HomeMy WebLinkAbout20201105_Coastal Hazard Report_10-7-2020Geotechnical C Geologic C Coastal C Environmental
5741 Palmer Way C Carlsbad, California 92010 C (760) 438-3155 C FAX (760) 931-0915 C www.geosoilsinc.com
October 7, 2020
Mr. Michael Lambert
920 E. Balboa Blvd
Newport Beach, CA 92663
SUBJECT: Coastal Hazard and Sea Level Rise Analysis for Remodel and Addition, 920
E. Balboa Blvd, Newport Beach, Orange County, California.
Dear Mr. Lambert:
In accordance with your request and authorization, GeoSoils, Inc. (GSI) is pleased to
provide this analysis regarding the potential coastal hazards, including the impact of future
sea level rise (SLR), on the proposed remodel project at 920 E. Balboa Blvd in
Newport Beach, California. The purpose of this report is to provide the hazard information
for your permit application typically requested by the City of Newport Beach and the
California Coastal Commission (CCC). Our scope of work includes a review of the State
of California Sea-Level Rise (SLR) Policy Guidance document (March 2018), CCC SLR
Guidance (November 2018), a review of City of Newport Beach Municipal Code (NBMC)
21.30.15.E.2 &E.3, a discussion of the proposed remodel and addition plans, a site
inspection, and preparation of this letter/report.
INTRODUCTION
The proposed project is a remodel and addition to an existing residence, in the City of
Newport Beach. Figure 1, downloaded from Google Maps (Bird’s Eye View), shows the
site in relation to the adjacent property, the boat dock, and the narrow navigation channel
within Newport Bay. The existing lowest finished first floor (FF) elevation of the residence
is about 8.35 feet NAVD88. The site is fronted by a bulkhead to about an elevation of 8.4
feet NAVD88 (shore protection), a boat dock, adjacent to a navigation channel in Newport
Bay. It is our understanding that the project may be required to include raising the
elevation of the top of the shore protection to at least the City minimum. The residential
structure is currently mapped by FEMA to be in the shaded X Zone, with no base flood
elevation (BFE). The bay side patio and the public street fronting the site (E. Balboa Blvd)
are in the FEMA AO Zone with a flood depth of 1 foot. It should be noted that the adjacent
navigation channel is mapped in the AE Zone with a BFE of +8 feet NAVD88.
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Figure 1. Subject site, 920 E. Balboa Blvd, adjacent properties, boat dock, and
Newport Bay channel.
DATA & DATUM
The datum used in this report is NAVD88, which is about 2.62 feet below the mean tide
level (MTL). The units of measurement in this report are feet (ft), pounds force (lbs), and
seconds (sec). Site elevations were taken from a topographic map prepared by Mark Scott
Petrie, dated August 2017, and project plans were discussed with Rod Jeheber, the
project designer. A site reconnaissance was performed in September 2020. There is only
an intertidal beach fronting the shore protection/bulkhead at the site.
HAZARD ANALYSIS
There are three different potential shoreline hazards identified at this site: 1) shoreline
movement/erosion, 2) waves and wave runup, 3) and flooding. For ease of review, each
of these hazards will be analyzed and discussed separately, followed by a summary of the
analysis including conclusions and recommendations, as necessary.
Shoreline Erosion Hazard
There is only an intertidal beach at the site. The high tide shoreline is on the bulkhead.
A review of historical aerial photographs available on Google Earth, dating back to 2002
show no beach fronting the site. The high tide shoreline is located essentially at the shore
protection/bulkhead. As sea level rises, the high tide shoreline location will remain at the
shore protection. Shoreline erosion will not impact the proposed development over the life
of the development.
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Current Flooding Hazard
The National Oceanographic and Atmospheric (NOAA) National Ocean Survey tidal data
station closest to the site, with a long tidal record, is located at Los Angeles Harbor (Station
94106600). The tidal datum elevations are as follows:
Mean High Water 4.55 feet
Mean Tide Level (MSL) 2.62 feet
Mean Low Water 0.74 feet
NAVD88 0.0 feet
Mean Lower Low Water -0.2 feet
During storm conditions, the sea surface rises along the shoreline (super-elevation) and
allows waves to break closer to the shoreline and runup on the beach. Super-elevation of
the sea surface can be accounted for by: wave set-up, wind set-up and inverse barometer,
wave group effects and El Niño sea level effects. The historical highest ocean water
elevation at the Los Angeles Harbor Tide station is +7.72 feet NAVD88 on January 10,
2005. In addition, Los Angeles Harbor Tide station reports that the elevation of 7.71 feet
NAVD88 is the 1% water elevation. For this analysis the historical highest water elevation
will be +7.7 feet NAVD88.
