HomeMy WebLinkAbout20200908_Coastal Hazards_8-24-2020Geotechnical • Geologic • Coastal • Environmental
5741 Pc1lmer Way• Carlsbad Cal1fornic1 D2010 , (,760) 43B-3155 • Ft\X (760) ~n-1-0915 • 'NWW.~Jeosoilsinc.com
August 24, 2020 WO 87952
Mr. & Mrs. Coop
Brion Jeannette Architecture
470 Old Newport Blvd.
Newport Beach, CA 92663
SUBJECT: Coastal Hazard and Sea Level Rise Discussion for New Residence, 408 Via
Lido Nord, Newport Beach, Orange County, California.
Dear Mr. & Mrs. Coop:
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 408 Via Lido Nord on Lido
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), CCC
SLR Guidance (November 2018), a review of City of Newport Beach Municipal Code
(NBMC) 21.30.15.E.2, a review of the proposed new residence plans, a site inspection,
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, the public boardwalk, the mostly intertidal beach, and the navigation
channel within Newport Bay. There is a privacy wall along the boardwalk to about
elevation +12.5 feet NAVD88. The proposed new privacy wall will be designed such that
it can be increased in height in response to SLR. The proposed finished first floor (FF)
elevation of the residence is 12.6 feet NAVD88. The site is currently mapped by FEMA to
be in the X Zone. The elevation of the street flow line is about +11.5 feet NAVD88 and the
public boardwalk elevation is about +8.7 feet NAVD88.
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Figure 1. Subject site, 408 Via Lido Nord, adjacent properties, public boardwalk, beach,
and Newport Bay channel.
DATA& DATUM
The datum used in this report is NAVD88, which is about 2.62 feet below the mean tide
level (MTL). The units of measurement in this report are feet (ft), pounds force (lbs), and
seconds (sec). Site elevations were taken from a topographic map and project plans
provided by Brion Jeannette Architecture. A site reconnaissance was performed in early
July 2020. The shoreline showed no signs of ongoing erosion. The particular section of
shoreline is a feeder beach for the ongoing Newport Bay navigation dredging program.
HAZARD ANALYSIS
There are three different potential shoreline hazards identified at this site: shoreline
movemenUerosion, 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. There is an intertidal beach bayward of the
public boardwalk/walkway. The beach is a receiver beach from dredging within the Newport
Bay navigation channels. The beach is maintained at a width that is adequate to protect
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the public boardwalk. The shoreline is essentially located just bayward of the City
boardwalk. The public boardwalk will prevent shoreline erosion from impacting the
proposed development over the life of the development, provided the boardwalk is
maintained and protected by the City.
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
Mean Tide Level (MSL)
Mean Low Water
NAVD88
Mean Lower Low Water
4.55 feet
2.62 feet
0.74 feet
0.0 feet
-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 Nino 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." When the
SLR Guidance document was adopted by the CCC in 2015, it stated that the best available
science for quantifying future SLR was the 2012 National Research Council (NRC) report
(NRC, 2012). The NRC (2012) is no longer considered the state of the art for assessing
the magnitude of SLR in the marine science communities. 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
et al., 2014). This 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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Probabilstic Proj«t/ons (In hxlt) (based on Kopp et al. 20,4) ----------------r---------~ ~---
MED IAN LIKELY RANGE 1-IN-20 CHANCE 1-IN-200 CHANCE
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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. In early 2019,
the Newport Beach City Council approved the use of the high estimate of the "low risk
aversion" scenario, which is 3.2 feet SLR by the year 2100. Interpolating between the years
2090 and 2100 provides a SLR of 2.9 feet in the year 2095. The City currently requires the
use of a lower probability SLR estimate. The design historical water elevation at the for
Newport Bay is elevation +7.7 feet NAVD88 (1 % water elevation). If 2.9 feet is added to
this 7.7 feet NAVD88 elevation, then future design maximum water level 10.6 feet
NAVD88 is determined.
Interpolating the above table, the very low probability SLR (0.5%) for the year 2095, low
emissions, SLR is -5.0 feet, and the high emissions, SLR is 6 feet. Based upon this table
there is a much lower probability (0.5%) of SLR of about 5.5 feet ((5.0+6.0)/2). This SLR
would account for future extreme bay water level of 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 Niiio effects, is +7.7 feet NAVD88. Based upon the elevation of the
access street flow line (11.5 feet NAVD88), the extreme Newport Bay water level will
exceed the height of the existing street flow line when SLR is 4.2 feet or greater. For the
likely COPC SLR estimate range (high emissions) the access street is safe from flooding
until beyond the year 2100. For the 0.5% SLR case this may occur in after the year 2080.
