HomeMy WebLinkAbout20190805_Hazard_Wave_Runup_ReportGeoSoils Inc.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
June 18, 2019
Mr. Eric Olsen
2728 E. Coast Highway, Suite A
Corona del Mar, CA 92625
SUBJECT: Coastal Hazard and W ave Runup Study, 5311 Seashore Drive, Newport
Beach, California.
Dear Mr. Olsen:
At your request, GeoSoils, Inc. (GSI) is pleased to provide this revised coastal hazard and
wave runup study for the property located at 5311 Seashore Drive, 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 CCC Sea-Level Rise
(SLR) document (updated November 2018), a review of City of Newport Beach Municipal
Code (NBMC) 21.30.15.E.2, a review of the site elevations, a review of the residence
plans, a site inspection, and preparation of this letter report. This report constitutes an
investigation of the wave and water level conditions expected at the site as a result of
extreme storm and wave action over the next 75 to 100 years. It also provides conclusions
and recommendations regarding the susceptibility of the property and the proposed new
residential structure to wave attack. The analysis uses design storm conditions typical of
the January 18-19, 1988 and the winters of 1982-83 and 1998 type storm waves and
beach conditions.
INTRODUCTION AND BACKGROUND
The subject site is located at 5311 Seashore Drive, Newport Beach, California. It is a
rectangular shaped parcel approximately 30 feet of ocean frontage by ~62 feet long with
an existing residential structure. Figure 1 is a recent aerial photograph of the site
downloaded from the internet. The proposed development consists of removal of the
existing residence and construction of a new residence. The site is fronted by a wide
sandy beach (currently > 380 feet wide), and the Pacific Ocean. This site is located at the
west end of the Newport Beach groin field and northwest of the Newport Pier, in a coastal
segment described as the W est Newport 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). The West Newport Beach
shoreline segment stretches from the Newport Pier to the east jetty of the Santa Ana River,
a distance o f a little more than 2.3 miles. In general, the movement of sand along a
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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.
Figure 1. Recent aerial photograph of the subject site. Note the 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 60 years
as a result of beach replenishment in the 1930's with sand from Newport Harbor and the
groin field. 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 325 feet. The narrowest recorded beach width occurred in 1965
(approximately 300 feet) prior to the beach stabilization and nourishment efforts. During
typical summer beach conditions, the beach width is in excess of 350 feet. Measurements
during our June 12, 2019 site inspection indicate that the mean high tide line is ~387 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
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in front of the subject site is typically over 350 feet wide and has provided more than
adequate protection for the property over the last several decades. In the recent 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.
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 W ater (MHW ). The units of
measurement in this report are feet (ft), pounds force (lbs), and seconds (sec). The NOAA
Nautical Chart #18746 was used to determine bathymetry. Beach profile data was
reviewed from USACOE (2002). Aerial photographs, taken semi-annually from 1972
through 2019, were reviewed for shoreline changes. Site elevations relative to NAVD88
were taken from a site survey by Apex Land Surveying Inc., dated 3/13/19. Development
plans were provided by Eric Olsen Design.
SITE BEACH EROSION AND WAVE ATTACK
In order to determine the potential for wave runup to reach the site, historical aerial oblique
photographs dating back to 1972 were reviewed. None of the photographs showed that
wave runup reached the site. Figure 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 March 2, 2018,
shows what could be described as the “normal” beach width (about 400 feet). A review of
the annual aerial vertical photographs over the last 47 years shows a wide beach even
though the photos were taken in the winter and spring, when the beach is seasonally the
narrowest. None of the reviewed photographs show water reaching within 300 feet of the
site. Based upon review of the aerial photographs, it is highly unlikely that the shoreline will
erode back to the site and allow direct wave attack on the existing or proposed
development. Based upon interviews with long-term local residents, the subject site has
not been subject to wave runup during the last 60 years. The residence has not flooded
from ocean water or from surface drainage due to its elevation relative to the city street
drainage paths. The adjacent city street is lower than the lowest grade on site. In the
future, wave runup 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 March 2018 (note the wide beach).
WAVE RUNUP AND OVERTOPPING
W ave runup is defined as the vertical height above the still water level to which a wave will
rise on a structure (beach slope) of infinite height. Overtopping is the flow rate of water
over the top of a finite height structure (the steep beach berm) as a result of wave runup.
