HomeMy WebLinkAbout20190208_GeoSoils Coastal Hazard Study 2-4-2019PA2019-024I
February 4, 2019
Mr. & Mrs. Pedicini
1526 East Oceanfront
Newport Beach, CA 92661
GeoSoils Inc.
SUBJECT: Coastal Hazard and Wave Runup Study, 1520 East Oceanfront, Newport
Beach, California.
Dear Mr. & Mrs. Pedicini:
At your request, GeoSoils, Inc. (GSI) is pleased to provide this coastal hazard and wave
runup study for the property located at 1520 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 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 1520 East Oceanfront, Newport Beach, California. It is a
rectangular shaped parcel approximately 40 feet wide by -90 feet long with an existing
residential structure. Figure 1 is an aerial photograph of the site taken in 2017
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 coastal
dune, and a wide sandy beach (approximately 400 feet to ocean), and the Pacific Ocean.
This shoreline is located between the Balboa Pier and the west jetty of Newport Bay
entrance, 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
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 2
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. Subject site in 2017. Note the vegetated sand dunes fronting the site, and 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 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 350 feet.
The narrowest beach width occurred in 1965 (approximately 400 feet) prior to the beach
stabilization and nourishment efforts. During typical summer beach conditions, the beach
width is in excess of 400 feet. Measurements during our site inspection indicate that the
mean high tide line is -420 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 about 400 feet wide and has provided more than adequate
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 3
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.
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 #187 46 was used to determine bathymetry. Beach profile data was reviewed
from USACOE (2002). Aerial photographs, taken semi-annually from 1972 through 2018,
were reviewed for shoreline changes. Site elevations relative to NAVD88 were taken from
a site survey by Apex Land Surveying Inc., dated 5/25/18. Development plans were
provided by Brandon Architects.
SITE BEACH EROSION AND WAVE ATTACK
In order to determine the potential for future wave runup to reach the site, historical aerial
photographs over the last five decades were reviewed. None of the photographs showed
that wave runup reached the site over the five-decade time frame. Figure 2, taken in
January 1980, shows the beach in front of the property including the dunes. These dunes
are 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 dunes, nor
has wave runup reach the dunes. Figure 3, taken February 2, 2000, shows what could be
described as the normal beach width (about 400 feet). Figure 4, downloaded from Google
Earth shows the site at the area from the Pier to the Newport Bay jetties in April 2018. Our
review of the annual aerial photographs over the last 50 years shows a wide beach seaward
of the site, 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 near the site allowing direct wave attack on the
proposed residence.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 4
Figure 2. Subject site, dunes, and very wide beach in 1980.
Figure 3. Subject site, dunes, and very wide beach in 2000. The photos show no change
over the 20-year period.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 5
Figure 4. Subject site, sports field, and very wide beach in April 2018. The photos show
no change over the 50-year period.
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 run up. As
waves encounter the beach at the subject site, water has the potential to rush up, and
sometimes crest, the beach berm. In addition, beaches can become narrower due to a
long-term erosion trend and sea level rise. Often, wave runup and overtopping strongly
influence the design and the cost of coastal projects.
Wave runup and overtopping is calculated using the US Army Corps of Engineers
Automated Coastal Engineering System, ACES. ACES is an interactive computer based
design and analysis system in the field of coastal engineering. The methods to calculate
runup and overtopping, implemented within this ACES application, are discussed in greater
detail in Chapter? of the Shore Protection Manual (1984) and Coastal Engineering Manual
(2004 ). The overtopping estimates calculated herein are corrected for the effect of onshore
winds. Figure 5 is a diagram showing the analysis terms.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 6
Figure 5. ACES input and output terms diagram.
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 25th Street to 40 1h Street has experienced
extreme storm wave erosion due to focusing of the waves by the canyon. The ACES
analysis was performed on an extreme wave condition when the beach is in a severely
eroded condition. However, it is important to point out that the waves during the 1982-83
El Nino 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:
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
Mean High Water
Mean Tide Level (MSL)
Mean Low Water
NAVD88
Mean Lower Low Water
GeoSoils Inc.
4.55 feet
2.62 feet
0.74 feet
0.0 feet
-0.2 feet
7
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 Nino 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 EICI reported that the elevation of 7.71 feet NAVD88 is the 1 %
water elevation. For this analysis the 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 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 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.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 8
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 4.1 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 Nino, and the 1997 El Nino events, and is therefore,
consistent with the methodology outlined in the CCC Sea-Level Rise Policy Guidance
document. The Newport Beach City Council recently 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 feet SLR case will
be considered with the elevation of the beach berm adjusted to +14.5 feet NAVD88. Table
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc.
