5 hours was reduced to 2.8
~ Maximum peak outflow was selected from all methods
~ Breach times of Keowee dams/dikes adjusted to maximize water
directed at the site
~ T ailwater effect below Jocassee dam was not considered
For Information On~
4
Duke
nergy 2011 Breach Analysis Summary
Jocassee Dam (postulated dam failure)
·:· Initial breach derived primarily from Froehlich regression
equations.
·:· Breach dimensions were adjusted based on physical
constraints of natural valley
•!• Jocassee breach parameters:
~ Top Width -1156 (64% of overall crest)
~ Bottom Width – 431 feet
~ Bottom Elevation – 800 msl
~ Breach Formation Time .. 2.8 hrs,
~ Peak outllow 5,400,000 cfs
For Information Only
5
1.2
O.l
‘I
\
\
\
2011 SE JocasseeDamBreach
Progression and Stage-Discharge Hydrographs
Jocassee Dam Breach Progression and Hydrographs
Case Z(lOOW)
S,OOO,(DJ
4,000,000
i 3.000,000 … J •
um,ooo
I,(DJ,(DJ
0 0
~~~~~~~~~~~~~~~~~~~ –
~-···–·—–·——————___..j
For Information Only
6
2011 Breach Analysis Summary
Keowee Dam/Dikes {postulated cascading dam failures)
·:· Overtopping failure trigger of two feet over the crest
·:· Cascading dam/dike failure on Keowee
» Keowee main dam- 2.8 hrs
» West Saddle Dam· 0.5 hrs
» Intake Canal Dike- 0.9 hrs
» Little River Dam -1.9 hrs
•!• Conservative assumptions were made to maximize the water
directed toward the power block
For Information Only
7
Model Development
HEC-RAS JD Model
Duke
nergy
————~,. ~l{;,) .
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2011 Breach Analysis Summary
2DModel
WATER SURF ACE ELEVATIONS AT KEOWEE DAM
Jocassee-Keowee Dam Breach Study
Pool Elevations at Keowee Dam
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0 1 2 3 4 5 6 7 I 9 10 11 1210
Model nme (hrs)

Updated Dam Failure Evaluation
Fukushima 2.1
Attributes of updated and refined dam failure analysis
·:· Updated methodology and present day regulatory guidance
·:· Pertormed to meet NUREG CR/7046, 2011 & ANS 2.8, 1992
·:· Realistic but still conservative assumptions
·:· Physical characteristics of the dams/dikes recognized
including materials and method/quality of construction
•!• Overtopping and Seismic are confirmed from the 2011 SEas
not being credible failure modes
12
For Information On~
–··-··-·-··–
Updated Dam Failure Evaluation
Fukushima 2.1
Overtopping of the Jocassee dam was confirmed not to be a credible failure mode
·:· The Jocassee dam and dikes include 15 feet of freeboard
•!• The Jocassee watershed is small relative to storage capacity -148 square miles
·:· The top of the spillways are located at 111 0 (full normal level)
1 Four diverse methods of assuring spillway gate operation
1 Rigorous spillway gate maintenance and surveillance testing as required and
monitored by FERC
•!• Lake management procedures require consideration of lower level to anticipate
additional storage needs for significant storms
1 Weekly rain forecast are prepared by Duke Energy to project rainfall for the basin
1 Precipitation monitoring has assured that no overtopping of the spillway gates has
occurred in 40 + years of operation
·:· PMF using current HRR-51 ,52 results in 3 feet of freeboard margin
·:· 2011 SE also concluded that overtopping was not credible
For Information On~
13
Duke
nergy
Updated Dam Failure Evaluation
Fukushima 2.1
Seismic Failure of the Dam was confirmed not to be a credible failure mode
·:· Seismic evaluation based on current FERC criteria using the 1989 EPRI Hazard Curves
» The Jocassee dam is designed to a 0.12 g horizontal ground acceleration (Oconee site is designed to a
0.1g horizontal ground acceleration).
·:· 2007 Updated Fragili~ Analysis
» High Confidence of a Low Probabili~ of Failure (HCLPF) of the dam by sliding 0.305 g
» Evaluation was performed by Applied Research & Engineering Sciences (ARES) Corp., formerly EQE, a
respected consulting firm in the area of seismic ·fragili~
» The ARES report concluded the median centered fragility value for failure of the dam is 1.64 g.
» Maximum Probabilistic Peak Ground Acceleration for a 2% probability of being exceeded within a 50 year
period is 0.197 g (using the United States Geologic Service hazard maps applicable to Jocassee).
