HomeMy WebLinkAbout20210208_Coastal Hazards Report_10-19-2020Geotechnical 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
October 19, 2020
Mr. Sean Norton
6806 W. Oceanfront
Newport Beach, CA 92663
SUBJECT: Coastal Hazard and Wave Runup Study, 6806 W. Oceanfront, Newport
Beach, California.
Dear Mr. Norton:
At your request, GeoSoils, Inc. (GSI) is pleased to provide this coastal hazard and wave
runup study for the property located at 6806 W. Oceanfront, 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) document (adopted March 2018), a review of City of Newport Beach Municipal Code
(NBMC) 21.30.15.E.2, a review of the site elevations, a discussion of the residence plans,
a site inspection, and preparation of this letter report. This report constitutes an
investigation of the wave and water level conditions expected at the site as a result of
extreme storm and wave action over the next 75 to 100 years. It also provides conclusions
and recommendations regarding the susceptibility of the property and the proposed new
residential structure to wave attack. The analysis uses design storm conditions typical of
the January 18-19, 1988, and the winters of 1982-83 and 1998 type storm waves and
beach conditions.
INTRODUCTION AND BACKGROUND
The subject site is located at 6806 W. Oceanfront, Newport Beach, California. The site is
a rectangular shaped parcel, approximately 30 feet of ocean frontage by ~75 feet long, with
an existing residential structure. Figure 1 is a 2018 Bird’s Eye aerial photograph of the site
downloaded from the internet. The proposed development consists of removal of the
existing residence and construction of a new residence. The site is fronted by a wide
sandy beach (> 540 feet wide), and the Pacific Ocean. This site is located near the Santa
Ana River south jetty and west of the Newport Beach groin field, in a coastal segment
described as the West Newport Beach segment of the Huntington Beach Littoral cell in the
US Army Corp of Engineers Coast of California Storm and Tidal Waves Study South Coast
Region, Orange County (USACOE 2002). The West Newport Beach shoreline segment
stretches from the Newport Pier to the east jetty of the Santa Ana River, a distance of a
little more than 2.3 miles. In general, the movement of sand along a shoreline depends
upon the orientation of the shoreline and the incoming wave direction. The movement of
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sand along this southern section of Newport Beach is generally to the east, but under wave
conditions from the south, the direction reverses.
Figure 1. April 2018 aerial photograph of the subject site. Note the wide beach.
USACOE (2002) contains historical beach profile and beach width data for the beach near
the site. The beach width has changed little over the past 60 years as a result of
replenishment in the 1930's and 1980's with fill from Newport Harbor and the stabilizing
effect of the nearby groins. The data shows that the actual beach width fronting the site
has increased since 1965. Figure 2 shows the beach width survey data from the USACOE
monitoring program. The closest monitoring station near the project is station 639+35.
During typical winter eroded beach conditions, the beach width may erode to about 350
feet. The narrowest the beach has been is about 300 feet in 1980, prior to a nourishment
project. From 1982 to the present, the beach has typically been over 400 feet wide and
up to 700 feet wide. In the long-term, the presence of the nearby groin field, a sand
source (Santa Ana River), and future nourishment projects will continue to stabilize the
shoreline fronting the site.
,. ...
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Figure 2. Mean sea level beach widths in the west Newport Beach area (USACOE 2002).
Despite efforts to control the movement of sand along the shoreline, the shoreline at this
section of the Newport Beach area does experience short-term erosion. The erosion is
temporary, and usually the result of an energetic winter. As stated before, there is no clear
evidence of any long-term erosional trend (USACOE 2002). The subject site is situated
up coast from an active sand sink, the Newport Submarine Canyon. The site is somewhat
sheltered from waves arriving from the south by canyon-induced wave refraction
(defocusing). This reduces the beach erosion potential by reducing the wave energy. The
wide sandy beach in front of the subject site is normally over 400 feet wide and has
provided more than adequate protection for the property over the last several decades.
In the past, no wave runup has overtopped/reached the site. The site has not been subject
to wave attack for at least the last 50 years. This includes the winter storms of 1982-83
and January 1988, the coastal engineering design storms for Southern California.
