HomeMy WebLinkAboutPA2022-0262_20221107_Coastal Hazards Report dated 09-28-22Geotechnical 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
September 28, 2022
Mr. & Mrs. Jacob
213-215 East Edgewater
Newport Beach, CA 92663
SUBJECT: Coastal Hazard and Sea Level Rise Discussion for New Residence and
Accessory Dwelling Unit (ADU) at 213-215 E Edgewater Ave, Newport
Beach, Orange County, California.
Dear Mr. & Mrs. Jacob:
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 and ADU at 213-215 E.
Edgewater 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 (November 2018), a review of City of Newport Beach Municipal Code
(NBMC) 21.30.15.E.2, a discussion of the proposed new residence and ADU plans, a site
inspection, and preparation of this letter report.
INTRODUCTION
The proposed project is a new residence and ADU, 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 City of Newport Beach owned bulkhead, a
small intertidal beach, the boat dock, and the navigation channel within Newport Bay. The
proposed finished first floor (FF) elevation of the residence is about elevation 9.3 feet
NAVD88. The structure will be designed with a concrete perimeter curb, which effectively
makes the FF at about elevation +10.6 feet NAVD88. The top of the City of Newport
Beach owned bulkhead is at about elevation 8.6 NAVD88 (shore protection). The top of
a privacy wall on the landward side of the bulkhead is at ~+10.3 feet NAVD88. The site
is currently mapped by FEMA to be in the shaded X Zone and the AO Zone, with a flood
depth of 1 feet above grade. The elevation of the alley is about +7 feet NAVD88 and the
public boardwalk elevation is about +9 feet NAVD88.
PA2022-0262
2
Figure 1. Subject site, 213-215 E. Edgewater Ave, adjacent properties, public boardwalk,
intertidal beach, boat dock, 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 and project preliminary plans were provided by Oatman
Architects, Inc, the project designer. A site reconnaissance was performed in September
2022. The visible portions of the offsite bulkhead were observed to be in good condition.
There is a small intertidal beach fronting the bulkhead and the site.
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.
PA2022-0262
3
Shoreline Erosion Hazard
There is no actual shoreline fronting the site. There is a small intertidal beach bayward of
the public walkway. The shoreline is essentially located at the City bulkhead. 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 November 2018 California Coastal Commission (CCC) SLR Guidance Update
document recommends that a project designer determine the range of SLR using the “best
available science.” The California Ocean Protection Council (COPC) adopted an update
to the State’s Sea-Level Rise Guidance in March 2018 which the CCC has adopted in
November 2018. These estimates are based upon a 2014 report entitled “Probabilistic
21st and 22nd century sea-level projections at a global network of tide-gauge sites” (Kopp
el at, 2014). This update included SLR estimates and probabilities for Los Angeles Harbor,
the closest SLR estimates to Newport Bay. The report provides SLR estimates based
upon various carbon emission scenarios known as a “representative concentration
pathway” or RCP. Figure 2 provides the March 2018 COPC data (from the Kopp et al 2014
report) with the CCC SLR adopted estimates (in feet) and the probabilities of those
estimate to meet or exceed the 1991-2009 mean.
PA2022-0262
4
Figure 2. Table from Kopp et al (2014) and COPC 2018, providing current SLR estimates
and probabilities for the Los Angeles Harbor tide station.
The CCC SLR Guidance (CCCSLRG) is based upon the California Ocean Protection
Council (COPC) update to the State’s Sea-Level Rise Guidance in March 2018. These
COPC estimates are based upon a 2014 report by Kopp, et al., 2014. The Kopp et al.
paper used 2009 to 2012 SLR modeling by climate scientists for the probability analysis,
which means the “best available science” used by the CCC is over 10 years old. The SLR
models used as the basis for the COPC and CCCSLRG have been in place for a couple
decades. The accuracy of any model can be determined by comparing the measured SLR
(real data) to the model predicted SLR (model prediction). If the model cannot predict, with
any accuracy, what will happen in the past, it is very unlikely that the model will increase
in accuracy when predicting SLR over the next 75 years. Simply put, if the model is not
accurate now, it will be even less accurate in the future.
NOAA currently provides the “best available” SLR science (NOAA, 2022). 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.
PA2022-0262
5
Figure 3. Taken from the USACOE SLR curve calculator program.
Looking at the table in Figure 3, the SLR base value in the year 2000 is 2.70 feet. Adding
0.1 feet to the base SLR value yields the value 2.8 for the year 2030. The model that most
closely predicts the currently measured SLR is the NOAA 2017 Low Model. This NOAA
model predicts about 1.5 feet of SLR in the year 2100. Examining Figure 2 for the year
2030 and 0.1 feet of SLR, the closest probability category is the lower limits of the “Likely
Range.”
