HomeMy WebLinkAbout912EastOceanfrontnewportGeoSoils Inc.
5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
October 4, 2019
Mr. Morcos Khalil
17221 Blue Spruce Lane
Yorba Linda, CA 92886
SUBJECT: Updated Coastal Hazard and W ave Runup Study for 912 East Oceanfront,
Newport Beach, California
Dear Mr. Khalil:
The following letter report is in response to your request for an updated coastal hazard and
wave runup study for the property located at 912 East Oceanfront, Newport Beach, CA.
The analysis is based upon site elevations, existing published reports concerning the local
coastal processes, and our site inspection and knowledge of local coastal conditions. This
report constitutes an investigation of the wave and water level conditions (including future
sea level rise) expected at the site in consequence of extreme storm and wave action over
the next 75 years. The information provided herein is intended to respond to the California
Coastal Commission (CCC) requirement for a discussion of coastal hazards at the site
including consideration of the recently approved CCC Sea-Level Rise (SLR) Policy
Guidance document. It also provides conclusions and recommendations regarding the
susceptibility of the property and proposed development to wave attack.
INTRODUCTION
The purpose of this wave runup study is to determine if the proposed development will be
subject to wave runup or coastal hazards over the typical life (75 years) of the development
and to provide the necessary hazard information for the CCC. If the property will be
subject to wave runup, the analysis will discuss how frequently it will occur, what the
predicted water volume and water height will be on the property, and how, if necessary, to
manage the overtopping waters. The analysis also determines if the property will be
subject to direct wave attack over the project life. If the property is subject to wave attack,
then the analysis will include design parameters for wave forces. The analysis uses design
storm conditions typical of the January 18-19, 1988 and winter of 1982-83 type storm
waves and beach conditions.
The subject site, 912 East Oceanfront, Newport Beach, is a rectangular parcel with
approximately 30 feet of ocean frontage. Figure 1 is an aerial photograph of the site and
adjacent properties downloaded with permission from the California Coastal Records
Project web site (http://www.californiacoastline.org/). The proposed development is to
replace an existing duplex with a new duplex. The site is fronted by a concrete public
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
boardwalk, a grass sports field, a wide sandy beach (total distance approximately 600 feet
wide to the mean high tide line), 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 W aves 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. The source of sediment for this
compartment is beach nourishment and sands from nearby rivers. The sink for sands is
the Newport Submarine Canyon.
Figure 1. Subject site, boardwalk, and sports field in September 2013.
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
USACOE (2002) contains historical beach profile and beach width data for the beach
fronting 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 groin. The data shows that the actual beach width fronting the site
has increased since 1965. Since 1967 to the present, the beach has been typically 400
feet wide, and as wide as 500 feet in the mid 1990s. Figure 2 is an April 2, 1928
photograph showing the shoreline, the very wide beach, and the site (USACOE, 2002).
In the long-term, the nearby sand source (Santa Ana River), and future nourishment
projects will continue to stabilize the shoreline fronting the site.
Figure 2. East Newport Beach and Newport Bay area in 1928 (USACOE 2002).
Despite efforts to control the movement of sand along the shoreline, the shoreline at this
section of Newport Beach area does experience short-term erosion. The erosion is
temporary, usually the result of an energetic winter. As stated before, there is no clear
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
evidence of any long-term erosional trend (USACOE, 2002). The wide sandy beach in
front of the subject site is normally over 500 feet wide and has provided more than
adequate protection for the property over at least the last nine decades. In the past
90 years, no wave runup has reached the site. This time period 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 NAVD88, which is about 2.62 feet below the mean tide
level (MTL). The units of measurement in this report are feet (ft), pounds force (lbs), and
second (sec). The site is mapped in the FEMA X Zone with less than 0.2% chance of
annual flooding (FEMA Panel 06059C0377J). The National Oceanographic and
Atmospheric Administration (NOAA) Nautical Chart was used to determine offshore slopes.
