HomeMy WebLinkAbout20210521_Coastal Hazards_5-7-2021Geotechnical 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
May 7, 2021
Mr. & Mrs. Lyman
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, 411
North Bay Front, Newport Beach, Orange County, California.
Dear Mr. & Mrs. Lyman:
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 411 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 plans of 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 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 +5.6 feet NAVD88 which means that FEMA has a site specific base flood elevation
(BFE) at the site of +6.6 feet NAVD88.
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Figure 1. Subject site, 411 North Bay Front , adjacent intertidal beach and Newport Bay
channel in 2019.
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 12/23/20, and project plans were provided by Brandon
Architects. A site reconnaissance was performed in April 2021. 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 8.5 feet NAVD88. There is only a narrow
intertidal beach fronting the bulkhead/walkway at the site and 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
aerial photographs available on Google Earth dating back to 1995 show no beach fronting
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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 California Coastal Commission (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 estimate 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. The design
historical water elevation at the for Newport Bay is elevation +7.7 feet NAVD88 (EICI 1%
water elevation). If 3.2 feet is added to this 7.7 feet NAVD88 elevation, then future design
maximum water level 10.9 feet NAVD88 is determined.
The “likely” sea level rise for the proposed project is 3.2 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 10.9 feet NAVD88 (7.7 feet NAVD88 + 3.2 feet SLR) to 13.2 feet
NAVD88 (7.7 feet NAVD88 + 5.5 feet SLR). 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 City bulkhead shore protection 8.5 feet NAVD88, the
extreme Newport Bay water level will exceed the height of the existing walkway bulkhead
when SLR is 0.8 feet or greater. For the likely COPC SLR estimate range (high
emissions) the bulkhead is safe from overtopping flooding until about the year 2060. For
SLR greater than 0.8 feet the height of the bulkhead will need to be further increased. For
the 0.5% SLR case this may occur about the year 2050. 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 proposed residence with an
effective FF at 10.9 feet NAVD88 will be asfe from flooding over the next 75 years under
the likely SLR.
Sea Level Rise Model Check
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 entitled “Probabilistic 21st and 22nd
century sea-level projections at a global network of tide-gauge sites” 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
Probabd1stlc Pro1ect1ons (m feet) (based on Kopp et al 2014)
LIKELY RANGE 1-IN-20 CHANCE 1-IN-200 CHANCE
5096 probability 66% probability 596 probability 0.596 probability
sea-level rise meets sea-level rise sea-level rise meets sea-level rise meets
or exceeds ... is between ... or exceeds ... or exceeds ...
Low Medium -High Extreme Risk
Aversion Risk Aversion Risk Aversion
High emissions 20!0 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
ow emissions 2080 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 mo· 1.4 0.9 2.2 3.1 6.0
High emissions mo· 2.3 1.6 3.3 4.3 7.1 11.5
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10 years old. The SLR models used as the basis for the COPC and CCCSLRG have
been in place for a decade. 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 over the approximate last 11 years,
it is very unlikely that the model will increase in accuracy when predicting SLR over the
next 100 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 global SLR shows a current SLR rate of
3 mm/yr. The rate can be used to calculate a sea level rise of 33.75 mm (0.111 ft) over the
last 11.25 years (Jan 2010 to March 2021). The NOAA Los Angeles Harbor SLR rate is
1.03 mm/yr. The rate can be used to calculate a sea level rise of 11.6 mm (0.038 ft) over
the last 11.25 years (Jan 2010 to March 2021). What is clear is that SLR in Santa Monica
is currently about 1/3 of the global SLR. What is also interesting is that the NOAA website
shows that SLR is not occurring in several locations and the ocean is actually getting lower
in elevation in these areas. Clearly “one size fits all” is not the best available science.
The COPC provided plots of the various SLR model projections over time starting in the
year 2010. Figure 3 attached is the model projections taken directly from the EICI. To
see which model is more accurately predicting SLR, the global data and the data for Los
Angeles harbor can be plotted onto the curves. Figure 4 attached is an enlargement of
a portion of Figure 3 to show the results. As stated before, the SLR in Santa Monica is
~1/3 of the global SLR over the same time period. The CCC Guidance SLR is over 5 times
the measured SLR in Los Angeles. More importantly the current global SLR trend
matches the USACE “Intermediate” SLR, which predict about 1.5 feet of SLR by the year
2100. The SLR for Los Angeles matches the USACE “Low” SLR, which predicts about 0.5
feet of SLR in the year 2100, an order of magnitude lower than the CCCSLRG (0.5 feet
versus 6.8 feet).
Figure 3. EICI
7.0 ...
■
6.0 .
5.0
4,0
1.0
COPCHlgh
COPClow
CA C0Htil Conservancy
USACE/ High
USA CE/ lntormodioto
USACE/ tow
\/ermefl and R3hmstorf
MHnndRange-
MARCH
2021
CCC SLR GUIDANCE LOS ANGELES 6.7 FT ------+I
■ -------
■ --------
. -.-. -'-.......................... -......................................................... .
0.0 •·-:...;-~:::::.:.:.:.:.::.:.:.:.:.:.:.:.:.:.:.:.;. _________________ ~------~
2010 2020 2030 2040 lOSO 2060 2070 2080 2090 2100
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Figure 4. Comparison of real SLR measurements to SLR Model predictions.
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 CCC SLR Guidance. The checking of the models is 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, and has been demonstrated to reasonably result in an error of
magnitude in the year 2100.
Regardless of the amount of SLR, 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.
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 bulkhead.
4' .o
-cu ~ .0
.0 CCC GUIDANCE
.0
MARCH
2021
0
YEAR
CCC GUIDANCE 2030
0.5% SLR 0.7 FEET
j
0
• • I
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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 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
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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 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.
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 ~2096 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 March 2021. 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
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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 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, 2021, 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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