HomeMy WebLinkAboutPA2022-0314_20230207_Coastal Hazards Report_dated 12-03-2018
3 December 2018
Mr. Randy Beers
W.T. Durant, Inc.
2706 St. Louis Avenue
Signal Hill, CA 90755
Re: Coastal Hazards Report for 944 Via Lido Nord, Newport Beach, CA
Dear Mr. Beers:
Simpson Gumpertz & Heger Inc. (SGH) is retained by W.T. Durant, Inc. (Durant) to provide a
Coastal Hazards Report for the property at 944 Via Lido Nord in Newport Beach, California. This
site is within the Shoreline Hazardous Area as defined by the City of Newport Beach. The
objective of the report is to evaluate and identify the primary coastal hazards affecting the project
site. This report has been developed in accordance with City of Newport Beach Municipal Code
Section 21.30.015(E)(2).
As part of the assessment, we conducted a site visit on 21 August 2018 as well as reviewed
relevant information in the following documents:
• Bulkhead Upgrade at Richard Steele Residence 944 Via Lido Nord by Richard K.
Shogren, dated 10 December 1987.
• Mr. & Mrs. R. Steele Residence Precise Grading Plan by Derek J. McGregor, dated
19 July 1987.
• Federal Emergency Management Agency Flood Insurance Rate Map, Map Number
06059C0381J, revised 3 December, 2009.
• National Research Council, Sea Level Rise for the Coasts of California, Oregon, and
Washington: Past, Present, and Future. Washington, D.C.: National Academy of
Sciences, 2012.
• American Society of Civil Engineers, ASCE 7-10 Minimum Design Loads and Associated
Criteria for Buildings and Other Structures. Reston, Virginia: American Society of Civil
Engineers, 2010.
• United States Army Corps of Engineers, Coastal Engineering Manual, EM 1110-2-1100,
2002.
Mr. Randy Beers – Project 187550 - 2 - 3 December 2018
1. QUALIFICATIONS OF PREPARER
This report has been prepared by William M. Bruin, P.E., D.PE of SGH. Mr. Bruin is a registered
Professional Engineer in six states (California Civil, No. C57867) and an ACOPNE Diplomate of
Port Engineering (D.PE No. 00063) with more than 22 years of risk consulting, marine civil and
structural engineering, as well as project management experience applied over a variety of
industrial, offshore, and marine projects. Mr. Bruin’s career has focused on condition
assessment, response evaluation, risk identification, hazard mitigation, due-diligence
assessment, asset management, as well as design applied for a wide variety of onshore, near-
shore, and offshore structures and facilities. Mr. Bruin has extensive experience repairing,
rehabilitating, and designing marine and waterfront structures.
Mr. Bruin has received the degrees of Bachelor of Science in Structural Engineering from the
University of California San Diego (UCSD) and Master of Science in Civil Engineering from Lehigh
University.
Mr. Bruin was selected to serve on two earthquake reconnaissance teams, travelling to disaster
locations in Haiti (2010) with EERI and Japan (2011) with ASCE-COPRI to investigate the
performance of marine and waterfront facilities subsequent to major earthquakes. He also visited
marine oil terminal sites impacted by the earthquake and tsunami in Chile (2010).
Mr. Bruin is also an active member of the ASCE-COPRI Ports and Harbors Committee and the
ASCE 61-19 Standards Committee (Seismic Design of Piers and Wharves). He is a contributing
author for the recent publishing of ASCE-COPRI Manual of Practice for Waterfront Facility
Inspection and Assessment (MOP 130). He also sits on a subcommittee developing the new
ASCE-COPRI Manual of Practice for the Rehabilitation of Waterfront and Marine Structures.
2. COASTAL HAZARD IDENTIFICATION
We have identified several coastal hazards that may affect the subject property, located on
Lido Island in Newport Bay. Where appropriate, design values for the various hazards have been
provided for evaluating the existing bulkhead structure as well as for any new development at
944 Via Lido Nord. The primary coastal hazards for this site include:
2.1 Wind
• ASCE 7-10 provides 3-sec. gust, design wind speeds for the western United States for
10, 25, 50, and 100-year Mean Recurrence Interval (MRI). A 75-year design life falls
between the 91 mph and 85 mph values reported for the 100-year and 50-year MRI
values, respectively. We have conservatively assumed a linear relationship to obtain a
75-year MRI.
• The 75-year MRI design wind speed for the site is 88 mph (3-sec. gust).
2.2 Waves
• Wave heights were developed for the project site using the United States Army Corps of
Engineers’ Coastal Engineering Manual (CEM) wave hindcasting method. A determined
wind speed is averaged for a duration appropriate for the longest fetch of the site to
develop incident waves.
Mr. Randy Beers – Project 187550 - 3 - 3 December 2018
• Due to the insufficient, site-specific wind speed data sets near the project site, the
100- year wave height for the project site was determined using the 100-year MRI value
listed in ASCE 7-10. A wind speed of 91 mph (3-sec. gust) was used.
• The extreme fetch from the project site runs west along the north shore of Balboa Island,
providing approximately 6,450 ft of open water for waves to develop.
• From the delft curve in the CEM, the equivalent wind speed over the provided fetch is
58.9 mph (32-minute duration).
• The 100-year storm significant wave height for the site is 2.37 ft, with a period of
2.2 seconds.
2.3 Current
• Newport Bay is a protected location. Currents at the site are not significant.
• The design current velocity for the site should be no more than 0.5 knots.