Future Tide Levels Due to Sea Level Rise
The CCC SLR Guidance document recommends that a project designer determine the
range of SLR using the “best available science.” The California Ocean Protection Council
(COPC) adopted an update to the State’s Sea-Level Rise Guidance in March 2018. These
new estimates are based upon a 2014 report entitled “Probabilistic 21st and 22nd century
sea-level projections at a global network of tide-gauge sites” (Kopp el at, 2014). The 2018
CCC SLR Guidance states that the COPC document is the “best available science.” The
COPC update included SLR estimates and probabilities for Los Angeles Harbor the closest
SLR estimates to Newport Beach. These SLR likelihood estimates are provided below in
Figure 2 taken from the Kopp et al 2014 report. The report provides SLR estimates based
upon various carbon emission scenarios known as a “representative concentration
pathway” or RCP. Figure 2 provides the March 2018 COPC data (from the Kopp et al 2014
report) with the latest SLR adopted estimates (in feet) and the probabilities of those
estimates to meet or exceed the 1991-2009 mean, based upon the best available science.
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Figure 2. Table from Kopp et al (2014) and COPC 2018, providing current SLR estimates
and probabilities for the Los Angeles Harbor tide station.
This table illustrates that SLR in the year 2100 for the likely range, and considering the
most onerous RCP (8.5), is 1.3 feet to 3.2 feet above the 1991-2009 mean. Interpolating
between the years 2090 and 2100 provides a “likely” SLR of 2.9 feet in the year 2095.
Interpolating between the years 2090 and 2100 provides a “0.5% probability SLR of 5.5
feet in the year 2095. The design historical water elevation at the for Newport Bay is
elevation +7.7 feet NAVD88 (Moffatt & Nichol 1% water elevation). The “likely” sea level
rise for the proposed project is 2.9 feet with a lower probability (~0.5%) of SLR of about 5.5
feet. This SLR would account for future extreme bay water level in the range of 10.6 feet
NAVD88 (7.7 feet NAVD88 + 2.9 feet SLR) to 13.2 feet NAVD88 (7.7 feet NAVD88 + 5.5
feet SLR) . The existing bulkhead is at elevation +8.4 feet NAVD88.
As stated before, the present maximum (1%) historical water elevation at the site, including
El Niño effects, is ~+7.7 feet NAVD88. Based upon the elevation of the shore protection,
the extreme Newport Bay water level will exceed the height of the existing bulkhead when
SLR is 0.7 feet or greater. For the likely COPC SLR estimate range (high emissions) the
site is safe from overtopping flooding until about the year 2040. For SLR greater than 0.7
feet, the height of the bulkhead will need to be further increased. For the 0.5% SLR case
this could occur in the year 2030. It should be noted that, if SLR is higher, flooding will not
occur constantly but rather only a few times a month, at the full moon and new moon, for
a period of about 1 hour.
The City of Newport Beach has recognized that in the future there will be a need to raise
the elevation of the bulkheads around Newport Bay. The City of Newport Beach Building
Department (CNBBD) has a standard drawing, and a regional plan for rehabilitating and
raising the bulkheads.
Probabilistic Projections (in feet) (based on Kopp et al. 2014)
l.lKE"lY RAN,;t Cf• A NC f C: HA NC f
sea-level rise meets sea-level rise sea-level rise meets
or exceeds ... is between ... or exceeds ...