A topographic map of the site and proposed finished floor elevations were provided by Site
Tech Inc., using NAVD88 as the vertical datum.
SITE BEACH EROSION & WAVE ATTACK
In order to determine the potential for future wave runup to reach the site, historical aerial
photographs over the last four decades were reviewed. None of the photographs showed
that wave runup reached the site over the four-decade time frame. Figure 3, taken in
January 1980, shows the beach in front of the property including the sports field. This field
is in all the historical photographs reviewed and shows no signs of being impacted by
erosion or wave runup. The beach has not eroded back to anywhere near the field, nor
has wave runup reach the field. Figure 4, taken February 2, 2000, shows what could be
described as the normal beach width (about 500 feet). Our review of the annual aerial
photographs over the last 50 years shows a wide beach seaward of the sports field, even
though the photographs were taken in the winter and spring, when the beach is seasonally
the narrowest. Based upon review of the aerial photographs, it is highly unlikely that the
shoreline will erode back to the sports field or near the site allowing direct wave attack on
the proposed residence.
GeoSoils Inc.5
5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
Figure 3. Subject site, sports field, and very wide beach in 1980.
Figure 4. Subject site, sports field, and very wide beach in 2000. The photos show no
change over the 20-year period.
. .
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
Figure 5. Wave runup terms from ACES manual.
WAVE RUNUP AND OVERTOPPING
As waves encounter the beach at the subject site, water can rush up, and sometimes over,
the beach berm. In addition, beaches can become narrower due to a long-term erosion
trend. Often, wave runup and overtopping, strongly influence the design and the cost of
coastal projects. 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 beach berm) as a result of
wave runup.
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 USACOE Coastal Engineering Manual. The overtopping estimates calculated
herein are corrected for the effect of onshore winds. Figure 5 is a diagram showing the
analysis terms.
The wave, wind, and water level data used as input to the ACES runup and overtopping
application was taken from the historical data reported in USACOE (1986 & 2002) and
updated, as necessary. The shorelines 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
II;
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
Canyon. Historically, the shoreline section of Newport Beach from 25 Street to 40 Streetthth
has experienced some 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
El Niño waves during the 1982-83 winter eroded beaches throughout southern California.
However, the subject property and adjacent properties were not subjected to direct wave
runup attack or wave induced flooding during those winter storms. The wave and water
level conditions on January 18-19, 1988 have been described by Dr. Richard Seymour of
the Scripps Institution of Oceanography as a “400-year recurrence” wave height event.
The property still was not subjected to wave overtopping attack during this event. 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 Ocean Survey tidal data station closest to the site is located at Newport
Beach (Station 9410580). The tidal datum elevations are as follows:
Mean Higher High W ater 5.27 feet
Mean High W ater 4.52 feet
Mean Tide Level (MSL) 2.62 feet
Mean Low W ater 0.8 feet
NAVD88 0.0 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. Maximum high tide is about +7.1 feet
NAVD88. The historical highest water elevation is +7.49 feet NAVD88 on January
28, 1983.
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.” W hen 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 22nd century sea-level projections at a global network of tide-gauge sites” (Kopp,
et al., 2014). This update included SLR estimates and probabilities for Los Angeles, the
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
closest SLR estimates to Newport Beach. These SLR likelihood estimates are provided
below in 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 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 estimates 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,” 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 4.0 feet. Interpolating for SLR in 2096, using the medium-high risk
aversion, an estimated SLR of 5.1 feet is determined. The maximum historical water
elevation at the Los Angeles tide station is elevation+7.72 feet NAVD88 on January 10,
2005. This actual high water record period includes the 1982-83 severe El Niño, and the
1997 El Niño events, and is therefore, consistent with the methodology outlined in the CCC
Sea-Level Rise Policy Guidance document. The Newport Beach City Council approved
the use of high estimate of the “low risk aversion” scenario, which is 3.2 feet by the year
2100, or about 3.1 feet in 2096. To be conservative, if 3.2 feet and 5.1 are added to this
7.7 feet NAVD88 elevation, then future design maximum water levels of 10.9 feet and 12.8
feet NAVD88 are determined.
