HomeMy WebLinkAboutPA2022-002_20220104_Coastal Hazards_11-8-21GeoSoils Inc.
November 8, 2021
Helle McIain
8 Strands, 913 Balmoral
2 Praed Street
London, UK W21JN
SUBJECT: Coastal Hazard and Wave Runup Study, 2172 East Oceanfront, Newport
Beach, California.
Dear Helle McIain:
At your request, GeoSoils, Inc. (GSI) is pleased to provide this coastal hazard and wave
runup study for the property located at 2172 East 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 latest CCC Sea-Level Rise (SLR)
Guidance document (November 2018), a review of City of Newport Beach Municipal Code
(NBMC) 21.30.15.E.2, a review of the site elevations, a discussion/review of the project
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 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
January 18-19, 1988, the winters of 1982-83, and 1998 type storm waves and beach
conditions.
INTRODUCTION AND BACKGROUND
The subject site is located at 2172 East Oceanfront, Newport Beach, California. It is an
irregular shaped ocean front parcel with an existing residential structure. Figure 1 is a
“Bird’s Eye” aerial photograph of the site taken in 2020 downloaded from the internet. The
proposed development consists of the removal of the existing residence and construction
of a new residence and other improvements. The site is fronted by a wide sandy beach
and the Pacific Ocean. This shoreline is located between the Balboa Pier and the west
jetty of Newport Harbor (at the jetty), in a coastal segment referred to as the Balboa 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). In general, the movement of sand along a shoreline depends upon the orientation
of the shoreline and the incoming wave direction. The movement of sand along this
southern section of Newport Beach is generally to the east, but under wave conditions from
the south, the direction reverses.
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Figure 1. Subject site in 2020. Note the nearby dune areas and the very wide beach.
USACOE (2002) contains historical beach profile and beach width data for the Newport
Beach area. At the subject site, the beach width has changed little over the past 70 years
as a result of beach nourishment in the 1930's with sand from Newport Harbor. The
available photographic data shows that the actual beach width has increased since 1965.
During typical winter beach conditions, the beach width may be reduced to about 550 feet.
The narrowest beach width occurred in 1965 (approximately 500 feet). During typical
summer beach conditions, the beach width is in excess of 600 feet. Measurements during
our September 2021 site inspection indicate that the mean high tide line is ~650 feet from
the site property line.
Despite efforts to control the movement of sand along the Newport coast, the shoreline at
this section of Newport Beach does experience short-term erosion. The erosion is
temporary and is largely the result of an energetic winter. As stated before, there is no clear
evidence of any long-term erosional trend (USACOE, 2002). The wide sandy beach in front
of the subject site is normally over 600 feet wide and has provided more than adequate
protection for the property over the last several decades. In the past, wave runup has not
reached the site, and the site has not been subject to wave attack for at least the last 60
years. This includes the winter storms of 1982-83, January 1988, and 1998, which are
considered the coastal engineering design storms for southern California.
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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 from 1972 through 2020, were reviewed
for shoreline changes. Site elevations relative to NAVD88 were taken from a site survey
by Guida Surveying Inc, dated March, 2020. Development plans were provided by Graham
Architecture, the 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 within 500 feet of the site since 1972. Figure 2, 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 what would be considered 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 3, taken in February 2021, shows what could be described
as the normal beach width (over 600 feet). A review of the aerial vertical photographs over
the last 45 years shows a very wide beach even though some of 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 500 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
70 years. The site has not flooded from ocean water or from surface drainage due to its
elevation relative to the city street drainage paths. The adjacent city streets are lower than
the lowest grade on site. In the future, wave runup will likely not reach the site under
severely eroded beach conditions and extreme storms.
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Figure 2. Shoreline fronting the subject in January 1988 after the “400-year” wave event.
Figure 3. Shoreline fronting the subject site in October 2020 (note the very wide beach).
