HomeMy WebLinkAboutPA2022-0295_20221205_Coastal Hazards Report dated 11-07-22
P M A C O N S U L T I N G , I N C .
CONSULTING STRUCTURAL ENGINEERS
28161 Casitas Ct. PH. (714) 717-7542
Laguna Niguel, CA 92677
e-mail: consulting@pma-bg.com
November 7, 2022
Ozzie Almendarez
OHA CONSTRUCTION
31234 W. Nine Drive
Laguna Niguel, CA 92677
RE: COASTAL HAZARDS ANALYSIS REPORT FOR CDP
6104 West Oceanfront
City of Newport Beach, County of Orange
PMA Job #51322
Dear Mr. Almendarez,
PMA Consulting, Inc. is pleased to provide this report regarding Coastal Hazards Analysis in for the
proposed development at the subject site. The site is adjacent to Pacific Ocean; thus, it may be subject to
Coastal Hazards such as, flooding, wave runup, and erosion. This study investigates the potential for the
aforementioned hazards to impact the proposed development on the site over the next 75 years and addresses
compliance with Coastal Hazards Analysis Report requirements and standards of NBMC Section 21.30.15.E.2.
STATEMENT OF THE PREPARER’S QUALIFICATIONS
Plamen Petrov, P.E., the preparer of the Coastal Hazards Analysis Report on this project, holds
Master of Science in Structural Engineering from University of Architecture, Structural Engineering &
Geodesy of Sofia, Bulgaria, and is a Licensed Civil Engineer by the State of California Certificate No.
C66947. For the last 22 years of his professional career, he has been actively involved in the design and
entitlement of many Waterfront Developments such as custom homes, seawalls, piers, platforms, floating
docks and marinas. A great number of Coastal Hazards Analysis Reports prepared by him have been
reviewed and accepted/approved by California Coastal Commission.
All the above being said, Plamen Petrov, P.E. shall be considered a qualified preparer for the Coastal
Hazards Analysis Report on this project.
Requirements in Appendix A for Step 1:
Establish the project sea level rise range for the proposed project’s planning horizon (life of
project) using the current best available science.
The State of California Sea-Level Rise Guidance 2018 update developed by the Ocean Protection
Council in close coordination with Policy Advisory Committee with representation
from California Natural Resources Agency, the Governor’s Office of Planning and Research, and the
California Energy Commission provides a bold, science-based methodology for state and local governments
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to analyze and assess the risks associated with sea-level rise, and to incorporate Sea-Level Rise into their
planning, permitting, and investment decisions, and it is considered the current best available science.
As reflected in the clouded area of the enclosed Table 28, based upon direct interpolation of the
data for High emissions 2090 & 2100 and Low Risk Aversion, over the project’s planning horizon of 75
years, the estimated Sea-Level Rise (SLR) for year 2097 shall be approximately 3.05’, which is the Sea-
Level Rise for the proposed project. Based on the highest high tide of +7.90’MLLW (7.70’NAVD88)
recorded in the project area, the above established Sea-Level Rise will account for bay water level of
+10.75’NAVD88.
As of March 23, 2021, City Council of City of Newport Beach has adopted new standards
establishing a minimum top of bulkhead/seawall elevation based on 5-year increments, reflected in
Table 2 below from City of Newport Beach Waterfront Projects Guidelines and Standards Harbor
Design Criteria for Commercial and Residential Facilities 2021 Edition.
Requirements in Appendix A for Step 2:
Determine how physical impacts from sea level rise may constrain the project site, including
erosion, structural and geologic stability, flooding, and inundation.
According to the enclosed Architectural Site Plan A-0.0, 1st Floor Finished Slab Elevation of the
proposed development is at +14.37’ NAVD88=+14.57’MLLW which follows the Base Flood Elevation
established for the area. Based on the SLR established in Step 1 above, 1st floor of the proposed
structure will remain above High Tide Sea level for more than 75 years, based on Low Risk Aversion.
As we well know, majority of the public streets in Newport Bay area are currently at much lower
elevations than the subject site and they will flood due to SLR way before the development on this site
becomes subject to flooding.
