HomeMy WebLinkAboutPA2023-0111_20230530_Coastal Hazards Report
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
May 25, 2023
Elizabeth Hanna
Brandon Architects
151 Kalmus Drive G-1
Costa Mesa, CA 92626
RE: COASTAL HAZARDS ANALYSIS REPORT FOR COASTAL
DEVELOPMENT PERMIT
Bob and Christine Nibeel; Applicant
206 Grand Canal
City of Newport Beach, County of Orange
PMA Job #53323
Dear Ms. Hanna,
PMA Consulting, Inc. is pleased to provide this report regarding Coastal Hazards Analysis for
the proposed development at the subject site. The site is adjacent to Newport Bay; 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 a 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. Since Year of 2000 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
1
governments 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 2098 shall be approximately
3.10’, which is the Sea- Level Rise for the proposed project. Based on the highest high tide of
+7.88’MLLW (7.70’NAVD88) recorded in the project area, the above established Sea-Level
Rise will account for bay water level of +10.80’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, top of slab at 1st floor of the
proposed development is at +9.00’ NAVD88=+9.20’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 until year of 2054, 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.
2
FLOODING HAZARD
The primary hazard due to flooding from the ocean waters for this site, like majority of the
sites located adjacent to Newport Bay, 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 Topographic Survey, top of Existing Seawall/Bulkhead in front of
the subject site is at an elevation of +8.62’NAVD88 (North American Vertical Datum of 1988).
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 4.1-6.7 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 top of slab elevation of the
proposed house will be at +9.00’ NAVD88, it will remain above the High Tide approximately
until year of 2054. Utilizing Flashings and Waterproofing for up to 23” above top of slab, as
reflected on the enclosed detail, and sandbags at openings, shall keep the building protected
from flooding until year of 2098.
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 below.
3
Due to its location, this site is not a subject to typical ocean waves and the associated wave
runup. Bay generated waves that may arrive at this site are very small wind waves and boat wakes.
These types of waves are generally dampened by the moored vessels and dock systems located in
front of the site and have no significant energy and runup effect. Tsunami type waves that approach
from the ocean shoreline will likely not reach the site for several reasons. There is no significant near
field source of a tsunami like the geologic conditions of some other places on Earth such as Japan, for
example. A far field tsunami reaching the ocean shoreline will likely not reach the site because of the
distance and developments between the shoreline and this site.
A near or far field tsunami propagating into Newport Bay proper would likely cause a seiche
or standing wave on the order of 1.3 feet traveling within the bay. At the highest anticipated tide in
Newport Beach of +7.88’MLLW this shall result in slight overtopping of the bulkhead/seawall. Due
to its very infrequent occurrence – 500-year recurrence interval – tsunami should not be
considered a significant impact over the life of the proposed structure -75 years.
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 change 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 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 & RECOMMENDATIONS:
In conclusion, flooding and wave runup will not significantly impact this property over
the proposed life of the development if the existing bulkhead/seawall remains in its current
condition.
The subject bulkhead/seawall was built by the City of Newport Beach circa 1929. Thus, it is
near its expected useful lifespan of 75 years. The bulkhead/seawall shows signs of distress and over
the next 25 years will most likely exhibit advanced deterioration. Therefore, the City has hired
Everest International Consultants, Inc. to assess the bulkhead at the entire Balboa Island and provide
recommendations for its repair or replacement. The recommendations are as follows:
1. Begin replacement of the existing seawall within 10 years from baseline 2010 per
Enclosed Figures 5.2, 5.3 & 5.5. This initial stage will consist of a perimeter seawall
constructed to 9.8 feet NAVD88 (10 ft MLLW) which would place the new wall 0.8 feet
above the current Base Flood Elevation of 9.0 feet NAVD88 (9.18 feet MLLW) - see
4
enclosed Comparison of Different Tidal Datums Graph. In the interim, augment the existing seawalls
by 6 to 8 inches either by adding a cap extension, or by being prepared to deploy sandbags around the
Balboa Island.
2. When necessary, extend the seawall by an additional 3 to 4 feet during lifetime of
spanning Years 2050 and 2060 (i.e., 40 to 50 years from baseline Years 2010).
3. When necessary, construct a deep well groundwater dewatering system to protect the
Balboa Island from subsequent high-water tables associated with highest extreme water
levels. If see levels rise as predicted, this would need to be done during a lifetime
spanning years 2050 and 2060.
Once the existing bulkhead is replaced in compliance with the enclosed Figures 5.2, 5.3
& 5.5, no additional protective device will be required during the economic life of the associated
structure, to protect it from flooding, wave runup or erosion.
The conclusion & recommendations of this report were 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.
Recommendations could change upon better certainty of the projected sea level rise. We make no
further warranty, either expressed or implied.
PMA Consulting, Inc. appreciates the opportunity to work with you towards the successful
completion of your project. Should you have any questions regarding this report, please contact us.
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 – Low Risk
Table 28: Projected Sea-Level Rise (in feet) for Los Angeles – Low & Medium High Risk
Datums for Newport Bay Entrance
Comparison of Different Tidal Datums
Flashing & Waterproofing Detail
Newport Beach OE S Quadrangle
Figures 5.2, 5.3 & 5.5
5
6
7
8
9
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.
10
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.
11
12
13
Seawall Assessment for Balboa Island and Little Balboa Island Main Report
Everest International Consultants, Inc. 2.3
Figure 2.1 Comparison of Different Tidal Datums
14
15
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
419000mE
3707
000
m
N
3707
000
m
N
08 08
09 09
3710 3710
11 11
12 12
13 13
14 14
15 15
16 16
17 17
18 18
19 19
3720 3720
3721
000
m
N
3721
000
m
N
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:
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Seal Beach
Newport Beach
Tustin
not printed
Laguna Beach
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not printed
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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
16
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