DATUM & DATA
The datum used in this report is North American Vertical Datum of 1988 (NAVD88) which
is 2.35 feet below NGVD29, and 4.49 feet below Mean High Water (MHW). The units of
measurement in this report are feet (ft), pounds force (lbs), and seconds (sec). The NOAA
Nautical Chart #18746 was used to determine bathymetry. Beach profile data was
reviewed from USACOE (2002). Aerial photographs, taken semi-annually from 1972
through 2019, were reviewed for shoreline changes. Site elevations relative to NAVD88
a: of!
~ " ;:
~ (I) cc
...J "' :.
Figure 36: MSL Beach Width, 1963-1997
West Newport Beach
800 ~-;:.-=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=--=,~
---+-639+35 -----648+33 --.-657+31 -----678+96 _,,,_697+47 ----e----713+49 --+-741+31 -AVE
700 +----------------------------------~---------<
500
400
300
200
100
0+-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~--.------1
1960 1965 1970 1975 1980
Date
1985 1990 1995 2000
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were taken from a site survey by South Coast Surveying Inc., dated April 2019.
Development plans were discussed with Eric Aust, project designer.
SITE BEACH EROSION AND WAVE ATTACK
In order to determine the potential for wave runup to reach the site, historical aerial oblique
photographs dating back to 1972 were reviewed. None of the photographs showed that
wave runup reached the site. Figure 3, taken in January 1988, shows a relatively wide
beach in front of the property. The photo was taken after the January 19, 1988,“400-year”
wave event and shows the eroded beach in front of the property. However, the beach did
not erode back to the site and no water reached the site. Figure 4, taken April 2, 2018,
shows what could be described as the “normal” beach width (about 500 feet). A review of
the annual aerial vertical photographs over the last 45 years shows a wide beach even
though the photos were taken in the winter and spring, when the beach is seasonally the
narrowest. None of the reviewed photographs show water reaching within 300 feet of the
site. Based upon review of the aerial photographs, it is highly unlikely that the shoreline will
erode back to the site and allow direct wave attack on the existing or proposed
development. Based upon interviews with long-term local residents, the subject site has
not been subject to wave runup during the last 60 years. The residence has not flooded
from ocean water or from surface drainage due to its elevation relative to the city street
drainage paths. The adjacent city street is lower than the lowest grade on site. In the
future, wave runup is unlikely to reach the site under severely eroded beach conditions and
extreme storms.
Figure 2. Shoreline fronting the subject in January 1988 after the “400-year” wave event.
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Figure 5. Wave runup terms from ACES analysis.
Figure 4. Shoreline fronting the subject site in April 2018 (note the wide beach).
WAVE RUNUP AND OVERTOPPING
Wave runup is defined as the vertical height above the still water level to which a wave will
rise on a structure (beach slope) of infinite height. Overtopping is the flow rate of water
over the top of a finite height structure (the steep beach berm) as a result of wave runup.
As waves encounter the beach at the subject site, water has the potential to rush up, and
sometimes crest, the beach berm. In addition, beaches can become narrower due to a
long-term erosion trend and sea level rise. Often, wave runup and overtopping strongly
influence the design and the cost of coastal projects.
Wave runup and overtopping are calculated using the US Army Corps of Engineers
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
runup and overtopping, implemented within this ACES application, are discussed in greater
detail in Chapter 7 of the Shore Protection Manual (1984) and Coastal Engineering Manual
(2004). The overtopping estimates calculated herein are corrected for the effect of
onshore winds. Figure 5 is a diagram showing the analysis terms.
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Oceanographic Data
The wave, wind, and water level data used as input for the ACES runup and overtopping
application were taken from the historical data reported in USACOE (1986) and USACOE
(2002), and updated as needed. The shoreline throughout southern California and fronting
this property have experienced many extreme storms over the years. These events have
impacted coastal property and beaches depending upon the severity of the storm, the
direction of wave approach, and the local shoreline orientation. The focusing of incoming
waves on the Newport Beach shoreline is controlled primarily by the Newport Submarine
Canyon. Historically, the section of Newport Beach from 25 Street to 40 Street hasthth
experienced extreme storm wave erosion due to focusing of the waves by the canyon. The
ACES analysis was modeled on an extreme wave condition when the beach is in a
severely eroded condition. However, it is important to point out that the waves during the
1982-83 El Niño winter eroded beaches throughout southern California. The subject
property and adjacent properties were not subject to wave runup during that winter. The
wave and water level conditions on January 18, 1988 have been described by Dr. Richard
Seymour of the Scripps Institution of Oceanography as a “400-year recurrence.” The
wave runup conditions considered for the analysis use the maximum unbroken wave at the
shoreline when the shoreline is in an eroded condition.
