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HomeMy WebLinkAboutPA2023-0118_20230627_Bulkhead Conditions Report_dated 05-17-2023Geotechnical C Geologic C Coastal C Environmental 5741 Palmer Way C Carlsbad, California 92010 C (760) 438-3155 C FAX (760) 931-0915 C www.geosoilsinc.com May 17, 2023 WO S8608 Ms. Gloria Mariman c/o LS Architecture 3111 Second Avenue Corona Del Mar, CA 92625 SUBJECT:Sea Level Rise Discussion and Bulkhead Condition Report for 54 Linda Isle, Newport Beach, Orange County, California. Dear Ms. Mariman: In accordance with the request and authorization, GeoSoils, Inc. (GSI) is pleased to provide this discussion regarding the potential coastal hazards, including the impact of future sea level rise (SLR), on the proposed new single family residence at 54 Linda Isle in Newport Beach. The proposed development includes removal of the existing residence, construction of a new residence, and replacement of the bulkhead deck. The site is located on Linda Isle in the eastern half of Newport Bay. This site is fronted by a concrete bulkhead that extends to several properties on either side of the site. The purpose of this report is to provide the SLR hazard and bulkhead 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 State of California Sea-Level Rise (SLR) Guidance document (CCCSLRG), a review of the latest SLR science from NASA and NOAA, a review of City of Newport Beach Municipal Code (NBMC) 21.30.15.E.2 and E.3, a site inspection, a review of the proposed residence plans, and preparation of this letter report. INTRODUCTION Figure 1, downloaded from Google Maps (Bird’s Eye View), shows the site in relation to the adjacent properties, the bulkhead, the private docks, and the Linda Isle lagoon in Newport Bay. The current top of the bulkhead deck is elevation ~9.1 feet NAVD898. Based upon our inspection of the bulkhead, and our knowledge of the bulkhead design, the height of the bulkhead can be increased. There is no beach at the site. The proposed lowest finished first floor (FF) elevation of the new residence is at about +10.9 feet NAVD88. The site is currently mapped by FEMA to be in the X Zone with the adjacent docks in Linda Isle lagoon in the AE Zone with a Base Flood Elevation (BFE) of 8 NAVD88 (FIRM 06059C0382K, effective 3/21/2019). 2 Figure 1. Subject site, adjacent properties, bulkhead, docks, and Linda Isle lag oon. DATA & DATUM The datum used in this report is NAVD88, which is about 2.62 feet below the mean tide level (MTL). The units of measurement in this report are feet (ft), pounds force (lbs), and seconds (sec). Site elevations were taken from a topographic map prepared byApex Land Surveying Inc, dated 12/16/2022. Proposed development elevations were taken from project plans provided by LS Architects, the project designer. HAZARD ANALYSIS There are three different potential coastal hazards identified at this site: shoreline movement/erosion, waves and wave runup, and flooding. For ease of review, each of these hazards will be analyzed and discussed separately, followed by a summary of the analysis including conclusions and recommendations, as necessary. 3 Shoreline Erosion Hazard There is no actual shoreline at the site. There is no hazard of shoreline erosion for the project. Current Flooding Hazard 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: Mean High Water 4.55 feet Mean Tide Level (MSL) 2.62 feet Mean Low Water 0.74 feet NAVD88 0.0 feet Mean Lower Low Water -0.2 feet During storm conditions, the sea surface rises along the shoreline (super-elevation) and allows waves to break closer to the shoreline and runup on the beach. Super-elevation of the sea surface can be accounted for by: wave set-up, wind set-up and inverse barometer, wave group effects and El Niño sea level effects. The historical highest ocean water elevation at the Los Angeles Harbor Tide station is +7.72 feet NAVD88 on January 10, 2005. In addition, EICI reported that the elevation of 7.71 feet NAVD88 is the 1% water elevation for Newport Bay. For this analysis the historical highest water elevation will be +7.7 feet NAVD88. Future Tide Levels Due to Sea Level Rise The CCCSLRG is based upon the California Ocean Protection Council (COPC) update to the State’s Sea-Level Rise Guidance in March 2018. These COPC estimates are based upon a 2014 report entitled “Probabilistic 21st and 22nd