Lo;] Medium -High Extreme Risk Aversion Risk Aversion Risk Aversion
High emissions 2030 0.3 0.2 0.5 0.6 0.7 1.0
2040 0 .5 0.4 0.7 0.9 1.2 1.7
2050 0.7 0.5 1.0 1.2 1.8 2.6
Low emissions 2060 0 .8 0.5 1.1 1.4 2.2
High emissions 2060 1.0 0.7 1.3 1.7 2.5 3.7
Low emissions 2070 0.9 0 .6 1.3 1.8 2.9
High emissions 2070 1.2 0 .8 1.7 2.2 3.3 5.0
Low emissions zoro 1.0 0 .6 1.6 2.1 3.6
High emissions 2080 1.5 1.0 2.2 2.8 4.3 6.4
Low emissions 2090 1.2 0.7 1.8 2.5 4.5
High emissions 2090 1.8 1.2 2.7 3.4 5.3 8.0
Low emissions 2100 1.3 0.7 2.1 3.0 5.4
High emissions 2100 2.2 1.3 3.2 4.1 6.7 9.9
Low emissions 2110· 1.4 0 .9 2.2 3.1 6.0
High emissions 2110· 2.3 1.6 3.3 4.3 7.1 11.5
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Waves and Wave Runup
The potential surface gravity waves (ocean swell) to arrive at this site is nil. Boat wakes
and wind waves are the only possible waves that can reach the bulkhead fronting the site.
Wave runup and overtopping of the bulkhead at the site is calculated using the USACOE
Automated Coastal Engineering System, ACES. ACES is an interactive computer-based
design and analysis system in the field of coastal engineering. The methods to calculate
wave runup and shore protection overtopping implemented within this ACES application
are discussed in greater detail in the 2004 Coastal Engineering Manual. A 0.5-foot high
wave was used in the ACES wave runup and overtopping analysis with a current maximum
historical water level of +7.7 feet NAVD88 (no SLR). This combination of wave and water
level represents an approximate 100-year recurrence interval oceanographic condition
under current sea level. Table I below is the computed output from the ACES program for
the wave runup analysis.
TABLE I
The calculated maximum wave runup under the current 100-year recurrence interval
conditions is just about 0.6 feet above the historical 100-year water level (elevation 8.3 feet
NAVD88). This is currently below the elevation of the existing bulkhead (+8.4 feet
NAVD88). In the future, with more than 0.7 feet of SLR, boat wakes may overtop the
bulkhead during the highest high tides. The project should be required to increase the
height of the bulkhead to the City minimum. The bulkhead can be increased in height
without any bayward encroachment. This is a SLR adaptation strategy recommended in
the 2018 CCC SLR guidance document.
ACES I l'tlde: Single Case I Functional Area: Wave -Structure Interaction
Application: Wave Runup and Overtopping on Impermeable Structures
Item Unit Value Smooth Slope
Runup and
Incident Wave Height Hi : ft 0 .500 Overtopping
Wave Period T: sec 3 .000
COTAN of Nearshore Slope COT("'): 20.000 920 East Water Depth at Structure Toe ds: ft 5 .000
COTAN of Structure Slope COTC8): 0 .000 Balboa Blvd Structure Height Above Toe hs : ft 5 .700
Wave Runup R: ft 0 .558 Bulkhead Onshore Wind Velocity U: ft/sec 0 .000 Overtopping Deepwater Wave Height H0 : ft 0 .540
Relative Height ds/H0: 9 .266
Wave Steepness H0/CgT"2): 0.001864
Overtopping Coefficient oc: 0.077000 No SLR Overtopping Coefficient Qstar0: 0 .050000
Overtopping Rate Q: ftA3/s-ft 0 .000 -
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Tsunami
Tsunami are waves generated by submarine earthquakes, landslides, or volcanic action.
Lander, et al. (1993) discusses the frequency and magnitude of recorded or observed
tsunami in the southern California area. James Houston (1980) predicts a tsunami of less
than 5 feet for a 500-year recurrence interval for this area. Legg, et al. (2002) examined
the potential tsunami wave runup in southern California. While this study is not specific to
the site, it provides a first order analysis for the area. The Legg, et al. (2002) report
determined a maximum open ocean tsunami height of less than 2 meters. The maximum
tsunami runup in the Newport Beach open coast area is less than 1 meter in height. Any
wave, including a tsunami, that approaches the site in will be refracted, modified, and
reduced in height by the Newport jetties, and as it travels into the bay. Due to the
infrequent nature and the relatively low 500-year recurrence interval tsunami wave height,
and the elevation of the proposed improvements, the site is reasonably safe from tsunami
hazards.