WAVE RUNUP AND OVERTOPPING
Wave runup is defined as the vertical height above the still water level to which a wave will
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Figure 4. Wave runup terms from ACES analysis.
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 is 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 4 is a diagram showing the analysis terms.
Oceanographic Data
The wave, wind, and water level data used as input to the ACES runup and overtopping
application were taken from the historical data reported in USACOE (1986) and USACOE
(2002). 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
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Newport Beach shoreline is controlled primarily by the Newport Submarine Canyon.
Historically, the section of Newport Beach from 25th Street to 40th Street has experienced
extreme storm wave erosion due to focusing of the waves by the canyon. The ACES
analysis was performed 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 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 Everest International Consultants Inc. (EICI, 2011) reported
that the elevation of 7.71 feet NAVD88 is the 1% water elevation. For this analysis the
design 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
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closest SLR estimates to Newport Beach. The report provides SLR estimates based upon
various carbon emission scenarios known as a “representative concentration pathway” or
RCP. Figure 5 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.
Figure 5. 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.
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LOW Medium -High Extreme Risk
Aversion Risk Aversion Risk 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 2110' 1.4 0 .9 2.2 3.1 6.0
High emissions 2110' 2.3 1.6 3.3 4.3 7.1 11.5
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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 6 provides the SLR model curves and tables for Los Angeles Harbor.
Figure 6. Taken from the USACOE SLR curve calculator program.
Looking at the table in Figure 6, 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 5 for the year
2030 and 0.1 feet of SLR, the closest probability category is the lower limits of the “Likely
Range.”
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12
10
8
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NOAA et al. 2017 Relative Sea Level Change Scenarios for: LOS ANGELES
2010 2020 2030 2040 2050 2060
Year
Huntington Hart>oi.
Scenarios for LOS ANG COLES NOAA.2017 VlM: -0.00328 feet/)'I"
All val!RS are expressed in ieet
Year NOAA2017 NOAA.2017 NOAA2017 NOAA2017 NOAA2017
VLM Low Int-Low Intermediate Int-High
2000 2.70 2.70 2 70 2.70 2.70
2010 267 2n 2n 283 290
2020 2.63 283 290 3.00 309
2030 260 293 303 316 336
2040 2.57 3 03 313 342 3.72
2050 2.54 3 13 329 372 4 24
2060 2.50 323 342 4.08 480
2070 2.47 3.32 359 4.44 546
2080 2.44 3.42 372 4.90 6-24
2090 2 40 3.49 3 85 5.36 710
2100 2.37 3.52 398 5.88 815
2070
NOAA.2017
High
2.70
293
3 16
352
4.08
483
5.69
6.67
7.82
9 13
10.61
2080
NOAA2017
Extreme
2.70
2.93
3.23
365
4.37
526
6.37
7.65
9.10
10.67
12.61
2090
__, NOAA2017 Extreme
__, NOAA2017 High
-.-f-lOAA2017 Int-High
--. f-lOAA2017 lntermedia1e
.-NOAA2017 lnt-lo\V
-+-NOAA2017 low
_.... f.fOAA2017 VU/1
2100
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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 5 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 Newport Beach is elevation +7.7 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
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 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 13.7 feet NAVD88 (7.7 feet NAVD88 + 6 feet SLR). 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 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.
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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 ft3/s-ft. For the calculated overtopping
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).