I, Table II, and Table Ill are the ACES output for these three SLR design conditions
Table I
ACES Mode: Sin!Jle Case Functional Area: Wave -Structure Interaction
Application: Wave Runup and Overtopping on ImperlJll':ahle i;tructures
Item Unit
Incident Wave Height Hi: ft
I.Jave Period T: sec
COTRN of Nearshore Slope COT(¢):
Water Depth at Structure Toe ds: rt
COTAN of Structure Slope COT(0):
Structure Height Above Toe hs: rt
Wave Runup R:
Onshore Wind Velocit\J U:
Deepw.,ter Wave Height 110:
Relative Height ds/H0:
I.Jave Steepness 110/CgT"Z):
Overtoppi11g Coeff icicnt o::
Overtopping Coefficient Qstar0:
Ovcrtopping Rate ri:
rt
ft/sec
ft
Table II
Incident 1-klve Height Hi:
Wave Period T:
COTAN of Nearshore Slope COT(¢):
W..,ter Depth at Structure Toe ds:
COTAN of StJoucture Slope COTCe):
Structure Height Above Toe hs:
1-klve Hu11up H:
Onsl10re IJind Velocity U:
Deepwater Wave Heiglit H0:
llcliltive Height ds/110:
Wave Steepness 110/Cr,1"2):
Overtopp i ng Coefficient o: :
Ovm-topping Co1!fficir!nt Qst.ft.r0:
Overiopping Rate Q:
ft
sec
ft
ft
ft
ft/sec
ft
Table II
Incident w..,...._~ Height Hi:
Wave Period T:
COTAN of Hedrsliore Slope C01'(9'):
I-kiter Depth at Structure Toe ds:
COTAH of Structure Slope COT(el:
Structure Height Above Toe )ls:
I.Jdve Runup n:
Onshore Wind Vclocit!) ll:
Deepwater Wave Heiglit H0:
Relative tlel!Jht ds/li0:
Wave 8tee1lness 110/(gT"?.):
Overtopping Coefficient o::
Overlapping Coefficient Qstar0:
Overtoppin!J !late Q:
ft
sec
rt
ft
ft
ft/sec
ft
8.998
16.878
1.160
2.013
0.000399
0.070000
0.070000
2.327
8.263
16.878
5.818
1.861
0.oo;xJOO
0.070000
0.070000
11.575
8.962
16.878
7.077
1.738
0.0009?8
0.070000
0.070000
15.607
,.w.-.-.-.-,,-.-.-.·.-.·.-.-.-.•.-.w.-.,.•.wu.•.-.. •.•.•.-.-. ....-,•.•.-.-.-.-.·.-.-.-.-.w,y."j
Soooth Slope
Runup and
Overtopph1!J
1520 EAST
OCEANFRONT
NEWPORT
BEACH
1.3 FT SLR
1520 EAST. \
OCEANFRONT!
Newport I
Beach
3.2 FT SLR
1520 EAST
CEANFRONT
NEWPORT
BEACH
rvS Ff SLR
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
9
PA2019-024
GeoSoils Inc. 10
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 ft3/s-ft. For the calculated overtopping
rate (Q=q), the height of water and the velocity of this water can be calculated using the
following empirical formulas provided by the USACOE (Protection Alternatives for Levees
and Floodwalls in Southeast Louisiana, May 2006, equations 3.1 and 3.6).
For SLR of-5 feet with an overtopping rate of 15.6 ft3/s-ft, the water height h 1= 2.9 feet and
the velocity, vc = 7.9 ft/sec. The runup water is not a sustained flow, but rather just a pulse
of water flowing across the beach. The 2004 USACOE Coastal Engineering Manual (CEM)
states as a wave bore travels across a sand beach, the height of the bore is reduced.
Based upon observations, this is about 1-foot reduction in bore height every 25 to 50 feet.
The site is about 400 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 subiect 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 modified, and reduced in height
by the land/dune seaward of the site. Due to the infrequent nature and the relatively low
500-year recurrence interval tsunami wave height, setback from the ocean, and the
elevation of the proposed improvements, the site is reasonably safe from tsunami hazards.
It should be noted that the site is mapped within the limits of the California Office of
Emergency Services tsunami innundation map, Newport Beach Quadrangle (State of
California 2009). The tsunami inundation maps are very specific as to their use. Their use
is for evacuation planning only. The limitation on the use of the maps is clearly stated in
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 11
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 pe1formance, in an earthquake or
tsunami, of any structure within or outside of the projected inundation area.
The CalOES maps model the inundation of a tsunami with an approximate 1,000 year
recurrence interval (0.1 % event). The Science Application for Risk Reduction (SAFRR)
tsunami study headed by USGS investigated a tsunami scenario with a 200-240 year
recurrence interval. The SAFRR modeling output is shown in Figure 7 and reveals that the
site is not within the more probable (0.4% event) tsunami inundation zone. The City of
Newport Beach and County of Orange have clearly marked tsunami evacuation routes for
the entire Newport Beach/Bay area.