It should be noted that the site is mapped within the limits of the California Office of
Emergency Services tsunami innundation map, Newport Beach Quadrangle (State of
California, 2009). The tsunami inundation maps are very specific as to their use. Their use
is for evacuation planning only. The limitation on the use of the maps is clearly stated in
the PURPOSE OF THIS MAP on every quadrangle of California coastline. In addition, the
following paragraph is taken from the CalOES Local Planning Guidance on Tsunami
Response concerning the use of the tsunami inundation maps.
Inundation projections and resulting planning maps are to be used for emergency
planning purposes only. They are not based on a specific earthquake and tsunami.
Areas actually inundated by a specific tsunami can vary from those predicted. The
inundation maps are not a prediction of the performance, in an earthquake or
tsunami, of any structure within or outside of the projected inundation area.
The City of Newport Beach and County of Orange have clearly marked tsunami evacuation
routes for the entire Newport Beach/Bay area.
CITY OF NEWPORT BEACH INFORMATION
Coastal Hazards Report (NBMC 21.30.15.E.2):
i. A statement of the preparer’s qualifications;
Mr. Skelly is Vice President and Principal Engineer for GeoSoils, Inc. (GSI). He has
worked with GSI for several decades on numerous land development projects
throughout California. Mr. Skelly has over 40 years experience in coastal
engineering. Prior to joining the GSI team, he worked as a research engineer at the
Center for Coastal Studies at Scripps Institution of Oceanography for 17 years.
During his tenure at Scripps, Mr. Skelly worked on coastal erosion problems
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throughout the world. He has written numerous technical reports and published
papers on these projects. He was a co-author of a major Coast of California Storm
and Tidal Wave Study report. He has extensive experience with coastal processes
in southern California. Mr. Skelly also performs wave shoring and uprush analyses
for coastal development, and analyzes coastal processes, wave forces, water
elevation, longshore transport of sand, and coastal erosion.
ii. Identification of coastal hazards affecting the site;
As stated in this hazard analysis, the typical coastal hazards to consider
are shoreline erosion, flooding, and wave/wake impacts. There is only an intertidal
beach fronting the site. Due to the navigation channel fronting the site, boat wakes
and wind waves will be able to overtop the existing bulkhead, with as little as 0.7
feet of SLR. There is a potential coastal hazard of flooding of the residence, with
an existing FF elevation of ~+8.4 feet NAVD88, if SLR exceeds 0.7 feet, and
somehow ocean or bay water reaches the site. For SLR higher than the current
estimates, adaptation strategies such as waterproofing the structure to above the
potential flood elevation, and increasing the height of the bulkhead can be
implemented, if required in the future.
iii. An analysis of the following conditions:
1. A seasonally eroded beach combined with long-term (75 year)
erosion factoring in sea level rise;
There is only an intertidal beach fronting the site with no seasonal changes
2. High tide conditions, combined with long-term (75 year) projections
for sea level rise;
Using the SLR estimates over the project 75-year design life, the range in the
year ~2095 is between 2.9 feet (likely) and 5.5 feet (0.5% probability). This
is the sea level rise range for the proposed project. This SLR range would
account for future extreme bay water levels in the range of 10.6 feet NAVD88
(7.7 feet NAVD88 + 2.9 feet SLR) and 13.2 feet NAVD88 (7.7 feet NAVD88
+ 5.5 feet SLR).
3. Storm waves from a one hundred year event or storm that compares
to the 1982/83 El Nino event;
No ocean waves can reach the site. Boat wakes and wind waves in the
navigation channel will not impact the residence provided the bulkhead is
increased in height.
4. An analysis of bluff stability; a quantitative slope stability analysis
that shows either that the bluff currently possesses a factor of safety
against sliding of all least 1.5 under static conditions, and 1.1 under
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seismic (pseudostatic conditions); or the distance from the bluff edge
needed to achieve these factors of safety; and
There is no bluff fronting the site. This condition does not occur at the site.
