HomeMy WebLinkAbout20210408_Sea Level Rise Discussion_2-12-2021•
Geotechnical • Geologic • Coastal • Environmental
5741 Palmer Way • Carlsbad, California 92010 • (760) 438-3155 • FAX (760) 931-0915 • www.geosoilsinc.com
February 12, 2021
Mr. Josh Merrell
c/o Anthony P. Massaro, Architect
Mars Hill Studio, Inc.
2533 Greenbrier Lane
Costa Mesa, CA 92626
SUBJECT: Sea Level Rise Discussion, 2182 Mesa Drive, Newport Beach, Orange
County, for Coastal Development Permit.
Dear Mr. Merrell:
At your request, GeoSoils Inc. (GSI) is pleased to provide a discussion of potential coastal
hazards for the proposed remodel/addition project at the subject property. 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, a review of the proposed plans,
and preparation of this letter report.
SITE CONDITIONS
The project site is located on Mesa Drive near the Upper Newport Bay, and is not on the
ocean or on the Upper Newport Bay wetland. The site is over 4 miles from the Pacific
Ocean with Newport Harbor, extensive development and public roads, between the site
and the ocean. The site is on relatively flat land and is bounded by the Upper Newport Bay
Nature Preserve (UNBNP) to the south. The UNBNP slopes gently at about 15% from
elevation + 69 NAVD88, to the public path at elevation +18 feet NAVD88, and to the
wetland boundary at about elevation +6 feet NAVD88. The active channel of Upper
Newport Bay is an additional +1,000 feet from the wetland boundary. From the top of the
site slope to the Upper Newport Bay flow channel is a distance of about 1,500 feet, see
Figure 1. The proposed remodel/addition is an additional +130 feet landward from the top
of slope property line. Due to the projects setback from Upper Newport Bay (and obviously
the Pacific Ocean), the site will not be subject to shoreline erosion or wave runup over the
project life (75 years). While the toe of the slope below the site may infrequently flood with
extreme SLR, the thick vegetation and slow water velocities will not cause erosion. The
only coastal hazard the slope near the site may be subject to is flooding of Upper Newport
Bay as a result of extreme SLR.
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Figure 1. Internet image from May 2019 showing the site relative to the public bike path,
Upper Newport Bay and active flow channel.
DATA&DATUM
The datum used in this report is NAVD88, which is about 2.64 feet below the mean tide
level. The units of measurement in this report are feet (ft), pounds force (lbs), and
seconds (sec). The site elevations relative to the NAVD88 datum were taken from the
topographic map prepared by RdM Surveying Inc. The remodel plans were provided by
Mars Hill Studio, Inc. Elevations not on the site were taken using Google Earth. The
proposed remodel/addition development is abut 130 feet from the top of the slope at an
elevation of about 70 feet NAVD88.
CURRENT FLOODING HAZARD
The National Oceanographic and Atmospheric National Ocean Survey (NOAA, 2010) tidal
data station closest to the site is located at Los Angeles Outer Harbor (Station 9410660).
The tidal datum elevations are as follows:
Highest Recorded Water 1/27/1983
Mean High Water
7.18 feet
4.55 feet
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Mean Sea Level (MTL)
NAVD88
Mean Lower Low Water
2.64 feet
0.0 feet
-0.2 feet
3
Ocean water level is dependent upon several factors including the tide, storm surge, wind
set up, inverse barometer, and climatic events (El Nino). This location is well away from
. the Pacific Ocean so the site will not be subject to wave or wind set up from the ocean.
The design maximum recorded water level is about +7.0 feet NAVD88. The highest
recorded elevation (7.18 feet NAVD88) for the ocean water level takes into account El Nino
conditions and storm surge that don't occur in Upper Newport Bay. The proposed project
has the lowest finished floor at about + 70 feet NAVD88 and the public bike path below is
at elevation +18 feet NAVD88. Under the current extreme Upper Newport Bay water level
conditions, the existing/proposed development, and even the public bike path, are not
subject to flooding.
FEMA
The Federal Emergency Management Agency (FEMA) provides Flood Insurance Rate
Maps (FIRM) that assess the current vulnerability of a site to flooding. The existing
structure is currently mapped in the FEMAXZone area outside the 1 % chance of flooding,
see Figure 2. The public bike path is also in the X Zone. The wetland portion of the
UN BNP is mapped in the FEMA AE Zone with a Base Flood Elevation (BFE) of+ 8 feet
NAVD88.
Figure 2. Effective FIRM showing the site in the FEMA X Zone.
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FUTURE FLOODING & SEA LEVEL RISE
Sea Level Rise
The CCC had initially adopted the National Research Council 2012 SLR estimates of 16.56
inches to 65.76 inches over the time period from 2000 to 2100. The initial adopted ranges
provided in the first CCC SLR Guidance provided no probability of occurrence. That is to
say that it is not clear as to the likelihood of any given SLR in the year 2096. The 1.25 feet
of SLR may be more likely than the 4. 75 feet SLR, or vice versa. The Guidance does
require the use of the best SLR science available. The March 2018 State of California Sea-
Level Rise Guidance, 2018 Update" by the California Ocean Protection Council {COPC)
provides more current SLR estimates within a probability frame work. The COPC provides
SLR estimates based upon various carbon emission scenarios known as a "representative
concentration pathway" or RCP. This 2018 COPC report has been adopted by the CCC
and provides an expansion of the April 2017 "Rising Seas in California." 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 ). The Kopp
report provided the SLR estimates in a more user friendly format as shown in TABLE I.
