Guidance for Performing a Tsunami, Surge, or Seiche Hazard Assessment

JAPAN LESSONS-LEARNED PROJECT DIRECTORATE

JLD-ISG-2012-06
Guidance for Performing a Tsunami, Surge, or
Seiche Hazard Assessment
Interim Staff Guidance
Revision 0

January 4, 2013

ML12314A412

JAPAN LESSONS-LEARNED PROJECT DIRECTORATE

JLD-ISG-2012-06
Guidance for Performing a Tsunami, Surge, or
Seiche Hazard Assessment
Interim Staff Guidance
Revision 0

ADAMS Accession No.: ML12314A412

*Via E-mail

OFFICE

NRR/JLD/PMB

NRO/DSEA/RHMB

NRR/JLD

NRR/JLD/PMB

NAME

GEMiller

HJones

ABaxter*

MMitchell

DATE

1/4/13

12/31/12

12/18/12

12/28/12

OFFICE

NRO/DSEA/RGS2

QTE

OGC

NRO/DSEA

NAME

CCook

JDougherty*

J. Biggins (NLO)

NChokshi

DATE

1/4/13

11/21/12

12/21/12

1/4/13

OFFICE

NRR/JLD

NAME

DSkeen (MMitchell for)

DATE

1/4/13

OFFICIAL RECORD COPY

January 4, 2013

ML12314A412

INTERIM STAFF GUIDANCE
JAPAN LESSONS-LEARNED PROJECT DIRECTORATE
GUIDANCE FOR PERFORMING A TSUNAMI, SURGE, OR SEICHE HAZARD
ASSESSMENT
JLD-ISG-2012-06

PURPOSE
This interim staff guidance (ISG) is being issued to describe to stakeholders methods
acceptable to the staff of the U.S. Nuclear Regulatory Commission (NRC) for performing a
tsunami, surge, or seiche hazard assessment for external flooding as described in NRC’s
March 12, 2012, request for information (Ref. 1) issued pursuant to Title 10 of the Code of
Federal Regulations (10 CFR), Section 50.54, “Conditions of licenses,” regarding
Recommendation 2.1 of the enclosure to SECY-11-0093, “Recommendations for Enhancing
Reactor Safety in the 21st Century, the Near-Term Task Force Review of Insights from the
Fukushima Dai-ichi Accident” (Ref. 2). Among other actions, the letter dated
March 12, 2012, requests that respondents reevaluate flood hazards at each site and
compare the reevaluated hazard to the current design basis at the site for each flood
mechanism. Addressees are requested to perform an integrated assessment if the current
design-basis flood hazard does not bound the reevaluated flood hazard for all mechanisms.
This ISG will assist operating power reactor respondents and holders of construction
permits under 10 CFR Part 50 in performing tsunami, surge, and seiche hazard
assessments. The guidance provided in this ISG describes methods that can be used as
part of performing the flooding hazard reanalysis requested in Enclosure 2 of the letter
dated March 12, 2012.

BACKGROUND
Following the events at the Fukushima Dai-ichi nuclear power plant, the NRC established a
senior-level agency task force referred to as the Near-Term Task Force (NTTF). The NTTF
conducted a systematic and methodical review of the NRC regulations and processes and
determined if the agency should make additional improvements to these programs in light of
the events at Fukushima Dai-ichi. As a result of this review, the NTTF developed a
comprehensive set of recommendations, documented in the enclosure to SECY-11-0093
(Ref. 2). These recommendations were enhanced by the NRC staff following interactions
with stakeholders. Documentation of the NRC staff’s efforts is contained in SECY-11-0124,
“Recommended Actions to be Taken Without Delay From the Near-Term Task Force
Report,” dated September 9, 2011 (Ref. 3), and SECY-11-0137, “Prioritization of
Recommended Actions to be Taken in Response to Fukushima Lessons Learned,” dated
October 3, 2011 (Ref. 4).
As directed by the staff requirements memorandum in the enclosure to SECY-11-0093
(Ref. 5), the NRC staff reviewed the NTTF recommendations within the context of the
NRC’s existing regulatory framework and considered the various regulatory vehicles
available to the NRC to implement the recommendations. SECY-11-0124 and
SECY-11-0137 established the staff’s prioritization of the recommendations based upon the
potential safety enhancements.

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As part of the staff requirements memorandum for SECY-11-0124, dated October 18, 2011
(Ref. 6), the Commission approved the staff's proposed actions, including the development
of three information requests under 10 CFR 50.54(f). The information collected will be used
to support the NRC staff's evaluation of whether further regulatory action should be pursued
in the areas of seismic and flooding design and emergency preparedness. In addition to
Commission direction, the Consolidated Appropriations Act, Public Law 112-074, which
contains the Energy and Water Development Appropriations Act, 2012, was signed into law
on December 23, 2011. Section 402 of the law requires a reevaluation of licensees' design
basis for external hazards.
In response to the aforementioned Commission and Congressional direction, the NRC
issued a request for information to all power reactor licensees and holders of construction
permits under 10 CFR Part 50 on March 12, 2012 (50.54(f) letter)((Ref. 1). The
March 12, 2012, 50.54(f) letter includes a request that respondents reevaluate flooding
hazards at nuclear power plant sites using updated flooding hazard information and presentday regulatory guidance and methodologies. The letter also requests the comparison of the
reevaluated hazard to the current design basis at the site for each potential flood
mechanism. If the reevaluated flood hazard at a site is not bounded by the current design
basis, respondents are requested to perform an integrated assessment. The integrated
assessment will evaluate the total plant response to the flood hazard, considering multiple
and diverse capabilities such as physical barriers, temporary protective measures, and
operational procedures. The NRC staff will review the responses to this request for
information and determine whether regulatory actions are necessary to provide additional
protection against flooding. This ISG is specific to the assessment of tsunami, surge, or
seiche hazards.
On October 26, 2012, the NRC staff issued a draft version of this ISG and published a
notice of its availability for public comment in the Federal Register (77 FR 65417). The 30day comment period ran October 26, 2012, through November 26, 2012, during which the
staff received 38 public comments. Comments were received related to the following topical
areas: (1) general comments; (2) comments specific to the storm surge evaluation; and
(3) comments specific to the tsunami evaluation. In public meetings on October 24-25,
2012, and November 14, 2012, the NRC staff interacted with external stakeholders to
discuss, understand, and resolve public comments. Modifications were made to text of the
ISG in response to the public comments and the outcomes of the public meetings. Full
detail of the comments, staff responses, and the staff’s bases for changes to the ISG are
contained in “NRC Response to Public Comments” to JLD-ISG-2012-06 (Docket ID NRC2012-0261) (Ref. 7).

RATIONALE
On March 12, 2012, the NRC issued a request for information to all power reactor licensees
and holders of construction permits under 10 CFR Part 50. The request was issued in
accordance with the provisions of Sections 161c, 103b, and 182a of the Atomic Energy Act
of 1954, as amended (the Act), and NRC regulation in Title 10 of the Code of Federal
Regulations, Part 50, Paragraph 50.54(f). Pursuant to these provisions of the Act and this
regulation, respondents were required to provide information to enable the staff to determine
whether a nuclear plant license should be modified, suspended, or revoked.

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The information request directed respondents to submit a reevaluated flooding hazard for
their sites using updated information and present-day regulatory guidance and
methodologies. This ISG describes an approach for performing an tsunami, surge, or
seiche hazard assessment.

APPLICABILITY
This ISG shall be implemented on the day following its approval. It shall remain in effect
until it has been superseded or withdrawn.

PROPOSED GUIDANCE
This ISG is applicable to holders of operating power reactor licenses and construction
permits under 10 CFR Part 50. For combined license holders under 10 CFR Part 52, the
issues in NTTF Recommendations 2.1 and 2.3 regarding seismic and flooding reevaluations
and walkdowns are resolved and thus, this ISG is not applicable.

IMPLEMENTATION
Except in those cases in which a licensee or construction permit holder under 10 CFR Part
50 proposes an acceptable alternative method for tsunami, surge, or seiche hazard
assessment, the NRC staff will use the methods described in this ISG to evaluate the results
of the assessment.

BACKFITTING DISCUSSION
This ISG does not constitute backfitting as defined in 10 CFR 50.109 (the Backfit Rule) and
is not otherwise inconsistent with the issue finality provisions in Part 52, “Licenses,
Certifications, and Approvals for Nuclear Power Plants,” of 10 CFR. This ISG provides
guidance on an acceptable method for responding to a portion of an information request
issued pursuant to 10 CFR 50.54(f). Neither the information request nor the ISG require the
modification or addition to systems, structures, or components, or design of a facility.
Applicants and licensees may voluntarily use the guidance in JLD-ISG-2012-06 to comply
with the request for information. The information received by this request may, at a later
date, be used in the basis for imposing a backfit. The appropriate backfit review process
would be followed at that time.

FINAL RESOLUTION
The contents of this ISG, or a portion thereof, may subsequently be incorporated into other
guidance documents, as appropriate.

ENCLOSURES
1. Guidance for Performing a Surge or Seiche Hazard Assessment
2. Guidance for Performing a Tsunami Hazard Assessment
3. Glossary

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REFERENCES
1. U.S. Nuclear Regulatory Commission, “Request for Information Pursuant to Title 10 of
the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3,
of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident,”
March 12, 2012, Agencywide Documents Access and Management System (ADAMS)
Accession No. ML12053A340.
2. U.S. Nuclear Regulatory Commission, “Recommendations for Enhancing Reactor Safety
in the 21st Century, The Near-Term Task Force Review of Insights from the Fukushima
Dai-ichi Accident,” Enclosure to SECY-11-0093, July 12, 2011, ADAMS Accession No.
ML111861807.
3. U.S. Nuclear Regulatory Commission, “Recommended Actions to be Taken Without
Delay From the Near Term Task Force Report,” SECY-11-0124, September 9, 2011,
ADAMS Accession No. ML11245A158.
4. U.S. Nuclear Regulatory Commission, “Prioritization of Recommended Actions to be
Taken in Response to Fukushima Lessons Learned,” SECY-11-0137, October 3, 2011,
ADAMS Accession No. ML11272A111.
5. U.S. Nuclear Regulatory Commission, “Staff Requirements - SECY-11-0093 - Near-Term
Report and Recommendations for Agency Actions Following the Events in Japan,”
August 19, 2011, ADAMS Accession No. ML112310021.
6. U.S. Nuclear Regulatory Commission, “Staff Requirements - SECY-11-0124 Recommended Actions to be Taken Without Delay From the Near-Term Task Force
Report,” October 18, 2011, ADAMS Accession No. ML112911571.
7. U.S. Nuclear Regulatory Commission, “NRC Responses to Public Comments, Japan
Lessons-Learned Project Directorate Interim Staff Guidance (JLD-ISG-2012-06):
Guidance for Performing a Tsunami, Surge, or Seiche Hazard Assessment in Response
to the March 2012 Request for Information Letter,” January 4, 2013, ADAMS Accession
No. ML12314A414.

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GUIDANCE FOR PERFORMING A SURGE OR SEICHE HAZARD ASSESSMENT

1.Introduction ...................................................................................................... - 2 1.1.Format of Guidance ....................................................................................... - 2 1.2.Historical Perspective .................................................................................... - 2 2.Acceptance Criteria .......................................................................................... - 4 2.1.Existing Regulatory Guidance ....................................................................... - 4 2.2.Updates to Guidance ..................................................................................... - 5 3.Surge Hazard Assessment .............................................................................. - 6 3.1.Overview ....................................................................................................... - 7 3.2.Meteorological Parameters ........................................................................... - 7 3.2.1.
Hurricane Parameters...................................................................... - 8 3.2.1.1. Probable Maximum Hurricane ........................................................ - 8 3.2.1.2. Joint Probability Method ................................................................. - 9 3.2.2.
Extra-tropical Storms and Squall Lines Parameters................... - 10 3.2.2.1. Empirical Simulation Technique ................................................... - 10 3.3.Surge Parameters ....................................................................................... - 11 3.3.1.
Datums............................................................................................ - 11 3.3.2.
Antecedent Water Levels .............................................................. - 11 3.3.2.1. Tides ............................................................................................. - 12 3.3.2.2. Initial Rise ..................................................................................... - 12 3.3.2.3. Long-Term Sea Level Rise ........................................................... - 12 3.3.3.
Surge Water Levels........................................................................ - 13 3.3.3.1. ADvanced CIRCulation Surge Model ........................................... - 13 3.3.3.2. Sea, Lake, Overland Surge from Hurricanes ................................ - 13 4.Seiche Hazard Assessment ........................................................................... - 14 5.Wave and Inundation Effects Associated with Surge or Seiche ................ - 15 5.1.Coincident Wave Heights ............................................................................ - 15 5.2.Inundation.................................................................................................... - 15 5.3.Wave Runup................................................................................................ - 16 5.4.Drawdown (Low Water Level) ..................................................................... - 16 5.5.Hydrostatic and Hydrodynamic Forces ........................................................ - 16 5.6.Debris and Water-Borne Projectiles ............................................................ - 16 5.7.Effects of Sediment Erosion or Deposition .................................................. - 16 6.Figures ............................................................................................................ - 18 7.References ...................................................................................................... - 21 -

Enclosure 1 to JLD-ISG-2012-06

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January 4, 2013

1.