As waves encounter the beach at the subject site, water has the potential to rush up, and
sometimes crest, the beach berm. In addition, beaches can become narrower due to a
long-term erosion trend and sea level rise. Often, wave runup and overtopping strongly
influence the design and the cost of coastal projects.
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Figure 4. W ave runup terms from ACES analysis.
W ave 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), and updated as needed. The shoreline throughout southern California and fronting
this property have experienced many extreme storms over the years. These events have
impacted coastal property and beaches depending upon the severity of the storm, the
direction of wave approach and the local shoreline orientation. The focusing of incoming
waves on the Newport Beach shoreline is controlled primarily by the Newport Submarine
Canyon. Historically, the section of Newport Beach from 25 Street to 40 Street hasthth
experienced extreme storm wave erosion due to focusing of the waves by the canyon. The
ACES analysis was 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
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Seymour of the Scripps Institution of Oceanography as a “400-year recurrence.” The
wave runup conditions considered for the analysis use the maximum unbroken wave at the
shoreline when the shoreline is in an eroded condition.
The National Oceanographic and Atmospheric (NOAA) National Ocean Survey tidal data
station closest to the site is located at Los Angeles Harbor (Station 94106600). The tidal
datum elevations are as follows:
Mean High W ater 4.55 feet
Mean Tide Level (MSL) 2.62 feet
Mean Low W ater 0.74 feet
NAVD88 0.0 feet
Mean Lower Low W ater -0.2 feet
During storm conditions, the sea surface rises along the shoreline (super-elevation) and
allows waves to break closer to the shoreline and runup on the beach. Super-elevation of
the sea surface can be accounted for by: wave set-up, wind set-up and inverse barometer,
wave group effects and El Niño sea level effects. The historical highest ocean water
elevation is +7.72 feet NAVD88 on January 10, 2005.
Future Tide Levels Due to Sea Level Rise
The California Coastal Commission (CCC) SLR Guidance document recommends that a
project designer determine the range of SLR using the “best available science.” 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
el at, 2014). This update included SLR estimates and probabilities for Los Angeles the
closest SLR estimates to Newport Beach. These SLR likelihood estimates are provided
below in Figure 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 estimate to meet or exceed the 1991-2009 mean, based upon the best available
science.
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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,” 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. 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 has approved the use of “low risk aversion”
scenario, which is 1.3 feet to 3.2 feet by the year 2100. If 1.3 and 3.2 feet are added to
this 7.7 feet NAVD88 elevation, then future design maximum water levels of 9.0 feet
NAVD88 and 10.9 feet NAVD88 are determined.
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 are 8.5 feet and 10.4 feet,
based upon a maximum scour depth at the toe of the beach slope of 0.5 feet NAVD88 and
water elevations of +9.0 feet NAVD88 and +10.9 feet NAVD88), then the design wave
heights (0.78xwater depth) will be about 7 feet and 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
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feet SLR case will be considered with the elevation of the beach berm adjusted to +14.5
feet NAVD88. Table I, Table II, and Table III are the ACES output for these three SLR
design conditions.
Table I
Table II
Table III
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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 350 feet away, so for the ~5 feet of SLR case, the wave bore
may travel about 130 feet from the shoreline, which is well short of the site. Rather than
being inundated by sea level rise, the beach and the nearshore will readjust to the new
level over time, such that waves and tides will see the same profile that exists today. This
is the principle of beach equilibrium and is the reason why we have beaches today even
though sea level has risen over 200 feet in the last 10,000 years. The overtopping
waters over the next 75 years 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. W hile this study is not specific to
the west Newport Beach site, it provides a first order analysis for the area. Figure 6 shows
the tsunami runup in the southern California bight. The maximum tsunami runup in the
west 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.
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Figure 6. Taken from Legg, et al. (2002). Note the maximum wave runup in the
west Newport Beach area is less than 2 meters.
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
assessm ent of the probability of reaching the projected height (probabilistic
hazard assessm ent) 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.
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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
the maximum short-term erosion rate at the subject site. There is no long-term erosion at
the site. The short-term erosion rate is calculated to be ~2.0 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 150 feet over the 75 year life of the development. The site is currently 387 feet
from the shoreline. If the beach retreats 150 feet in the next 75 years then the site will be
~237 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.
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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, http://walrus.wr.usgs.gov/coastal_processes/cosmos/. Using the modeling program
the vulnerability of the site to three different SLR scenarios and the100 year storm can be
assessed. However, the following are the limitations as to the use of the CoSMoS model.