•!• Jocassee dam is included in the seismic model of the Oconee Probable Risk Assessment.
» The combination of the updated seismic fragility with the seismic hazard curve results in a negligible risk
contribution from seismic events.
» In a letter dated 11/20/07 and in the 1/28/11 SE report, the NRC concluded that there is a negligible risk
For Information On~
14
~ Froehlich. 2008
· ~ Walder & O’Connor
Models Considered
Regression Analysis
~ MacDonald & Langridge-Monopolis 1984
~ Xu & Zhang 2009
For Information Only
. 15
Duke Selecdon of Xu & Zhang 2009
nergy Basis
•!• Most current regression method developed and validated with
the largest data base of dam failures:
» 182 earth and rockflll dam failures compiled
» 75 failures w/ sufficient info to develop breach regression models
•!• Empirical formulas that account for physical characteristics of
dam/reservoir: dam type, failure mode, height, dam erodibility,
reservoir shape/storage)
·:· 33 of the 75 failures were on large dams ( ~ 15 meters )
•!• Applies to multi-zoned dams
•!• Method yields realistic but conservative breach parameters
•!• Recognized by industry experts
For Information Only
16
•!• Jocassee Dam – Xu & Zhang
Breach Parameters
Fukushima Update
) Starting reservoir elevation 1110 (normal full pond)
) Rockfill dam with low erodibility classification
) Piping failure initiating at 1020 feet msl (Sunny Day Failure)
) Breach parameters:
IT op Width • 701′ (39% of overall crest)
I Bottom Width – 431′
I Bottom Elevation – 870’
I Breach Formation Time:
1 Xu & Zhang- 29.2 hrs.(14.2 hours piping +16.0 open weir)
1 Froehlich -16.0 hours (open weir)
I Peak outllow: 1,7 60,000 cfs
For Information Only
17
Jocassee Dam
Low Erodibility Classification
(b)(7}(F)
18
For Information Only
Fukushima Model
JOCASSEE DAM BREACH PARAMETERS
Remvo~ . Breach
Crest S I Bottom Breach Bottom Avenge Righ Side L 1 Sid Tune to Top of B 1 .. I
Structare Elevation • El t~(ft Failure Mode Elevation (ft Bre~b Width Breach t e e Failure Breaeh reach Bitiation
(haij e:• I mij (I) M(l) Slope(b)ISiope(1l) (Hr) M(~ Progmsiln ilev:n(ft
Jocassee
112)
Darn
4Jl )66 O.)J O.)J 29.2 1m Sile Wave !,!120
I
1,110 810
Breach Formation Time
Xu & Zhang definition: 29.2 ( 13.2 hours piping + 16.0 hours open weir)
Froehlich definition: 16.0 hours open weir
19
For Information Only
Duke
nergy
Fukushima Model Jocassee Dam Breach
Progression and Stage-Discharge Hydrographs
1.20
& 1.00
1
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r·IK)
1
&
Jocassee Dam Breach Progression and Hydrographs
BEPLE
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~~~~~~~~~~~~~~-~~~flml
-Headwater -TaUwaltr -Breach Procrusion -Breach DiKhargr
—- Breachlnit~lion • – – – Breach FOI’lllalion COmplele
..
Breach Fonnation Time; Xu & Zhang definition:· 29.2 (13.2 hours piping+ 16.0 hours open weir) Froehlich definition: -16.0 hours open weir
For Information On~
20
·:· Keowee Dam
Breach Parameters
Fukushima Update
~ Starting reservoir elevation 800 (normal full pond)
~ Homogeneous earth fill dam
~ Overtopping failure trigger of two feet over the crest at 817 msl by
rapid rise of Keowee reservoir over the crest
~ Multiple simultaneous breach initiation formation points across the
Keowee dam and West Saddle dam
·:· Cascading dam/dike failure on Keowee
~ Keowee main dam- 0.75 hrs
~ West Saddle Dam • 0.5 hrs (shorter than main dam, ratio of height)
For Information Only
21
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Breach Progression HEC-RAS
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Relative Time Progression
—- ————— ————~——————–
For Information On~
22
Duke
nergy Fukushima JD Modeling
830
820
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800
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ij 750
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~ 740
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Final BEP LE 1-D Model Performance
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Model Time • hours
-BEP LE HW -BEP LE TW
“”—~~–~——“”-“”
For Information Only
23
Duke
nergy
Fukushima 2.1 2D Modeling
Keowee Dam Breach Progression
0.8 ..J—–+-~——~+——+
c
~ 0.7 r—
~ 0.6 T—+–1 –+—+
.,. I –
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-~~~~
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+Keowee Dam Sine Wave Breach {HEC-RAS)
-Keowee Dam 2-D Breach
0 ..,…..; ……,. !…—…1—-!——4- —+—-+—-r—+—l
16.2 16.3 16.4 16.5 16.6 16.7 16.8 16.9 17
Time (hr)
For Information Only
24
Duke
nergy
Fukushima 2D ·
Modeling Velocity
and Flow Pattern
at 17 hrs.