The CCCSLRG document recommends that a project designer determine the range of
SLR using the “best available science.” The NOAA information provided above, and in
NOAA 2022, is more current than the CCCSLRG. The NOAA information provides the
“best available science” for SLR prediction and is required to be used. Currently, the SLR
model that the CCC is “requiring” to be used for development is incorrect by a factor of
about 4 as to the amount of the SLR in Los Angeles.
Figure 2 illustrates that SLR in the year 2100 for the Likely Range, and considering the
most onerous RCP (8.5), is 1.3 feet to 3.2 feet above the 1991-2009 mean. In addition,
based upon this 2018 COPC SLR report, the 5% probability SLR for the project is
estimated to be less than 4.1 feet and a 0.5% probability that SLR will be between 5 feet
PA2022-0262
6
and 6 feet in the year 2097. This 0.5% SLR is based upon the interpolation of the low
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. The likely SLR range would account for future
extreme bay water levels in the range of 9 feet NAVD88 (7.7 feet NAVD88 + 1.3 feet SLR)
and 10.9 feet NAVD88 (7.7 feet NAVD88 + 3.2 feet SLR). There is a 0.5% probability that
bay water will meet or exceed 14.4 feet NAVD88 (7.7 feet NAVD88 + 6.7 feet SLR). The
top of the city bulkhead is at elevation 8.6 feet NAVD88. 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 bulkhead (+8.6 feet NAVD88), 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 (high emissions) the bulkhead is safe
from overtopping beyond the year 2040. For SLR greater than 0.9 feet the height of the
City bulkhead will need to be increased. For the 0.5% probability SLR case this may occur
around the year 2040. The site has a privacy wall that extends up to elevation +10.3 feet
NAVD88, which will protect the site from bay waters coming directly over the bulkhead and
onto the property. SLR will need to be greater than 2.6 feet for the bay water at the highest
tide to flood over the top of the privacy wall. For the “likely” SLR this will be about the year
2090 and for the 0.5% SLR case this would be after the year 2060. Finally, it should be
noted that, if the bay water is higher than the bulkhead, flooding will not occur constantly
but rather only a few times a month, at the full moon and new moon, for a period of about
1 hour.
The City of Newport Beach has recognized that in the future there will be a need to raise
the elevation of the boardwalks and bulkheads around the Newport Bay. The City of
Newport Beach Building Department (CNBBD) has a standard drawing, and a regional plan
for rehabilitating and raising the bulkheads. Flooding from the bay and from the beach will
result in flooding of the public roads in the Newport Beach area. Recent action by the City
Council has raised the minimum private bulkhead elevation for new development to be
10.9 feet NAVD88. In addition, the updated Waterfront Project Design Guidelines and
Standards require that the bulkhead can be design to accommodate an increase in height
to +14.4 feet NAVD88 or greater. Based upon our inspection of the existing city bulkhead,
the bulkhead system is capable of being extended in height to+14.4 feet NAVD88.
Waves and Wave Runup
The potential surface gravity waves (ocean swell), boat wakes and wind waves to arrive
at this site is nil. The site is located behind the intertidal beach and the public walkway.
Tsunami
Tsunami are waves generated by submarine earthquakes, landslides, or volcanic action.
PA2022-0262
7
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
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
PA2022-0262
8
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 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 bulkhead/walkway is increased, in the future, 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 a stable intertidal beach near the site. There are no seasonal
changes in the beach. As SLR occurs the intertidal beach may become
smaller or disappear altogether.
2. High tide conditions, combined with long-term (75 year) projections
for sea level rise;
Using the likely NOAA estimate over the project 75-year design life, the SLR
in the year ~2097 is ~1.5 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 (1.5 feet
to 6 feet) for the proposed project. This SLR would account for future
extreme bay water level of 9.7 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 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
PA2022-0262
9
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 the
Balboa Peninsula, 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 ability to waterproof the building if
necessary, 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 the 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. These are a site specific adaptation strategies.
PA2022-0262
10
CONCLUSIONS
• The proposed residential and ADU structure with the implementation of the SLR
adaptation strategies (waterproofing to elevation ~+10.6 feet NAVD88 and the
future raising of the City’s bulkhead) will not be adversely impacted by potential
coastal hazards including 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
PA2022-0262
11
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
N O A A 2 0 2 2 , S e a L e v e l R i s e R e p o r t e m a i l l i n k .
https://oceanservice.noaa.gov/hazards/sealevelrise/sealevelrise-tech-report.html
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.
PA2022-0262