5. Demonstration that development will be sited such that it maintains
a factor of safety against sliding of at least 1.5 under static conditions
and 1.1 under seismic (pseudostatic) conditions for its economic life
(generally 75 years). This generally means that that setback necessary
to achieve a factor of safety of 1.5 (static) and 1.1 (pseudostatic) today
must be added to the expected amount of bluff erosion over the
economic life of the development (generally 75 years);
There is no bluff fronting the site. There is no potential for sliding. This
condition does not occur at the site.
iv. On sites with an existing bulkhead, a determination as to whether the
existing bulkhead can be removed and/or the existing or a replacement
bulkhead is required to protect existing principal structures and adjacent
development or public facilities on the site or in the surrounding areas; and
The existing shore protection (bulkhead) is necessary to protect the existing
structure, the adjacent properties, and the public facilities and infrastructure.
v. Identification of necessary mitigation measures to address current
hazardous conditions such as siting development away from hazardous areas
and elevating the finished floor of structures to be at or above the base floor
elevation including measures that may be required in the future to address
increased erosion and flooding due to sea level rise such as waterproofing,
flood shields, watertight doors, moveable floodwalls, partitions, water-
resistive sealant devices, sandbagging and other similar flood-proofing
techniques.
The project (addition of above the first floor) is safe from the coastal hazard
of flooding by the proposed elevation of the finished floor. The existing
residence FF is at about elevation +8.4 feet NAVD88 with the bulkhead at
elevation ~+8.4 feet NAVD88. To further adapt to SLR, the shore bulkhead
can be increased in height about 2.2 feet. If a higher bulkhead (higher than
+10.6 feet NAVD88) is required then the existing bulkhead needs further
inspection (excavation behind it) to determine if an additional increase in
height is feasible or if the bulkhead needs to be replaced. It is important to
point out that SLR will not impact this property alone. It will impact all of the
Newport Bay low lying areas. The public streets throughout the Newport
Beach coastal area, including Balboa Island and the Balboa Peninsula, will
flood with lower SLR before the existing residence (with a FF of 8.4 feet
NAVD88 floods). It is very likely that the community will soon adopt some of
the SLR adaptation strategies that are currently being considered by the City
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of Newport Beach. These strategies involve raising, or adding/replacing the
bulkheads, beaches and walkways that surround the bay, and waterproofing.
These are site specific adaptation strategies.
Bulkhead condition report shall include (NBMC 21.30.15.E.3):
i. A statement of the preparer’s qualifications;
Mr. Skelly is Vice President and Principal Engineer for GeoSoils, Inc. (GSI). He has
worked with GSI for several decades on numerous land development projects
throughout California. Mr. Skelly has over 40 years experience in coastal
engineering. Prior to joining the GSI team, he worked as a research engineer at the
Center for Coastal Studies at Scripps Institution of Oceanography for 17 years. Mr.
Skelly has extensive experience in shoreline erosion, bluff erosion, soils
engineering, and the design, permitting, and construction of shore protection
devices. Projects include levee engineering and design in San Francisco Bay,
seawall and marina engineering in Baja California Sur, coastal boardwalk design
and protection in Pacifica, and seawall projects throughout southern California.
ii. An analysis of the condition of any existing bulkhead including whether the
top elevation meets current City standards, the conditions of the sheetpiles
or panels, the condition of existing tiebacks and/or deadmen or similar, and
any other relevant conditions;
The bulkhead is part of a series of independent bulkhead systems (or shore
protection systems) that extend to the properties on either side of the site. The wall
was visually inspected by the undersigned in September 2020. Our visual
inspection of the bulkhead revealed that the structure appears to be in good
condition and not in need of maintenance. The bulkhead does not meet the current
City’s top of bulkhead elevation requirement. It should be noted that very few
bulkheads in the Newport Bay area meet this requirement. Based upon our
observations and experience it is GSI’s opinion that the bulkhead can be increased
in height up to 3 feet. However, if additional bulkhead height is required, it is our
recommendation that a structural assessment of the wall be undertaken after a
portion of the patio is removed. The assessment should include determination of
the wall dimensions, the bulkhead’s expected life, and the ability to add up to an
additional 2.5 feet of new wall on top of the raised bulkhead. This would put the top
of the bulkhead at about elevation +13.9 feet NAVD88, which is above the 0.5%
probability SLR in 75 years design bay water level.