Inundated areas shown should not be used for navigation, regulatory, permitting,
or other legal purposes. The U.S. Geological Survey provides these data “as is” for
a quick reference, emergency planning tool but assumes no legal liability or
responsibility resulting from the use of this information.
Figure 9 is the output of the CoSMoS program. The modeling shows that the streets,
including the main arterial street, will flood during the 100 year event with 125 cm (~4.1
feet) of SLR. The site may experience minor flooding. The flood waters will come from the
bay and not from the ocean. The lowest proposed finished floor is at +11.0 feet NAVD88
and above the adjacent street flow line of 9.2 feet NAVD88.
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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, which is currently the 2018 COPC
Report.
Using the latest CCC SLR guidance and the City of Newport Beach City Council SLR
guidance, the range of estimate over the project design life that range in the year ~2095
is between 1.3 feet and 3.2 feet. In addition, the analysis herein considered a less than
“likely” SLR of about 5 feet. This is the sea level rise range for the proposed project, 1.3
feet to 5.1 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
~5 feet of SLR. The proposed finished floor elevation of +11 feet NAVD88 is above the
maximum future water elevation which includes 3.2 feet of SLR. If SLR exceeds 3.2 feet
the lower 18 inches of the structure will need to be waterproofed, but only if Newport Bay
waters are allowed to reach the site. 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
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document provides very little means or methods for predicating shoreline erosion due to
SLR. If a very conservative future erosion rate due to SLR of 2.0 ft/yr is used, then the
shoreline will move about 150 feet over the life of the development. The site is over 350
feet from the shoreline. Rather than being inundated by sea level rise, the beach and the
nearshore will readjust to the new level over time such that waves and tides will see the
same profile that exists today. This is the principle of beach equilibrium and is the reason
why we have beaches today even though sea level has risen over 200 feet in the last
10,000 years. The proposed project is reasonably safe from shoreline erosion due to the
site distance from the shoreline.
Step 3. Determine how the project may impact coastal resources, considering the
influence of future sea level rise upon the landscape as well as potential impacts of
sea level rise adaptation strategies that may be used over the lifetime of the project.
The project will not impact coastal resources considering sea level rise.
Step 4. Identify alternatives to avoid resource impacts and minimize risks throughout
the expected life of the development.
The project does not impact resources and minimizes flood risk through the project design.
Step 5. Finalize project design and submit CDP application.
The project architect will incorporate this report into the design.
Coastal Hazards Report shall include (NBMC 21.30.15.E.2):
i. A statement of the preparer’s qualifications;
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.
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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. The United States Geological Survey (USGS) provides the
most a comprehensive assessment of shoreline change including this section of coastline.
The USGS short-term erosion rate is calculated to be ~2.0 ft/yr or 150 feet over the 75
year life of the development. The site is currently 380 feet or more from the shoreline. If
the beach retreats 150 feet in the next 75 years then the site will be 230 feet from the
shoreline. A beach width of 200 feet or greater is recognized as sufficient to protect the
back shore from extreme events. The site is safe from shoreline erosion over the design
life of the development due to the significant setback from the current shoreline and future
shoreline with SLR. The proposed development will not need shore protection over the
life of the development
2. High tide conditions, combined with long-term (75 year) projections
for sea level rise;
Using the latest CCC SLR guidance and the City of Newport Beach City Council SLR
guidance, the range of estimate over the project design life that range in the year ~2094
is between 1.3 feet and 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, 1.3
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 1.3 and 5.1 feet are added to this 7.7 feet NAVD88 elevation, then future
design maximum water levels (“high tide conditions”) of 9 feet NAVD88 and 12.8 feet
NAVD88 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 ~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
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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 350 feet away, so for the
largest SLR case, the wave bore may travel about 130 feet from the shoreline which is well
short of the site. Rather than being inundated by sea level rise, the beach and the
nearshore will readjust to the new level over time, such that waves and tides will see the
same profile that exists today. This is the principle of beach equilibrium and is the reason
why we have beaches today even though sea level has risen over 200 feet in the last
10,000 years. The overtopping waters over the next 75 years most likely will not reach the
subject site, even under the extreme design conditions and maximum possible shoreline
erosion.