The National Oceanographic and Atmospheric (NOAA) National Ocean Survey tidal data
station closest to the site is located at Los Angeles Harbor (Station 9410660). 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 is +7.72 feet NAVD88 on January 10, 2005.
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
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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 6 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 6 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
estimated to meet or exceed the 1991-2009 mean, based upon the best available science.
Figure 6. Table from Kopp et al (2014) and COPC 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,” with 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 0.5% probability SLR for the project is estimated to be 6.0 feet
(interpolating between the years 2090 and 2100 and between the low and high emissions).
The design maximum historical water elevation is +7.72 feet NAVD88. 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 2018 Sea-Level Rise
Policy Guidance document. To be conservative, if 3.2 feet and 6.0 feet are added to this
7.7 feet NAVD88 elevation, then future design maximum water levels of 10.9 feet NAVD88
and 13.7 feet NAVD88 are the result.
The wave that typically generates the greatest runup is the wave that has not yet broken
when it reaches the toe of the beach. It is not the largest wave to come into the area.
The larger waves generally break farther offshore of the beach and lose most of their
energy before reaching the shoreline. If the total water depth is 10.4 feet, based upon a
maximum scour depth at the toe of the beach slope of 0.5 feet NAVD88 and water
elevation+10.9 feet NAVD88), then the design wave height (0.78xwater depth) will be
LOW ~dlum -High Extreme Risk
Aversion Risk Aversion Risk Aversion
High emissions ZOlO 0.3 0.2 0.5 0.6 0.7 1.0
1040 0.5 0.4 0.7 0.9 1.2 1.7
1050 0.7 0.5 1.0 1.2 1.8 2.6
Low emissions 1060 0 .8 0.5 1.1 1.4 2.2
High emissions 1060 1.0 0.7 1.3 1.7 2.5 3.7
Low emissions 1070 0.9 0 .6 1.3 1.8 2.9
High emissions 1070 1.2 0 .8 1.7 2.2 3.3 5.0
Low emissions 1080 1.0 0 .6 1.6 2.1 3.6
High emissions 1080 1.5 1.0 2.2 2.8 4.3 6.4
Low emissions 1090 1.2 0.7 1.8 2.5 4.5
High emissions 1090 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 2110· 1.4 0 .9 2.2 3.1 6.0
High emissions 2110' 2.3 1.6 3.3 a.3 7.1 11.5
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about 8.5 feet, respectively. The slope of the beach is about 1/12 (v/h) and the near-shore
slope was chosen to be 1/80 (v/h). The height of the beach at the berm is about +13 feet
NAVD88. It should be noted that the height of the beach berm will increase as sea level
rises. The beach is a mobile deposit that will respond to the water elevation and waves.
To be conservative an additional 6.0 feet SLR case will be considered with the elevation
of the beach berm adjusted to +15 feet NAVD88. Table I, and Table II are the ACES
output for these two SLR design conditions.
Table I
Table II
For the highest SLR case, the calculated overtopping rate of the beach, under the eroded
beach conditions with 6.0 feet of future SLR, is 15.6 ft /s-ft. For the calculated overtopping3
rate (Q=q), the height of water and the velocity of this water can be calculated using the
following empirical formulas provided by the USACOE (Protection Alternatives for Levees
and Floodwalls in Southeast Louisiana, May 2006, equations 3.1 and 3.6).