century sea-level projections at a global network of tide-gauge sites” by Kopp, et al., 2014. The Kopp et al. paper used 2009 to 2012 SLR modeling by climate scientists for the probability analysis, which means the “best available science” in the CCCSLRG is over 10 years old. The SLR models used as the basis for the COPC and CCCSLRG have been in place for about two decades. The accuracy of any model can be determined by comparing the measured SLR (real time data) to the model predicted SLR (model prediction). The National Oceanic and Atmospheric Administration (NOAA) has been measuring SLR globally, and specifically at Los Angeles Harbor. The NOAA Los Angeles SLR rate is 1.04 mm/yr as shown in Figure 2. The rate can be used to calculate a sea level rise of 24.8 mm ( 0.08 ft) over the last 23 years (2000 through December 2022). If we assume that the SLR do not change significantly in the next 7 years (which is likely) the amount of SLR will be about 0.1 feet (30X1.04= 31.2 mm or ~0.1 feet). 4 Figure 2. Latest measure SLR at Los Angeles from NOAA (2023). NOAA also provides plots of the most current SLR model projections (best available science) over time starting in the year 2000. Figure 3, is the model projections taken NOAA, which is more current SLR science than from the COPC used models. To see which model is more accurately predicting SLR, the data for Los Angeles can be either plotted onto the curves or estimated from the table below the curves. Figure 3. NOAA 2021 SLR projections for Los Angeles. 5 Recognizing that in the year 2000 the SLR zero line is 2.70 feet, and using the current Los Angeles SLR data (trends), SLR should be (2.70 + 0.1 feet) 2.8 feet in the year 2030. Looking at the table in Figure 3 for the year 2030 (6.5 years from now) reveals that Los Angeles SLR is tacking below the NOAA 2017 Low model curve. The Low model predicts a SLR rise total in the year 2100 of less than 1 foot. In contrast, the model the CCC was requiring to be used and analyzed is the high emissions scenario and the 0.5% probability. For the year 2030 the CCC required SLR is 0.7 feet which is 7 times greater than the 0.1 feet that is being measured. Over the 75 year life of the development this results in very significant difference in what the CCC requires and what is the current best available science. The CCCSLRG document recommends that a project designer determine the range of SLR using the “best available science.” The NOAA SLR information provided above is more current than the CCCSLRG. The checking of the models is the “best available science” for SLR prediction and is required to be used. Currently, the SLR model that the CCC is “requiring” to be used for development is incorrect by more than a factor of 7 as to the measured amount of the SLR in Newport Beach. Clearly, the CCC required model has inflated SLR, is incorrect, and over time will likely become more and more inaccurate. The CCCSLRG document recommends that a project designer determine the range of SLR using the “best available science.” The NOAA SLR information provided above is more current than the CCC SLR Guidance. Figure 4 provides the NASA 2023 IPCC AR 6 models with the SLR estimates (in meters) for the Los Angeles NOAA station, and the model probabilities of those estimate to meet or exceed the 1995-2014 baseline. The likely SLR in the year 2100 (SSP3-7.0) is 0.54 meters (1.77 feet) and the unlikely (very low probability ~0.5%) in the year 2100 (SSP5-8.5) is 0.76 meter (about 2.5 feet). The NOAA and NASA IPCC AR 6 data/models are the currently best available science and are required by the CCCSLRG to be used. Finally, it is our understanding the COPC is revising their previous SLR estimates and that they are more consistent with the NOAA and NASA data/models. 