HomeMy WebLinkAbout20191218_Coastal Hazards Report_12-17-2019Geotechnical 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
December 17, 2019
Mr. & Mrs. Capparelli
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, 117
North Bayfront, Newport Beach, Orange County, California.
Dear Mr. & Mrs. Capparelli:
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 117 North 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),
the CCC SLR Guidance (Npovember 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 +9.23 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 newly 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 The City of Newport Beach adopted the
elevation of +9 feet NAVD88 as the minimum finished floor (FF) height for new residential
development on Balboa Island.
PA2019-263
2
Figure 1. Subject site, 117 North Bayfront , and adjacent dock and Newport 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 9/3/19, and project plans dated 12/15/19 were provided by
Brandon Architects. A site reconnaissance was performed in December 2019. The visible
portions of the offsite walkway/bulkhead were observed to be in good condition. There is
not beach fronting the bulkhead/walkway at the site or 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 no shoreline fronting the site. A review of historical aerial photographs available
on Google Earth dating back to 1995 show not beach fronting the site and the adjacent
PA2019-263
3
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.” 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.
PA2019-263
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.
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 in the range of 13.2 feet NAVD88 (7.7
feet NAVD88 + 5.5 feet SLR). The existing offsite bulkhead (North Bayfront public access
walkway) 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 0.9
feet or greater. For the likely COPC SLR estimate range (high emissions) the walkway is
safe from overtopping flooding until about the year 2050. For SLR greater than 0.9 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 2035. It should be noted that, if SLR is higher,
flooding the walkway 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 +9.23 feet
NAVD88 the structure will be safe from flooding for SLR less than 1.5 feet.
PA2019-263
5
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 10 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.
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 GSI’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 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.
Waves and Wave Runup
The potential surface gravity waves (ocean swell), boat wakes and wind waves to arrive
PA2019-263
6
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.
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
PA2019-263
7
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 no beach
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 ~2095 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 2018. 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.
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.
PA2019-263
8
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
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
PA2019-263
9
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 (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
PA2019-263
10
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.
PA2019-263