4. An analysis of bluff stability; a quantitative slope stability analysis
that shows either that the bluff currently possesses a factor of safety
against sliding of all least 1.5 under static conditions, and 1.1 under
seismic (pseudostatic conditions); or the distance from the bluff edge
needed to achieve these factors of safety; and
There is no bluff fronting the site. This condition does not occur at the site.
5. Demonstration that development will be sited such that it maintains
a factor of safety against sliding of at least 1.5 under static conditions
and 1.1 under seismic (pseudostatic) conditions for its economic life
(generally 75 years). This generally means that that setback necessary
to achieve a factor of safety of 1.5 (static) and 1.1 (pseudostatic) today
must be added to the expected amount of bluff erosion over the
economic life of the development (generally 75 years);
There is no bluff fronting the site. There is no potential for sliding.
iv. On sites with an existing bulkhead, a determination as to whether the
existing bulkhead can be removed and/or the existing or a replacement
bulkhead is required to protect existing principal structures and adjacent
development or public facilities on the site or in the surrounding areas; and
There is no bulkhead fronting the site. No shore protection will be necessary to protect
the development over the next 75 years.
v. Identification of necessary mitigation measures to address current
hazardous conditions such as siting development away from hazardous areas
and elevating the finished floor of structures to be at or above the base floor
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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 feet of SLR. The proposed finished floor elevation of
+11.0 feet NAVD88 is at reasonably safe for SLR up to 3.2 feet. Site drainage from non-
ocean waters is provided by the project civil engineer. If a future erosion rate due to SLR
of 2.0 ft/yr is used, then the shoreline will move about 150 feet over the life of the
development. The site is over 350 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.
LCP COMPLIANCE DISCUSSION
The proposed new residential development is located over 350 feet from the current
shoreline and will not be impacted by shoreline erosion over the design life of the structure.
It is unlikely that wave runup or overtopping will reach the development over the design life.
The project includes a ~3.0 feet high privacy wall along the seaward property line. In the
unlikely event that the shoreline is eroded back to near the site, and wave overtopping bore
reaches the site, this wall would prevent wave flooding from reaching the development.
The project avoids flood hazards due to is location away from the shoreline, the elevation
of the finished floor of the development above the beach and site grades, and the
protection afforded by the privacy wall (flood shield). The proposed finished floor elevation
is at +11.0 feet NAVD88. The project incorporates building materials (concrete and other
waterproof materials) that are resilient to temporary flooding and can be adapted for
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5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
additional waterproofing in the future, if necessary. Future adaptation could include a new
waterproof composite material (plastic/fiber glass) siding to the entire building or available
flood/dam systems (Quick Dam) to exclude water from coming onto the site. The project
is designed and sited to avoid coastal hazards per Newport Beach LCP Flood Hazard
Policies and CLUP Policy 2.8.1-2. The project as proposed minimizes risks to life and
property due to coastal hazards and will not require a shoreline protective device over the
project economic life (75 years) per CLUP Policy 2.8.6-10.
CONCLUSIONS
•There is a very wide (>350 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 very conservative FUTURE retreat rate of 2.0 feet/year is used, it would account
for about 150 feet of retreat over the life of the structure. This conservative retreat
rate will not reduce the beach to less than 225 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 significant wave overtopping in the recent past.
•The proposed finished first floor (FF) elevation for the structure is above the street
flow line (landward of the residence).
•The current mean high tide line is about 387 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.
•The site is protected from wave overtopping by a ~3.0 feet high privacy wall at the
seaward property line in the unlikely event that wave runup reaches the site over the
project economic life (75 years).
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
GeoSoils Inc.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
device over the life of the proposed development. There are no recommendations
necessary for avoidance or minimization of coastal hazards.
LIMITATIONS
Coastal engineering is characterized by uncertainty. Professional judgements presented
herein are based partly on our evaluation of the technical information gathered, partly on
our understanding of the proposed construction, and partly on our general experience. Our
engineering work and judgements have been prepared in accordance with current
accepted standards of engineering practice; we do not guarantee the performance of the
project in any respect. This warranty is in lieu of all other warranties express or implied.
Respectfully Submitted,
_______________________
GeoSoils, Inc.
David W . Skelly, MS
RCE #47857
*The term "certify" is used herein as defined in Division 3, Chapter 7, Article 3, § 6735.5. of the C alifornia
Business and Professions Code (2007).
GeoSoils Inc.20
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
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