Introduction

The purpose of this interim staff guidance (ISG) is to provide the U.S. Nuclear Regulatory
Commission (NRC) staff with a technical basis for reviewing storm surge or seiche hazard
assessments per the March 12, 2012, letters issued to operating nuclear power plants and
holders of construction permits in accordance with the provisions of Sections 161.c, 103.b,
and 182.a of the Atomic Energy Act of 1954, as amended (the Act), and NRC regulations in
10 CFR 50.54(f).
All coastal nuclear power plant sites must consider the potential for flooding from
hurricanes, windstorms, and squall lines, as well as storm surge, seiche, and windwaves as
part of the hazard reevaluation.
1.1.

Format of Guidance

Section 1.2 (Historical Perspective) discusses the evolution in surge and seiche regulatory
guidance during the time period between the licensing of the operating plants and the
licensing activities for new reactors. Section 2 (Acceptance Criteria) continues with a
discussion of existing regulatory guidance (Section 2.1) and guidance updates (Section 2.2)
based on the ongoing new reactor safety reviews and current state of knowledge. Section 2
gives particular attention to terms and definitions, as well as current good practices.
Section 3 (Surge Hazard Assessment) closely follows the format provided in Section 2.4.6
of Regulatory Guide 1.206, “Combined License Applications for Nuclear Power Plants,” and
NUREG-0800, “Standard Review Plan for the Review of Safety Analysis Reports for Nuclear
Power Plants (LWR [light-water reactor] Edition)” (SRP). Section 3.1 (Overview) describes
the Hierarchical Hazard Assessment (HHA) approach and the role that deterministic and
combined deterministic-probabilistic methods play in surge hazard assessments. Section
3.2 (Meteorological Parameters) describes deterministic and combined deterministicprobabilistic storm-generating methods for input into numerical surge models, which are
discussed in Section 3.3. In Section 3.3 (Surge Parameters), pre-surge modeling steps are
discussed, beginning with vertical datums (Section 3.3.1) followed by antecedent water
levels (Section 3.3.2). Section 3.3.3 (Surge Water Levels) provides a discussion of two
state-of-the-art surge models that the NRC and other Federal agencies use.
A discussion of seiche hazard assessment is provided in Section 4. Section 5 (Wave and
Inundation Effects for Surge and Seiche), which discusses post-numerical modeling effects,
follows it. Factors that should be considered in all surge and seiche hazard assessments
include coincident wave heights, inundation, and wave runup and drawdown, which are
described in Sections 5.1 through 5.4. Sections 5.5 through 5.7 discuss factors that should
be considered for “wet” sites, including hydrostatic and hydrodynamic forces, debris and
waterborne projectiles, and the effects of sediment erosion and deposition. References are
provided in Section 7.
1.2.

Historical Perspective

In 1959, the U.S. Army Corps of Engineers (USACE) contracted the National Weather
Service (NWS) to develop a hypothetical hurricane that could be used to design hurricane
protection projects along the Gulf and Atlantic Coasts of the United States. The NWS, as
part of its National Hurricane Research Project, set out to define “the most severe storm that
is considered reasonably characteristic of a region.” A storm with such characteristics was
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termed the “Standard Project Hurricane” (SPH). The U.S. Weather Bureau Report No. 33
(Graham and Nunn, 1959) describes this effort.
NWS Technical Report 23 (Schwerdt et al., 1979) redefined the SPH as “a steady-state
hurricane having a severe combination of values of meteorological parameters that will give
high sustained wind speeds reasonably characteristic of a given region,” removing the idea
from the definition of the SPH that the SPH pertained to the “most severe storm” for a
particular area. The concept of a “probable maximum hurricane” (PMH) also was
introduced as “a hypothetical steady-state hurricane having a combination of values of
meteorological parameters that will give the highest sustained wind speed that can probably
occur at a specified coastal location.” The PMH was intended to be an event much rarer
than the SPH, but NWS Report 23 (NWS 23), “Meteorological Criteria for Standard Project
Hurricane (SPH) and Probable Maximum Hurricane (PMH) Wind Fields, Gulf and East
Coasts of the United States,” did not offer an objective definition. In 2007, the evaluation of
the PMH characteristics was superseded by the adoption of the probable maximum storm
surge (PMSS) hazard assessment.
Historically, design-basis surge and seiche hazard flood estimates for nuclear power plants
(NPPs) have been developed using deterministic analysis approaches based on the
“probable maximum” or “maximum credible” event concept (i.e., the event thought to have
“virtually no risk of exceedance”). The level of analysis may range from very conservative,
based on simplifying assumptions, to detailed analytical estimates of each facet of the floodcausing mechanism studied.
In response to Hurricane Katrina in 2005, the NRC formed a storm surge research program
focused on developing modern, risk-informed, hazard assessment techniques and
additional guidance through cooperation with the National Oceanic and Atmospheric
Administration (NOAA) and USACE. This research program produced several technical
reports. NOAA, U.S. Department of Energy (DOE) laboratories, USACE, and commercial
contractors currently are assisting the NRC’s Office of New Reactors (NRO) in reviewing
storm surge hazards and updating regulatory guidance.
In 2009, the NRC’s Office of Nuclear Regulatory Research (RES) tasked the USACE
Engineer Research and Development Center/Coastal and Hydraulics Laboratory (ERDC
CHL) to review NOAA Technical Report NWS 23 and NRC Regulatory Guide 1.59, “Design
Basis Floods for Nuclear Power Plants.” ERDC CHL found that several assumptions in the
PMH described in NWS 23 are not consistent with the current state of knowledge and
recommended that the PMH concept be updated in accordance with new theoretical
concepts and data (USACE, 2009).
The 2009 ERDC CHL report also states that the ocean model recommended in Regulatory
Guide 1.59 (1977) is “extremely limited by restrictions and simplifications made in order to
make the problem computationally tractable given the computer resources available in the
early to mid-1970’s” (Resio et al., 2012; USACE, 2009). The review findings recommended
adoption of a modern combined system of wind, wave, and coastal circulation models that
properly define the physical system and include an appropriate nonlinear coupling of the
relevant processes. Thus, the simplified methods provided in Appendix C, “Simplified
Methods of Estimating Probable Maximum Surges,” of Regulatory Guide 1.59 (1977) are not
considered acceptable or used for new reactor application storm surge hazard
assessments. However, the approach provided in NWS 23 (1979) is still acceptable for
licensing decisions.
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2.

Acceptance Criteria

2.1.

Existing Regulatory Guidance

The applicable regulatory requirements for identifying surge and seiche hazards are as
follows:
•

10 CFR Part 50, “Domestic Licensing of Production and Utilization Facilities.”
General Design Criterion 2 (GDC 2), “Design Bases for Protection against Natural
Phenomena,” of Appendix A, “General Design Criteria for Nuclear Power Plants,”
requires that structures, systems, and components important to safety be designed
to withstand the effects of natural phenomena such as floods, tsunamis, and seiches
without loss of capability to perform their safety functions. Criterion 2 also requires
that design bases for these structures, systems, and components reflect
(1) appropriate consideration of the most severe of the natural phenomena that have
been historically reported for the site and surrounding region with sufficient margin
for the limited accuracy and quantity of the historical data and the period when the
data have been accumulated, (2) appropriate combinations of the effects of normal
and accident conditions with the effects of the natural phenomena, and (3) the
importance of the safety functions to be performed.

•

10 CFR Part 100, “Reactor Site Criteria,” requires that physical characteristics of the
site, including seismology, meteorology, geology, and hydrology, be taken into
account when determining the acceptability of a site for a nuclear power reactor.

Other NRC guidance documents, such as NUREGs and regulatory guides, describe
methods that the NRC staff considers acceptable to use in implementing specific parts of
the agency’s regulations, to explain techniques the staff uses in evaluating specific
problems or postulated accidents, and to provide guidance to applicants and licensees.
Compliance with recommendations contained in the NRC guidance is not mandated. Thus,
in addition to the applicable regulatory requirements, the NRC staff uses appropriate
sections of the following guidance documents for the identified acceptance criteria:
•

NUREG-0800, “Standard Review Plan for the Review of Safety Analysis Reports for
Nuclear Power Plants (LWR Edition),” provides guidance to NRC staff in performing
safety reviews under 10 CFR Part 50 and 10 CFR Part 52, “Licenses, Certifications,
and Approvals for Nuclear Power Plants.” Section 2.4.5 provides general guidance
for estimating flooding due to storm surge and seiche.

•

NUREG/CR-7046, “Design-Basis Flood Estimation for Site Characterization at
Nuclear Power Plants in the United States of America,” issued November 2011,
provides present-day methodologies and technologies that can be used to estimate
design-basis floods at nuclear power plants for a range of flooding mechanisms.
Sections 3.5, 3.6, Appendix E, and Appendix F provide additional guidance and an
illustrative case study for a probable maximum storm surge analysis (Prasad et
al., 2011).

•

Regulatory Guide 1.59, “Design Basis Floods for Nuclear Power Plants,” Revision 2,
issued August 1977, as supplemented by best current practices (NRC, 1977).

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•

Regulatory Guide 1.27, “Ultimate Heat Sink for Nuclear Power Plants,” Revision 2
(NRC, 1976a).

•

Regulatory Guide 1.102, “Flood Protection for Nuclear Power Plants,” Revision 1,
provides guidance for the protection of nuclear power plants from flooding
(NRC, 1976b).

•

Regulatory Guide 1.206, “Combined License Applications for Nuclear Power Plants.”
Section C.I.2.4.5 provides general guidance for estimating flooding due to storm
surge and seiche (NRC, 2007).
•

ANSI/ANS-2.8-1992, “American National Standard for Determining Design Basis
Flooding at Nuclear Reactor Sites,” provides a methodology for estimating storm
surges and seiches at estuaries and coastal areas on oceans and large lakes.
Appendix C gives a simplified method of estimating surges on the Atlantic and Gulf
Coasts (ANS, 1992).

•

JLD-ISG-2012-05 provides guidance for performing the integrated assessment for
flooding, when necessary (NRC, 2012b).

2.2.

Updates to Guidance

In the SRP 2007 update, the adoption of the PMSS superseded the evaluation of the PMH
characteristics. The 2007 update also clarified the PMH. The SRP relates the PMSS and
the PMH when it states that the “PMSS is the surge that results from a combination of
meteorological parameters of a probable maximum hurricane (PMH)…and has virtually no
probability of being exceeded in the region involved.” To avoid confusion with strictly
probabilistic flood hazard assessments, the “probable maximum” terminology referenced in
NUREG-0800, Regulatory Guide 1.59, Regulatory Guide 1.206, and ANSI/ANS-2.8-1992 is
not used in this guidance. Instead, the terms “simulated” and “design basis” are used and
the following terms are defined in the Appendix:
•
•
•
•

simulated hurricane (SH)
simulated wind storm (SWS)
simulated storm surge (SSS)
design-basis storm surge (DBSS)

No other Federal agencies, such as the USACE, NOAA, and the Federal Emergency
Management Agency (FEMA), currently use the “probable maximum” or “standard project”
terminology for storm surge. However, NRC guidance uses these terms. This document is
the first attempt to make NRC guidance more consistent with the guidance of other Federal
agencies.
NUREG-0800, Revision 3 (March 2007), recommends the DBSS that the PMH induces
should be estimated as recommended by Regulatory Guide 1.59 and supplemented by
current best practices. However, the determination of the storm surge from bathystrophic
models (Bretschneider, 1966; Bodine, 1969; Pararas-Carayannis, 1975) used in Regulatory
Guide 1.59, which is based on earlier wind field calculations, is not consistent with the

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current state of knowledge. Therefore, the DBSS estimates using the simplified methods
provided in Appendix C of Regulatory Guide 1.59 (1977) are not considered acceptable and
are not used for new reactor application storm surge hazard assessments. However, the
approach in NWS 23 (1979) is still acceptable for licensing decisions. The current practice
in storm-surge modeling is based on the use of coupled hydrodynamic ocean circulation and
wave models, both driven by a planetary boundary layer (PBL) model that provides
atmospheric forcing (Figure 1). Storm surge models should be validated using historical
information and data in the region of interest.
For seiche, analytical methods can be used for screening. However, if seiche cannot be
eliminated from further consideration using analytical methods, numerical modeling will be
necessary. Seiche models should be validated using historical information and data in the
region of interest.
The NRC Web site (NRC, 2012) provides combined license (COL) and early site permit
safety analysis reports and NRC requests for additional information (RAIs) addressing surge
and windwave evaluations associated with recent new reactor reviews.

