HomeMy WebLinkAboutPA2022-020_20220119_Coastal Hazards Report_11-5-21Geotechnical 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
November 5, 2021
Mr. & Mrs. Gray
1324 Bienveneda Ave
Pacific Palisades, CA 90272
SUBJECT: Coastal Hazard and Sea Level Rise Discussion for Remodel/Addition, 415
North Star Lane, Newport Beach, Orange County, California.
Dear Mr. & Mrs. Gray:
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 remodel/addition at 415 North Star Lane 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 and 21.30.15.E.3, a review of the proposed plans, and preparation of this
report.
INTRODUCTION
The proposed project is a remodel and addition to the subject site residence in the City of
Newport Beach. The site is fronted by a concrete bulkhead with a retaining wall on top, a
boat dock, and a navigation channel within Lower Newport Bay. The effective elevation
of the bulkhead system is +10.9 feet NAVD88. Based upon our site and bulkhead
inspection, in the future, the bulkhead system can be increased in height to a minimum
height of 14.4 feet NAVD88 to adapt to SLR. The finished first floor (FF) of the residence
is ~+11.5 feet NAVD88. The surface drainage flow line on North Star Lane is at about
elevation +10 feet NAVD88. Figure 1, downloaded from Google Maps (Bird’s Eye View),
shows the site in relation to the adjacent properties and Lower Newport Bay. The
residence is currently mapped by FEMA (FIRM Panel 06059C0382K) to be in the X Zone
with no base flood elevation (BFE). The bulkhead and adjacent navigation channel are in
the FEMA AE Zone with a BFE of +8 feet NAVD88.
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Figure 1. Subject site, 415 North Star Lane, adjacent properties, docks, and navigation
channel within Lower Newport Bay.
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 Toal
Engineering Inc., dated 10/11/21. Preliminary development plans were provided by
Michael Lee Architects, the project designer. A site reconnaissance was performed in
September 2021. There is no beach or shoreline fronting the site.
HAZARD ANALYSIS
There are three different potential shoreline hazards for ocean and waterfront
development: 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 actual beach or shoreline at the site proper. The elevation of the mudline at
the bulkhead is below the Newport Bay water elevation.
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Waves and Wave Runup
The potential surface gravity waves (ocean swell) to arrive at this site is nil. Boat wakes
are the only possible waves that can reach the bulkhead fronting the site. However, boat
wakes are typically small due to speed restriction within the channel. Anticipated wave
runup and overtopping of the bulkhead at the site was 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 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 future 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 water
level conditions is about 0.84 feet above the 100-year water level or about elevation +8.5
feet NAVD88. This is currently below the effective elevation of the bulkhead. With the
bulkhead system elevation at +10.9 feet NAVD88 and SLR up to 2.4 feet (+8.5 NAVD88
+ 2.4 feet SLR = 10.9 NAVD88), waves/wakes will not overtop the bulkhead. Any
wake/wave runup waters that reach near this elevation will have a low velocity, no energy,
and no erosion capacity. It should be noted that under higher future SLR conditions the
height of the bulkhead can be increased to prevent overtopping.
ACES I l'klde : Single Case I Functional Area: Wave -Structure Interaction
App I icat ion: Wave Runup and Overtopping on Impermeable Structures
Item Unit Value Smooth Slope
Runup and
Incident Wave Height Hi: ft 0.750 Overtopping
Wave Period T: sec 3.500
COTAN of Nearshore Slope COTC!II): 20.000 415 North Star Water Depth at Structure Toe ds: ft 7.200 lane COTAN of Structure Slope COTC8): 0.000
Structure Height Above Toe hs: ft 8.500 No SLR
Wave Runup R: ft 0.838 Bulkhead
Onshore Wind Velocity u: ft/sec 8.139 Overtopping
Deepwater Wave Height H0: ft 0 .813
Relative Height ds/H0: 8 .860
Wave Steepness H0/CgT"2): 0 .002062
Overtopping Coefficient «: 0.070000
Overtopping Coefficient Qstar0: 0 .070000
Overtopping Rate Q: ftA3/s-ft 0.000
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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
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 Newport Bay. 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 Lower Newport Bay. The report provides SLR estimates
based upon various carbon emission scenarios known as a “representative concentration
pathway” or RCP. Figure 3 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.