Figure 7. SAFRR tsunami modeling output for the site.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 12
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 8, 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. Recent Coastal Commission staff reports have used an estimated erosion of 1 foot
of SLR results in 40 feet of shoreline retreat for similar coastal settings. This has been used
with no technical justification and is likely a conservative estimate. Even if this rate were
used with 3.2 feet of SLR (the highest of the City of Newport Beach approved range) the
retreat would be 128 feet over the 75 year life of the development. The site is currently
about 400 feet from the shoreline. If the beach retreats 128 feet in the next 75 years then
the site will be -272 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.
Hunti\1gton
j 40 --1 ... 1 .............................. ) .. State.ltearth.~
ACCRETIOf ' i West Ne;1wport Bem~h
1520 East
Ocealnfront
---
"'"'""""'"'""'"""}·""'""''-'"""'"'"'""-'"'''"""'"'"""""""""'"""'"''"''
2 METEmi/vEAR
!-. ~
Figure 8. Shoreline change rate in meters per year from USGS 2006.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 13
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 West Balboa, the main arterial street, will flood during the 100 year event with 125
meter (-4.1 feet) of SLR. The site may flood slightly. However, the area flooding will come
from the bay and not from the ocean. The lowest habitable finished floor is at +15. 75 feet
NAVD88 and above the adjacent flow line in the alley. 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. However, if SLR exceeds 7 feet it may
be necessary to waterproof the lower -18 inches of the structure to eliminate short term
flooding impact on the structure, in the future.
Figure 9. Output for USGS CoSMoS vulnerability modeling.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 14
CCC SLR GUIDANCE INFORMATION
Step 1. Establish the projected sea level rise range for the proposed project's
planning horizon using the best available science, which is currently the 2012 NRC
Report.
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 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 +15. 7 4 feet NAVD88 is above the
maximum future water elevation. If SLR exceeds 7 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 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 128 feet over the life of
the development under 3.2 feet SLR. The site is about 400 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.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 15
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. 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. The site is about 400 feet from the shoreline. If the beach retreats 128 feet
in the next 75 years then the site will be 272 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
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 16
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 Nino and the 1997
El Nino 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
overtopping rate is 15.6 ft3/s-ft, the water height h 1 is 2.9 feet, and the velocity, vc is 7.9
ft/sec. The runup water is not a sustained flow, but rather just a pulse of water. The 2004
USACOE Coastal Engineering Manual (CEM) states as a wave bore travels across a sand
beach, the height of the bore is reduced. Based upon observations, this is about 1-foot
reduction in bore height every 25 to 50 feet. The site is about 400 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.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 17
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
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
+15. 75 feet NAVD88 is at reasonably safe for SLR up to 6. 7 feet. 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 about 400 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
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 18
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 (-400 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 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 with 3.2 feet
SLR. The site is about 400 feet from the shoreline. The beach would be about 272
feet wide (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 about 400 feet from the site and it is unlikely that
over the life of the structure that the mean high tide line will reach within 270 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.
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc.
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).
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155
PA2019-024
GeoSoils Inc. 20
REFERENCES
Aerial Fotobank, San Diego web site www.landiscor.com.
Coastal Engineering Manual 2004, US Army Engineer Waterways Experiment Station,
Coastal Engineering Research Center, US Government Printing Office, Washington, DC.
Everest International Consultants, Inc., 2011, Assessment of seawall structure integrity and
potential for seawall over-topping for Balboa Island and Little Balboa Island, main report,
No Project No., dated April 21.
Kopp, Robert E., Radley M. Horton Christopher M. Little Jerry X. Mitrovica Michael
Oppenheimer D. J. Rasmussen Benjamin H. Strauss Claudia Tebaldi Radley M. Horton
Christopher M. Little Jerry X. Mitrovica Michael Oppenheimer D. J. Rasmussen Benjamin
H. Strauss Claudia Tebaldi "Probabilistic 21st and 22nd century sea-level projections at a
global network of tide-gauge sites" First published: 13 June 2014 Legg, Mark R., Borrero,
Legg, Mark R., Borrero, Jose C., and Synolakis, Costas E., Evaluation of tsunami risk to
southern California coastal cities, in The 2002 NEHRP Professional Fellowship Report.
Shore Protection Manual, 1984, 4th ed. 2 Vols, US Army Engineer Waterways Experiment
Station, Coastal Engineering Research Center, US Government Printing Office,
Washington, DC.
State of California, County of San Diego, 2009, "Tsunami Inundation Map for Emergency
Planning, Newport Beach Quadrangle," 1 :24,000 scale, dated June 1.
USACOE (US Army Corps Of Engineers), 1986, "Southern California Coastal Processes
Data Summary" Ref# CCSTW 86-1.
USACOE (US Army Corps Of Engineers), 2002, Coast of California Storm and Tidal Waves
Study South Coast Region, Orange County.
USACOE, 2013, "Incorporating Sea Level Change in Civil Works Programs," ER 1100-2-
8162, dated 31 December.
USGS 2006, "National Assessment of Shoreline Change Part 3: Historical Shoreline
Change and Associated Coastal Land Loss Along Sandy Shorelines of the California
Coast", Open File Report 2006-1219,
5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155