3.

Surge Hazard Assessment

All coastal nuclear power plant sites and nuclear power plant sites located adjacent to
cooling ponds or reservoirs subject to potential hurricanes, windstorms, and squall lines
must consider the potential for inundation from storm surge and windwaves. For example, a
hurricane, extra-tropical storm, or squall line could cause a water-level change in an
adjacent body of water. The resulting change in water levels, if not considered in the project
design, could affect safety-related structures located at the plant site.
All water wave processes, including surge, consist of generation, propagation, and
dissipation. Section 3 of this ISG (Surge Hazard Assessment) describes the HHA approach
and the role that deterministic and combined deterministic-probabilistic methods play in
surge hazard assessments. Section 3.2 (Meteorological Parameters) provides three surge
generation approaches. For hurricanes, Section 3.2.1 (Hurricane Parameters) discusses a
deterministic approach in Section 3.2.1.1 (Probable Maximum Hurricane) and a combined
deterministic-probabilistic approach in Section 3.2.1.2 (Joint Probability Method). Similarly,
for extra-tropical storms and squalls lines (Section 3.2.2), Section 3.2.2 (ANSI/ANS-2.81992) and Section 3.2.2.1 (Empirical Simulation Technique) provide deterministic and
combined deterministic-probabilistic surge generation approaches.
Section 3.3 (Surge Parameters) addresses the propagation of surge phase beginning with a
discussion of datums (Section 3.3.1). Starting a surge hazard assessment with bathymetric
and topographic data using appropriate vertical datums is essential to correctly reference
water levels with site elevations. For additional margin, Section 3.3.2 (Antecedent Water
Levels) provides guidance on the determination of pre-surge model propagation stillwater
levels using astronomical tides (Section 3.3.2.1), initial rise (Section 3.3.2.2), and sea-level
rise (Section 3.3.2.3). Section 3 ends with the surge propagation phase described in
Section 3.3.3 (Surge Water Levels). Section 3.3.3.1 (ADvanced CIRCulation Surge Model
(ADCIRC)) and Section 3.3.3.2 (Sea, Lake, Overland Surge from Hurricanes (SLOSH))
provide a discussion of two state-of-the-art surge models that the NRC and other Federal
agencies currently use.

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3.1.

Overview

Site hazard assessments follow a progressive screening approach, consisting of a series of
progressively refined methods that increasingly use more detailed site-specific data to
demonstrate whether the site is protected from the adverse effects of severe floods. This
approach (Figure 2) is formalized in the HHA approach described in NUREG/CR-7046
(Prasad et al., 2011). The HHA approach provides a roadmap for applying a hierarchy of
conceptual and mathematical models for the efficient determination of design-basis flood
mechanisms and levels.
Probabilistic-only and the deterministic-only approaches to the estimation of very lowprobability storm surges have their strengths and deficiencies, depending on the safety
hazard assessment objective. Previous site hazard assessments for storm surge have used
a deterministic-only HHA approach. However, other Federal agencies recently begun to join
the two approaches to provide some advantages over either approach implemented
independently (Resio et al., 2012). This document is the first attempt to make NRC
guidance more consistent with other Federal agency guidance.
The USACE has developed a probabilistic-deterministic methodology for storm surge
hazard assessment that can be combined with the HHA approach to provide a DBSS with
risk information. The methodology uses an integrative, interdisciplinary approach that
incorporates state-of-the-art knowledge in hurricane science, hydrology, and probabilistic
methods. This methodology involves the following steps:
(1)

Selection of a stochastic set of simulated storm tracks affecting the region of interest.

(2)

Hydrodynamic simulation of the region of interest using a high-resolution surge
model and the simulated storm tracks to generate time histories of wind speeds and
corresponding time histories of storm surge heights at sites within the affected
region.

(3)

Use of wind speed and storm surge height information generated in Steps (1) and (2)
to develop probabilistic information on the joint probability of wind speed and storm
surge height events (Resio et al., 2012).

Regardless of the method used, an assessment of sensitivities and uncertainties should be
provided for model parameters that may have significant influence on design-basis storm
surge estimates.
3.2.

Meteorological Parameters

Storm surge can result from several different types of storms (e.g., tropical cyclones, extratropical cyclones, squall lines, and hybrid storms). For example, extra-tropical cyclones,
also known as Northeasters, move along the Atlantic coast with winds from the northeast
onto the shoreline, typically producing winds ranging from 30 to 40 mph (48 to 64 km/h) with
gusts that can exceed 74 mph (119 km/h). Although below hurricane force, these winds can
persist for several days to a week and generate large waves and storm surges. In
comparison, wind speed and storm surge elevations are more severe in hurricanes. Their
shoreline effects tend to be more localized, and they are generally confined to stretches of
coastline of about 65 miles (105 km) or fewer.

-7-

For the storm surge hazard assessments, the historical record for each storm type
appropriate to the region should be examined to determine estimates for extreme winds.
This detailed analysis of historical storm events in the region should be augmented by
synthetic storms parameterized to account for conditions more severe than those in the
historical record, but considered to be reasonably possible on the basis of technical
reasoning.
This guidance considers four techniques for synthetic storm generation:
•
•
•
•

Probable Maximum Hurricane (PMH)
Joint Probability Method (JPM)
ANSI/ANS-2.8-1992
Empirical Simulation Technique (EST)

PMH and JPM are used for generation of synthetic hurricanes (Figure 3). ANSI/ANS-2.81992 and EST are used to generate synthetic extra-tropical storms and squall lines.
3.2.1. Hurricane Parameters
This section applies to all coastal sites, excluding the Great Lakes, as described in
ANSI/ANS-2.8-1992.
3.2.1.1.

Probable Maximum Hurricane

The NOAA NWS Technical Report 23 (Schwerdt et al., 1979) describes the PMH method in
detail. PMH meteorological parameters, as described in NUREG-0800, Section 2.4.5,
define the physical attributes of the PMH to derive wind fields that can serve as input into an
atmospheric model. Storm surge model simulations are performed with numerous
combinations of PMH parameters to obtain the highest design-basis storm surge (DBSS) at
the site.
NOAA NWS Technical Report 23 (NWS 23) provides methods for estimating PMH wind
fields. The PMH is defined as a hypothetical steady-state hurricane with a combination of
values of meteorological parameters that will give the highest sustained wind speed that can
probably occur at a specified coastal location (NOAA, 1979). The term steady-state is
meant to indicate that there is no change in the value of hurricane wind-field parameters
during, at least, the last several hours before the PMH makes landfall. The meteorological
parameters that define the PMH wind field include the hurricane peripheral pressure, central
pressure, radius of maximum winds, forward speed, and track direction. Note that the
NWS 23 method provides no risk information (e.g., return period) and is only applicable to
the deterministic storm surge analysis of hurricanes.
The PMH parameter values in NWS 23 were based on data from historical hurricanes from
1851 to 1977 and were presented for multiple locations along the Gulf of Mexico and
Atlantic Ocean coastlines corresponding to their milepost distances from the U.S. to Mexico
border. Comparisons of hurricane climatology during the period evaluated in NWS 23 with
hurricanes making landfall after 1975 indicate that the NWS 23 parameters for the PMH are
still applicable (NOAA, 2007; Ho et al., 1987; Knutson et al., 2010). However, consistent
with NUREG-0800, Section 2.3, a detailed site- or region-specific hurricane climatology
study should be provided to show that the PMH parameters are consistent with the current
state of knowledge.
-8-

Surge elevation increases with increasing hurricane size. In addition, based on site-specific
topography or bathymetry, the increase in storm surge with increasing hurricane size may
reach an upper bound. Thus, this behavior should be further investigated by varying the
PMH size (radius of maximum wind) beyond the upper bound specified in NWS 23 for a
PMH approaching the site (Irish et al., 2008a; Resio and Westerink, 2008). ANSI/ANS-2.81992, Section 7, provides additional guidance on the critical combinations of PMH
parameters.
Appendix E, “Flooding from Storm Surges: A Case Study,” of NUREG/CR-7046 contains an
example of how the PMH wind field is estimated using the NWS 23 procedure.
3.2.1.2.

Joint Probability Method

The JPM (Myers, 1970) approach quantifies the return periods of storm surges. Statistical
simulation methods such as JPM are needed for coastal flood frequency analysis primarily
because of the unavailability of sufficient historical record from which to derive frequencies
by more conventional means, such as gage analysis. Hurricanes, for example, are both
sporadic and of limited spatial extent, contributing to a great deal of sample variation
(sample error) in local tide gage records. As such, JPM is widely used in coastal flood
studies that USACE and FEMA perform. For example, Federal agencies adopted the JPM
for critical post-Katrina determinations of hurricane surge frequencies (IPET, 2007).
The JPM has been used for simulating hurricanes since the late 1960s. The original JPM
application, while not called JPM, was developed for predicting wave loads on offshore
structures in the Gulf of Mexico (Russell, 1968). The JPM approach that Russell used was
a full Monte Carlo simulation in which model hurricanes were simulated using straight-line
segments with wind and wave fields computed using hurricane wind and wave models. The
methodology was first introduced because the number of historical events (hurricanes) at
any one location is insufficient to enable standard statistical techniques (such as extreme
value analyses) to estimate flood risk, wave height risk, wind speed risk, etc. The JPM
method can be used as an alternative to PMH for deterministic storm surge analysis or used
as an option in a combined deterministic-probabilistic analysis for risk information.
The JPM approach is a simulation methodology that relies on the development of statistical
distributions of key hurricane input parameters (central pressure, radius of maximum winds,
translation speed, and heading) and sampling from these distributions to develop model
hurricanes. The simulation results in a family of modeled storms that preserve the
relationships between the various input model parameters, but provides a way to model the
effects and probabilities of storms that have not yet occurred. The method known as
JPM-OS (Joint Probability Method–Optimum Sampling) also can be used, which reduces
the number of JPM simulated storms needed (Toro et al., 2010).
Resio et al. (2007) first introduced long duration tracks that mimic the behavior of hurricanes
while they are off shore (and generating a wave field). Vickery et al. (2000a) introduced
modeling the full storm track from a wind-only point of view. The simulation methodologies
that Resio et al. (2007) and Vickery et al. (2000b) used both attempt to properly model the
correlations between storm intensity (central pressure) and radius to maximum winds
(RMW). Vickery et al. (2000a) also modeled a relationship between RMW and the
Holland B (Holland, 1980) parameter. Overall, the JPM approach has the conceptual
advantage of considering all possible storms consistent with the local climatology, each
-9-

weighted by its appropriate rate of occurrence. Unlike the NWS 23 method, the key model
hurricane parameters are developed through an analysis of continuously updated local
climatology derived from NOAA’s historical hurricane database (HURDAT; Landsea et al.,
1996; Landsea et al., 2004; Blake et al., 2007; Blake and Gibney, 2011; and NOAA, 2012b).
All parameter combinations analyzed (each defining a synthetic storm) should be simulated
using a surge model constructed to accurately represent the site’s bathymetry, topography,
and ground cover.
For examples of detailed discussions and guidance on the application of the JPM to coastal
issues see Ferro (2007), Niedorodu et al. (2010), Phan et al. (2007), Resio et al. (2007;
2012), Schmalz (1983), Scheffner et al. (1996), and Toro (2007). Divoky and Resio (2007)
provides a comparison of JPM and EST methods.
The NRC and the American Society of Civil Engineers (ASCE) also used the JPM method
for design-basis hurricane wind speeds for nuclear power plants (Vickery et al., 2011;
NRC, 2011) and minimum design loads for buildings and other structures (ASCE, 2010).
3.2.2. Extra-tropical Storm and Squall Line Parameters
A detailed site- or regional-specific meteorological study consistent with SRP Section 2.3
should be conducted to identify applicable mechanisms and to verify that the ANSI/ANS-2.81992 assumptions reflect the most severe meteorological parameters. This applies to all
coastal sites, including the Great Lakes (ANSI/ANS-2.8-1992).
The ANSI/ANS-2.8-1992 standards provide detailed guidance on extra-tropical windstorms
(Section 7.2 of ANSI/ANS-2.8-1992) and squall lines (Section 7.3 of ANSI/ANS-2.8-1992).
For the Great Lakes, a set of fixed criteria of extra-tropical storm parameters is provided
instead of a meteorological study (Sections 7.2.2.3.1 and 7.2.2.3.3 of ANSI/ANS-2.8-1992).
In addition, Section 7.2.3.1 of ANSI/ANS-2.8-1992 states that “[a] moving squall line should
be considered for the locations along Lake Michigan where significant surges have been
observed because of such a meteorological event. The possible region of occurrence
includes others of the Great Lakes.”
3.2.2.1.