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Figure 3. 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 about 10 years old. The
SLR models used as the basis for the COPC and CCCSLRG have been in place for over
a decade. 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.
The National Oceanic and Atmospheric Administration (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
21.5 years and next 8.5 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 4 provides the SLR model curves and tables for Los Angeles Harbor.
LOW Medium -High Extreme Risk
Aversion Risk Aversion R:lsk Aversion
High emissions 2030 0 .3 0.2 0.5 0.6 0.7 1.0
2040 0 .5 0.4 0.7 0.9 1.2 1.7
2050 0.7 0.5 1.0 1.2 1.8 2.6
Low emissions 2060 0 .8 0.5 1.1 1.4 2.2
High emissions 2060 1.0 0.7 1.3 1.7 2.5 3.7
Low emissions 2070 0.9 0 .6 1.3 1.8 2.9
High emissions 2070 1.2 0 .8 1.7 2.2 3.3 5.0
Low emissions 2080 1.0 0 .6 1.6 2.1 3.6
High emissions 2080 1.5 1.0 2.2 2.8 4.3 6.4
Low emissions 2090 1.2 0.7 1.8 2.5 4.5
High emissions 2090 1.8 1.2 2.7 3.4 5.3 8.0
Low emissions 2100 1.3 0.7 2.1 3.0 5.4
High emissions 2100 2.2 1.3 3.2 4.1 6.7 9.9
Low emissions mo· 1.4 0 .9 2.2 3.1 6.0
High emissions mo· 2.3 1.6 3.3 4.3 7.1 11.5
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Figure 4. Taken from the USACOE SLR curve calculator program.
Looking at the table in Figure 4, 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 3 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 information provided above is more current
than the CCCSLRG. The checking of the models 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 3 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 4.1 feet and a 0.5% probability that SLR will be between 5 feet and 6 feet
in the year 2096. The design historical water elevation at the for Lower Newport Bay is
elevation +7.7 feet NAVD88. This actual high water record period includes the 1982-83
ro 13 ~ z
14
12
10
8
6
NOAA et al. 2017 Relative Sea Level Change Scenarios for: LOS ANGELES
2010 2020 2030 2040 2050 2060
Year
HurmngtOn Hartxx.
Scena.nos for LOS ANGELES NOAA2017 Vl.M: -0.00328 feeiiyr-All values are expres5ed .n feet
Year NOAA2017 NOM2017 NOAA2017 NOM2017 NOM2017 VLM Low Int-Low Intermediate Int-High
2000 270 270 270 270 270
2010 2.67 2.77 277 2.83 290
2020 2.63 283 290 3.00 3.09
2030 2.60 2.93 3 03 3.16 336
2040 2.57 3 03 3.13 342 3.72
2050 2.54 3.13 329 3.72 4 24
2060 2.50 3 23 3 42 4.08 480
2070 2.47 332 3.59 4.44 5.46
2080 2 44 3 42 3 72 4.90 6 24
2090 2.40 3.49 385 5.36 710
2100 2.37 3.52 398 5.88 815
2070 2080
NOAA2017 NOAA2017 High Extreme
270 210
2.93 2.93
3.16 3.23
3 52 3.65
4.08 4.37
4.83 5.26
5.69 6.37
6.67 7.65
7.82 9.10
9.13 10.67
10.61 12.61
2090
-+-NOAA2017 Extreme
-+-NOAA2017 High
_,._ NOAA2017 Int-High
-+-NOAA2017 lnterrnediale
-+-NOAA2017 Int-Low
-+-NOAA2017 Low
-+-NOAA2017VU,1
2100
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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. This SLR range would account for future
extreme back 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 13.2 feet NAVD88 (7.7 feet NAVD88 + 5.5
feet SLR). The existing bulkhead has an effective elevation +10.9 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, the extreme
Lower Newport Bay water level will exceed the height of the bulkhead when SLR is 3.2 feet
or greater. For the likely COPC SLR estimate range (high emissions) the bulkhead is safe
from overtopping until about the year 2100. For SLR greater than 3.2 feet the height of the
bulkhead will need to be increased. For the 0.5% probability SLR case this may occur in
about the year 2070. 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. In addition, flooding of the site does not mean that
the residence will flood.
