HomeMy WebLinkAbout20190528_Coastal Hazard - Sea Level RiseGeotechnical 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
April 24, 2019
Mr. & Mrs Stupin
Brandon Architects
151 Kalmus Drive, Suite G-1
Costa Mesa, CA 92626
SUBJECT: Coastal Hazard and Sea Level Rise Discussion for New Residence, 3312 &
3324 Via Lido Nord, Newport Beach, Orange County, California.
Dear Mr. & Mrs Stupin:
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 3312 & 3324 Via Lido Nord
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), a
review of City of Newport Beach Municipal Code (NBMC) 21.30.15.E.2 &E.3, a discussion
of the proposed residence addition plans, a site inspection, and preparation of this letter
report.
INTRODUCTION
The proposed project is new single-family residence on two adjacent lots in the City of
Newport Beach. Figure 1, downloaded from Google Maps (Bird’s Eye View), shows the
2 adjacent sites (site) in relation to the adjacent properties and Newport Bay channel. The
proposed finished first floor (FF) elevation of the residence is +10 feet NAVD88. The site
is fronted by a continuous concrete bulkhead at about elevation +7.5 feet NAVD88. The
continuous bulkhead on both sites is topped by low height walls to elevation 8.8 feet
NAVD88 (33120 and 9.5 feet NAVD88, and fronted by private docks, along a Newport Bay
navigation channel. The site has been mapped by FEMA to be in the X Zone with no base
flood elevation (BFE). It should be noted that the adjacent Newport Bay channel is
mapped in the AE Zone with a BFE of +8 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.
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Figure 1. Subject site, 3312 & 3324 Via Lido Nord, 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 2/16/18, and project plans were provided by Brandon
Architects, the project designer. A site reconnaissance was performed on April 15, 2019.
There is no beach fronting the bulkhead at 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
The is no beach at the site. During low tide no sand is exposed. Due to the fact that the
site is on a channel on the north end of Newport Bay, the shoreline is located essentially
at the bulkhead. As sea level rises the shoreline will remain at the bulkhead. The
proposed project will bring the top of the shore protection to a minimum design elevation
of +10.6 feet NAVD88. 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, Everest International Consultants, Inc., (EICI, 2011) 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 existing shore protection will be increased to a minimum elevation of +10.6 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 shore
protection, the extreme Newport Bay water level will exceed the height of the shore
protection when SLR is 2.9 feet or greater. This SLR is greater than the lower estimate of
the likely project sea level rise range. For the likely COPC SLR estimate range (high
emissions) the bulkhead is safe from overtopping flooding beyond the year 2090. For SLR
greater than 2.9 feet the height of the shore protection will need to be increased. For the
0.5% SLR case this may occur in about the year 2070. 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.
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.
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Wave runup and overtopping of the bulkhead and walls at the site is calculated using the
USACOE Automated Coastal Engineering System, ACES. ACES is an interactive
computer-based design and analysis system in the field of coastal engineering. The
methods to calculate wave runup and shore protection overtopping implemented within this
ACES application are discussed in greater detail in the 2004 Coastal Engineering Manual.
A 0.75-foot high wave was used in the ACES wave runup and overtopping analysis with
a current maximum historical water level of +7.7 feet NAVD88 (no SLR). This combination
of wave and water level represents an approximate 100-year recurrence interval
oceanographic condition under current sea level. Table I below is the computed output
from the ACES program for the wave runup analysis.
TABLE I
The calculated maximum wave runup under the current 100-year recurrence interval
conditions is just about 0.8 feet above the historical 100-year water level (elevation 8.5 feet
NAVD88). This is currently below the elevation of the bulkhead with the additional
concrete walls on top. It is likely why the walls have been added. In the future, with more
than 2 feet of SLR, boat wakes during the highest high tides may overtop the bulkhead and
walls. The project proposes to increase the height of bulkhead to a minimum of +10.6 feet
NAVD88. The bulkhead can be increased in height without any bayward encroachment.