It should be noted that, if SLR is higher, flooding the street 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. With the FF at elevation +12.6 feet NAVD88 the structure will be safe from flooding
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for SLR less than 4.9 feet. For the 5% COPC SLR estimate range (high emissions) the
structure is safe from flooding until beyond the year 2100. For the 0.5% SLR case this
may occur about the year 2090.
The Kopp et al. paper used 2009 to 2012 SLR modeling for the probability analysis, which
means the "best available science" as determined by the CCC is almost 1 O years old. The
CCC SLR Guidance requires the use of the "best available science." Dr. Reinhard Flick
from the Scripps Institution of Oceanography has provided information that global sea level
from 1992 to 2018 has resulted in 8.32 centimeters of relatively uniform SLR in the past
26 years. This information is shown on Figure 3 taken from the CCC SLR Guidance
(2015). This current measurement shows that SLR is tracking more on the intermediate
SLR prediction curves, which is more like a 50% (median) probability SLR in the year 2100,
as shown in Figure 2.
~----------------~2.1Jm{7.0ft.)
lOO --------~---~--------1~--------------li,gh,est · 70m
Observed
I •
3.2 mmryea, j
5':8Ml"OS
'
I
• I 8.32 cm
.40 ,__ ___ ~------+---
I 1000 1950 2000 ~ "''" 0 Year N
1.37 m (4.5 fl:.)
lnlQlrt>11iJ,.Jtu-l~19h , I 2 m
lnll!'rrne<J1altt·low · O.:i rn
2100
.\lodilkd from Figun· 5 of th<.' California Coastal Commis'iion S(';t LC'\'C'I IUS(' Policy Guidanc('
documL'lll adopted Augusl 12, 2015.
Figure 3. Current global SLR plotted on SLR prediction curves (graphic taken from
TerraCosta Consulting).
The recent global SLR measurement provided in Figure 3 shows that the current SLR
trend, is not following the higher SLR estimate curves. It is GS l's professional opinion that
the methodology and SLR estimates suggested by the CCC SLR Guidance, based upon
current SLR trends, are an overestimate of SLR over the project design life of 75 years.
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. With SLR greater than 3 feet the entire Lido
Island can be flooded from the several sections of the island shoreline that do not currently
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have a shore protection device in place. Flooding through these areas will result in
flooding of the access roads to hundreds of homes which are not on the shoreline. The
island will require some form of shore protection before there is flooding of the residences.
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.
Boast 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.
Inunda tion projections and resulting planning maps are to be used f or emergency
planning purposes only. They are not based on a sp ecific earthquake and tsunami.
Areas actually inundated by a specific tsunami can vary f rom those predicted. The
inundation maps are not a prediction of th e pe,formance, in an earthquake or
tsunami, of any stru cture within or outside of the projected in unda tion area.
The City of Newport Beach and County of Orange have clearly marked tsunami evacuation
routes for the entire Newport Beach/Bay area.
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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.
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 small mostly
intertidal beach near the site but is not part of the site. Boat wakes and wind waves
are too small, even with sea level rise (SLR), to potentially flood the residence
provided the offsite boardwalk/walkway is maintained to mitigate SLR impacts. 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 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 water proofing the structure to above the potential flood elevation, and increasing
the height of the offsite walkway are implemented if requ ired , 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 stable mostly intertidal beach near the site that is maintained by
nouirshment. There are no seasonal changes in the beach. As SLR occurs
the intertidal beach may become smaller and likely shift higher in elevation
based upon the equilibrium beach principal.
2. High tide conditions, combined with long-term (75 year) projections
for sea level rise;
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Using the likely CCC SLR estimate over the project 75-year design life, the
SLR in the year -2095 is 2.9 feet. There is a 0.5% probability that SLR could
be 5.5 feet in the next 75 years. This is the design sea level rise range (2.9
feet to 5.5 feet) for the proposed project. This SLR would account for future
extreme bay water level of 10.6 feet NAVD88 to 13.2 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 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 adjace.nt
development or public facilities on the site or in the surrounding areas; and
There is no bulkhead on the site.
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.
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The project is safe from the coastal hazard of flooding by the proposed
elevation of the finished floor, and the ability to waterproof the building, if
necessary. To further adapt to SLR, the City will likely protect the streets
and residences of the island, 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 the Lido Island, Balboa Peninsula and Balboa Island, 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 of residences. These are a site
specific adaptation strategies.
CONCLUSIONS
• The proposed residential structure with the implementation of the SLR adaptation
strategies (design for future water proofing to above elevation +13.2 feet NAVD88
and the future protection of all the island residences by the City) will not be
adversely impacted by potential coastal hazards including a 5.5 feet 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 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.
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.
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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, 2020, 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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