HomeMy WebLinkAboutPA2022-0187_20220826_Coastal Hazards ReportGeotechnical 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
March 23, 2022
Mr. & Mrs. Hedge
c/o Brandon Architects
151 Kalmus Drive, Suite G-1
Costa Mesa, CA 92626
SUBJECT: Coastal Hazard and Sea Level Rise Discussion for New Residence, 1400
West Bay Avenue, Newport Beach, Orange County, California.
Dear Mr. & Mrs. Hedge:
In accordance with the request and authorization, GeoSoils, Inc. (GSI) is pleased to
provide this discussion regarding the potential coastal hazards, including the impact of
future sea level rise (SLR), on the proposed new residence at 1400 West Bay Avenue 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 (CCCSLRG), a review of City of Newport Beach Municipal Code (NBMC)
21.30.15.E.2 and E.3, a review of the proposed plans, and preparation of this letter report.
INTRODUCTION
The proposed project is new single-family 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 properties, Newport Bay, the bulkhead, and private docks at the site The
bulkhead is on the subject property and extends up to elevation +8.4 feet NAVD88. Based
upon our site inspection, the height of the bulkhead can be increased without additional
bayward encroachment. The City of Newport Beach requires the bulkhead elevation, at
this time, to be at a minimum of 10.9 feet NAVD88 with the ability to increase the height
up to 14.4 feet NAVD88. The project includes the raising of the bulkhead and the
bulkhead return wall along 14th Street. Plans for this modification of the bulkhead will be
provided by others. There is no beach at the site proper. The proposed finished first floor
(FF) elevation of the residence is at or above +9 feet NAVD88. The site is currently
mapped by FEMA to be in the Shaded X Zone with the adjacent Newport Bay in AE Zone
with a base flood elevation of +8 feet NAVD88.
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Figure 1. Subject site, 1400 West Bay Avenue, adjacent properties, bulkheads, and
private docks on Newport Bay.
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 Apex
Surveying Inc. Proposed development elevations were discussed with Brandon Architects,
the project designer. A site reconnaissance was performed in early March 2022.
HAZARD ANALYSIS
There are three different potential shoreline hazards identified at this site: 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
There is no actual shoreline at the site proper. The bulkhead will prevent erosion of the
site even in consideration of SLR provided the recommendations of this report are
incorporated into the project.
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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 CCCSLRG 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 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.
The National Oceanic and Atmospheric Administration (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 3 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 information provided above is more current than
the CCCSLRG. The checking of the models 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 estimates and the high
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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 13.7 feet NAVD88 (7.7 feet NAVD88 + 6 feet SLR). The top
of the bulkhead is at elevation +8.4 feet NAVD88. The City requires the bulkhead to be
raised to elevation +10.9 Feet NAVD88 as a condition of the redevelopment of the site. As
stated before, the present maximum historical water elevation at the site, including El Niño
effects, is ~+7.7 feet NAVD88. Based upon the raised elevation of the bulkhead, the
extreme Newport Bay water level will exceed the height of the bulkhead when SLR is 3.2
feet or greater. For the likely COPC SLR estimate range the bulkhead is safe from
overtopping beyond the year 2100. For SLR greater than 3.2 feet the height of the
bulkhead will need to be further increased. For the 0.5% probability SLR case this may
occur in about 55 years. 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. In addition, flooding of the site does not
mean that the residence will flood.
The proposed residence FF elevation is above +9 feet NAVD88. Based upon the proposed
FF elevation, the extreme Newport Bay water level will exceed the height of the lowest FF
when SLR is 1.3 feet or greater. For the likely COPC SLR estimate range (high emissions)
the residence is safe from flooding until about the year 20605. For the 0.5% SLR case this
may occur in about the year 2045. Again, 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 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. Based upon our visual inspection and review of the bulkhead plans, the existing
bulkhead system is 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. Boat
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wakes are very small due to speed restriction in the channel and there is insufficient fetch
to produce wind waves or more than a couple inches.
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.