For SLR of 6 feet with an overtopping rate of 15.6 ft3/s-ft, the water height h1= 2.9 feet and
the velocity, vc = 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)
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ACES I t'ode : Single Case I Funct iona l Area: Wave -Structure Interaction
App I icat ion: Wave Runup and Overtopping on l111perireable Structures
Item Unit Value I Sroooth SI ope I Runup and
Incident Wave Height Hi: ft 8.500 Overtopp i ng
Wave Period T: sec 15 .oc:o
COTAN of Nearshore Slope COT("): 80.0C:O 2172 East Water Depth at Structure Toe ds: ft 10 .900
COTAN of Structure Slope COTCeJ: 12 .oc:o Oceanfront Structure Height Above Toe hs: ft 12 .500
Wave Runup H: ft 8 .263 New port
Onshore Wind Uelocity U: ft/sec 16 .878 Beach Deepwater Wave Height H0: ft 5 .818
Relati.....e Height ds/H0: 1.861
Wave Steepness H0/CgT'2l: 0.000808
Overtopping Coefficient "' 0.070000 3.2 FT SLR Overtopping Coefficient Qstar0: 0.070000
Overtopping Rate Q: ftA3/s-ft 11.575
I
ACES I t'ode : Single Case I Functional Area: Wave -Structure Interaction
Application: Wave Runup and Overtopp i ng on Impermeable Structures
Item Unit Va lue I Sroooth Slope Runup and
Incident Wa1,,.,1e Height Hi f t 10.0C:O 01,,.,1ertopp i ng
Wa1Je Period T sec 15.0C:O
CO TAN of Nearshore SI ope COT(") 80.0C:O 2172 East Water Depth at Structure Toe ds f t 12.300
CO TAN of Structure SI ope COTCel 12.0C:O Oceanfront Structure Height Abo1Je Toe hs ft 11.0C:O
Wa1,,.,1e Runup
Onshore Wind Velocity
Deepwater Wa1,,.,1e Height
Relati1,,.,1e Height
Wa1,,.,1e Steepness
01,,.,1ertopping Coefficient
01,,.,1ertopping Coefficient
01,,.,1ertopp i ng Rate
f:: 3/2 0.5443,v .i-; ,h1
H u
H0
ds/H0
H0/CgT'2l
" Qstar0
Q
ft 8 .962 Newport ft/sec 16.878
ft 7.077
1.738 Beach
0.000978
0.070000 6.0 FT SLR 0.070000
ftA3/s-ft 15.607
V e
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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 600 feet away, so for the 6 feet of SLR case, the wave bore may travel
about 150 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.
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. 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 will be refracted, modified, and reduced
in height by the Newport jetties, as it travels into the bay, or over the development land
seaward of the site. Due to the infrequent nature and the relatively low 500-year recurrence
interval tsunami wave height, setback from the ocean, 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 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.
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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 7 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 7. SAFRR tsunami modeling output for the site.
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 predication 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 8 is portion of a figure from USGS 2006 (Figure 39, page 62) and shows
shoreline change at the subject site. There is no long-term (purple) or short-term erosion
rate at the site. Even if a short-term rate of 1 ft/yr was used as the long-term rate (this
would be very conservative analysis), the retreat would be 75 feet over the 75 year life of
the development. The site is currently over 600 feet from the shoreline. If the beach
retreats 75 feet in the next 75 years then the site will be ~525 feet from the shoreline. A
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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.
Figure 8. Shoreline change rate in meters per year from USGS 2006.
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, https://ourcoastourfuture.org. Using the modeling program the vulnerability of the
site to three different SLR scenarios with shoreline erosion 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.
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Figure 9 is the output of the CoSMoS program. The modeling shows that the shoreline
does not erode to even near the site, that the streets including East Balboa, the main
arterial street, will flood during the 100 year event with 175 cm (~5.7 feet) of SLR. The road
near site may flood slightly. However, the area flooding will come from the bay and not from
the ocean. The lowest finished floor is above + 13.5 feet NAVD88 and well above the
adjacent flow line in the alley at ~+11.4 feet NAVD88. Based upon the CoSMoS modeling,
the development is reasonably safe from flooding over the design life of the development
due to the proposed elevation of the finished floor and setback from the ocean.
Figure 9. 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.
Using the latest CCC SLR guidance, the SLR estimate over the project design life the
“likely” range in the year ~2096 is 3.0 feet to 3.2 feet. In addition, the analysis herein
considered a less than “likely” SLR of 6.0 feet. This is the sea level rise range for the
proposed project, 3.2 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.