Empirical Simulation Technique

The Empirical Simulation Technique (EST) (Scheffner et al., 1999) quantifies the return
periods of storm surges. Statistical simulation methods, such as EST, are necessary for
coastal flood frequency analysis primarily because there is an insufficient historical record
from which frequencies could be derived by more conventional means, such as gage
analysis. For this reason, USACE and FEMA widely use EST in coastal flood studies that
they have performed.
The EST method is an option for a combined deterministic-probabilistic methodology.
However, unlike tropical storms, a set of storm parameters does not easily represent extratropical storms. Thus, the EST frequency analysis is recommended to determine storm
surge stillwater return periods for extra-tropical storms.
EST site estimates are based entirely on the historical storms and flood levels observed at
that site. Alternate life cycles are simulated by assuming that storm occurrence follows a
Poisson process and by implementing a bootstrap resampling from the set of observed
events to construct synthetic records. Flood frequency and variability estimates are then
- 10 -

derived from this synthetic data. The only assumption is that future events will be
statistically similar in magnitude and frequency to past events. The method begins with an
analysis of historical events that have affected a specific location. The selected database of
events is then parameterized to define the characteristics of the event and the impacts of
that event. Parameters that define the storm are referred to as input vectors. Response
vectors define storm-related impacts, such as surge elevation, inundation, and shoreline or
dune erosion, etc. These input and response vectors are then used as a basis for
generating life-cycle simulations of storm-event activity with corresponding impacts.
For detailed discussions and guidance on the application of the EST method to coastal
issues, see, for example, Scheffner et al. (1996), Scheffner et al. (1999), Wilbury et al.
(2007), Zimmer (2008), RENCI (2011), and FEMA (2011, 2012). The USACE Coastal
Engineering Design and Analysis System (CEDAS) includes an EST model for the
generation of storm profiles (USACE, 2012b). Divoky and Resio (2007) compare the JPM
and EST methods.
3.3.

Surge Parameters

This section provides guidance on propagation of the surge phase and includes a
discussion of datums and antecedent water levels (astronomical tides, initial rise, and sealevel rise). In addition, this section provides guidance on determining surge water levels.
3.3.1. Datums
There are two types of datums: tidal and fixed. For example, mean sea level pertains to the
local mean sea level (MSL), which is a tidal datum based on astronomical tides. A tidal
datum is determined over a 19-year National Tidal Datum Epoch. North American Vertical
Datum of 1988 (NAVD88) and National Geodetic Vertical Datum of 1929 (NGVD29) are
fixed geodetic datums whose elevation relationships to local MSL and other tidal datums
may not be consistent from one location to another. NAVD88 replaced NGVD29 as the
national standard geodetic reference for heights.
Licensees select the applicable datum to conform to site-specific requirements (e.g., local
and state requirements) as well as best practices and engineering judgement. Once
selected, the datum should be applied universally for all flood evaluations and
documentation.
3.3.2. Antecedent Water Levels
Antecedent water levels should be included in storm surge DBSS estimation. Regulatory
Guide 1.59 (NRC, 1977) and ANSI/ANS-2.8-1992 recommend that the 10 percent
exceedance high tide be used to represent the antecedent water level. In addition, long term
sea level changes should also be considered. For example, antecedent water level should
be taken as the sum of the stillwater depth (i.e., mean sea or lake level), 10 percent
exceedance high tide, and long-term sea-level rise. Because of the non-linear wave effects,
the antecedent water level should be applied as the initial storm surge model stillwater level.
Section 5 addresses post-modeling storm surge water level additions, such as wind waves
and wave runup.

- 11 -

3.3.2.1.

Tides

In computing the surge level, the 10% exceedance high tide should be considered to occur
coincidentally with the storm surge. The 10% exceedance high tide is the high-tide level that
is equaled or exceeded by 10% of the maximum monthly tides over the tidal epoch (a
continuous 21-yr period in most locations). This tide can be determined from the recorded
tide or from the predicted astronomical tide. If astronomical tides are used, sea level
anomaly should be added. Sea level anomalies (also referred to as initial rise) are
departures of the water surface elevation from astronomical tides due to various
meteorological and oceanographic forcings. Historical and current tide observations,
information on tidal datums, as well as predicted tide levels can be found on the NOAA
Tides and Currents Web site (NOAA, 2012a). NOAA maintains a network of tide gage
stations along the U.S. shoreline, including the Great Lakes.
3.3.2.2.

Initial Rise

For locations where the 10 percent exceedance high spring tide is estimated from observed
tide data, Regulatory Guide 1.59 and ANSI/ANS-2.8-1992 indicate that a separate estimate
of the initial rise is not necessary. This approach for estimating 10 percent exceedance high
tide, based on recorded tides, intrinsically includes the effects of initial rise.
3.3.2.3.

Long-Term Sea Level Rise

Relative sea-level rise is the combined effect of water-level change and land subsidence.
The NOAA National Ocean Service, the U.S. Global Change Research Program, and the
Intergovernmental Panel on Climate Change (IPCC) monitor and report sea-level rise
information, which also should be included in design-basis flood analysis for coastal sites
(IPCC, 2007).
NOAA maintains tide gage stations along the U.S. shoreline (NOAA, 2012a) and has
evaluated the trend of sea-level rise. Measurements at any given tide station include both
global sea-level rise and vertical land motion, such as subsidence, glacial rebound, or largescale tectonic motion. Thus, the long-term sea-level rise should be derived for the expected
life of the nuclear power plant based on the trend in site or regional tide gage station data.
As part of the HHA approach, regional or global sea-level rise trends can be added in initial
storm surge simulations to the site or regional observed trend for additional margin.

- 12 -

3.3.3. Surge Water Levels
This section provides guidance on methods for computation of surge water levels. Storm
surge models developed by Federal agencies, such as USACE or academic and research
institutions, that are currently being used in standard engineering practice are adequate for
storm surge hazard analysis. However, other models may be used with documentation of
their site-specific application as outlined in Section 5.3 of NUREG/CR-7046. For examples
of current state-of-the-art storm surge models, the following models developed by Federal
agencies are described:
•
•

ADvanced CIRCulation Surge Model (ADCIRC)
Sea, Lake, Overland Surge from Hurricanes (SLOSH)

3.3.3.1.

ADvanced CIRCulation Surge Model

The development of the ADCIRC model occurred at the USACE Dredging Research
Program as a family of two- and three-dimensional finite element-based models (Luettich,
Westerink, and Scheffner, 1992; Westerink et al., 2008). An important feature of the model
is its ability to simulate tidal circulation and storm-surge propagation over very large
computational domains while simultaneously providing high resolution in areas of complex
shoreline configuration and bathymetry.
The USACE hurricane modeling system used for the safety evaluation of new reactor COL
applications (Resio, 2012) combined various wind models (TC96 PBL), the Wave Prediction
Model (WAM) offshore and steady-state spectral wave (STWAVE) nearshore wave models,
and the ADCIRC basin to channel scale unstructured grid circulation model (Figure 1).
For detailed discussions and guidance on the application of ADCIRC to coastal issues, see,
for example, Dean et al. (2004), Luettich and Westerink (2004), Coastal Protection and
Restoration Authority of Louisiana (2007), IPET (2007), Toro (2007), Blandon and Vickery
(2008), Westerink et al. (2008), and Resio et al. (2007, 2012). Refer to Resio (2012) for
application of the ADCIRC model to new reactors using the JPM-OS method.
3.3.3.2.

Sea, Lake, Overland Surge from Hurricanes

NOAA developed the SLOSH (Sea, Lake, Overland Surge from Hurricanes) computer
model to forecast real-time hurricane storm surge levels on continental shelves, across
inland bodies of water and along coastlines, including inland routing of water levels. SLOSH
is a depth-averaged two-dimensional finite difference model on curvilinear polar, elliptical, or
hyperbolic grid schemes. Modification of storm surges because of the overtopping of
barriers (including levees, dunes, and spoil banks), the flow through channels and
floodplains, and barrier cuts and breaches are included in the model. The effects of local
bathymetry and hydrography also are included in the SLOSH simulation. SLOSH also
incorporates an atmospheric model for tropical cyclones.
The SLOSH model inputs are hurricane pressure difference, hurricane track description
including landfall location, forward speed, and size, given as the radius of maximum wind,
which define the physical attributes of a hurricane in performing a storm surge simulation
(Jelesnianski, 1992). NOAA provides two models: (1) SLOSH Display Program, and (2)
SLOSH v3.95 FORTRAN code. The SLOSH Display Program is only valid for Category 1
through Category 5 hurricanes. Therefore, SLOSH Display Program results and methods
- 13 -

extrapolating these results beyond Category 5 hurricanes are not acceptable for licensing
reviews. The SLOSH v3.95 FORTRAN code using NWS-23, JPM, and EST methods is one
acceptable software package for performing storm surge hazard assessments. Details of
SLOSH model formulation and application can be found in Jelesnianski (1992), NOAA
(2006, 2009), and Glahn et al. (2009).
SLOSH model predictions have been validated against observed hurricane surge levels at
several locations (Jelesnianski, 1992; Jarvinen, 1985). For example, as an emergency
management tool, SLOSH is applied to the entire U.S. East Coast, Gulf of Mexico
coastlines, Hawaii, Guam, Puerto Rico, and the U.S. Virgin Islands. The errors of the
SLOSH model predictions, defined by subtracting the observed surge water levels from
model predictions, were evaluated for 10 storms in 8 SLOSH model basins, 90 percent of
which were in the Gulf of Mexico. Based on a comparison of the SLOSH simulated surge
heights against observations, NOAA concludes that the model results generally stayed
within ± 20 percent for significant surges (Jarvinen, 1985).
SLOSH does not include astronomical tides, wave run ups, or additional heights generated
by wind-driven or breaking waves on top of the stillwater storm surge. In addition, the
SLOSH v3.95 FORTRAN code that NWS provides contains a limitation in which grid cells
with elevations greater than 10.7 meters (m) (35 feet (ft)) NAVD88 were removed from the
flooding computation (i.e., these cells could never be flooded). NWS confirmed that the
10.7 m (35 ft) limit for surge in the SLOSH program is historical and does not pose any
particular problems when it is relaxed. The SLOSH program code should be validated with
and without the changes in the code to determine that the changes in the code are effective
and accurate in allowing flooding at elevations greater than 10.7 m (35 ft). One method is to
compare the same hurricane scenario for each code through validation against historical
storm surge data.
NOAA has developed the Extra-Tropical Storm Surge Model (ET-Surge; NOAA, 2012d),
which can use a separate planetary boundary wind model in conjunction with a modified
SLOSH model to predict storm surge based on large extra-tropical storms as opposed to the
tropical storms for which SLOSH was originally developed (Kim et al., 1996).
Appendix E of NUREG/CR-7046 contains an example of how the DBSS is estimated using
SLOSH and the NWS 23 procedure.

4.

Seiche Hazard Assessment

Seiche is an oscillatory wave generated in lakes, bays, or gulfs as a result of seismic or
atmospheric disturbances and with a period ranging from a few minutes to a few hours. The
oscillatory modes for the body of water in question should be calculated from a variety of
potential sources. Sources to consider include (1) local or regional forcing phenomena,
such as barometric pressure fluctuations, strong winds, rapid changes in wind direction,
surge associated with passage of local storms; and (2) distant but large forcing mechanisms
such as distant storms, tsunami, or earthquake-generated seismic waves. For bodies of
water with simple geometries, modes of oscillation can be predicted from the shape of the
basin using analytical formulas. For example, the resonance within a makeup water
reservoir may be approximated by a rectangular basin(s) using an approach provided in the
USACE Coastal Engineering Manual (CEM) (USACE, 2008; Dean and Dalrymple, 1991).

- 14 -

Most natural bodies of water have variable bathymetry and irregular shorelines and may be
driven by a combination of forcing mechanisms. For such bodies, seiche periods and water
surface profiles should be determined through numerical long-wave modeling. The USACE
SMS or CEDAS modeling systems, as well as documented models, such as the Princeton
Ocean Model, should be used for complex seiche analyses. Appendix F of NUREG/CR7046 (Prasad et al., 2011) provides a case study of seiche flooding using analytical
formulas.