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INTRODUCTION
The subject site is currently separated from the shoreline by an approximately 350 feet wide relatively
flat sandy beach, as reflected on the following Photo. The area of the proposed development has been mapped
by FEMA as Map Zone VE 14, with a based flood elevation (BFE) of +14.00’ NAVD88. This implies, that
the top of the beach face slope at shoreline at elevation approximately +14.55’NAVD88, as reflected on the
enclosed Topographic Survey, is approximately 6” higher than the water which travels across the beach,
towards the site, to the landward extent of FIRM Mapped VE Zone.
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The FIRM estimates that the VE 14 Zone is about 250 feet from the seaward property line with a BFE of
+14’NAVD88. Site natural grades are at average about +14.55’NAVD88. In reality, the water height at
approximately +14’NAVD88 berm crest will be way lower than the site elevation, based on the USACOE
CEM statement that when a typical wave bore travels across a sandy beach, it loses about 1’ of height every
25 feet to at most 50 feet horizontally.
FLOODING HAZARD
The primary hazard due to flooding from the ocean waters for this site, like majority of the sites
located adjacent to Pacific Ocean, would be due to long term Sea-Level Rise. The current water levels in
Newport Bay are reflected on the enclosed Datums for Newport Bay Entrance.
According to the enclosed Architectural Site plan A-0.0, 1st Floor Finished Slab Elevation of the
proposed development is at +14.37’ NAVD88=+14.57’MLLW.
.
While Sea-Levels have been Rising for decades, higher rates of raise are forecast for the coming
century because of climate change – see enclosed table 28. Increases can be attributed to warmer temperatures,
which cause water to expand, as well more liquid mass caused by melting of ice caps. Current estimates of
future Sea-Level Rise generally fall in the range of 1-3 ft for the year 2100. Global warming may impact
flooding in other ways as well. Warmer water could intensify North Pacific storms, bringing greater wind and
wave energy to shoreline in winter and higher intensity precipitation.
The Newport Beach Peninsula portion of the Pacific Institute California Flood Risk Map is shown
herein as OE S Quadrangle. The dark blue colored areas show the areas where a 100-year Sea-Level Rise of
55 inches is added to the existing FEMA coastal flood elevation shown in light blue. Obviously, the entire
Newport Bay area will be affected if sea level rises 55 inches by the year 2100.
If the sea level rises in the next several decades as currently estimated, regional measures to
mitigate the potential flooding hazard shall be taken. Since 1st Floor Finished Slab Elevation of the
proposed development is at +14.37’ NAVD88=+14.57’MLLW, it will remain below the High Tide for
more than 75 years. In the event that SLR prediction of 6.7’ (Medium-High Risk Aversion) for year
2100 holds true or gets higher, block walls along site property lines with minimum top of wall elevation
of 14.4’NAVD88 will act as a protection device. Thus, the proposed development shall not be a subject
to Flooding over the economic life of the structure.
WAVE RUNUP
Wave runup is the uprush of water from wave action on a shore barrier intercepting Stillwater level.
On steeply sloped shorelines, the rush of water up the surface of the natural beach, including dunes and bluffs,
or the surface of a manmade structure, such as revetment or vertical
wall can result in flood elevations higher than those of the crest of wind-driven waves. See Wave Runup
Sketch & Diagram below.
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During a storm, the sea level rises along the shoreline and allows for waves to break closer to the
shoreline and runup on the beach. As acknowledged in Flooding Hazard paragraph above, the historical
highest water elevation in Newport Beach is 7.90 feet above MLLW (approximately 7.70
feet above NAVD88).
For the highest SLR case, the calculated overtopping rate of the beach, under the eroded beach
conditions with 6.0 feet of future SLR is 15.6 ft³/s-ft. For the calculated overtopping rate (Q=q), the height of
water and the velocity of this water can be calculated using the empirical formulas provided by the USACOE
(Protection Alternatives for Levees and Floodwalls in Southeast Louisiana, May 2006, equations 3.1 and 3.6).
For SLR of 6.0 feet with an overtopping rate of 15.6 ft³/s-ft, the water height h = 2.9 feet and the 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 600 feet away, so for the 6.0 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. Due to this principle of beach equilibrium, we have beaches today, even though sea
level has risen over couple of hundred feet for the last ten thousand years.