TABLE I
LOW Medium -High Extreme Risk
Aversion Risk Aversion Risk Aversion
i lW;H1 emissions 2030 0.5 0.4 0.6 0.7 0.9 1.1
2f!40 0.7 0.5 0.9 1.0 l.3 1.8
2!)50 0.9 0.7 1.2 l.4 2.0 2.8 -t0w emlss!ons 101.iO 1.0 0.7 -1.3 1.7 2.5
i!lgri llmlsslons 2060 1.2 0.9 l.6 1.9 2.7 3.9 --I.ow emissions 2010 1.2 0.9 -1.6 2.0 3.1
H19l1 emlsslO!lS 2070 1.5 1.1 2.0 2.5 3.6 5.2 --Low tmlsslom 2080 1.4 1.0 -1.9 2.4 4.0
High emlssfons 2080 1.9 1.3 -2.5 3.1 4.6 6.7
tow emissions 2090 1.6 1.0 2.2 2.9 4.8
High emissions 2090 2.2 1.6 -3.0 3.8 5.7 8.3
LW! @llSSiOilS mrn 1.7 1.1 -2.5 3.3 5.8
myll i!mlSSlO!lS W.Hl 2.6 1.8 -3.6 4.6 7.1 10.2
This table illustrates that SLR in the year 2100 for the "likely" range, considering the most
onerous RCP {8.5), is 1.8 feet to 3.6 feet above the 1991-2009 mean. This can be
interpolated to be about 3.3 feet above the 2020 mean {sea level is higher now than in
2009) over the next 75 years. Based upon this SLR report, the maximum probable SLR
for the project is estimated to be 3.3 feet. There also is a 0.5% probability that SLR can be
about 6.4 feet {interpolated [[5. 7 + 7.1 ]/2]). The maximum historical water elevation in
Newport Bay is -+ 7 .0 feet NAVD88. This elevation does not include the long-term sea
level rise prediction. If 1.8 and 6.4 feet are added to this 7 .0 feet NAVD88 elevation, then
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future design maximum water level range of 8.8 feet NAVD88 to 13.4 feet NAVD88 is
determined. The maximum design future water level is 13.4 feet NAVD88. Even if SLR
is 7.1 feet in the year 2100 under the 0.5% probability "meet or exceed," the temporary
water elevation at the toe of the slope will be about +14.1 feet NAVD88, which is still below
the pubric bike path and well below the development on the site.
TSUNAMI
It should be noted that the site is mapped well outside the limits of the California Office of
Emergency Services (CalOES) 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 area.
SLR & 100 YEAR STORM
The USGS has also developed a model called the Coastal Storm Modeling System
(CoSMoS) for assessment of the vulnerability of coastal areas to SLR and the 100 year
storm._ Using the modeling program the vulnerability of the site to different SLR scenarios
with shoreline erosion and the 100 year storm can be assessed. However, the following
are the limitations as to the use of the CoSMoS model.
Inundated areas shown should not be used for navigation, regulatory, permitting,
or other legal purposes. The U.S. Geological Survey provides these data "as is" for
a quick reference, emergency planning tool but assumes no legal liability or
responsibility resulting from the use of this information.
Figure 3 is the output of the CoSMoS program. The modeling shows that the wetland
shoreline does not erode and not even the public bike path will flood during the 100 year
event with 200 cm {~6.6 feet) of SLR. Based upon the CoSMoS modeling, the
development is safe from erosion and flooding over the design life of the development due
to the proposed project setback from the wetland and the site elevation.
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Shorallne Po;ition (No hold the line/No nourtsh.) SLR 200
[l Projected Shoreline
Max WiNe Runup during Flood 200an SLR+ \'lave !00
()
, .• . Rood-prone Low-lying Areas .. ' 200anSLR+Wa-;elOO .·.
Rood Hazard 200cm SLR + Wave
100
i::r
Rood Depth 200cm SLR + V/iNe
100
No Data
: o cm (0ftl
l•··\50 cm (8.2 ft)
soo cm (16,4 ft)
750 cm (24.6 ft)
Santa Cruz Rood Depth 200an
SLR+ Wave 100
No Data
· o cm(0ftl
I,·. ·;250 cm (8,2 ft)
· 500 cm (16.4 ft)
750 cm (24.6 ft)
Figure 3. CoSMoS output for the site with 6.6 feet of SLR and allowing for erosion.
CITY OF NEWPORT BEACH INFORMATION
Coastal Hazards Report (NBMC 21.30.15.E.2):
i. A statement of the preparer's qualifications;
6
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;
The typical coastal hazards to consider are shoreline erosion, flooding, and wave
impacts. The site is too far from both the Pacific Ocean and the active Upper
Newport Bay Channel for waves and erosion to impact the development. This
report demonstrates that flooding or even erosion from flooding will not impact the
site. There are no coastal hazards affecting the site over the project design life.
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iii. An analysis of the following conditions:
1. A seasonally eroded beach combined with long-term (75 year)
erosion factoring in sea level rise;
This condition will not occur at the site over the design life of the project.
2. High tide conditions, combined with long-term (75 year) projections
for sea level rise;
There is a 0.5% probability that SLR could be 6.4 feet in the next 75 years.
This SLR would account for future Upper Newport Bay water level of 13.4
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);
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.
v. Identification of necessary mitigation measures to address current
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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 and no mitigation measures or
adaptation strategies are necessary.
CONCLUSIONS
The project is not within the influence of coastal hazards (erosion, waves, and flooding)
over the design life of the project (75 years). No SLR mitigation measure or adaptation
strategies are needed over the life of the development.
If you need additional clarification, I can be contacted at the number above.
Respectfully submitted,
GeoSoils, Inc.
David W. Skelly MS, PE
RCE#47857
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REFERENCES
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
NOAA, 2021, Web Sites, 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 Sea Level Rise Guidance 2018 Update, by Ocean Protection Council,
dated in March 2018.
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