iii. Recommendations regarding the need for repair, augmentation or
replacement of the bulkhead or any parts thereof;
In conclusion, based upon our understanding of the project, the bulkhead should be
added to in order to meet the City standard elevation. If more than 3 feet of height
increase is required then an additional structural inspection should be performed
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after a portion of the patio is removed. The wall should be replaced if it is
determined to be inadequate to protect the site in consideration of future SLR.
iv. If augmentation or replacement in the existing alignment is necessary,
recommendations that will avoid seaward encroachment of the bulkhead;
The augmented or new shore protection can be located within the current bulkhead
footprint. The bulkhead can be increased in height up to 3 feet without additional
inspection and without any bayward encroachment.
v. If replacement is necessary and the existing bulkhead is not in alignment
with adjacent bulkheads, recommended alternatives that will relocate the
bulkhead in as much in alignment with adjacent bulkheads and as far
landward, as possible.
Replacement is not necessary at this time and the existing bulkhead is aligned with
the adjacent bulkhead to the west. If replacement is necessary in the future, then
the new bulkhead can be located in the same footprint as the existing bulkhead.
CONCLUSIONS
• A review of aerial photographs over the last few decades shows only an intertidal
shoreline at the site.
• The residence has not been subject to flooding, erosion damage, or wave runup
attack in the past.
• The proposed project is a remodel and addition to above the first floor elevation
which is well above potential coastal hazards. The existing structure, with a FF of
about +8.4 feet, will not be adversely impacted by potential coastal hazards
including a 0.7 feet sea level rise. The bulkhead should be increased in height to
meet the City bulkhead height requirements at this time (up to 3 feet). If more than
a 3-foot increase in height is necessary, then the bulkhead should be further
structurally assessed to determine if the height can be further increased or if a
replacement bulkhead is necessary. Based upon the design of the residence,
additional waterproofing can be added, if needed, to mitigate hazards due to SLR
greater than 0.7 feet coming to the property from the adjacent low lying public
streets. The site will be part of a community wide response to mitigate SLR
hazards.
RECOMMENDATIONS
Based upon the analysis and discussion herein, the proposed development is reasonably
safe from coastal hazards for the next 75 years including shoreline movement, waves and
wave runup, and flooding with future SLR provided the recommendations herein are
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followed. It should be noted that future flooding hazards due to SLR are shared by all
development around Newport Bay. The public roads for access to the site will be
impassable due to ocean flooding long before the flood water level approaches the FF
elevation of the development. SLR impacts will be a regional problem and only solved by
a regional management plan. The proposed City of Newport Beach bulkhead
modification/replacement plan will likely mitigate any SLR impacts on the project. The
proposed development will neither create nor contribute significantly to erosion, geologic
instability, or destruction of the site or adjacent area.
The opportunity to be of service is sincerely appreciated. If you should have any
questions, please do not hesitate to contact me.
Respectfully submitted,
GeoSoils, Inc.
David W. Skelly MS, PE
RCE#47857
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REFERENCES
Everest International Consultants, Inc., 2011, Assessment of seawall structure integrity and
potential for seawall over-topping for Balboa Island and Little Balboa Island, main report,
No Project No., dated April 21.
Kopp, Robert E., Radley M. Horton Christopher M. Little Jerry X. Mitrovica Michael
Oppenheimer D. J. Rasmussen Benjamin H. Strauss Claudia Tebaldi Radley M. Horton
Christopher M. Little Jerry X. Mitrovica Michael Oppenheimer D. J. Rasmussen Benjamin
H. Strauss Claudia Tebaldi “Probabilistic 21st and 22nd century sea-level projections at
a global network of tide-gauge sites” First published: 13 June 2014
Newport Beach, “Waterfront Project Guidelines and Standards, Harbor Design Criteria
Commercial & Residential Facilities,” 2017 Edition
NOAA, 2018, Web Site, Maps http://anchor.ncd.noaa.gov/states/ca.htm Tidal Datums
http://www.opsd.nos.noaa.gov/cgi-bin/websql/ftp/query_new.pl
State of California, County of Orange, 2009, “Tsunami Inundation Map for Emergency
Planning, Newport Beach Quadrangle,” 1:24,000 scale, dated June 1.
State of California Sea Level Rise Guidance 2018 Update, by Ocean Protection Council,
dated in March 2018.
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