Probabilistic Projections (i n feet) (based on Kopp et al . 2014)
5091. probab111ty 6691. probability 591. probability 0 591, probab1l1ty
sea-level nse meets sea-level rise sea-level nse meets sea-level nse meets
or exceeds 1s between or exceeds or exceeds
Low Med ium -High Risk
Aversion Risk Aversion
High emissions 10!0 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
1010 0.7 0 .5 1.0 1.2 1.8 2 .6 ----
, Low emissions 1060 0.8 05 11 1.4 22
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 emJsSlons 1070 1.2 0.8 1.7 2.2 3.3 5.0
Low emlSSlons 1010 1.0 0.6 1.6 2.1 3.6
~ Hlih emlsSloas 1080 15 10 22 2.8 43 64
Low emissions 1090 1.2 0.7 1.8 2.5 4.5
~ H'!h emissions 1090 1.8 1.2 2.7 3.4 5.3 8.0
, Low emissions 1100 1.3 0.7 2.1 3.0 5 .4
High emJsSlons 1100 2 .2 1.3 32 41 6.7 99
, Low emissions 1110' 1.4 0.9 2.2 3.1 6.0
High emJssJons 1110' 2 .3 16 3.3 4 .3 71 11.5
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 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 depths 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 5.1 feet SLR case will be considered with the elevation
of the beach berm adjusted to +14.5 feet NAVD88. Table I, and Table II are the ACES
output for these two SLR design conditions
TABLE I
ACES I l't:lde: Single Case I Functional Area: Wave -Structure Interaction
Application: Wave Runup and Overtopping on Impermeable Structures
Item Unit Value Smooth Slope
Runup and
Incident Wave Height Hi: ft 8.500 Overtopping
Wave Period T: sec 15.000
COTAN of Nearshore Slope COT(s,!): 80.000 912 East Water Depth at Structure Toe ds: ft 10.900
COTAN of Structure Slope COT<8): 12.000 Oceanfront Structure Height Above Toe hs: ft 12.500 .
Wave Runup R: ft 8.263 Newport
Onshore Wind Velocity U: ft/sec 16.878 Beach Deepwater Wave Height HO: ft 5.848
Relative Height ds/HO: 1.864
Wave Steepness HO/(gT"2): 0.000808
Overtopping Coefficient (X: 0.070000 3.2 FT SLR Uvertopping l:oefl'icient (Jstaro: (:),(:)'/(:)(:)(:)(:)
Overtopping Rate Q: ft~3/s-ft 11.575
I
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
TABLE II
For the highest SLR case, the calculated overtopping rate of the beach, under the eroded
beach conditions with ~5 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 ~5 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 500 feet away, so for the 5.1 feet of SLR case, the wave bore
may travel about 200 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
ACES I Mode: Single Case I Functional Area: Wave -Structure Interaction
App Ii cat ion: Wave Runup and Overtopping on Impermeable Structures
Item
Incident Wave Height Hi:
Wave Period T:
COTAN of Nearshore Slope COT(SIS):
Water Depth at Structure Toe ds:
COTAN of Structure Slope COTC8):
Structure Height Above Toe hs:
Wave Runup R:
Onshore Wind Velocity U:
Deepwater Wave Height H0:
Relative Height ds/H0:
Wave Steepness H0/(gT"2):
Overtopping Coefficient
Overtopping Coefficient
Overtopping Rate
I-12 q = 0.5443 '\I~ ,h1
0::
Qstar0:
Q:
Unit Value Smooth Slope
Runup and
ft 10.000 Overtopping
sec 15.000
80.000 912 East ft 12.300
12.000 Oceanfront ft 14.000
ft 8.962 NEWPORT
ft/sec 16.878 BEACH ft 7.077
1.738
0.000978
0.070000 5.1 FT SLR 0.070000
ft~3/s-ft 15.607
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
Figure 7. Taken from Legg, et al. (2002). Note the maximum wave runup
in the east Newport Beach area is less than 2 meters.