0 2 4 6 810121416182022242628303234363840
25
For Information Only
Duke
nergy
Fukushima 2D
Modeling Velocity
and Flow Pattern
at 20 hrs.
2 4 6 8 1012141618 20 2224 2628 3032 34 36 3840
For Information Only
Breachi
Keowee Dam
Fukushima JD-2D
Modeling Results
Intake Dike
HEC·RAS 2-D HEC·RAS 2·D
Maximum Water Surfaces
Keowee Dam Intake Dike
HEC-RAS 2-D HEC·RAS 2·D
Elevation Decimal 11me Elevation Decimalllme Elevation Decimal Time Elevation Decimal Time
~Ql ~~
Maximum Water Surfaces
Swale Tallwater
HEC·RAS 2·D HEC·RAS 2-D
Elevation Decimalllme Elevation Decimalllme Elevation Dedmal11me Elevation Decimal llme
817.5 815.5 16.53 787.4
For Information Only
27
Sensitivity Analysis
Model Peak Outflow (cfs)
McDonald & Langridge-Monopolis 1984 1,566,381
Costa, 1985 1,634,480
Xu & Zhang, 2009 1}60,000
Evans, 1986 1,803,331
SCS, 1981 2,647,711
Bureau of Reclamation, 1982 3,046,462
McDonald & Langridge-Monopolis 1984 5,093,603 (upper envelope)
Froehlich (with additional conservatism), 2008 5,440,000
Data in this table based on Wah12004, JanuaiY 28, 2011 SE and updated Xu & Zhang data
1 00+ HEC-RAS studies pertormed with varied breach parameters and control variables
Erodiblity was the most significant factor influencing the breach parameters for Xu & Zhang 2009
Bias of conservatism w~h realism
For Information Only
28
·Independent Peer Review
Joe Ehasz, P.E.
David Bowles, Ph. D P.E. P.H.
Independent Review
Breach Parameters
• FERC Board of Consultant Review
Gonzalo Castro, Ph.D., P.E.
James Michael Duncan, Ph.D., P.E.
James F Ruff, Ph.D., P. E.
Gabriel Fernandez, Ph.D., P.E.
For Information On~
29
·:· Taum Sauk
Comparative Ana~sis
Large Modern Dam Failures
) Overtopping failure initiated by human error {previous overtopping events had occurred)
) Random rockfill embankment supporting the inner concrete liner loosely placed by end dumping the material
without compaction except for the top 16′ of 84′ height
) The embankment was constructed on a very steep downstream slope of 1.3H to 1V with a 10 high concrete
parapet wall along the crest of the dam
) Embankment was high~ erodible and contained over 45% sand sized material (also evident in unusual
level of surtace erosion from rain events)
·:· .Teton
) earthen dam with majority of dam constructed of highly erodible windblown silt (infant mortality event)
) No transition zones (sand and/or fine fl~ers) were included between the silt core and the sand & gravel
) Thin layer of small rock fill on both up and downstream faces with a majori~ of protection relied upon mix of
sand, gravel and cobble
) Piping failure at 130′ below the crest due to inadequate protection of impervious core trench material
) Breach top width 781’ (“”25% of overall crest)
·:· Hell Hole
) True rockfill dam, with upstream sloping impervious core with massive rock fill sections up and down stream
to support and protect the core.
) Failure caused by overtopping during construction due to an intense rain event that could not be passed
through the construction diversion tunnel
) After overtopping of the core started, the dam took 26 hours to complete the breach and emp~ the upstream
reservoir 30
For Information Only
Modification Scope
Updated
•!• Modifications for protection from dam failure (under review):
1. Relocation of external backup power transmission line
2. Intake Dike embankment protection
3. East embankment protection
4. Discharge Diversion wall
·:· Modifications for Local Intense Precipitation (under review):
~ Transformer relocation
~ Diversion walls and drainage canals
~ Aux building and Turbine building protection
For Information Only
31
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