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Mean High Water Shorelin1
Max Wave Runup during Rood
175an SlR + Wave 100
50 cm {8.2 ft)
S00 cm 06.4 ft)
7S0 cm {24.6 ft)
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The analysis herein shows that it is unlikely that wave runup will reach the site even with
6.0 feet of SLR. The lowest habitable finished floor elevation will be at or above elevation
13.5 feet NAVD88. Site drainage from non-ocean waters is provided by the project civil
engineer. The CCCSLRG 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 CCCSLRG document provides very little means or methods for predicating
shoreline erosion due to SLR. If a conservative future erosion rate due to SLR of 1 ft/yr,
then the shoreline will move about 75 feet over the life of the development under 6 feet
SLR. The site is currently over 600 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.
For SLR greater than 6 feet, which will not likely occur for many decades, waterproofing of
the lower portions of the structure can be added to mitigate potential flooding impacts. 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 on Balboa Island, and Balboa Peninsula
will flood with lower SLR well before the subject site floods. 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. This is a regional adaptation strategy. The project
design is suitable for a site specific SLR future adaptation strategy to waterproof the
structure(s) up to an elevation above the impact of SLR. In addition, there are currently
several very effective temporary flood control systems such as Quick Dams or even sand
bagging that can be used in the future.
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):
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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;
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,
including factoring in SLR of up to 6 feet. If a conservative future erosion rate due to SLR
of 1 ft/yr, then the shoreline will move about 75 feet over the life of the development. The
site is currently over 600 feet from the shoreline. If the beach retreats 75 feet in the next
75 years then the site will be ~525 feet or more 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 “likely” SLR estimate over the project design life
in the year ~2096 is 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, 3.2 feet to
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 CCCSLRG
document. Per the Guidance, this elevation includes all short-term oceanographic effects
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on sea level, but not the long-term sea level rise prediction. If 3.2 feet and 6 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 are determined.
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 feet, the beach
overtopping rate is 15.6 ft3/s-ft, the water height h1 is 2.9 feet, and the velocity, vc is 7.9
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 currently over 600 feet away, so for
the largest SLR case, the wave bore may travel about 150 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 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.
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
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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
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 feet of SLR. The habitable finished floor elevation at or above
elevation +13.5 feet NAVD88 is reasonably safe for over 6 feet of SLR. Site drainage from
non-ocean waters is provided by the project civil engineer. If a conservative future erosion
rate due to SLR of 1 ft/yr, then the shoreline will move about 75 feet over the life of the
development with 6 feet SLR. The site is currently over 600 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 reasonably safe from shoreline erosion
due to the setback of the development to the potential future MHT line in consideration of
SLR. Finally, in the future if necessary, the residence can be retrofitted with waterproofing
to an elevation above the flooding potential elevation along with flood shields and other
flood proofing techniques. 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 (>600 feet) sandy beach in front of the property 99.99% of the
time.
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• 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.
• There is no long-term shoreline erosion. If a very conservative FUTURE retreat rate
of 1 feet/year is used, it would account for about 75 feet of retreat over the life of the
structure. This conservative retreat rate will not reduce the beach to less than 300
feet in nominal width (200 feet width of beach is recognized by coastal engineers
as a sufficiently wide enough beach to provide back-shore protection).
• The site has not been subject to any wave overtopping in the past.
• The finished first floor elevation for the structure is above the street flow line
(landward of the residence).
• The current mean high tide line is over 640 feet from the site and it is unlikely that
over the life of the structure that the mean high tide 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 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.
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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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
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http://www.opsd.nos.noaa.gov/cgi-bin/websql/ftp/query_new.pl
Shore Protection Manual, 1984, 4th ed. 2 Vols, US Army Engineer Waterways Experiment
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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
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Change and Associated Coastal Land Loss Along Sandy Shorelines of the California
Coast”, Open File Report 2006-1219,
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