It is unlikely that overtopping waters over the next 75 years will reach the subject site, even
under extreme weather conditions. Due to the sand profile in front of the site, even if some waters reach
the site, they will not cause erosion and/or damage, because of their relatively low velocity.
EROSION HAZARD
Erosion refers to the wearing or washing away of coastal lands. Beach erosion is a chronic problem
along many open ocean shores of the United States. To meet the needs for comprehensive analysis of
shoreline movement, the United States Geological Survey has conducted analysis of historical shoreline
changes along open ocean sandy shores of the conterminous United States and
has produced an Open-File Report 2006-1219 entitled “National Assessment of Shoreline Change Part 3:
Historical Shoreline Change and Associated Coastal land Loss Along Sandy Shorelines of the California
Coast”. The report looks at survey data of the following periods: 1800s, 1920s-1930s, and 1950s-1970s,
whereas the lidar shoreline is from 1998-2002. The report looks at both long-term and short-term changes.
According to the report, the average rate of long-term shoreline changes for the State of California was
0.2±0.1 m/yr., and accretional trend. The average rate of short-term shoreline change for the state was
erosional; with an average rate of -0.2±0.4 m/yr. The beach footprint of this site is stabilized and not subject
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to significant long-term erosion. Review and analysis of historical aerial photographs and field measurements
for seawall repairs in the area show no change in the position of the shoreline over the last several decades.
The future shoreline changes over the next 75 years are assumed to be the same as in the previous several
decades. However, there is a rapid rate of Sea-Level Rise predicted in the next 75 years. If that
prediction holds true, the rapid Sea-Level Rise may accelerate shoreline erosion, but it shall not impact
the structure on the subject lot over its economic life.
CONCLUSION
In conclusion, flooding, wave runup and erosion will not significantly impact this property over
the proposed life of the development. Thus, need for a shoreline protective devise other that the above-
mentioned site block walls is not anticipated over the economic life of the proposed structure to protect
it from flooding, wave runup or erosion.
The above conclusion was prepared based on the existing conditions, proposed drawings, current
projection of future Sea-Level Rise, and within the inherent limitations of this study, in accordance with
generally acceptable engineering principles and practices. We make no further warranty, either expressed or
implied.
PMA Consulting, Inc. appreciates the opportunity to be of service to you. Should you have any
questions regarding this report, please give us a call.
Respectfully submitted,
Plamen Petrov, P.E.
Principal
Enclosures:
Location Map
Aerial View
Topographic Survey
Architectural Site Plan A-0.0
Table 28: Projected Sea-Level Rise (in feet) for Los Angeles 2100 Low & Medium-High Risk Aversion
Table 28: Projected Sea-Level Rise (in feet) for Los Angeles 2097 Low Risk Aversion
Datums for Newport Bay Entrance
Newport Beach OE S Quadrangle
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Probabilistic Projections (in feet) (based on Kopp et al. 2014)
H++ scenario
(Sweet et al.