ACES I ltlde : Single Case I Functional Area: Wave -Structure Interaction
Application: Wave Runup and Overtopping on Impermeable Structures
Item Unit Ualue I Snooth Slope I Runup and
Incident Wave Height Hi: ft 8.500 Overtopp i ng
Wave Period T: sec 15.000
COTAN of Nearshore Slope COTC~l: 80.000 6806W Water Depth at Structure Toe ds: ft 10.900
COTAN of Structure Slope COTC8l: 12.000 Oceanfront Structure Height Above Toe hs: ft 12.500
Wave Runup H: ft 8.263 Newport
Onshore Wind Uelocity U: ft/sec 16.878 Beach Deepwater Wave Height H0: ft 5.818
Helativc Height ds1H0; 1.B61
Wave Steepness H0/CyT"2l: 0.000808
Overtopping Coefficient "' 0.070000 3.2 FT SLR 01..1ertopping Coefficient Qstar0: 0.070000
Overtopping Rate Q: ft,...3/s-ft 11.575
I
-ACES I ltlde : Single Case J Fu net Iona l Area: Wave -Structure Interaction
Appl !cation: Wave Runup and Overtopping on Impermeable Structures
Item Unit Value I Snooth Slope
~ --Runup and
Incident '-'Ja.ve Height Hi ft 10.000 Overtopp i ng
'-'Ja.ve Period T sec 15 .000
COTAN of Nearshore Slope COTC,>) 80.000 6806W '-'Ja.ter Depth at Structure Toe ds ft 12.300
COTAN of Structure Slope COTC8l 12 .000 Oceanfront Structure Height Above Toe hs ft 11.000
'-'Ja.ve Runup R ft 8.962 Newport Onshore Wind Velocity u ft/sec 16.878
Deepwater Wave Height H0 f t 7 .077 Beach Relative Height ds/li0 1.738
Wave Steepness H8,CgT"2l 0.000978 Overtopping Coefficient " 0.070009 6.0 FT SLR Overtopping Coefficient Qstar0 0.070009
Overtopping Rate Q ft·31s-ft 15 .607
C ,., q = 0.5443,1~ ,h/·
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Figure 7. Note the maximum wave runup in Newport Beach
area is less than 2 meters.
1For SLR of 6.0 feet with an overtopping rate of 15.6 ft /s-ft, the water height h = 2.9 feet3
cand the velocity, v = 7.9 ft/sec. The runup water is not a sustained flow, but rather just
a pulse of water flowing across the beach. The 2004 USACOE Coastal Engineering
Manual (CEM) states as a wave bore travels across a sand beach, the height of the bore
is reduced. Based upon observations, this is about 1-foot reduction in bore height every
25 to 50 feet. The site is over 500 feet away, so for the 6.0 feet of SLR case, the wave
bore may travel about 130 feet from the shoreline, which is well short of the site. Rather
than being inundated by sea level rise, the beach and the nearshore will readjust to the
new level over time, such that waves and tides will see the same profile that exists today.
This is the principle of beach equilibrium and is the reason why we have beaches today
even though sea level has risen over 200 feet in the last 10,000 years. The overtopping
waters over the next 75 years are unlikely to reach the subject site, even under
extreme design conditions.
TSUNAMI
Tsunamis are waves generated by submarine earthquakes, landslides, or volcanic action.
Lander, et al. (1993) discusses the frequency and magnitude of recorded or observed
tsunamis 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 east Newport Beach site, it provides a first order analysis for the area. Figure 7 shows
the tsunami runup in the southern California bight, Legg, et al. (2002). The maximum
tsunami runup in the east Newport area is less than 2 meters in height. Any wave,
including a tsunami, that approaches the site in east Newport Beach will be refracted,
modified, and reduced in height by the Newport Submarine Canyon. The Legg, et al.
(2002) report determined a maximum open ocean tsunami height of less than 2 meters.
Because of the wide beach, it is very unlikely that a 2-meter tsunami will be able to reach
the site with sufficient energy to cause significant structural damage.
I
~ 2 ,
' Normalized
Runup
Figure LO. Map sho'\ving ma:xitnum n.inup normalized 10 the maxin,um seanoor/island u plift for each
o f the seven Catalina Fault tsuna.rnigenic eart.h quake scenarios modeled in th.is study (fa 1.llt parame ters
in Table 4).
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It should be noted that the site is mapped within 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 two paragraphs were taken from the CalOES Local Planning
Guidance on Tsunami Response concerning the use of the tsunami inundation maps.
In order to avoid the conflict over tsunami origin, inundation projections are based on worst-case
scenarios. Since the inundation projections are intended for emergency and evacuation planning,
flooding is based on the highest projection of inundation regardless of the tsunami origin. As such,
projections are not an assessment of the probability of reaching the projected height (probabilistic
hazard assessment) but only a planning tool.
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 CalOES maps model the inundation of a tsunami with an approximate 1,000 year
recurrence interval (0.1% event). The Science Application for Risk Reduction (SAFRR)
tsunami study headed by USGS investigated a tsunami scenario with a 200-240 year
recurrence interval. The SAFRR modeling output is shown in Figure 8 and reveals that the
site is not within the more probable (0.4% event) tsunami inundation zone. The City of
Newport Beach and County of Orange have clearly marked tsunami evacuation routes for
the entire Newport Beach/Bay area.
