HomeMy WebLinkAbout20190410_Coastal_Hzrd_Sea_Rise_ReportGeotechnical C Geologic C Coastal C Environmental
5741 Palmer Way C Carlsbad, California 92010 C (760) 438-3155 C FAX (760) 931-0915 C www.geosoilsinc.com
March 20, 2019
South Bayfront Waterpointe, LLC
c/o Brandon Architects
151 Kalmus Drive, Suite G-1
Costa Mesa, CA
92626 USA
SUBJECT: Coastal Hazard and Sea Level Rise Discussion for New Residence,
402 South Bayfront, Newport Beach, Orange County, California.
Dear Sirs:
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 402 South Bayfront, 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),
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 +9.0 feet NAVD88. The site is fronted by a public
boardwalk along a Newport Bay channel. Balboa Island is protected by a City of Newport
Beach owned and maintained concrete seawall/bulkhead. The site is currently mapped
by FEMA to be in the AE Zone with a BFE of +8 feet NAVD88. FEMA is proposing to
adopt a new FIRM map for the area soon. While the future FIRM map is currently not
effective, the proposed future FEMA FIRM does not change the site zone designation or
the elevation of the site BFE. The City of Newport Beach adopted the elevation of +9 feet
NAVD88 as the minimum finished floor (FF) height for new residential development.
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Figure 1. Subject site, 402 South Bayfront , and adjacent bay channel in 2018.
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 5/15/18, and project plans were discussed with Brandon
Architects. A site reconnaissance was performed in March 2019. The visible portions of
the offsite walkway/bulkhead were observed to be in good condition. There is a small
intertidal beach fronting the bulkhead/walkway near 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.
Shoreline Erosion Hazard
There is no shoreline fronting the site. There is a small intertidal beach bayward of the
public walkway. Shoreline erosion will not impact the proposed development over the life
of the development.
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Current Flooding Hazard
The National Oceanographic and Atmospheric (NOAA) National Ocean Survey tidal data
station closest to the site with a long tidal record (Everest International Consultants Inc.
(EICI), 2011) is located at Los Angeles Harbor (Station 94106600). The tidal datum
elevations are as follows:
Mean High Water 4.55 feet
Mean Tide Level (MSL) 2.62 feet
Mean Low Water 0.74 feet
NAVD88 0.0 feet
Mean Lower Low Water -0.2 feet
During storm conditions, the sea surface rises along the shoreline (super-elevation) and
allows waves to break closer to the shoreline and runup on the beach. Super-elevation of
the sea surface can be accounted for by: wave set-up, wind set-up and inverse barometer,
wave group effects and El Niño sea level effects. The historical highest ocean water
elevation at the Los Angeles Harbor Tide station is +7.72 feet NAVD88 on January 10,
2005. In addition, EICI reported that the elevation of 7.71 feet NAVD88 is the 1% water
elevation. For this analysis the historical highest water elevation will be +7.7 feet
NAVD88.
Future Tide Levels Due to Sea Level Rise
The 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
el at, 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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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 Newport
Beach City Council recently 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 design historical water elevation
at the for Newport Bay is elevation +7.7 feet NAVD88 (Moffatt & Nichol 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.
The “likely” sea level rise for the proposed project is 2.9 feet with a lower probability (~5%)
of SLR of about 4.0 feet. This SLR would account for future extreme bay water level in the
range of 10.6 feet NAVD88 (7.7 feet NAVD88 + 2.9 feet SLR). There is a low probability
that bay water will meet or exceed 11.7 feet NAVD88 (7.7 feet NAVD88 + 4.0 feet SLR).
The existing offsite bulkhead is proposed to be increased by the City in the future. 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 shore protection,
the extreme Newport Bay water level will exceed the height of the existing walkway
bulkhead when SLR is 1.3 feet or greater. For the likely COPC SLR estimate range (high
emissions) the site is safe from overtopping flooding until about the year 2060. For SLR
greater than 1.3 feet the height of the walkway bulkhead will need to be further increased.
For the 0.5% SLR case this may occur in about the year 2060. 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 bulkheads around Balboa Island. The City of Newport Beach Building
Department (CNBBD) has a standard drawing, and a regional plan for rehabilitating and
raising the bulkheads.
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Waves and Wave Runup
The potential surface gravity waves (ocean swell), boat wakes and wind waves to arrive
at this site is nil.
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.
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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 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 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 water proofing 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 CCC SLR estimate over the project 75-year design life, the
SLR in the year ~2095 is 2.9 feet. This is the design sea level rise for the
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proposed project. This SLR would account for future extreme bay water
level of 10.6 feet NAVD88 (7.7 feet NAVD88 + 2.9 feet SLR).
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 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
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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 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.
CONCLUSIONS
• The proposed residential structure with the implementation of the SLR adaptation
strategies (water proofing and the future raising of the City’s bulkhead) will not be
adversely impacted by potential coastal hazards including a 2.9 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 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.
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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, 2013, 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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