2017)
*Single
scenario
MEDIAN LIKELY RANGE 1-IN-20 CHANCE 1-IN-200 CHANCE
50% probability
sea-level rise meets
or exceeds…
66% probability
sea-level rise
is between…
5% probability
sea-level rise meets
or exceeds…
0.5% probability
sea-level rise meets
or exceeds…
Low
Risk
Aversion
Medium - High
Risk Aversion
Extreme
Risk Aversion
High emissions 2030 0.3 0.2 - 0.5 0.6 0.7 1.0
2040 0.5 0.4 - 0.7 0.9 1.2 1.7
2050 0.7 0.5 - 1.0 1.2 1.8 2.6
Low emissions 2060 0.8 0.5 - 1.1 1.4 2.2
High emissions 2060 1.0 0.7 - 1.3 1.7 2.5 3.7
Low emissions 2070 0.9 0.6 - 1.3 1.8 2.9
High emissions 2070 1.2 0.8 - 1.7 2.2 3.3 5.0
Low emissions 2080 1.0 0.6 - 1.6 2.1 3.6
High emissions 2080 1.5 1.0 - 2.2 2.8 4.3 6.4
Low emissions 2090 1.2 0.7 - 1.8 2.5 4.5
High emissions 2090 1.8 1.2 - 2.7 3.4 5.3 8.0
Low emissions 2100 1.3 0.7 - 2.1 3.0 5.4
High emissions 2100 2.2 1.3 - 3.2 4.1 6.7 9.9
Low emissions 2110* 1.4 0.9 - 2.2 3.1 6.0
High emissions 2110* 2.3 1.6 - 3.3 4.3 7.1 11.5
Low emissions 2120 1.5 0.9 - 2.5 3.6 7.1
High emissions 2120 2.7 1.8 - 3.8 5.0 8.3 13.8
Low emissions 2130 1.7 0.9 - 2.8 4.0 8.1
High emissions 2130 3.0 2.0 - 4.3 5.7 9.7 16.1
Low emissions 2140 1.8 0.9 - 3.0 4.5 9.2
High emissions 2140 3.3 2.2 - 4.9 6.5 11.1 18.7
Low emissions 2150 1.9 0.9 - 3.3 5.1 10.6
High emissions 2150 3.7 2.4 - 5.4 7.3 12.7 21.5
STATE OF CALIFORNIA SEA-LEVEL RISE GUIDANCE
APPENDIX 3: SEA-LEVEL RISE PROJECTIONS FOR ALL 12 TIDE GAUGES | 72
TABLE 28: Projected Sea-Level Rise (in feet) for Los Angeles
Probabilistic projections for the height of sea-level rise shown below, along with the
H++ scenario (depicted in blue in the far right column), as seen in the Rising Seas
Report. The H++ projection is a single scenario and does not have an associated
likelihood of occurrence as do the probabilistic projections. Probabilistic projections
are with respect to a baseline of the year 2000, or more specifically the average
relative sea level over 1991 - 2009. High emissions represents RCP 8.5; low emissions
represents RCP 2.6. Recommended projections for use in low, medium-high and
extreme risk aversion decisions are outlined in blue boxes below.
*Most of the available climate model experiments do not extend beyond 2100. The resulting
reduction in model availability causes a small dip in projections between 2100 and 2110, as well as
a shift in uncertainty estimates (see Kopp et al. 2014). Use of 2110 projections should be done with
caution and with acknowledgement of increased uncertainty around these projections.
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Probabilistic Projections (in feet) (based on Kopp et al. 2014)
H++ scenario
(Sweet et al.
2017)
*Single
scenario
MEDIAN LIKELY RANGE 1-IN-20 CHANCE 1-IN-200 CHANCE
50% probability
sea-level rise meets
or exceeds…
66% probability
sea-level rise
is between…
5% probability
sea-level rise meets
or exceeds…
0.5% probability
sea-level rise meets
or exceeds…
Low
Risk
Aversion
Medium - High
Risk Aversion
Extreme
Risk Aversion
High emissions 2030 0.3 0.2 - 0.5 0.6 0.7 1.0
2040 0.5 0.4 - 0.7 0.9 1.2 1.7
2050 0.7 0.5 - 1.0 1.2 1.8 2.6
Low emissions 2060 0.8 0.5 - 1.1 1.4 2.2
High emissions 2060 1.0 0.7 - 1.3 1.7 2.5 3.7
Low emissions 2070 0.9 0.6 - 1.3 1.8 2.9
High emissions 2070 1.2 0.8 - 1.7 2.2 3.3 5.0
Low emissions 2080 1.0 0.6 - 1.6 2.1 3.6
High emissions 2080 1.5 1.0 - 2.2 2.8 4.3 6.4
Low emissions 2090 1.2 0.7 - 1.8 2.5 4.5
High emissions 2090 1.8 1.2 - 2.7 3.4 5.3 8.0
Low emissions 2100 1.3 0.7 - 2.1 3.0 5.4
High emissions 2100 2.2 1.3 - 3.2 4.1 6.7 9.9
Low emissions 2110* 1.4 0.9 - 2.2 3.1 6.0
High emissions 2110* 2.3 1.6 - 3.3 4.3 7.1 11.5
Low emissions 2120 1.5 0.9 - 2.5 3.6 7.1
High emissions 2120 2.7 1.8 - 3.8 5.0 8.3 13.8
Low emissions 2130 1.7 0.9 - 2.8 4.0 8.1
High emissions 2130 3.0 2.0 - 4.3 5.7 9.7 16.1