5.

Wave and Inundation Effects Associated with Surge or Seiche

This section relates to the wave dissipation phase in which surge and seiche wave action
can directly affect the site. Wave action includes deep and shallow water-wave generation.
Wind-generated wave activity that can occur independently of, or coincidentally with storm
surge or seiche should be included in surge and seiche flood hazard analyses. Available
records should be used to characterize the wave climate near the site using measures such
as significant and maximum wave heights. Tides, wave setup, wave runup, splash, or
overtopping, as appropriate, also should be considered in the analyses and surge and
seiche flooding estimates.
Section 5.1 (Coincident Wave Heights) provides guidance on the calculation of wind waves
that can occur coincidentally with the storm surge or seiche stillwater level. If the inundation
(Section 5.2) reaches the site, other factors such as wave runup (Section 5.3), drawdown
(Section 5.4), hydrostatic and hydrodynamic forces (Section 5.5), debris and water-borne
projectiles (Section 5.6), and the effects of sediment erosion and deposition (Section 5.7)
should be considered, as appropriate.
5.1.

Coincident Wave Heights

ANSI/ANS-2.8-1992 recommends using the USACE Shore Protection Manual (SPM)
(USACE, 1984) for analyzing wave action. However, the USACE CEM (USACE, 2008) has
superseded the SPM. The CEM recommends methods to apply to areas with simple
bathymetry. Per the HHA approach, a numerical model may be needed, depending on the
complexity of the bathymetry.
If needed, the current practice in storm-surge modeling is coupled hydrodynamic ocean
circulation and wave models, both driven by a planetary boundary layer (PBL) model that
provides the atmospheric forcing (Figure 1). Per USACE CEM guidance, off-coast wave
activity is determined using either the WAM or WAVEWATCHIII models. For nearshore and
surf zone wave processes, SWAN (Simulating Waves Nearshore) or STWAVE (STeady
State spectral WAVE) are capable of computing the wave conditions. For detailed
discussions and guidance on the application of these models, see Smith et al. (2001), Smith
and Sherlock (2007), and USACE (2012).
5.2.

Inundation

Inundation effects should be evaluated and typically are available from standard surge
models.

- 15 -

5.3.

Wave Runup

Wave runup can be calculated using the lesser of the maximum wave height (1.67 x the
significant wave height) or the maximum breaker height, in accordance with ANSI/ANS-2.81992 and the USACE CEM (USACE, 2008). Wave runup models also can be used in
addition to the calculation of overtopping rates when waves encounter a shoreline or
embankment. The inputs include wave type, breaking criteria, wave height, wave period,
structure slope, structure height, slope type, material used (e.g., rip-rap, rubble, tetrapods),
and roughness coefficient. In calculating overtopping rates, the relative heights of the
embankment to the still-water level are important. For state-of-the-art solutions to wave
runup, the USACE Automated Coastal Engineering System (ACES) is available from the
CEDAS interface (USACE, 2012b).
5.4.

Drawdown (Low Water Level)

Drawdown may be an issue when safety-related structures and equipment (e.g., UHS
intakes) depend on water sources where storm surge or seiche may affect the availability of
water (NRC, 1976a).
Numerical models, such as ADCIRC and SLOSH, provide a visual or quantitative estimation
of low-water level conditions. Thus, storm surge and seiche model flooding elevation data
should be retained and used for a detailed analysis of low-flow conditions.
5.5.

Hydrostatic and Hydrodynamic Forces

The hydrostatic and hydrodynamic forces should be determined when storm surge or seiche
flood levels impinge on flood protection or safety-related structures, systems and
components (SSCs). Thus, storm surge or seiche model current velocity and wave and
wind data should be retained and used for a detailed analysis of hydrostatic and
hydrodynamic forces.
The USACE CEM provides guidance on hydrostatic and hydrodynamic forces for coastal
structures (USACE, 2008).
5.6.

Debris and Water-Borne Projectiles

The effect from debris and waterborne projectiles should be considered when storm surge
or seiche flood levels impinge on flood protection or safety-related SSCs. Thus, storm
surge or seiche model current velocity and wave and wind data should be retained and used
for a detailed analysis of debris and waterborne projectiles.
5.7.

Effects of Sediment Erosion or Deposition

The impact of sediment erosion and deposition should be considered when storm surge or
seiche flood levels impinge on flood protection, safety-related SSCs, and foundation
materials. Thus, storm surge or seiche model current velocity plus wave and wind data
should be retained and used for a detailed analysis of the effects of sediment erosion and
deposition.

- 16 -

The USACE CEM provides guidance on the impacts of sediment erosion and deposition for
coastal structures (USACE, 2008).

- 17 -

6.

Figures

PBL Model input:
SH, SWS

Surge Model:
SLOSH
ADCIRC

Offshore Waves:
WAM, WAVEWATCHIII
Nearshore Waves:
STWAVE, SWAN

Figure 1. Storm Surge Modeling System (Resio et al., 2012)

- 18 -

1

Def inition or ref inement of
meteorological parameters f or
hurricanes as well as extra-tropical
storms and squall lines, as applicable
[ISG Section 3.2]

Def inition or ref inement of surge
parameters including antecedent water
levels (astronomical tides, initial rise,
and sea level rise), as applicable
[ISG Section 3.3.2]

2

Computation of surge water levels using
meteorological and surge parameters
[ISG Section 3.3.3]

3

Evaluation of wave and inundation
ef f ects
[ISG Section 5]
4

5

No

Surge elevation
< Site elevation?

Yes

6

Can variables &
parameters be
f urther ref ined?
No

Storm surge assessment
complete
7

Figure 2. Storm Surge Hierarchical Hazard Assessment

- 19 -

Yes

Figure 3. Illustration of 200 Sy
ynthetic Storm Tracks (Emanuel, 2012)

- 20 -

7.

References

American National Standards Institute, ANSI/ANS-2.8-1992, “American National Standard
for Determining Design Basis Flooding at Nuclear Reactor Sites,” La Grange Park, IL.
American Society of Civil Engineers and the Structural Engineering Institute,
ASCE/SEI 7-2010, “Minimum Design Loads for Buildings and Other Structures.”
Blake, E.S., E.N. Rappaport, and C.W. Landsea, 2007, “The Deadliest, Costliest and Most
Intense United States Tropical Cyclones from 1851–2006 (and Other Frequently Requested
Hurricane Facts),” Technical Memorandum NWS-TPC-5, NOAA, Silver Spring, MD.
Blake, E.S. and E.J. Gibney, 2011, “The Deadliest, Costliest and Most Intense United States
Tropical Cyclones from 1851–2010 (and Other Frequently Requested Hurricane Facts),”
Technical Memorandum NWS-TPC-6, NOAA, Silver Spring, MD.
Blandon, B.O. and P.J. Vickery, 2008, “North Carolina Coastal Flood Analysis System
Hurricane Parameter Development,” Technical Report TR-08-06, Renaissance Computing
Institute, Chapel Hill, NC.
Bodine, B.R., 1969, “Hurricane Surge Frequency Estimated for the Gulf Coast of Texas,”
Technical Memorandum No. 26, U.S. Army Corps of Engineers, Coastal Engineering
Research Center, Washington, DC.
Bodine, B.R., 1971, “Storm Surge on the Open Coast Fundamental and Simplified
Prediction,” Technical Memorandum No. 35, U.S. Army Corps of Engineers, Coastal
Engineering Research Center, Washington, DC.
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GUIDANCE FOR PERFORMING A TSUNAMI HAZARD ASSESSMENT

1.Introduction ...................................................................................................... - 2 1.1.Format of Guidance ....................................................................................... - 2 1.2.Historical Perspective .................................................................................... - 2 2.Acceptance Criteria .......................................................................................... - 3 2.1.Regulatory Guidance ..................................................................................... - 3 2.2.Updates to Guidance ..................................................................................... - 4 3.Tsunami Hazard Assessment .......................................................................... - 5 3.1.Overview ....................................................................................................... - 5 3.2.Historical Tsunami Data ................................................................................ - 6 3.3.Source Generator Characteristics ................................................................. - 7 3.4.Tsunami Computational Model Initial Conditions........................................... - 7 3.4.1.
Datums.............................................................................................. - 7 3.4.2.
Antecedent Water Levels ................................................................ - 7 3.4.2.1. Tides ............................................................................................... - 7 3.4.2.2. Initial Rise ....................................................................................... - 8 3.4.2.3. Long-Term Sea-Level Rise ............................................................. - 8 3.5.Tsunami Propagation Computational Modeling Tools ................................... - 8 4.Wave and Inundation Effects for Tsunami ..................................................... - 9 4.1.Inundation...................................................................................................... - 9 4.2.Wave Runup.................................................................................................. - 9 4.3.Drawdown (Low Water Level) ....................................................................... - 9 4.4.Hydrostatic and Hydrodynamic Forces ........................................................ - 10 4.5.Debris and Waterborne Projectiles .............................................................. - 10 4.6.Effect of Sediment Erosion and Deposition ................................................. - 10 5.References ...................................................................................................... - 11 -

Enclosure 2 to JLD-ISG-2012-06

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January 4, 2013

1. Introduction
The purpose of this interim staff guidance (ISG) is to provide the U.S. Nuclear Regulatory
Commission (NRC) staff with a technical basis for reviewing tsunami hazard site
characteristics per the March 12, 2012, letters issued to operating nuclear power plants in
accordance with the provisions of Sections 161.c, 103.b, and 182.a of the Atomic Energy
Act of 1954, as amended (the Act), and NRC regulations in 10 CFR 50.54(f).
1.1.

Format of Guidance

Section 1.2 (Historical Perspective) discusses the evolution in tsunami regulatory guidance
during the time between the licensing of the operating plants and the licensing activities for
new reactors. Section 2 (Acceptance Criteria) continues with a discussion of the existing
regulatory guidance (Section 2.1) and guidance updates (Section 2.2) based on the ongoing
new reactor safety reviews and current state of knowledge. Particular attention is given
here to tsunami term definitions and current best practices.
Section 3.1 (Overview) describes the Hierarchical Hazard Assessment (HHA) approach and
the role that deterministic and combined deterministic-probabilistic methods play in tsunami
hazard assessments. The tsunami source generation is discussed in Section 3.2 (Historical
Tsunami Data) and Section 3.3 (Source Generator Characteristics). Section 3.4 discusses
tsunami model initial conditions. Section 3.5 (Tsunami Propagation Models) describes the
state-of-the-art tsunami models that the NRC, industry, and other Federal agencies currently
use.
Section 4 (Wave and Inundation Effects of Tsunami) consists of tsunami wave dissipation
and where tsunami wave action can directly affect the site. Wave action includes deep and
shallow water wave generation. Tides, wave setup, wave runup, splash, or overtopping, as
appropriate, should be considered in the analyses and included in tsunami flooding
estimates. Inundation (Section 4.1) looks at the horizontal distance that tsunami wave
propagates inland before dissipation (wave breaking). If the inundation reaches the site,
wave runup (Section 4.2), drawdown (Section 4.3), hydrostatic or hydrodynamic forces
(Section 4.4), debris and waterborne projectiles (Section 4.5) and the effects of sediment
erosion and deposition (Section 4.6) should be considered. References are provided in
Section 5.
1.2.

Historical Perspective

In response to the 2004 Indian Ocean tsunami, the NRC coordinated a tsunami safety study
in 2005 with the National Tsunami Safety initiative that the National Oceanic and
Atmospheric Administration (NOAA) conducted. The Pacific Northwest National Laboratory
(PNNL) and the Pacific Marine and Environmental Laboratory (PMEL), which is a part of
NOAA, conducted the NRC tsunami hazard study. This effort resulted in the publication of
two documents: NUREG-CR 6966 (Prasad, 2008), which was published in final form in
March 2009, and NOAA Technical Memorandum OAR PMEL-136, “Scientific and Technical
Issues in Tsunami Hazard Assessment of Nuclear Power Plant Sites,” which was published
in 2007.
In 2006, the NRC also initiated a long-term tsunami research program. This program, which
includes cooperative work with the U.S. Geological Survey (USGS) and NOAA, was
designed both to support activities associated with the licensing of new nuclear power plants
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in the U.S. and to support development of new regulatory guidance. This research program
has resulted in several publications and made important contributions to tsunami modeling
approach and standards, as summarized in conference papers by Kammerer (2008).
The NRC research program includes assessment of both seismic- and landslide-based
tsunamigenic sources in both the near and far fields. The inclusion of tsunamigenic
landslides, an important category of sources that affect tsunami hazard levels for the
Atlantic and Gulf Coasts, is a key difference between NRC’s research program and most
other tsunami hazard assessment programs that existed at the time. The initial phase of
work undertaken by the USGS as part of the research program consisted of collection,
interpretation, and analysis of available offshore data, with significant effort focused on
characterizing offshore near-field landslides and analyzing their tsunamigenic potential and
properties. This work is summarized in ten Brink et al. (2008). In addition, a compendium
of eight papers was published in a special edition of Marine Geology Special Issue:
Tsunami Hazard along the U.S. Atlantic Coast, Volume 264, Issues 1-2, (2009), which
documents the results of the NRC research program.
More recently, as part of the NRC research program, the USGS has performed studies to fill
in gaps in the original data set. The USGS and NRC have also investigated the potential for
increased implementation of probabilistic hazard assessment methods. This effort included
holding a workshop to investigate probabilistic hazard assessment of landslide-induced
tsunami (Geist and ten Brink, 2012). The NRC may augment its guidance on tsunami
hazard assessments after the completion of ongoing research.

