HomeMy WebLinkAbout20190722_Bulk Head-Hazard Report_6-6-2019Geotechnical 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
June 6, 2019
Mr. & Mrs. Campbell
601 Via Lido Soud
Newport Beach CA 92663
SUBJECT: Revised Coastal Hazard and Sea Level Rise Discussion for New Residence,
605 Via Lido Soud, Newport Beach, Orange County, California.
Dear Mr. & Mrs. Campbell:
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 605 Via Lido Soud 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 new residence plans, a site inspection, and preparation of this letter report.
INTRODUCTION
The proposed project is new single-family residence on Lido 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, the boat docks, and a Newport Bay channel. The
proposed finished first floor (FF) elevation of the residence is about 12.8 feet NAVD88. The
site is fronted by a concrete bulkhead to about elevation +12.25 feet NAVD88 (shore
protection), and a private dock, along a Newport Bay navigation channel. The bulkhead
has a slight jog at about the mid point of the bulkhead. It is our understanding that the
project includes the addition of a pile (4 new piles) supported deck, such that the deck
forms a continuous patio across the site. It also proposes an increase in the height of the
bulkhead to about +12.5 feet NAVD88. The site is currently 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. FEMA is proposing
to adopt a new FIRM map for the area in March 2019. The proposed FEMA FIRM shows
a small area of the site to be 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, 605 Via Lido Soud, and adjacent Newport Bay channel in 2016.
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 1/17/19, and project plans were discussed with South Coast
Architects. A site reconnaissance was performed on January 2019. There is small
intertidal 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 a small intertidal beach at the site. During low tide about 15 feet of sand “beach”
is exposed. The site is located on a channel on the south side of Lido Island and the
shoreline is located essentially at the bulkhead. As sea level rises the amount of exposed
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beach at low tide will diminish. However, the high tide shoreline location will remain at the
bulkhead. The current shoreline will remain at the bulkhead and 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, the 2011 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, which was also adopted by the CCC in November 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 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), COPC 2018, and CCC 2018 providing current SLR
estimates and probabilities for the Los Angeles 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 addition,
based upon this 2018 COPC SLR report, the 5 % probability SLR for the project is
estimated to be 4.1 feet. The maximum historical water elevation at the Los Angeles tide
station is elevation+7.72 feet NAVD88 on January 10, 2005. This actual high water record
period includes the 1982-83 severe El Niño, and the 1997 El Niño events, and is therefore
consistent with the methodology outlined in the CCC Sea-Level Rise Policy Guidance
document. The Newport Beach City Council recently approved the use of “low risk
aversion” scenario for residential development, which is 1.3 feet to 3.2 feet by the year
2100. If 1.3 and 3.2 feet are added to this 7.7 feet NAVD88 elevation, then future design
maximum water levels of 9.0 feet NAVD88 and 10.9 feet NAVD88 are determined.
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 bay water levels in the range of 9.0 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 low probability
that bay water will meet or exceed 11.7 feet NAVD88 (7.7 feet NAVD88 + 4.0 feet SLR).
The existing shore protection is at elevation of +12.29 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 about 4.6 feet or
greater. This SLR is greater than the 2100 “likely” project sea level rise range and the less
likely 5% probability SLR. For the likely COPC SLR estimate range (high emissions) the
proposed bulkhead is safe from overtopping flooding beyond the year 2100. For SLR
greater than 4.6 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 2090. It should be noted that, if SLR is
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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.
Wave runup and overtopping of the bulkhead 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 well below the elevation of the existing bulkhead (+12.25 feet
NAVD88). In the future, with more than 4 feet of SLR, boat wakes during the highest high
tides may overtop the bulkhead. The project proposes to increase the height of bulkhead
to a minimum of +12.5 feet NAVD88. The bulkhead can be increased in height without any
bayward encroachment. This is a SLR adaptation strategy recommended in the 2018 CCC
SLR guidance document.
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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
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
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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
are shoreline erosion, flooding, and wave/wake impacts. There is only an intertidal
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 based upon the
current accepted SLR estimates. For SLR higher than the current estimates,
adaptation strategies such as waterproofing the structure to above the potential
flood elevation, and increasing the height of the bulkhead can be 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 only an intertidal beach fronting the site with no seasonal changes.
The width of the intertidal beach may decrease with SLR.
2. High tide conditions, combined with long-term (75 year) projections
for sea level rise;
Using the CCC SLR estimates over the project 75-year design life, the range
in the year ~2094 is between 1.3 feet and 4 feet. This is the sea level rise
range for the proposed project. This SLR range would account for future
extreme bay water levels in the range of 9 feet NAVD88 (7.7 feet NAVD88
+ 1.3 feet SLR) and 11.1 feet NAVD88 (7.7 feet NAVD88 + 4.0 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 until SLR is over 4 feet.
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
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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.
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 project design, which can
accommodate future waterproofing. To further adapt to higher than
expected SLR, the shore protection can 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.
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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
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 series of independent bulkhead systems (concrete
retaining walls) that extend to the properties to the east and west of the site. The
shore protection was visually inspected by the undersigned in January, 2017. Our
visual inspection of the bulkhead revealed that the structure is in good condition and
not in need of maintenance. There does not appear to be a tieback system to
restrain the concrete wall. The face of the concrete showed minor signs of wear.
The wall is vertical with no signs of bayward rotation. The improvements (patio and
residence) 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 wall be inspected to verify the depth and below grade
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
existing wall condition should be verified prior to constructing the new residence.
Based upon the condition a new bulkhead may be needed.
iv. If augmentation or replacement in the existing alignment is necessary,
recommendations that will avoid seaward encroachment of the bulkhead;
The proposed project calls for a new pile supported deck that effectively increases
the height of the existing bulkhead. 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.
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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 project proposes a pile supported deck over the existing bulkhead. The plans
for this will be provided by others. In addition, after demolition of the building, the
condition of the existing bulkhead will be assessed.
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.
• The proposed residential structure 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 bulkhead be inspected
to verify the condition. 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
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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