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
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. 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 west 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
al
t
~
I
:!a
3.0
2.5
2..(J
1.5
1.0
o.s
0 .0
1 20
100
80
60
40
20
0
0
Ca.eel
C.ase2
ca.e-e3
Ca.aa4
20 40 GO 80
lmorneters
100 1 20
Cases
Ca:se6
C.a:ce:7
\40
Normalized
Runup
0 .0 0.5 1.0 1 .5 2.0
·Figure 10. Map showi n g max imum runup normalized to the maximum seafloor/i s lan d u pl i ft for each
or t he seven Catalin a Faul t ts una_migenic eru·tl1quake scenarios modeled in t his study (fa ult parnme ters
in Table 4).
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
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 tsunam i.
Areas actually inundated by a specific tsunami can vary from those predicted. The
inundation maps are not a prediction of the performance, in an earthquake or
tsunami, of any structure within or outside of the projected inundation area.
The City of Newport Beach and County of Orange have clearly marked tsunami evacuation
routes for the entire Balboa Peninsula.
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.
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
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 West Balboa, the main arterial
street, will flood during the 100 year event with 150 cm (~5 feet) of SLR. The alley 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 or above +12.4 feet NAVD88 and above the adjacent
flow line in the alley at 9.4 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.
Figure 8. 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 and the City of Newport Beach City Council SLR
guidance, the SLR estimate over the project design life that 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 5.1
feet. This is the sea level rise range for the proposed project, 3.2 feet to 5.1 feet.
912 East Oceanfront
-._
■
Flood Depth 1SCkm SLR + Wave
100
No Data
0cm
250 cm
500 cm
750 cm
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
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
5.1 feet of SLR. The proposed lowest habitable finished floor elevation of +12.4 feet
NAVD88 is above the design 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 conservative future erosion rate due to SLR of 40 feet for every foot of SLR,
then the shoreline will move about 200 feet over the life of the development under 5 feet
SLR. 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.
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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 W ave 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. If a conservative future erosion rate due to SLR of 40 feet for
every foot of SLR, then the shoreline will move about 200 feet over the life of the
development. The site is over 500 feet from the shoreline. If the beach retreats 200 feet
in the next 75 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;
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Using the latest CCC SLR guidance and the City of Newport Beach City Council SLR
guidance, the SLR estimate over the project design life in the year ~2100 is 3.2 feet. In
addition, the analysis herein considered a less than “likely” SLR of about 5.1 feet. This is
the sea level rise range for the proposed project, 3.2 feet to 5.1 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 is added to this 7.7 feet NAVD88 elevation, then future design maximum water level
(“high tide conditions”) of 10.9 feet NAVD88 is 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 ~5 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 over 500 feet away, so for the
largest SLR case, the wave bore may travel about 200 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
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
(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 5.1 feet of SLR. The proposed habitable finished floor elevation
of +12.4 feet NAVD88 is reasonably safe for SLR. Site drainage from non-ocean waters
is provided by the project civil engineer. If a conservative future erosion rate due to SLR
of 40 feet for every foot of SLR, then the shoreline will move about 128 feet over the life
of the development under 3.2 feet SLR. 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.
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
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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
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 (>500 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.
•The long-term shoreline erosion rate is small, if any long-term erosion occurs at all.
If a conservative FUTURE retreat rate of 2 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 enough beach to
provide back-shore protection).
•The site has not been subject to any wave overtopping in the past.
•The proposed 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 500 feet from the site and it is unlikely that
over the life of the structure that the mean high tide line will reach within 300 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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5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
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 C alifornia
Business and Professions Code (2007).
GeoSoils Inc.20
5741 Palmer Way, Suite D, Carlsbad CA 92010 S7046 760-438-3155
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