The residence FF elevation is +11.5 feet NAVD88. Based upon the FF elevation, the
extreme Lower Newport Bay water level will exceed the height of the lowest FF when SLR
is 3.8 feet or greater. For the likely COPC SLR estimate range (high emissions) the
residence is safe from flooding until after the year 2100. For the 0.5% SLR case this may
occur in about the year 2080. Again, 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 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 area. Recent action by the City Council has
raised the minimum 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.
Based upon our visual inspection and review of the bulkhead plans, the existing bulkhead
system is capable of being extended in height to a least +14.4 feet NAVD88.
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
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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
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;
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As stated in this hazard analysis, the typical coastal hazards to consider
are shoreline erosion, flooding, and wave/wake impacts. There is no beach at the
site. Boat wakes and wind waves are too small, even with sea level rise (SLR), to
potentially flood the proposed residence provided the bulkheads in the area are
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), and as such the City of Newport Beach has a standard drawing(s), 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 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 ~2096 is 2.9 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 (2.9 feet
to 6 feet) for the proposed project. This SLR would account for future
extreme bay water level of 10.6 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
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);
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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 a bulkhead system on the site and it is necessary to protect the
development and adjacent development. The existing bulkhead system is
in good condition and at the current minimum required elevation.
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 bulkhead
system height (and ability to increase in height), the elevated finished floor
elevation, and the ability to waterproof the building, if necessary. It is
important to point out that SLR will not impact this area 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 entire community will soon adopt some of the SLR
adaptation strategies that are currently being considered by the City of
Newport Beach. The City recently raised the minimum bulkhead elevation
to 10.9 feet NAVD88. 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.
BULKHEAD CONDITION REPORT
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.
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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
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 system was visually inspected and are in good condition. The
bulkhead/retaining wall, with the top at elevation+10.9 feet NAVD88, does meet the
current City’s top of bulkhead elevation requirement of +10.9 feet NAVD88. Based
upon our visual observations and knowledge of bulkhead design, it is GSI’s opinion
that the bulkhead system height can be increased without any bayward
encroachment.
iii. Recommendations regarding the need for repair, augmentation or
replacement of the bulkhead or any parts thereof;
Augmentation of the bulkhead system will not be necessary to meet the current City
height requirement. In the future the bulkhead system can be increased in height
to a minimum elevation of +14.4 feet NAVD88 to adapt to SLR. The increase in
height of the bulkhead can be accomplished without further bayward encroachment
and is an SLR adaptation strategy.
iv. If augmentation or replacement in the existing alignment is necessary,
recommendations that will avoid seaward encroachment of the bulkhead;
No bulkhead augmentation is necessary now. In the future, an additional increase
in height can be accomplished within the current bulkhead footprint.
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.
The site bulkhead, even with the augmentation in height, can remain aligned with
the adjacent bulkheads.
CONCLUSIONS
• The residential structure, with a FF of ~+11.5 feet NAVD88, is reasonably safe from
the unlikely 0.5% SLR hazards until about the year 2080. The current structure
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design is such that implementation of additional SLR adaptation strategies (design
for future waterproofing to above an elevation impacted by SLR and the future
protection of area by adoption of a resiliency plan by the community) will not be
adversely impacted by potential coastal hazards including a 6 feet sea level rise or
more over the next minimum 75 years. The site will be part of a community wide
response to mitigate SLR hazards.
• An augmented bulkhead system is not necessary at this time to meet the current
City standard height of +10.9 feet NAVD88. A future height increase to a minimum
elevation of +14.4 feet NAVD88 can be accomplished without further bayward
encroachment of the bulkhead.
• For the most part, in the entire Newport Beach coastal and bay areas, including the
Balboa Peninsula, and other developed islands within the bay, flooding with a lower
SLR is likely to occur. Such flooding will occur well before any part of the residence,
located in Lower Newport Bay, will flood.
• Provided the recommendations of this report are implemented during the project
construction, no additional 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 area 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.
FEMA Website, 2021 https://msc.fema.gov/portal/home
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,” March 23, 2021.
NOAA, 2021, 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.
PA2022-020