This is a SLR adaptation strategy recommended in the CCC SLR guidance document.
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
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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
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 coastal hazards affecting the site;
As stated in this hazard analysis, the typical coastal hazards to consider
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are shoreline erosion, flooding, and wave/wake impacts. There is no beach
fronting the site. Boat wakes and wind waves are too small, even with sea level rise
(SLR), to flood the residence provided the bulkhead is maintained. There is not a
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 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 fronting 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. This is the design sea level rise for the
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. The analysis herein shows that boat
wakes and wind waves will not impact the residence.
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 that 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.
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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
The shore protection is necessary to protect the existing structure, the
adjacent properties, 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 and the design which can accommodate future
waterproofing. To further adapt to SLR higher than 2.9 feet, the shore
protection can be increased in height to above ~+12.0 feet NAVD88 (or as
high as needed), 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.
Bulkhead condition report shall include (NBMC 21.30.15.E.3):
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. Mr.
Skelly has extensive experience in shoreline erosion, bluff erosion, soils
engineering, and the design, permitting, and construction of shore protection
devices. Projects include levee engineering and design in San Francisco Bay,
seawall and marina engineering in Baja California Sur, coastal boardwalk design
and protection in Pacifica, and seawall projects throughout southern California.
ii. An analysis of the condition of any existing bulkhead including whether the
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top elevation meets current City standards, the conditions of the sheetpiles
or panels, the condition of existing tiebacks and/or deadmen or similar, and
any other relevant conditions;
The bulkhead is part of a continuous bulkhead system that extends to the properties
to the east and west. The shore protection was visually inspected by the
undersigned on April 15, 2019. Our visual inspection of the bulkhead wall revealed
that the structure is in good condition and not in need of maintenance. There
appears to be tiebacks to restrain the concrete panels. The face of the panels
showed minor signs of wear (loss of concrete float). The panels were all vertical
with no signs of bayward rotation. The improvements behind the bulkhead
precluded any excavation on the landward side of the bulkhead. We recommend
that after the existing improvements are demolished and removed that the tiebacks
be inspected to verify their condition.
iii. Recommendations regarding the need for repair, augmentation or
replacement of the bulkhead or any parts thereof;
In conclusion, based upon our inspection, the bulkhead/shore protection is in good
condition and NOT in need of any repair or maintenance at this time. However, the
tieback condition should be verified prior to constructing the new residence. In
addition, the bulkhead should be augmented to increase the height to a minimum
+10.6 feet NAVD88.
iv. If augmentation or replacement in the existing alignment is necessary,
recommendations that will avoid seaward encroachment of the bulkhead;
As part of the proposed project, the bulkhead/shore protection can be increased in
height without any bayward encroachment. In the future, if additional augmentation
is needed as part of the regional SLR adaptation program, the bulkhead can be
increased in height without any bayward encroachment.
v. If replacement is necessary and the existing bulkhead is not in alignment
with adjacent bulkheads, recommended alternatives that will relocate the
bulkhead in as much in alignment with adjacent bulkheads and as far
landward, as possible.
Replacement is not necessary.
CONCLUSIONS
• A review of aerial photographs over the last several decades shows no shoreline at
the site.
• The site has not been subject to flooding, erosion damage, or wave runup attack in
the past.
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• The proposed residential structure with the implementation of the SLR adaptation
strategies (water proofing and raising the bulkhead) will not be adversely impacted
by potential coastal hazards including a ~4.0 feet sea level rise over the next
minimum 75 years. The site will be part of a community wide response to mitigate
SLR hazards.
• 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. We recommend that after
the existing improvements are demolished and removed that the tiebacks be inspected to
verify their condition. If necessary, an additional increase in the height of the bulkhead,
other than the proposed increase to +10.6 feet NAVD88 as part of the project, will also
prevent flooding in the future. 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, 2018, 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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