HomeMy WebLinkAboutPA2022-0204_20220915_Coastal Hazards Report dated 08-29-22Geotechnical 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
August 29, 2022 WO S8275
Robert D. Olson
RD Olson Development
520 Newport Center Drive, Suite 600
Newport Beach, CA 92660
SUBJECT: Coastal Hazard Analysis for New Residence and Second Unit at 921-925 Via
Lido Soud, Newport Beach, CA.
Dear Mr. Olson:
In accordance with your request and authorization, GeoSoils, Inc. (GSI) is pleased to
provide this discussion regarding the coastal hazards, including the impact of future sea
level rise (SLR) on the proposed new residential structure and second unit at 921- 925 Via
Lido Soud. The purpose of this report is to provide the project 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), the latest National
Oceanographic and Atmospheric Administration (NOAA, 2022) SLR science, a review of
City of Newport Beach Municipal Code (NBMC) 21.30.15.E.2 and E.3, a review of the
proposed project plans, a site inspection, and preparation of this letter report.
INTRODUCTION & SITE INSPECTION
The subject site is two adjacent parcels, located on the southeast corner of Lido Isle, in
Newport Beach. The site is has been in common ownership for more than 25 years and
is developed with a residence and guest house. The proposed developed is to remove the
residence and guest house and replace them with a new residence and second unit.
There is a concrete panel bulkhead fronting the 921 Via Lido Soud parcel and a recently
approved new pile and stem wall bulkhead at 925 Via Lido Soud parcel. Figure 1 shows
a Bird’s Eye View of the site and adjacent properties downloaded from the internet. The
site inspection was performed by the undersigned 1n January 2022.
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Figure 1. Subject site, 921- 925 Via Lido Soud and adjacent properties.
HAZARD ANALYSIS
There are three different potential shoreline hazards identified at this site for the proposed
development: shoreline movement/erosion, waves and wave runup, 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
The is an intertidal beach at the site. However, there is no beach above the highest tide.
During an very low tide some wet sand is exposed. Due to the fact that the site is on a
channel on the south side of Lido Island, the shoreline is located essentially at the
bulkhead line as extend from the adjacent properties. As sea level rises the shoreline will
remain at the bulkhead line. The bulkhead at 921 Via Lido Sound and the new bulkhead
at 925 Via Lido Soud meet the current City requirements with regards to the minimum top
of bulkhead elevation (Minimum 10.9 feet NAVD88) and the ability to adapt to SLR (Up to
or above +14.4 feet NAVD88). The bulkhead heights can be increased without any
bayward encroachment. The bulkheads are designed such that shoreline erosion will not
impact the site and the adjacent properties 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 (Everest International Consultants Inc.
(EICI), 2011) 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, EICI reported 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 November 2018 California Coastal Commission (CCC) SLR Guidance Update
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 which the CCC has adopted in
November 2018. These 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). This update included SLR estimates and probabilities for Los Angeles Harbor,
the closest SLR estimates to Newport Bay. 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
estimate to meet or exceed the 1991-2009 mean.
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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.
The CCC SLR Guidance (CCCSLRG) is based upon the California Ocean Protection
Council (COPC) update to the State’s Sea-Level Rise Guidance in March 2018. These
COPC estimates are based upon a 2014 report by Kopp, et al., 2014. The Kopp et al.
paper used 2009 to 2012 SLR modeling by climate scientists for the probability analysis,
which means the “best available science” used by the CCC is about 10 years old. The
SLR models used as the basis for the COPC and CCCSLRG have been in place for over
a couple decades. The accuracy of any model can be determined by comparing the
measured SLR (real data) to the model predicted SLR (model prediction). If the model
cannot predict, with any accuracy, what will happen in the past, it is very unlikely that the
model will increase in accuracy when predicting SLR over the next 75 years. Simply put,
if the model is not accurate now, it will be even less accurate in the future.
NOAA currently provides the best available SLR science (NOAA, 2022). The NOAA has
been measuring SLR globally and at Los Angeles Harbor. The NOAA Los Angeles Harbor
SLR rate is 1.03 mm/yr. The rate can be used to calculate a sea level rise of 30.9 mm (0.1
ft) over the last 22 years and next 8 years (Jan 2000 to Jan 2030), a period of 30 years.
NOAA also provides the latest SLR model curves and tables for the Los Angeles Harbor
NOAA Station. Figure 3 provides the SLR model curves and tables for Los Angeles
Harbor.
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Figure 3. Taken from the USACOE SLR curve calculator program.