Figure 8. SAFRR tsunami modeling output for the site.
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SHORELINE EROSION WITH FUTURE SLR
The California Coastal Commission (CCC) Sea Level Rise (SLR) Guidance suggests the
use of the highest erosion rate available for the prediction of the future shoreline erosion
due to SLR (Appendix B, page 237). The United States Geological Survey (USGS, 2006)
performed a comprehensive assessment of shoreline change including this section of
coastline. Figure 9 is portion of a figure from USGS 2006 (Figure 39, page 62) and shows
the maximum short-term erosion rate at the subject site. There is no long-term erosion at
the site (purple line). The short-term erosion rate is calculated to be ~2.0 ft/yr (green line).
Even if the short-term rate was used as the long-term rate (this would be very conservative
analysis), the retreat would be 150 feet over the 75 year life of the development. The site
is currently about 355 feet from the shoreline. If the beach retreats 150 feet in the next
75 years then the site will be ~205 feet from the shoreline. A beach width of 200 feet is
recognized as sufficient to protect the back shore from extreme events. The site is safe
from shoreline erosion over the design life of the development due to the significant
setback from the current shoreline and future shoreline with SLR. The proposed
development will not need shore protection over the life of the development.
Figure 9. Shoreline change rate in meters per year from USGS 2006.
Shoreline Change: San Pedro Region
+-----Accretion Erosion ~
Los Angeles Harbor
20
30
2 m/yr
Bolsa hica State Beach
E 40 ::.
~ SITE, 0 ..c:
West Nj wport Beach
"' .;
C) '-' C e 0 .; "'C I "' ., Q.
<.) = C "' f! "' "' - - -- - - - -i5 .. 50 .;
" .c :,
"'
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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, http://walrus.wr.usgs.gov/coastal_processes/cosmos/. Using the modeling program
the vulnerability of the site to three different SLR scenarios and the100 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 10 is the output of the CoSMoS program. The modeling shows that the streets
including Pacific Coast Highway, the main arterial street, will flood during the 100 year
event with 150 cm (~5.7 feet) of SLR. The site may experience minor flooding. The flood
waters will come from the bay and not from the ocean. The lowest proposed finished floor
will be a minimum of 12 inches above the adjacent street flow line of ~13 feet NAVD88.
Figure 10. Output for USGS CoSMoS vulnerability modeling.
CCC SLR GUIDANCE INFORMATION
Step 1. Establish the projected sea level rise range for the proposed project’s
planning horizon using the best available science, which is currently the 2012 NRC
Report.
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Using the latest CCC SLR guidance and the City of Newport Beach City Council SLR
guidance, the range of estimate over the project design life that range in the year ~2095
is between 1.3 feet and 3.2 feet. In addition, the analysis herein considered a less than
“likely” SLR of about 6.0 feet. This is the sea level rise range for the proposed project, 1.3
feet to 6.0 feet.
Step 2. Determine how physical impacts from sea level rise may constrain the
project site, including erosion, structural and geologic stability, flooding, and
inundation.
The analysis herein shows that it is unlikely that wave runup will reach the site even with
6.0 feet of SLR. The proposed finished floor elevation of above +13.4 feet NAVD88 is
above the likely maximum future water elevation. Site drainage from non-ocean waters is
provided by the project civil engineer. The CCC Sea-Level Rise Policy Guidance document
states, “predictions of future beach, bluff, and dune erosion are complicated by the
uncertainty associated with future waves, storms and sediment supply. As a result, there
is no accepted method for predicating future beach erosion.” The CCC-approved SLR
document provides very little means or methods for predicating shoreline erosion due to
SLR. If a very conservative future erosion rate due to SLR of 2.0 ft/yr is used, then the
shoreline will move about 150 feet over the life of the development. The site is over 500
feet from the shoreline. Rather than being inundated by sea level rise, the beach and the
nearshore will readjust to the new level over time such that waves and tides will see the
same profile that exists today. This is the principle of beach equilibrium and is the reason
why we have beaches today even though sea level has risen over 200 feet in the last
10,000 years. The proposed project is reasonably safe from shoreline erosion due to the
site distance from the shoreline.
