HomeMy WebLinkAbout20210412_Coastal Hazards_3-29-2021GeoSoils Inc.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
March 29, 2021
Mr. & Mrs. Cefalia
1740 East Oceanfront
Newport Beach, CA 92661
SUBJECT: Coastal Hazard and Wave Runup Study, 1740 East Oceanfront, Newport
Beach, California.
Dear Mr. & Mrs. Cefalia:
At your request, GeoSoils, Inc. (GSI) is pleased to provide this coastal hazard and wave
runup study for the property located at 1740 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 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
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 1740 East Oceanfront, Newport Beach, California. It is a
rectangular shaped parcel approximately 50 feet wide by 80 feet long with an existing
residential structure. Figure 1 is a “Bird’s Eye” aerial photograph of the site taken in 2019
downloaded from the internet. The proposed development consists of the removal of the
existing residence and construction of a new residence using the existing foundation. 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, 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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5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
Figure 1. Subject site in 2019. Note the vegetation fronting the site, the 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 300 feet.
The narrowest beach width occurred in 1965 (approximately 300 feet). During typical
summer beach conditions, the beach width is in excess of 375 feet. Measurements during
our March 8, 2021 site inspection indicate that the mean high tide line is ~390 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 375 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 RdM Surveying Inc, dated November 2, 2020. Development plans were provided by
Rost Architecture and Interiors, 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 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 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
October 28, 2020, shows what could be described as the normal beach width (over 375
feet). A review of the aerial vertical photographs over the last 45 years shows a 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
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 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 street is 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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5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
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
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
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5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
Figure 4. Wave runup terms from ACES analysis.
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
Newport Beach shoreline is controlled primarily by the Newport Submarine Canyon.
Historically, the section of Newport Beach from 25 Street to 40 Street has experiencedthth
extreme storm wave erosion due to focusing of the waves by the canyon. The ACES
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5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
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 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 initially 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 22nd century sea-level projections at a global network of tide-gauge sites” (Kopp el al,
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
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5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
Figure 5 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 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 estimated to
meet or exceed the 1991-2009 mean, based upon the best available science.
Figure 5. 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.
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LOW Medium. High extreme Risk
Aversion Risk Aversion Risk Aversion
H lgh 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 13 1.8 2.9
H lgh emissions 2070 1.2 0.8 1.7 2.2 3.3 5.0
Low emissions 2080 1.0 0.6 1.6 2.1 3.6
High emissions 2080 1.5 1.0 2.2 2.8 4.3 6.4
Low emissions 2090 1.2 0.7 1.8 2.5 4.5
High emissions 2090 1.8 1.2 2.7 3.4 5.3 8.0
Low emissions 2100 1.3 0.7 2.1 3.0 5.4
High emissions 2100 2 . .2 1.3 3.2 4.1 6.7 9.9
Low emissions mo· 1.4 0.9 2.2 3.1 6.0
High emissions mo· 2.3 1.6 3.3 4.3 7.1 11.5
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5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
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.
Table I
Table II
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ACES I t'ode : Single Case I Functional Area: Wave -Structure Interaction
Application: Wave Runup and Overtopp i ng on I mpermea b I e Structures
Item Unit Value I Sn-oath Slope I Runup and
Incident Waive Height Hi: ft 8.500 O,vertopp i ng
Wave Period T: sec 15 .000
COTAN of Nearshore Slope core .. i: 80.000 1740 East Water Depth at Structure Toe ds: ft 10. 900
COTAN of Structure Slope coreeJ: 12.000 Oceanfront Structure Height Above Toe hs: ft 12.500
Wave Runup ff; ft 8.263 Newport
Onshore Wind Uelocity U: ft/sec 16 .878 Beach Deep1Jater Wave Heig-ht H0: ft 5.848
Relative Height ds/H0: 1.864
Wa.11..Je Steepness H0/Cgr"2l: 0.000808
Overtopping Coefficient "' 0.070000 3.2 FT SLR Overtopping Coefficient Qstar0: 0.070000
Overtopp i ng Hate Q: ftA3/s-ft 11.575
I
ACES I t'ode : Single Case I Fu net iona 1 Area: Waive -Structure Inte ract ion
Application: Wave Runup and Overtopp i ng on Impern::ab le Structure s
Item Unit Ualue I Smooth Slope Runup and
Incident Wave Height Hi ft 10.000 Overtopp i ng
Wave Period T sec 15 .000
COTAN of Nearshore Slope core .. i 80.000 1740 East Water Depth at Structure Toe ds ft 12.300
COTAN of Structure Slope coreel 12 .000 Oceanfront Structure Height Above Toe hs ft 14.000
Wave Runup R ft 8.962 Newport Onshore Wind Ueloc ity u ft/sec 16 .878
Deepl,Jil,ter Wave Height H0 ft 7.077 Beach Relative Heigllt ds/H0 1.738
Wave Steepness H0/Cgr"2l 0.000978
Overtopp i ng Coefficient " 0.070000 6.0 FT SLR Overtopp i ng Coefficient Qstar0 0.070000
Overtopp i ng Rate Q ftA3/s-ft 15 .607
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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).
1For SLR of 6 feet with an overtopping rate of 15.6 ft /s-ft, the water height h = 2.9 feet and3
cthe 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 375 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
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q = 0.5443.Ji,h.i Jll
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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 6 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 6. SAFRR tsunami modeling output for the site.
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5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
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 7 is portion of a figure from USGS 2006 (Figure 39, page 62) and shows
the no short-term erosion rate near or at the subject site. There is no long-term erosion at
the site. The highest nearby short-term erosion rate is calculated to be ~1 ft/yr. Even if the
short-term rate 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 375 feet from the shoreline. If the beach retreats 75 feet in the next 75 years then the
site will be ~300 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.
Figure 7. Shoreline change rate in meters per year from USGS 2006.
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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 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.
Figure 8 is the output of the CoSMoS program. The modeling shows that the shoreline
does not erode to 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 at +15.58 feet NAVD88 and well above the adjacent flow
line in the alley at ~+11.6 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.
Figure 8. Output for USGS CoSMoS vulnerability modeling.
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floo:j Hazard (no data) 175cm SLR+WavelOO
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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.
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 about elevation
15.58 feet NAVD88. 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 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 about 390 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 decades, waterproofing of the
lower portions of the structure below elevation +13.7 feet NAVD88 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
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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):
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 390 feet from the shoreline. If the beach retreats 75 feet in the next 75
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years then the site will be ~300 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 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
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
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 currently about 390 feet away, so
for the largest SLR case, the wave bore may travel about 100 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
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There is no bluff fronting the site. This condition does not occur at the site.
5. Demonstration that development will be sited such that it maintains
a factor of safety against sliding of at least 1.5 under static conditions
and 1.1 under seismic (pseudostatic) conditions for its economic life
(generally 75 years). This generally means that 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
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 15.58 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 about 390 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.
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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 (>375 feet) sandy beach in front of the property 99.99% of the
time.
• A review of aerial photographs over the last five decades generally 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 well above the street flow line
(landward of the residence).
• The current mean high tide line is 390 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.
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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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