2.

Acceptance Criteria

2.1.

Regulatory Guidance

The applicable regulatory requirements for identifying tsunami hazards are as follows:
•

10 CFR Part 50, “Domestic Licensing of Production and Utilization Facilities.”
General Design Criterion 2 (GDC2), “Design Bases for Protection against Natural
Phenomena,” of Appendix A, “General Design Criteria for Nuclear Power Plants,”
requires that structures, systems, and components (SSCs) important to safety be
designed to withstand the effects of natural phenomena such as floods, tsunami, and
seiches without loss of capability to perform their safety functions. Criterion 2 also
requires that design bases for these SSCs reflect (1) appropriate consideration of
the most severe of the natural phenomena that have been historically reported for
the site and surrounding region with sufficient margin for the limited accuracy and
quantity of the historical data and the period of time in which the data have been
accumulated, (2) appropriate combinations of the effects of normal and accident
conditions with the effects of the natural phenomena, and (3) the importance of the
safety functions to be performed.

•

10 CFR Part 100, “Reactor Site Criteria,” requires that physical characteristics of the
site, including seismology, meteorology, geology, and hydrology, be taken into
account when determining the acceptability of a site for a nuclear power reactor.

Other NRC guidance documents, such as NUREGs and regulatory guides (RGs) describe
methods that the NRC staff considers acceptable to use in implementing specific parts of
the agency’s regulations, to explain techniques the staff uses in evaluating specific
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problems or postulated accidents, and to provide guidance to applicants and licensees.
Compliance with recommendations contained in the guidance is not mandated. Thus, in
addition to the applicable regulatory requirements, the staff uses appropriate sections of the
following regulatory guides for the identified acceptance criteria:
•

NUREG-0800, “Standard Review Plan for the Review of Safety Analysis Reports for
Nuclear Power Plants (LWR [light-water reactor] Edition)” provides guidance to NRC
staff in performing safety reviews under 10 CFR Part 50 and 10 CFR Part 52,
“Licenses, Certifications, and Approvals for Nuclear Power Plants.” Section 2.4.5
provides general guidance for estimating flooding because of tsunami hazards.

•

NUREG/CR-6966, “Tsunami Hazard Assessment at Nuclear Power Plant Sites in the
United States of America,” provides present-day methodologies and technologies
that can used to estimate design-basis floods at nuclear power plants for tsunami
hazards (Prasad, 2009).

•

Regulatory Guide 1.27, “Ultimate Heat Sink for Nuclear Power Plants, Revision 2”
(NRC, 1976a).

•

Regulatory Guide 1.102, “Flood Protection for Nuclear Power Plants,” Revision 1
(NRC, 1976b) provides guidance for the protection of nuclear power plants from
flooding.

•

Regulatory Guide 1.206, “Combined License Applications for Nuclear Power Plants,”
2007. Section C.I.2.4.5 provides general guidance for estimating flooding due to
tsunami hazards (NRC, 2007).

•

JLD-ISG-2012-05 provides guidance for performing the integrated assessment for
flooding, when necessary (NRC, 2012b).

2.2.

Updates to Guidance

Section 2.4.6 of NUREG-75/087 (1975) provided guidance on tsunami hazard safety
reviews. However, this guidance included few details or quantitative techniques. To fill this
information gap, the NRC funded a study of tsunami hazard on the Pacific, Atlantic, and Gulf
Coasts of the United States, which was published as NUREG/CR-1106 (Brandsma et al.,
1979). However, NUREG/CR-1106 only addresses distant seismic-generated tsunami and
does not consider the effects of locally generated tsunami (e.g., submarine landslides).
RG 1.59 (1977) mentions tsunami as a source of flooding but does not provide detailed
guidance on tsunami hazards assessment. Regulatory Guide 1.59 is currently being
updated and will include guidance on tsunami hazard assessments.
NOAA Technical Memorandum OAR PMEL-135 (“Standards, Criteria, and Procedures for
NOAA Evaluation of Tsunami Numerical Models”) and NOAA Technical Memorandum OAR
PMEL-136 (“Scientific and Technical Issues in Tsunami Hazard Assessment of Nuclear
Power Plant Sites”) were produced in response to the 2004 Indian Ocean tsunami. These
documents form the basis of the 2007 tsunami-related updates to NUREG-0800. Additional
publications addressing tsunami hazards include NUREG/CR-6966 (Prasad, 2008), and the
work of ten Brink et al. (2008).
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No other Federal agencies, such as the U.S. Army Corps of Engineers (USACE), National
Oceanic and Atmospheric Administration (NOAA), and Federal Emergency Management
Agency (FEMA) currently use the “probable maximum” or “standard project” terminology.
However, existing NRC guidance continues to use these terms. This document is the first
attempt to make NRC guidance more consistent with the guidance of other Federal
agencies. In this ISG, the term design-basis tsunami hazard (DBTH) replaces probable
maximum tsunami (PMT).
For examples of new reactor tsunami hazard safety assessments, the NRC Web site
(NRC, 2012a) provides combined license and early site permit safety analysis reports and
related NRC requests for additional information (RAIs).

3.

Tsunami Hazard Assessment

All coastal nuclear power plant sites (including sites located adjacent to oceans, seas, lakes,
rivers, and other inland bodies of water) must consider tsunami hazards. For example, a
tsunami could cause a water-level change in an adjacent body of water. The resulting
change in water levels, if not considered in the project design, could affect safety-related
structures located at the plant site. If eliminated from consideration, detailed hydrological
and geological reasoning should be provided and should be consistent with Sections 2.4
and 2.5 of the Standard Review Plan.
All water wave processes, including tsunami, consist of generation, propagation, and
dissipation. Section 3.1 (Overview) describes the Hierarchical Hazard Assessment (HHA)
approach and the role that deterministic and combined deterministic-probabilistic methods
play in tsunami hazard assessments. The tsunami source generation phase is discussed in
Section 3.2 (Historical Tsunami Data) and Section 3.3 (Source Generator Characteristics).
Section 3.4 discusses tsunami model initial conditions, beginning with guidance on vertical
datums (Section 3.4.1). Starting a tsunami hazard assessment with bathymetric and
topographic data using appropriate vertical datums is essential to correctly reference water
levels with site elevations. For additional margin, Section 3.4.2 (Antecedent Water Levels)
provides guidance on the determination of pre-tsunami model propagation stillwater levels
using astronomical tides (Section 3.4.2.1), initial rise (Section 3.4.2.2), and sea-level rise
(Section 3.4.2.3). Section 3.5 (Tsunami Propagation Models) ends the tsunami propagation
phase with descriptions of the state-of-the-art tsunami models that the NRC, industry, and
other Federal agencies currently use.
3.1.

Overview

Design-basis flood (DBF) estimation for power plant sites in tsunami hazard zones should
consider the effects of tsunami or tsunami-like waves, including runup, flooding, erosion,
hydrodynamic forces, debris loads, and rundown or return flow of water. The absence of
tsunami events in the site or regional historical record, or upriver location from a coast, is
not a sufficient basis to eliminate the need for a detailed tsunami hazard assessment.
If a regional or site-specific screening, as described in NUREG/CR-6966 (Prasad, 2008),
determines a site is subject to tsunami hazards, a detailed assessment should be
undertaken to ensure that the plant design bases account for these hazards adequately.
This step should include identification of potential tsunami source mechanisms, estimation
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of source characteristics, initiation of the tsunami wave, propagation toward the site, and
estimation of tsunami hazards at the site. For deterministic and probabilistic approaches, a
detailed description of the controlling tsunami generator (e.g., location, dimensions,
orientation, and maximum displacement) should be provided. In addition, a detailed
description of the analysis procedure and models used to estimate tsunami wave height and
period at the site, as well as the development of input parameters, should be included.
For tsunami hazard safety evaluations, a deterministic screening approach consisting of a
series of progressively more refined methods that increasingly use more detailed sitespecific data is used to demonstrate whether the site is protected from the adverse effects
of severe floods. This approach has been formalized in the HHA approach described in
NUREG/CR-7046 (Prasad et al., 2011) and NUREG/CR-6966 (Prasad, 2008).
On the other hand, the use of probabilistic methods facilitates estimation of a range of
tsunami and their associated probabilities rather than focusing on a single, large tsunami
that is construed to represent an upper bound. Probabilistic tsunami hazard assessment
(PTHA) combines the use of deterministic hydrodynamic ocean wave and source generation
models and probabilistic methods. Although the NRC has not published guidance on
frameworks and toolsets for PTHA, the NRC will accept PTHA and deterministic approaches
for tsunami hazard reevaluations. Example applications of PTHA methodologies can be
found in the technical literature (e.g., Uslu, 2008; Geist, E.L. and T. Parsons; Arcas and
Uslu, 2010). The NRC continues to sponsor research in this area with USGS and NOAA
(Gonzalez et al., 2009; Geist and Parsons, 2006; ten Brink et al., 2009).
Regardless of which approach is adopted, a tsunami hazard submittal should include an
assessment of sensitivities and uncertainties that may have significant influence on DBTH
estimates. The details for reporting of the tsunami hazard assessment can be found in
RG 1.206 and NUREG-0800.
3.2.

Historical Tsunami Data

Reviews should be conducted of historical tsunami data, including regional records,
eyewitness reports, and recently available tide gauge and real-time bottom pressure gauge
data (NUREG-0800 and RG 1.206). UREG/CR-6966 (Prasad, 2008) provides further
details and additional guidance.

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3.3.

Source Generator Characteristics

A regional or site-specific survey and assessment of tsunamigenic sources should be
performed to determine if a tsunami poses a hazard to the site. The survey and
assessment should include all potential near-field and far-field sources and mechanisms
that could generate a tsunami. Nuclear power plant sites located near the ocean should
consider hazards from oceanic tsunami. Inland sites should consider the possibility of
tsunami-like waves generated in water bodies within the region (e.g., due to hill-slope failure
or seismic sources). Any relevant paleo-tsunami evidence also should be assessed. The
assessment can be accomplished through a review of existing information. NUREG/CR6966 (Prasad, 2008) provides further details and additional guidance. The USGS technical
report, “Evaluation of Tsunami Sources with the Potential to Impact the U.S. Atlantic and
Gulf Coasts” (ten Brink et al., 2008), also provides additional information on the location and
characteristics of potential tsunami sources for the Atlantic and Gulf coases. Several
studies have also characterized sources for the Pacific Ocean (e.g., Uslu, 2008; and Arcas
and Uslu, 2012). .
3.4.

Tsunami Computational Model Initial Conditions

3.4.1. Datums
Datums may be tidal or fixed. For example, mean sea level pertains to the local mean sea
level (MSL), which is a tidal datum based on astronomical tides. A tidal datum is
determined over a 19-year National Tidal Datum Epoch. North American Vertical Datum of
1988 (NAVD88) and National Geodetic Vertical Datum of 1929 (NGVD29) are fixed geodetic
datums having elevation relationships to local MSL and other tidal datums may not be
consistent from one location to another. NAVD88 replaced NGVD29 as the national
standard geodetic reference for heights.
Licensees select the applicable datum to conform to site-specific requirements (e.g., local
and state requirements) as well as best practices and engineering judgement. Once
selected, the datum should be applied universally for all flood evaluations and
documentation.
3.4.2. Antecedent Water Levels
Antecedent water levels should be included in storm surge DBTH estimation. Regulatory
Guide 1.59 (NRC, 1977) and ANSI/ANS-2.8-1992 recommendations that the 10 percent
exceedance high tide be used to represent the antecedent water level for storm surge can
also be applied to DBTH estimates. In addition, long term sea level changes should also be
considered. For example, antecedent water level should be taken as the sum of the
stillwater depth (i.e., mean sea or lake level), 10 percent exceedance high tide, and longterm sea-level rise. Because of the non-linear wave effects, the antecedent water level
should be applied as the initial tsunami model stillwater level. Section 4 addresses postmodeling tsunami water level additions, such as wind waves and wave runup.
3.4.2.1.