Step 3. Determine how the project may impact coastal resources, considering the
influence of future sea level rise upon the landscape as well as potential impacts of
sea level rise adaptation strategies that may be used over the lifetime of the project.
The project will not impact coastal resources considering sea level rise.
Step 4. Identify alternatives to avoid resource impacts and minimize risks throughout
the expected life of the development.
The project does not impact resources and minimizes flood risk through the project design.
Step 5. Finalize project design and submit CDP application.
The project architect will incorporate this report into the design.
Coastal Hazards Report shall include (NBMC 21.30.15.E.2):
i. A statement of the preparer’s qualifications;
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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 co-authored 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 herein, the coastal hazards to consider for ocean front sites are shoreline
erosion, flooding, and wave impacts.
iii. An analysis of the following conditions:
1. A seasonally eroded beach combined with long-term (75 year)
erosion factoring in sea level rise;
As discussed herein, due to the very wide beach, the site is safe from shoreline erosion,
even factoring in SLR. The United States Geological Survey (USGS) provides the most
a comprehensive assessment of shoreline change including this section of coastline. The
USGS short-term erosion rate is calculated to be ~2.0 ft/yr or 150 feet over the 75 year life
of the development. The site is currently 500 feet or more from the shoreline. If the beach
retreats 150 feet in the next 75 years then the site will be 350 feet from the shoreline. A
beach width of 200 feet or greater is recognized as sufficient to protect the back shore from
extreme events. The site is safe from shoreline erosion over the design life of the
development due to the significant setback from the current shoreline and future shoreline
with SLR. The proposed development will not need shore protection over the life of the
development
2. High tide conditions, combined with long-term (75 year) projections
for sea level rise;
Using the latest CCC SLR guidance the range of SLR over the project design life that
range in the year ~2095 is between 1.3 feet and 6.0 feet. The highest recorded water
elevation on record in the vicinity of the site is 7.7 feet NAVD88. This actual high water
record covers 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. Per the Guidance, this elevation includes all short-term oceanographic effects
on sea level, but not the long-term sea level rise prediction. If 1.3 and 6.0 feet are added
to this 7.7 feet NAVD88 elevation, then future design maximum water levels (“high tide
conditions”) of 9 feet NAVD88 and 13.7 feet NAVD88 are determined.
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3. Storm waves from a one hundred year event or storm that compares
to the 1982/83 El Nino event;
For the design wave with the maximum runup on the beach and SLR of 6.0 feet, the beach
1covertopping rate is 15.6 ft /s-ft, the water height h is 2.9 feet, and the velocity, v is 7.93
ft/sec. The runup water is not a sustained flow, but rather just a pulse of water. The 2004
USACOE Coastal Engineering Manual (CEM) states as a wave bore travels across a sand
beach, the height of the bore is reduced. Based upon observations, this is about 1-foot
reduction in bore height every 25 to 50 feet. The site is about 350 feet away. So for the
largest SLR case, the wave bore may travel about 130 feet from the shoreline which is well
short of the site. Rather than being inundated by sea level rise, the beach and the
nearshore will readjust to the new level over time, such that waves and tides will see the
same profile that exists today. This is the principle of beach equilibrium and is the reason
why we have beaches today even though sea level has risen over 200 feet in the last
10,000 years. The overtopping waters over the next 75 years most likely will not reach the
subject site, even under the extreme design conditions and maximum possible shoreline
erosion.
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.
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 fronting the site. No shore protection will be necessary to protect
the development over the next 75 years.
v. Identification of necessary mitigation measures to address current
hazardous conditions such as siting development away from hazardous areas
PA2021-024
16
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 analysis provided in the hazard study verifies that it is unlikely that wave runup will
reach the site even with 6.0 feet of SLR. The proposed finished floor elevation of above
13.4 feet NAVD88 is safe for reasonable estimates of SLR. Site drainage from non-ocean
waters is provided by the project civil engineer. If a future erosion rate due to SLR of 2.0
ft/yr is used, then the shoreline will move about 150 feet over the life of the development.
The site is about 500 feet from the shoreline. Rather than being inundated by sea level
rise, the beach and the nearshore will readjust to the new level over time such that waves
and tides will see the same profile that exists today. This is the principle of beach
equilibrium and is the reason why we have beaches today even though sea level has risen
over 200 feet in the last 10,000 years. The proposed project is reasonably safe from
shoreline erosion due to the site distance from the shoreline.
