HomeMy WebLinkAboutPA2022-125_20220606_GeoSoils Report_06-02-22Geotechnical 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
June 2, 2022 WO S8368
Mr. George Karahalios
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, 607
North Bay Front, Newport Beach, Orange County, California.
Dear Mr. Karahalios:
In accordance with your 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 607 North Bay Front, on
Balboa Island 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),
the CCC SLR Guidance (November 2018), a review of City of Newport Beach Municipal
Code (NBMC) 21.30.15.E.2, a review of the preliminary plans for the proposed residence
prepared by Brandon Architects, a site inspection, and preparation of this letter report.
INTRODUCTION
The proposed project is a new single-family residence on the north side of Balboa Island,
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 and Newport Bay. The proposed
finished first floor (FF) elevation of the residence is +9.13 feet NAVD88, with a perimeter
curb to elevation +10.9 feet NAVD88. The site is fronted by a public boardwalk and a
narrow intertidal beach along a Newport Bay channel. Balboa Island is protected by a City
of Newport Beach owned and maintained concrete seawall/bulkhead. The site is mapped
by FEMA to be in the AO Zone with a flood depth of 1 feet. The elevation of the public
road flow line is about +6 feet NAVD88 which means that FEMA has a site specific base
flood elevation (BFE) at the site of +7 feet NAVD88.
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Figure 1. Subject site, 607 North Bay Front , adjacent intertidal beach and Newport Bay
channel in 2021.
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
Land Surveying, Inc., dated 7/27/21, and preliminary project plans were provided by
Brandon Architects. A site reconnaissance was performed in May 2022. The visible
portions of the offsite walkway/bulkhead were observed to be in good condition. The City
owned bulkhead has recently be increased in height to elevation 8.6 feet NAVD88. There
is only a narrow intertidal beach fronting the bulkhead/walkway in front of the site and in
the general area.
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 an intertidal beach in the site area but at very high tide there is no beach. There
is no actual shoreline (beach above the high tide) fronting the site. A review of historical
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aerial photographs available on Google Earth dating back to 1995 show no beach fronting
the site above the maximum high tide line and the adjacent public walkway. Shoreline
erosion will not impact the proposed development over the life of the development.
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
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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 13.7 feet NAVD88 (7.7 feet NAVD88 + 6 feet SLR). 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 offsite City owned
bulkhead, the extreme Newport Bay water level will exceed the height of the bulkhead
when SLR is 0.9 feet or greater. For the likely COPC SLR estimate range the bulkhead
is safe from overtopping beyond the year 2050. For SLR greater than 0.9 feet the height
of the City bulkhead will need to be further increased. 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 at about +9.1 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 1.4 feet or greater. For the likely COPC SLR estimate range (high
emissions) the residence is safe from flooding until about the year 2065. 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 on Balboa Island.
Waves and Wave Runup
The potential surface gravity waves (ocean swell), boat wakes and wind waves to arrive
at this site is nil. While the site is near a navigation channel, the geometry of the small
navigation channel fronting the site, and the presence of the boat docks, preclude waves
from reaching the offsite bulkhead.
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
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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 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
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.
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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 a no beach
above the high tide fronting the site. Boat wakes and wind waves are too small,
even with sea level rise (SLR), to potentially flood the residence provided the offsite
bulkhead/walkway is increased to mitigated SLR. The City of Newport Beach has
recognized that in the future there will be a need to raise the elevation of the
bulkheads on Balboa Island 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 offsite
walkway/bulkhead 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 at the site. There is a public intertidal beach on the bay
side of the public boardwalk and bulkhead.
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 2.9 feet. There is a very low probability SLR
estimate of 5.5 feet in 75 years that is not currently support by the measured
SLR through May 2022. This is the design sea level range for the proposed
project. This SLR would account for future extreme bay water level of 10.6
feet NAVD88 to 13.2 feet NAVD88 over the next 75 years.
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 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
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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 no bulkhead on the site. However, the nearby City of Newport
Beach bulkhead protects this property along with the other properties on
Balboa Island, 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 proposed
elevation of the finished floor, the perimeter curb, the ability to waterproof
the building, if necessary, in the future, and the presence of the nearby
walkway/bulkhead. To further adapt to SLR, the City owned bulkhead is
planned to be increased in height, in the future. 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 well before the residence 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.
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CONCLUSIONS
• The proposed residential structure with the implementation of the SLR adaptation
strategies (waterproofing and the future raising of the City’s bulkhead) will not be
adversely impacted by potential coastal hazards including probable sea level rise
over the next minimum 75 years. The site will be part of a community wide response
to mitigate SLR hazards.
• 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 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, 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 San Diego, 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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