Low emissions 2140 1.8 0.9 - 3.0 4.5 9.2
High emissions 2140 3.3 2.2 - 4.9 6.5 11.1 18.7
Low emissions 2150 1.9 0.9 - 3.3 5.1 10.6
High emissions 2150 3.7 2.4 - 5.4 7.3 12.7 21.5
STATE OF CALIFORNIA SEA-LEVEL RISE GUIDANCE
APPENDIX 3: SEA-LEVEL RISE PROJECTIONS FOR ALL 12 TIDE GAUGES | 72
TABLE 28: Projected Sea-Level Rise (in feet) for Los Angeles
Probabilistic projections for the height of sea-level rise shown below, along with the
H++ scenario (depicted in blue in the far right column), as seen in the Rising Seas
Report. The H++ projection is a single scenario and does not have an associated
likelihood of occurrence as do the probabilistic projections. Probabilistic projections
are with respect to a baseline of the year 2000, or more specifically the average
relative sea level over 1991 - 2009. High emissions represents RCP 8.5; low emissions
represents RCP 2.6. Recommended projections for use in low, medium-high and
extreme risk aversion decisions are outlined in blue boxes below.
*Most of the available climate model experiments do not extend beyond 2100. The resulting
reduction in model availability causes a small dip in projections between 2100 and 2110, as well as
a shift in uncertainty estimates (see Kopp et al. 2014). Use of 2110 projections should be done with
caution and with acknowledgement of increased uncertainty around these projections.
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Newport BeachNewport Beach
Costa MesaCosta MesaCosta MesaCosta MesaHuntington BeachHuntington Beach
¬«1
¬«55
¬«1
¬«55
117°52’30"W
117°52’30"W
117°55’0"W
117°55’0"W
117°57’30"W
117°57’30"W
118°0’0"W
118°0’0"W
33°37’30"N
33°37’30"N
33°35’0"N
33°35’0"N
33°32’30"N
33°32’30"N
33°30’0"N
33°30’0"N
407000mE
407000mE
08
08
09
09
410
410
11
11
12
12
13
13
14
14
15
15
16
16
17
17
18
18
419000mE
419000mE3707000mN37 07000mN08 08
09 09
3710 3710
11 11
12 12
13 13
14 14
15 15
16 16
17 17
18 18
19 19
3720 37203721000mN3721000mN
This information is being made available for informational purposes only. Users of this informationagree by their use to hold blameless the State of California, and its respective officers, employees,
agents, contractors, and subcontractors for any liability associated with its use in any form. This work
shall not be used to assess actual coastal hazards, insurance requirements, or property values
and specifically shall not be used in lieu of Flood Insurance Studies and Flood Insurance Rate Maps issued by the Federal Emergency Management Agency (FEMA).
Data Sources: US Geological Survey, Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Coastal ServicesCenter (CSC), Scripps Institution
of Oceanography, Phillip WIlliams and Associates, Inc. (PWA), US Department of Agriculture (USDA), California Coastal Commission, and National Aeronautics and Space Administration (NASA). Imagery from ESRI and i-cubed.
Created by the Pacific Institute, Oakland, California, 2009.
California Flood Risk: Sea Level Rise
00.511.520.25
Miles
01230.5
Kilometers
1:
2:
3:
4:
5:
6:
7:
8:
Seal Beach
Newport Beach
Tustin
not printed
Laguna Beach
not printed
not printed
not printed867
1 2 3
54
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£¤
")
¬«
Interstate
US Highway
State Highway
County Highway
Grid coordinates:
UTM Zone 11N meters
Adjoining Quadrangles:
Map extents match USGS 7.5 minute topographic maps
Project funded by the California Energy Commission’s Public Interest Energy Research Program, CalTrans,and the California Ocean Protection Council
Newport Beach OE S Quadrangle
NAD83 GCS degrees
Coastal Zone Boundary
Current Coastal Base Flood
(approximate 100-year flood extent)
Sea Level Rise Scenario Coastal Base Flood + 1.4 meters (55 inches)
Landward Limit of Erosion High Hazard Zone in 2100
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