2.4 Beach Erosion
• From the design drawings, dated 1987, there was 5.25 ft of clearance from the top of the
pile cap to the sand at the face of the bulkhead. We observed the beach to be on average
6.0 ft below the pile cap, with approximately 0.75 ft of erosion.
• Assuming a constant rate from 1987 to 2018, the erosion rate at the site for evaluating
the bulkhead is 0.29 in./year (approximately 1 ft every 41 years).
2.5 Sea Level Rise
• Sea level rise (SLR) as stated by NRC’s 2012 report for the Los Angeles area is as
follows:
• SLR ranges from 5 in. to 24 in. by 2050
• SLR ranges from 17 in. to 66 in. by 2100
• With a 75-year design life, we have assumed linear interpolation for sea level rise
projections for the year 2093 from the NRC values of 2050 and 2100.
• For evaluation of the bulkhead, a median 75-year SLR of 2.58 ft (31 in.) is appropriate.
Where the uncertainty of the NRC prediction and/or the risk of exceeding the median
predictions requires reduction, the higher end of the predictions should be used.
2.6 Flooding
• The FEMA Flood Insurance Rate Map (FIRM) determined the 100-yr Newport Bay Base
Flood Elevation (BFE) is +9.0 ft NAVD88. This includes 1 ft of wave.
• The elevation of the existing bulkhead wall pile cap currently sits at +11.22 ft NAVD88.
The wall currently has 26.6 in. of freeboard above the BFE.
Mr. Randy Beers – Project 187550 - 4 - 3 December 2018
2.7 Tidal Conditions
• Tidal conditions for the site can be characterized by NOAA Station No. 941058 (Newport
Beach, Newport Bay, CA) and summarized below:
Tide
Current
Water Levels
(ft, MLLW)
75-yr SLR
Water Levels
(ft, MLLW)
75-yr SLR
Water Levels
(ft, NAVD88)
Extreme Observed High Water (’83) 7.67 - -
Mean Higher High Water 5.41 7.99 7.51
Mean High Water 4.67 7.25 7.07
Mean Sea Level 2.77 5.35 5.17
Mean Low Water 0.92 3.50 3.32
Mean Lower Low Water 0.0 2.58 2.40
Extreme Observed Low Water (’88) -2.35 - -
3. HAZARD ANALYSIS
This section analyses the project site for five scenario conditions detailed in Municipal Code
Section 21.30.015(E)(2)(c).
Condition i - A seasonally eroded beach with long-term projections for sea level rise
• The existing bulkhead was designed assuming a beach sand elevation of -0.38 ft
NAVD88. The current beach elevation is +5.22 ft NAVD88.
• With slow erosion rates predicted for the site, beach erosion is not a concern for bulkhead
stability.
• SLR does not impact beach erosion rates at this site.
Condition ii - High tide conditions, combined with long-term projections for sea level rise
• The pile cap of the existing bulkhead is at +11.88 ft NAVD88.
• At Mean Higher High Water (MHHW) with 75-year SLR, the water elevation is +7.51 ft
NAVD88, leaving 4.37 ft of freeboard below the top of the bulkhead.
• At the extreme observed high water (1983) with 75-year SLR, the water elevation is
+10.07 ft NAVD88, leaving 1.81 ft of freeboard below the top of the bulkhead.
Condition iii - Storm waves from a one hundred (100) year event
• The pile cap of the existing bulkhead is at +11.88 ft NAVD88.
• The 100-year wave is 2.37 ft.
• The 100-yr FEMA Flood Elevation is +9.0 ft NAVD88, including 1 ft of wave. The
resulting water elevation is +10.37 ft NAVD88, leaving 1.51 ft of freeboard below the top
of the bulkhead.
Mr. Randy Beers – Project 187550 - 5 - 3 December 2018
Condition iv - An analysis of bluff stability
• Not applicable - There is no bluff at this site.
Condition v - Demonstration that development will be sited such that it maintains a factor
of safety against sliding of the bluff
• Not applicable - There is no bluff at this site.
4. SITES WITH AN EXISTING BULKHEAD
Pursuant with Municipal Code Section 21.30.015(E)(2)(d), the existing bulkhead is required to
protect existing principal structures and adjacent developments. The existing bulkhead cannot
be removed without some remediation.
5. IDENTIFICATION OF MITIGATION MEASURES
To mitigate hazards described above, the following actions are recommended for any future
development at the site:
• Overtopping of the bulkhead may occur during flood events with large waves over the
75-year design life considering SLR. SGH suggests any new development at this site
consider flood, tide, wave, and SLR in determining base floor elevations. Elevation is
the most effective mitigation for these types of hazards.
• For any new development, we suggest the existing bulkhead be inspected and existing
structural condition be documented.
• For any new development, we suggest the existing bulkhead be evaluated considering
existing condition and the loads associated with the planned development as well as
those for a 100-year storm wave height, 75-year beach erosion, 75-year SLR, and flood
heights provided herein with tidal conditions. The adequacy of the existing structure for
the proposed development should be verified and documented in the City of Newport
Beach Bulkhead Condition Report in accordance with Municipal Code Section
21.30.015(E)(3).
If there are any questions regarding this, please do not hesitate to contact me at (510) 457-4449
or by e-mail at WMBruin@SGH.com.
Sincerely yours,
SIMPSON GUMPERTZ & HEGER INC.
William M Bruin, P.E.
Senior Principal
CA License No. C57867
I:\OAK\Projects\2018\187550.00-LIDO\WP\002WMBruin-L-187550.00.els_2018-12-03 Coastal Hazards Report - 944 Via Lido
Nord.docx
12/3/2018