Looking at the table in Figure 3, the SLR base value in the year 2000 is 2.70 feet. Adding
0.1 feet to the base SLR value yields the value 2.8 for the year 2030. The model that most
closely predicts the currently measured SLR is the NOAA 2017 Low Model. This NOAA
model predicts about 1.5 feet of SLR in the year 2100. Examining Figure 2 for the year
2030 and 0.1 feet of SLR, the closest probability category is the lower limits of the “Likely
Range.”
The CCCSLRG document recommends that a project designer determine the range of
SLR using the “best available science.” The NOAA information provided above is more
current than the CCCSLRG. The NOAA information provides the “best available science”
for SLR prediction and is required to be used. Currently, the SLR model that the CCC is
“requiring” to be used for development is incorrect by a factor of about 4 as to the amount
of the SLR in Los Angeles.
Figure 2 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. In addition,
based upon this 2018 COPC SLR report, the 5% probability SLR for the project is
estimated to be less than 4.1 feet and a 0.5% probability that SLR will be between 5 feet
and 6 feet in the year 2097. This 0.5% SLR is based upon the interpolation of the low
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estimates and the high estimates for 2090 and 2100, recognizing that the interpolation is
exponential and not linear( (4.5 + 5.4)/2 = ~5 and (5.3 + 6.7)/2 = ~6 feet)). The design
historical water elevation for Newport Bay is elevation +7.7 feet NAVD88. This actual high
water record period includes the 1982-83 severe El Niño, and the 1997 El Niño events, and
is therefore consistent with the methodology outlined in the CCCSLRG document.
The “likely” sea level rise range for the proposed project is 1.3 feet to 3.2 feet with a lower
probability (~5%) of SLR of about 4.0 feet. This SLR range would account for future
extreme bay water levels in the range of 9 feet NAVD88 (7.7 feet NAVD88 + 1.3 feet SLR)
and 10.9 feet NAVD88 (7.7 feet NAVD88 + 3.2 feet SLR). There is a 0.5% probability that
bay water will meet or exceed 14.4 feet NAVD88 (7.7 feet NAVD88 + 6.7 feet SLR). The
top of the lowest bulkhead is at elevation 13.13 feet NAVD88 at 925 Via Lido Soud. As
stated before, the present maximum historical water elevation at the site, including El Niño
effects, is ~+7.7 feet NAVD88. Based upon the elevation of the lowest bulkhead (+13.13
feet NAVD88), the extreme Lower Newport Bay water level will exceed the height of the
bulkhead when SLR is 5.4 feet or greater. For the likely COPC SLR estimate range (high
emissions) the bulkhead is safe from overtopping beyond the year 2110. For SLR greater
than 5.4 feet the height of the bulkhead will need to be increased. For the 0.5% probability
SLR case this may occur after the year 2090. It should be noted that, if the bay water is
higher than the bulkhead, 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 boardwalks and bulkheads around the Newport Bay. The City of
Newport Beach Building Department (CNBBD) has a standard drawing, and a regional plan
for rehabilitating and raising the bulkheads. Flooding from the bay and from the beach will
result in flooding of the public roads in the Newport Beach area. Recent action by the City
Council has raised the minimum bulkhead elevation for new development to be 10.9 feet
NAVD88. In addition, the updated Waterfront Project Design Guidelines and Standards
require that the bulkhead can be design to accommodate an increase in height to +14.4
feet NAVD88 or greater. Based upon our inspection of the existing bulkhead at 921 Via
Lido Soud and review of the 925 Via Lido Soud bulkhead plans, the bulkhead systems are
capable of being extended in height to a least +14.4 feet NAVD88.
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 proposed 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 0.75-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) and the base of
the proposed bulkhead at 0.5 feet NAVD88. This combination of wave and water level
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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 0.8 feet above the historical 100-year water level, or about 8.5 feet
NAVD88. This is currently well below the elevation of the lowest bulkhead (+13.13 feet
NAVD88). In the future, with more than 4.7 feet of SLR, boat wakes during the highest
high tides may overtop the shore protection. As verified by the inspection at 925 Via Lido
Soud and the 921 Via Lido Soud plans, the shore protection can be increased in height
without any bayward encroachment. This is a SLR adaptation strategy as recommended
in the CCCSLRG document.
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 meters 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.