Tides

In computing the surge level, the 10 percent exceedance high tide should be considered to
occur coincidentally with the storm surge. The 10% exceedance high tide is the high-tide
level that is equaled or exceeded by 10 percent of the maximum monthly tides over the tidal
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epoch (a continuous 21-yr period in most locations). This tide can be determined from the
recorded tide or from the predicted astronomical tide. If astronomical tides are used, sea
level anomaly should be added. Sea level anomalies (also referred to as initial rise) are
departures of the water surface elevation from astronomical tides due to various
meteorological and oceanographic forcings. Historical and current tide observations,
information on tidal datums, as well as predicted tide levels can be found on the NOAA
Tides and Currents Web site (NOAA, 2012a). NOAA maintains a network of tide gage
stations along the U.S. shoreline, including the Great Lakes.
3.4.2.2.

Initial Rise

For locations where the 10 percent exceedance high spring tide is estimated from observed
tide data, RG 1.59 and ANSI/ANS-2.8-1992 indicate that a separate estimate of the initial
rise is not necessary. This approach for estimating 10 percent exceedance high tide, based
on recorded tides, intrinsically includes the effects of initial rise. For other locations, the
initial rise must be estimated and used as an input to the tsunami inundation calculations or
included in the tsunami inundation calculations themselves.
3.4.2.3.

Long-Term Sea Level Rise

Relative sea-level rise is the combined effect of water-level change and land subsidence.
The NOAA National Ocean Service, the U.S. Global Change Research Program, and the
Intergovernmental Panel on Climate Change (IPCC) monitor and report sea-level rise
information, which also should be included in design-basis flood analysis for coastal sites
(IPCC, 2007).
NOAA maintains tide gage stations along the U.S. shoreline (NOAA, 2012a) and has
evaluated the trend of sea-level rise. Measurements at any given tide station include both
global sea-level rise and vertical land motion, such as subsidence, glacial rebound, or largescale tectonic motion. Thus, the long-term sea-level rise should be derived for the expected
life of the nuclear power plant based on the trend in site or regional tide gage station data.
As part of the HHA approach, regional or global sea-level rise trends can be added in initial
storm surge simulations to the site or regional observed trend for additional margin.
3.5.

Tsunami Propagation Computational Modeling Tools

This section describes the tsunami generation and propagation phase with a discussion of
the state-of-the-art computational tsunami modeling tools that the NRC, industry, and other
Federal agencies currently use.
The National Tsunami Hazard Mitigation Program, sponsored by NOAA, currently uses
several complex tsunami computational modeling tools to produce tsunami inundation and
evacuation maps for Alaska, California, Hawaii, Oregon, and Washington. The
computational modeling packages include MOST, developed originally by University of
Southern California researchers (1998); COMCOT (Cornell Multi-grid Coupled Tsunami
Model), developed at Cornell University (1995); and TSUNAMI2, developed at Tohoku
University in Japan (1996). All three packages solve the depth-integrated and 2D horizontal
(2HD) nonlinear shallow-water equations with differing finite-difference algorithms. There
are a number of additional computational modeling tools that can be used to solve shallowwater wave propagation problems, including the finite element model ADCIRC (ADvanced
CIRCulation Model for Oceanic, Coastal and Estuarine Waters, 1994).
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Computational modeling tools based on the shallow-water equation have been shown to be
reasonably accurate throughout the evolution of a tsunami, and are widely used. However,
these tools lack the capability to simulate dispersive waves, which could be the predominate
features in landslide-generated tsunami, and for tsunami traveling a long distance. Several
higher-order depth-integrated wave hydrodynamics models (Boussinesq models) are now
available for simulating nonlinear and weakly dispersive waves, such as COULWAVE
(Cornell University Long and Intermediate Wave Modeling Package, 2002) and FUNWAVE
(Fully Nonlinear Boussinesq Wave Model, 2000). The major difference between the two is
in their treatment of moving shoreline boundaries. During 2003, COULWAVE was applied
to the 1998 Papua New Guinea tsunami with a landslide source; the results agreed
reasonably well with field surveys and observed data. Recently, several finite element
models also have been developed based on Boussinesq-type equations. NUREG/CR-6966
(Prasad, 2008) provides additional details and guidance.
See NOAA Technical Memorandum OAR PMEL-135 “Standards, Criteria, and Procedures
for NOAA Evaluation of Tsunami Numerical Models” (Gonzalez et al., 2007) for additional
guidance on validation, benchmarking, and quality control.

4.

Wave and Inundation Effects for Tsunami

This section describes the wave dissipation phase, in which tsunami wave action can
directly affect the site. Wave action includes deep and shallow water wave generation.
Tides, wave setup, wave runup, splash, or overtopping, as appropriate, should be
considered in the analyses and included in tsunami flooding estimates.
Section 4.1 (Inundation) looks at the horizontal distance that tsunami wave propagates
inland before dissipation (wave breaking). If the inundation reaches the site, other factors
such as wave runup (Section 4.2), drawdown (Section 4.3), hydrostatic or hydrodynamic
forces (Section 4.4), debris and waterborne projectiles (Section 4.5), and the effects of
sediment erosion and deposition (Section 4.6) should be considered, as appropriate.
4.1.

Inundation

Inundation effects should be evaluated and are typically available from standard tsunami
model outputs.
4.2.

Wave Runup

Tsunami wave runup guidance is provided in NUREG/CR-6966. Wave runup can also be
provided by tsunami models. For state-of-the-art solutions to tsunami wave runup, see Liu
et al., 2008.
4.3.

Drawdown (Low Water Level)

Drawdown is an issue when safety-related structures and equipment (e.g., UHS intakes)
depend on water sources that a tsunami has the potential to affect (NRC, 1976a).
Tsunami numerical models such as MOST, FUNWAVE, COULWAVE, TSUNAMI and
COMCOT can provide a visual and quantitative estimation of low water-level conditions.
Thus, tsunami model flooding elevation data should be retained and used for a detailed
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analysis of low-flow and low-water conditions. See NUREG/CR-6966 for additional details
(Prasad, 2008).
4.4.

Hydrostatic and Hydrodynamic Forces

The hydrostatic and hydrodynamic forces should be determined when tsunami flood levels
impinge on flood protection or safety-related SSCs. Thus, tsunami model current velocity,
wave, and wind data should be retained and used for a detailed analysis of hydrostatic and
hydrodynamic forces.
The USACE CEM (USACE, 2008) and NUREG/CR-6966 (Prasad, 2008) provides guidance
on hydrostatic and hydrodynamic forces for coastal structures.
4.5.

Debris and Waterborne Projectiles

The effect from debris and waterborne projectiles should be considered when tsunami flood
levels impinge on flood protection or safety-related SSCs. Thus, tsunami model current
velocity, and wave data should be retained and used for a detailed analysis of debris and
waterborne projectiles. See NUREG/CR-6966 for additional details (Prasad, 2008).
4.6.

Effect of Sediment Erosion and Deposition

The impact of sediment erosion and deposition should be considered when tsunami flood
levels impinge on flood protection, safety-related SSCs and foundation materials. Thus,
tsunami model current velocity, wave, and wind data should be retained and used for a
detailed analysis of the effects of sediment erosion and deposition.
The USACE CEM provides guidance on the impacts of sediment erosion and deposition for
coastal structures (USACE, 2008).

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5.

References

American National Standards Institute, ANSI/ANS-2.8-1992, “American National Standard
for Determining Design Basis Flooding at Nuclear Reactor Sites,” La Grange Park, IL.
Arcas, D. and Uslu, B., 2010, A Tsunami Forecast Model for Crescent City, California,
NOAA OAR Special Report, PMEL Tsunami Forecast Series: Vol. 2, 112 pp.
Brandsma, D., D. Divoky, and L. Hwang, 1979, “Tsunami Atlas for the Coasts of the Coasts
of the United States,” NUREG/CR-1106, Prepared for the U.S. Nuclear Regulatory
Commission, Tetra Tech, Inc.
Briggs, M.J., H. Yeh, and D.T. Cox, 2010. “Physical Modeling of Tsunami Waves,” in
Handbook of Coastal and Ocean Engineering, (Y.C. Kim, Ed), World Scientific Publishing
Co., Singapore, pp. 1073-1105.
Dean, R.G. and Dalrymple, R.A., 1991, Water Wave Mechanics for Engineers and
Scientists, World Scientific Pub. Co., Teaneck, NJ.
Geist, E.L. and T. Parsons, 2006, “Probabilistic analysis of tsunami hazards,” Natural
Hazards (2006) 37: 277-314.
Geist, E. L. and U. ten Brink, 2012, “NRC/USGS Workshop Report: Landslide Tsunami
Probability,” U.S. Geological Survey.
Gonzalez, F.I., et al., 2009, Probabilistic tsunami hazard assessment at Seaside, Oregon,
for near- and far-field seismic sources, Journal of Geophysical Research, 114, C11023,
doi:10.1029/2008JC005132)
Intergovernmental Panel on Climate Change (IPCC), 2007a, Climate Change 2007:
Synthesis Report, Core Writing Team, R.K. Pachauri and A. Reisinger (eds.), Geneva,
Switzerland.
Intergovernmental Panel on Climate Change (IPCC), 2007b, Solomon, S., et al., eds.,
Climate Change 2007: The Physical Science Basis, Cambridge University Press,
Cambridge, United Kingdom and New York.
Kammerer A., U. ten Brink, V. Titov, 2008, “Overview of the U.S. Nuclear Regulatory
Commission Collaborative Research Program to Assess Tsunami Hazard for Nuclear Power
Plants on the Atlantic and Gulf Coasts,” Proceedings of the 14th World Conference on
Earthquake Engineering, Beijing China, October 2008.
Kammerer A., U. ten Brink, D. Twichell, E. Geist, J. Chaytor, J. Locat, H. Lee,
B. Buczkowski, and M. Sansoucy, 2008, “Preliminary Results of the U.S. NRC Collaborative
Research Program to Assess Tsunami Hazard for Nuclear Power Plants on the Atlantic and
Gulf Coasts,” Proceedings of the 14th World Conference on Earthquake Engineering,
Beijing China, October 2008.

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Karl, T.R., J.M. Melillo, T.C. Peterson, and S.J. Hassol, eds., 2009, Global Climate Change
Impacts in the United States, Cambridge University Press, Cambridge,
www.globalchange.gov/usimpacts.
Liu, P., H. Yeh, and C. Synolakis (Eds.), 2008. Advanced Numerical Models for Simulating
Tsunami Waves and Runup, Advances in Coastal and Ocean Engineering, Vol. 10, World
Scientific Publishing Co., Singapore, 344 pp.
Liu, P., C. Synolakis, and H. Yeh, 1991. “Report on the International Workshop on LongWave Runup,” Journal of Fluid Mechanics, Vol. 229, pp. 675-688.
Luettich, R.A., J.J. Westerink, and N.W. Scheffner, 1992, “ADCIRC: An advanced threedimensional circulation model for shelves, coasts, and estuaries,” Report 1, Theory and
Methodology of ADCIRC-2DDI and ADCIRC-3DL, Technical Report DRP-92-6, U.S. Army
Engineer Waterways Experiment Station, Vicksburg, VA.
Luettich, R.A. and J.J Westerink, 2004, “Formulation and numerical implementation of the
2D/3D ADCIRC finite element model version 44, XX.” Available at:
http://adcirc.org/adcirc_theory_2004_12_08.pdf.
Marine Geology Special Issue: Tsunami Hazard along the U.S. Atlantic Coast, Vol. 264,
Issues 1-2, 2009.
National Oceanic and Atmospheric Administration (NOAA), 2007a, NOAA Technical
Memorandum OAR PMEL-135, by Gonzalez, F.I., E. Bernard, U. Kanoglu, C.E. Synolakis,
and V.V. Titov, “Standards, Criteria, and Procedures for NOAA Evaluation of Tsunami
Numerical Models,” Pacific Marine Environmental Laboratory, Seattle, WA.
NOAA, 2007b, NOAA Technical Memorandum OAR PMEL-136, by Gonzalez, F.I.,
E. Bernard, P. Dunbar, E. Geist, B. Jaffe, U. Kanoglu, J. Locat, H. Mofjeld, A. Moore,
C. Synolakis, and V. Titov, “Scientific and Technical Issues in Tsunami Hazard Assessment
of Nuclear Power Plant Sites,” Pacific Marine Environmental Laboratory, Seattle, WA.
NOAA, 2012, “Tides and Currents Online,” Web site: http://tidesandcurrents.noaa.gov/.
NRC, 1976a, Regulatory Guide 1.27, “Ultimate Heat Sink for Nuclear Power Plants,
Revision 2,” Washington, DC.
NRC, 1976b, Regulatory Guide 1.102, “Flood Protection for Nuclear Power Plants,”
Revision 1, Washington, DC. ADAMS Accession No. ML003740308.
NRC, 1977, Regulatory Guide 1.59, “Design Basis Floods for Nuclear Power Plants,”
Revision 2, Washington D.C. with errata dated July 30, 1980, Washington, DC. ADAMS
Accession No. ML003740388.
NRC, 1978, Regulatory Guide 1.70, “Standard Format and Content of Safety Analysis
Reports for Nuclear Power Plants,” Revision 3, Washington, DC. ADAMS Accession No.
ML011340122.
NRC, 2007, Regulatory Guide 1.206, “Combined License Applications for Nuclear Power
Plants,” Washington, DC. ADAMS Accession No. ML070720184.