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 43 years experience in coastal
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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 costal 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 no beach fronting
the site. Boat wakes and wind waves are too small, even with sea level rise (SLR),
to potentially erode the beach or flood the proposed residence provided the bulkhead
is raised per the City requirement. 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 and as such the City of Newport Beach Building Department (CNBBD)
has a standard drawing, and a regional plan for rehabilitating and raising the
bulkheads. There is no potential coastal hazard of flooding of the development
provided adaptation strategies such as waterproofing the structure to above the
potential flood elevation, and increasing the height of the bulkhead is 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 a no beach at 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. This SLR would account for future
extreme bay water level of 10.9 feet NAVD88 to 13.7 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.
4. An analysis of bluff stability; a quantitative slope stability analysis that
shows either that the bluff currently possesses a factor of safety against
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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 the 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
There is a private bulkhead on the site. Based upon our inspection of the
bulkhead, the height of the bulkhead can be increased to adapt to SLR with
no additional bayward encroachment. The project includes the raising of the
height of the bulkhead to the required City minimum elevation of +10.9. The
bulkhead extension engineering will be provided by others.
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 increase in
height of the bulkhead, proposed elevation of the finished floor, and the ability
to waterproof the building, if necessary. To further adapt to SLR, the
structure can be retrofitted with waterproofing up to above the potential flood
elevation. It is important to point out that SLR will not impact this island alone.
It will impact all of the Newport Bay low lying areas. The public streets
throughout the Newport Beach coastal area, including the Lido Island, Balboa
Peninsula and Balboa Island, will flood with lower SLR well before the
residence floods. It is very likely that the Bay Island 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,
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or adding/replacing the bulkheads, beaches and walkways that surround the
bay, and waterproofing of residences. 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 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 concrete bulkhead is in good condition. The bulkhead, at elevation +8.4 feet
NAVD88, does not meet the current City’s top of bulkhead elevation requirement
(10.9 feet NAVD88). It should be noted that very few bulkheads in the Newport Bay
area meet this newer elevation requirement. The actual design, not elevation, of the
bulkhead does meet the City standard.
iii. Recommendations regarding the need for repair, augmentation or
replacement of the bulkhead or any parts thereof;
Augmentation of the bulkhead will be necessary for the project to be in conformance
with the current City height requirements. The increase in height is an SLR
adaptation strategy. In the future the bulkhead can be increased in height to a
minimum elevation of +14.4 feet NAVD88 to adapt to SLR. The increase in height
of the bulkhead can be accomplished without further bayward encroachment and 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 augmented bulkhead can be located within the current bulkhead footprint.
v. If replacement is necessary and the existing bulkhead is not in alignment
with adjacent bulkheads, recommended alternatives that will relocate the
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bulkhead in as much in alignment with adjacent bulkheads and as far
landward, as possible.
There are no other bulkhead to the east of the site. The bulkhead has a concrete
wall return along 14th Street. The bulkhead is in alignment with the bulkhead on the
property to the west.
CONCLUSIONS
• Current SLR measurements near the site reveal that SLR is tracking along the
NOAA 2017 low model. This model predicts a SLR of about 1 feet in the year 2100.
The CCCSLRG required SLR model currently over estimates SLR by a factor of
about 4. Based upon current and accurate SLR modeling it is likely the proposed
development is safe from coastal hazards without raising the bulkhead in the future.
• The proposed residential structure with the implementation of the SLR adaptation
strategies (design for future waterproofing to above elevation +13.7 feet NAVD88
and the increase in height of the bulkhead in the future) will not be adversely
impacted by potential coastal hazards including a 6 feet sea level rise over the next
minimum 75 years. The site will be part of a community wide response to mitigate
SLR hazards.
• An augmented bulkhead is currently needed to be in conformance with the City of
Newport Beach requirements. Plans for the bulkhead height extension will be
provided by others.
• 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 Bay Island,
including the subject property, will flood. It only requires a few of the protective
bulkheads around Newport Bay to remain at low levels to allow flooding of the
streets.
• Provided the recommendations of this report are implemented during the project
construction, no site specific 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.
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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.
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,” Revised 2021 Edition
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, 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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