The public streets will flood due to SLR long before the residence will be impacted by SLR.
The shoreline fronting the site is stable and an increase in the water elevation will likely not
increase shoreline erosion. The proposed project is safe from shoreline erosion due to the
setback of the development to the potential future Mean High Tide (MHT) line in
consideration of SLR. It is very likely that the community will adopt SLR adaptation
strategies that are currently being considered by the City of Newport Beach. These
strategies involve raising/replacing the bulkheads, beaches, and walkways that surround
the bay. These are site specific adaptation strategies.
CONCLUSIONS
• There is a very wide (>500 feet) sandy beach in front of the property 99.99% of the
time.
• A review of aerial photographs over the last five decades shows no overall shoreline
retreat and a wide sand beach in front of the property, even at times when the
beach is seasonally at its narrowest.
• The long-term shoreline erosion rate is small, if any long-term erosion occurs at all.
If a very conservative FUTURE retreat rate of 2.0 feet/year is used, it would account
for about 150 feet of retreat over the life of the structure. This conservative retreat
rate will not reduce the beach to less than 350 feet in nominal width (200 feet width
of beach is recognized by coastal engineers as a sufficiently wide beach to provide
back-shore protection).
• The site has not been subject to any significant wave overtopping in the recent past.
PA2021-024
• The proposed finished first floor (FF) elevation for the structure is above the street
flow line (landward of the residence).
• The current mean high tide line is over 540 feet from the site and it is unlikely that
over the life of the structure, the MHT line will reach within 200 feet of the property.
In conclusion, wave runup and overtopping will not significantly impact this site over the life
of the proposed improvements. The proposed development will neither create nor
contribute significantly to erosion, geologic instability, or destruction of the site or the
adjacent area. There are no recommendations necessary for wave runup protection. The
proposed project minimizes risks from flooding. GSI certifies* that coastal hazards will not
impact the property over the next 75 years and that there is no anticipated need for a shore
protection device over the life of the proposed development. There are no
recommendations necessary for avoidance or minimization of coastal hazards.
LIMITATIONS
Coastal engineering is characterized by uncertainty. Professional judgements presented
herein are based partly on our evaluation of the technical information gathered, partly on
our understanding of the proposed construction, and partly on our general experience. Our
engineering work and judgements have been prepared in accordance with current
accepted standards of engineering practice; we do not guarantee the performance of the
project in any respect. This warranty is in lieu of all other warranties express or implied.
Respectfully Submitted,
_______________________
GeoSoils, Inc.
David W. Skelly, MS
RCE #47857
*The term "certify" is used herein as defined in Division 3, Chapter 7, Article 3, § 6735.5.
of the California Business and Professions Code (2007).
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REFERENCES
Coastal Engineering Manual 2004, US Army Engineer Waterways Experiment Station,
Coastal Engineering Research Center, US Government Printing Office, Washington, DC.
FEMA Website, 2020 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
Legg, Mark R., Borrero, Jose C., and Synolakis, Costas E., Evaluation of tsunami risk to
southern California coastal cities, in The 2002 NEHRP Professional Fellowship Report.
NOAA, 2020, https://tidesandcurrents.noaa.gov/datums.html?id=9410660
Shore Protection Manual, 1984, 4th ed. 2 Vols, US Army Engineer Waterways Experiment
Station, Coastal Engineering Research Center, US Government Printing Office,
Washington, DC.
State of California, County of San Diego, 2009, “Tsunami Inundation Map for Emergency
Planning, Newport Beach Quadrangle,” 1:24,000 scale, dated June 1.
USACOE (US Army Corps Of Engineers), 1986, "Southern California Coastal Processes
Data Summary" Ref # CCSTW 86-1.
USACOE (US Army Corps Of Engineers), 2002, Coast of California Storm and Tidal
Waves Study South Coast Region, Orange County.
USACOE, 2013, “Incorporating Sea Level Change in Civil Works Programs,” ER 1100-2-
8162, dated 31 December.
USGS 2006, “National Assessment of Shoreline Change Part 3: Historical Shoreline
Change and Associated Coastal Land Loss Along Sandy Shorelines of the California
Coast”, Open File Report 2006-1219.
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