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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, 2011). 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 45 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
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 analysis
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
for the proposed development are shoreline erosion, flooding, and wave/wake
impacts. There is no beach above the highest water fronting the site. Boat wakes
and wind waves are too small, even with sea level rise (SLR), to overtop the
bulkheads. There is no potential coastal hazard of flooding provided adaptation
strategies such as increasing the height of the bulkheads and waterproofing the
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structure (the proposed lowest FF elevation Is +13.5 feet NAVD88) to above the
potential flood elevation (minimum elevation 14.4 feet NAVD88), are 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 no beach fronting the site.
2. High tide conditions, combined with long-term (75 year) projections
for sea level rise;
Using the likely CCC SLR estimate over the project 75-year design life, the
SLR in the year ~2097 is 3.2 feet. There is a 0.5% probability that SLR could
be 6 feet in the next 75 years. This is the design sea level rise range (3.2 feet
to 6 feet) for the proposed project. The CCC uses a 0.5% high emission
SLR estimate in the year 2100 of 6.7 feet. This SLR raneg of SLR would
account for future extreme bay water level of 10.9 feet NAVD88 to 14.4 feet
NAVD88.
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. The analysis herein shows that boat
wakes and wind waves will not impact the project.
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
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.
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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
There are bulkheads in front of the site. The bulkheads are necessary to
protect the proposed development, the adjacent existing residential
structures, 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 is safe from the coastal hazard of flooding by the elevation of the
top of the bulkheads (lowest elevation is 13.13 feet NAVD88). To further
adapt to SLR, the shore protection can be increased in height to above +14.4
feet NAVD88, in the future. The proposed lowest FF elevation is +13.5 feet
NAVD88. The construction material is such that the development can be
retrofitted with waterproofing to an elevation above any potential flooding. 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, Lido Island and the
Balboa Peninsula, will flood with lower SLR well before the development
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 of
Newport Beach. These strategies involve raising, or adding/replacing the
bulkheads, beaches and walkways that surround the bay, and waterproofing.
These are a 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 45 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
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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 fronting 921 Via Lido Soud is in good condition and meets the current
City standard. The panels are vertical and the concrete cap shows no signs of
spalling or significant distress. The landward side of the bulkhead should be further
inspected when the existing residence is removed and the condition of any
restraining members (tie-back and deadman) can be further inspected. The
bulkhead at 925 Via Lido Soud has been recently permitted and meets all of the city
requirements.
iii. Recommendations regarding the need for repair, augmentation or
replacement of the bulkhead or any parts thereof;
Augmentation of the bulkheads in the future is feasible from an engineering
viewpoint. Both of the bulkheads can be increased in height up to a minimum
elevation of 14.4 feet NAVD88. The increase in height is an SLR adaptation
strategy.
iv. If augmentation or replacement in the existing alignment is necessary,
recommendations that will avoid seaward encroachment of the bulkhead;
The augmentation of the site bulkheads can be located within the current bulkhead
footprints. No seaward encroachment is necessary.
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.
The bulkheads are aligned with the adjacent bulkheads.
CONCLUSIONS
• The proposed residential structure and second unit have a lowest FF elevation of
+13.5 feet NAVD88. This is above the City recommended minimum FF elevation.
With the implementation of the SLR adaptation strategies (design for future
waterproofing to above elevation +14.4 feet NAVD88 and the increase in height of
the bulkheads) the development will not be adversely impacted by potential coastal
hazards including a 6.7 feet sea level rise over the next minimum 75 years. The site
will be part of a community wide response to mitigate SLR hazards.
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• An augmented bulkhead is currently not needed but will be needed to protect the
residences with SLR greater than 5.8 feet. Augmentation would be necessary to
protect the other residences , streets, and infrastructure on Lido Island, regardless
of the development on the site.
• For the most part, in the remainder of the Newport Beach coastal area, including the
Balboa Peninsula, and other developed islands within the bay, flooding with a lower
SLR is likely to occur. Such flooding will occur well before any part of the proposed
development will flood.
• Provided the recommendations of this report are implemented during the project
construction, no additional protective devices will be necessary to protect the
proposed development from any existing or anticipated future coastal hazards for
the next 75 years or more.
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 for the next 75 years. 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 Bay Island 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.
FEMA Website, 2022 https://msc.fema.gov/portal/home
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,” March 23, 2021.
N O A A 2 0 2 2 , S e a L e v e l R i s e R e p o r t e m a i l l i n k .
https://oceanservice.noaa.gov/hazards/sealevelrise/sealevelrise-tech-report.html
NOAA, 2022, 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, 2011, “Updated Tsunami Inundation Map for
Emergency Planning, Newport Beach Quadrangle,” 1:24,000 scale.
State of California Sea Level Rise Guidance 2018 Update, by Ocean Protection Council,
dated in March 2018.
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