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NRC, 2012a, U.S. Nuclear Regulatory Commission Web site, “New Reactors,”
(http://www.nrc.gov/reactors/new-reactors.html).
NRC, 2012b, Japan Lessons-Learned Project Directorate Interim Staff Guidance (JLD-ISG),
JLD-ISG-2012-05, “Performance of an Integrated Assessment,” Washington, DC. ADAMS
Accession No. ML12311A214.
Prasad, R., 2008, NUREG/CR-6966, “Tsunami Hazard Assessment at Nuclear Power Plant
Sites in the United States of America,” U.S. Nuclear Regulatory Commission,
Washington, DC. ADAMS Accession No. ML091590193.
Prasad, R., L.F. Hibler, A.M. Coleman, and D.L. Ward, 2011, “Design-Basis Flood
Estimation for Site Characterization at Nuclear Power Plants in the United States of
America,” NUREG/CR-7046, Washington, DC.
ten Brink, U., et al., 2008, “Evaluation of Tsunami Sources with the Potential to Impact the
U.S. Atlantic and Gulf Coasts: USGS Administrative Report to the U.S. Nuclear Regulatory
Commission, U.S. Geological Survey.
ten Brink, U. (Editor), 2009, Special Issue: “Tsunami Hazard Along the U.S. Atlantic Coast,”
Marine Geology, Volume 264, Issues 1-2.
Uslu, B., 2008, “Deterministic and Probabilistic Tsunami Studies in California from Near and
Farfield Sources,” Ph.D. Dissertation, University of Southern California.
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Engineering Research Center, Waterways Experiment Station, Vicksburg, MS, Fourth
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Coastal and Hydraulics Laboratory.
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Corps of Engineers, Coastal and Hydraulics Laboratory,
http://chl.erdc.usace.army.mil/cedas.
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2, No. 6, 531-536.
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Raghuraman, 2007. “Effects of the 2004 Great Sumatra Tsunami: Southeast Indian Coast,”
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Coastal, Ocean Eng., 132(6), 496–500.
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- 13 -

Yeh, H. and K.-M. Mok, 1990. “On Turbulence in Bores,” Physics of Fluids, Vol. 2, pp. 821828, 1990.

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Appendix: GLOSSARY AND ACRONYMS
ADCIRC – Advanced Circulation Model.
ASCE - American Society of Civil Engineers
ANS - American Nuclear Society
ANSI - American national Standards Institute
Bootstrap Sampling – Bootstrap sampling is the practice of estimating properties of an
estimator (such as its variance) by measuring those properties when sampling from an
approximating distribution. One standard choice for an approximating distribution is the
empirical distribution of the observed data. In the case where a set of observations can be
assumed to be from an independent and identically distributed population, this can be
implemented by constructing a number of re-samples of the observed dataset (and of equal
size to the observed dataset), each of which is obtained by random sampling with
replacement from the original dataset.
CFR - Code of Federal Regulations
Coastal: Refers to the near-shore regions of any water body (e.g., ocean, bay, sea, sound,
lake, or estuary) where wind wave or gravity wave phenomena may occur, not solely to
regions adjacent to the open ocean.
Coastal Storm Modeling System (C-Storm) - The U.S. Army Corps of Engineer’s
Engineering Research and Development Center's Coastal Storm Modeling System
(CSTORM-MS) is a physics-based modeling capability for simulating tropical and extratropical storm, wind, wave, water level and coastal response (erosion, breaching, and
accretion).
COMCOT - Cornell Multi-grid Coupled Tsunami Model
COULWAVE - Cornell University Long and Intermediate Wave Modeling
Design Basis Storm Surge (DBSS) - The most adverse storm surge flooding at the nuclear
power plant site caused by a Simulated Wind Storm (SWS) or Simulated Hurricane (SH)
due to a combination of severe meteorological storm parameters, critical path, and rate of
movement.
Design Basis Tsunami Hazard (DBTH) – Formerly probable maximum tsunami (PMT),
DBTH is tsunami for which the impact at the site is derived from the use of best available
scientific information to arrive at a set of scenarios reasonably expected to affect the nuclear
power plant site taking into account: (a) appropriate consideration of the most severe of the
natural phenomena that have been historically reported or determine from geological and
physical data for the site and surrounding area, with sufficient margin for the limited
accuracy, quantity, and period of time in which the historical data have been accumulated;
(b) appropriate combinations of the effects of normal and accident conditions with the

Enclosure 3 to JLD-ISG-2012-06

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January 4, 2013

DRAFT
ENCLOSURE 3
effects of the natural phenomena; and (c) the importance of the safety functions to be
performed.
Empirical Simulation Technique (EST) - Procedure for simulating multiple life-cycle
sequences of non-deterministic multi-parameter systems. Based on a Bootstrap
resampling-with-replacement, interpolation, and subsequent smoothing technique, EST
employs random sampling of a finite length database to generate a larger database. The
basic assumption is that future events are statistically similar in magnitude and frequency to
past events.
Extra-tropical Cyclone - A storm that forms outside the tropics, sometimes as a tropical
storm or hurricane.
FUNWAVE – Fully Nonlinear Boussinesq Model.
Grade Elevation - Topographical elevation of the site near facilities of the nuclear power
plant usually used as a base reference to describe elevations of other SSCs.
Hierarchical Hazard Assessment (HHA) Approach – HHA approach is a progressively
refined, stepwise estimation of site-specific hazards that evaluates the safety of SSCs with
the most conservative plausible assumptions consistent with available data. The HHA
process starts with the most conservative simplifying assumptions that maximize the
hazards from the probable maximum event for each natural flood-causing phenomenon
expected to occur in the vicinity of a proposed site.
HURDAT - The National Weather Service and the National Hurricane Center’s official
hurricane database for the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea, including
those that have made landfall in the United States, is currently being updated, See Landsea
et al. (2004).
Hurricane - A tropical cyclone with winds of 74 mph or more. Normally applied to such
storms in the Atlantic Basin and the Pacific Ocean east of the International Date Line.
Hydrodynamic Loads - Hydrodynamic loads are loads that result from water flowing against
and around a rigid structural element or system. The hydrodynamic loads can include the
effects of broken and non-breaking waves striking structures, initial impact of a rapidly
varying flood wave (e.g. dam break or tsunami flood wave), and drag forces on a structure
(caused by the pressure differential between the upstream and downstream side of the
structure).
Inundation - The distance that a storm surge penetrates onto the shore, measured
horizontally from the mean sea level position of the water's edge. It is usually measured as
the maximum distance for a particular segment of the coast.
Joint Probability Method (JPM) – JPM is a simulation methodology that relies on the
development of statistical distributions of key tropical or extra-tropical wind storm
parameters and sampling from these distributions. The simulation results in a group of
modeled storms that preserves the relationships with the historical storms but provides a
means to model the effects and probabilities of storms that have not yet occurred.
JPM-OS - JPM-Optimal Sampling
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DRAFT
ENCLOSURE 3
Maximum Breaker Height - The maximum wave height that can be achieved during
shoaling.
MOST - Method of Splitting Tsunami
NAVD88 - North American Vertical Datum of 1988
NGVD29 - National Geodetic Vertical Datum of 1929
NOAA - National Oceanic and Atmospheric Administration
NRC - U.S. Nuclear Regulatory Commission
NWS - National Weather Service
Planetary Boundary Layer (PBL) – The planetary boundary layer (PBL), also known as the
atmospheric boundary layer (ABL), is the lowest part of the atmosphere and its behavior is
directly influenced by its contact with a planetary surface.
Probable Maximum Events - Probable maximum events are thought to approach the
physical limits of the phenomena, are deterministic in nature, and are thought to exceed
historical occurrences of the phenomena at the time of the analysis.
Probable Maximum Hurricane (PMH) - The PMH is a hypothetical hurricane having a
combination of characteristics that generate the most severe storm surge that can
reasonably occur in the particular region.
Probable Maximum Wind Storm (PMWS) - A hypothetical extra-tropical cyclone that might
result from the most severe combination of meteorological storm parameters that is
considered reasonably possible in the region involved. The windstorm approaches the point
under study along a critical path and at an optimum rate of movement, which will result in
the most adverse flooding.
Probable Maximum Storm Surge (PMSS) - The PMSS is generated by the Probable
Maximum Hurricane (PMH) or Probable Maximum Windstorm (PMWS).
RAI - Request for additional information
Seiche - An oscillation of the water surface in an enclosed or semi-enclosed water body that
is initiated by an external cause (e.g., barometric pressure fluctuations, strong winds, rapid
changes in wind direction, surge associated with passage of storms, tsunami, or local
landslides).
SER - Safety Evaluation Report
Significant Wave Height - In physical oceanography, the significant wave height (SWH or
Hs) is defined traditionally as the mean wave height (trough to crest) of the highest third of
the waves (H1/3). Nowadays, it is usually defined as four times the standard deviation of the
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surface elevation – or equivalently as four times the square root of the zeroth-order moment
(area) of the wave spectrum. The symbol Hm0 is usually used for that latter definition. The
significant wave height may thus refer to Hm0 or H1/3; the difference in magnitude between
the two definitions is only a few percent.
Simulated Hurricane (SH) - A hypothetical tropical cyclone (Hurricane) generated by the
probable maximum hurricane (PMH) or synthetic storm methodology (JPM and EST) using
a combination of meteorological storm parameters considered reasonably possible for the
region involved. The simulated hurricane approaches the nuclear power plant site along
multiple paths and rates of movement.
Simulated Tsunami (ST) – A hypothetical tsunami propagated by a tsunami numerical
model using input from variable tsunami sources (e.g., earthquakes, submarine landslides)
and source parameters (e.g., landslide volume, fault length, slip amount, etc).
Simulated Wind Storm (SWS) – A hypothetical extra-tropical cyclone generated through the
synthetic storm methodology (JPM and EST) using a combination of meteorological storm
parameters considered reasonably possible for the region involved. The SWS approaches
the nuclear power plant site along multiple paths and rates of movement.
SLOSH - Sea, Lake, Overland Surge from Hurricanes
SMS – Surface Modeling System
SPH - Standard Project Hurricane
Still Water Level (SWL) – The water level in the absence of wave effects.
Storm Surge - Storm surge is the rise of offshore water elevation caused principally by the
shear force of tropical or extra-tropical winds acting on the water surface and the associated
pressure differential.
SWAN – Simulating Waves Nearshore.
STWAVE - STeady State spectral WAVE
Tropical Cyclone - low-pressure weather system in which the central core is warmer than
the surrounding atmosphere. The term "tropical cyclone" is also used in the Indian Ocean
and around the Coral Sea off northeastern Australia to describe storms called "hurricanes"
and "typhoons" in other areas.
Tsunami - A series of water waves caused by the displacement of a large volume of a body
of water, typically an ocean or a large lake. Earthquakes, landslides, submarine landslides,
glacier calvings, meteorite impacts and other disturbances above or below water all have
the potential to generate a tsunami.
UHS - ultimate heat sink
USACE - U.S. Army Corps of Engineers
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WAM - WAve prediction Model
Wave Runup - Wave runup is the maximum vertical extent of wave uprush on a beach or
structure above the still water level (SWL).
Wave Setup - Additional water level that is due to the transfer of wave-related momentum to
the water column during the wave-breaking process.
Wind Waves - Waves generated by wind passing over the surface of an open body of water
caused by wind shear forces along the water surface and air pressure differences across
the wave crest.

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