6 Figure 4. NASA SLR tool IPCC AR6 estimates for Las Angeles NOAA tide station. Measurements and models from NASA show that SLR is tracking to be about 1.8 feet to 2.4 feet in the year 2100. Measurements and models from NOAA have SLR to be between 0.66 feet to 5.3 feet (NOAA-2107 Int-High) in the year 2100. The typical design life of residential development is about 75 years or about the year 2100. Based on the discussion above (the current best available science), the SLR range for the project is about 2 feet (likely) to 6 feet (unlikely). Using the design ocean water elevation 7.7 feet NAVD88, the potential range of Newport Bay water level in the year 2100 due to SLR is 9.7 feet NAVD88 (likely) to 13.7 feet NAVD88 (unlikely). The City of Newport Beach has recognized that in the future there will be a need to raise the elevation of the boardwalks and bulkheads around the Newport Bay. Previous action by the City Council has raised the minimum private bulkhead elevation for new development to be 10.9 feet NAVD88. In addition, the updated Waterfront Project Design 7 Guidelines and Standards require that the bulkhead or other protective improvements can be designed to accommodate an increase in height to +14.4 feet NAVD88 or greater. Based upon our inspection and knowledge of typical bulkhead construction (concrete panel with deadman type tie-back restraint), the 54 Linda Isle bulkhead is capable of being extended in height to +14.4 feet NAVD88. Waves and Wave Runup The potential surface gravity waves (ocean swell) to arrive at this site is nil. Boat wakes and wind waves are the only possible waves that can reach the bulkhead fronting the site. Boat wakes are very small due to speed restriction within the small lagoon, and there is insufficient fetch to produce wind waves of more than a couple inches. Wave runup is not expected to impact the proposed redevelopment over the design life of the project. 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. 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 in will be refracted, modified, and reduced in height by the Newport jetties, and as it travels into the bay. Due to the infrequent nature and the relatively low 500-year recurrence interval tsunami wave height, 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 (CalOES) tsunami innundation map, Newport Beach Quadrangle. The tsunami inundation maps are very specific as to their use. Their use is for evacuation planning only. The limitation on the use of the maps is clearly stated in the PURPOSE OF THIS MAP on every quadrangle of California coastline. In addition, the following paragraph is taken from the CalOES Local Planning Guidance on Tsunami Response concerning the use of the tsunami inundation maps. 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 performance, in an earthquake or tsunami, of any structure within or outside of the projected inundation area. The City of Newport Beach and County of Orange have clearly marked tsunami evacuation routes for the entire Newport Beach/Bay area. 8 CITY OF NEWPORT BEACH INFORMATION Coastal Hazards Report (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 44 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 shoaling 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 in this hazard analysis, the typical coastal hazards to consider are shoreline erosion, flooding, and wave/wake impacts. There is no beach at or near the site, so there is no shoreline erosion hazard for the project. Boat wakes and wind waves are too small, even with sea level rise (SLR), to potentially flood the proposed residence provided the private bulkhead is maintained to mitigate SLR impacts. The City of Newport Beach has recognized that in the future there will be a need to raise the elevation of the bulkheads around Newport Bay and as such the City of Newport Beach Building Department (CNBBD) has a standard drawing, and a regional plan for rehabilitating and raising the bulkheads. There is no potential coastal hazard of flooding of the development provided adaptation strategies such as being able to waterproofing the residential structure above the 10.9 feet NAVD88 FF elevation, and increasing the height of the site bulkhead are implemented as part of the project. iii. An analysis of the following conditions: 1. A seasonally eroded beach combined with long-term (75 year) erosion factoring in sea level rise; There is no beach near the site. The project will not be impacted by shoreline erosion. 2. High tide conditions, combined with long-term (75 year) projections for sea level rise; Using the best available SLR science estimates over the project 75-year 9 design life, the likely SLR in the year ~2100 will be between 1 feet and 3 feet. There is a less than 0.5% probability that SLR could be 6 feet or greater feet in the next 75 years. Thus the design sea level rise range for the proposed project is 2 feet to 6 feet. This SLR would account for future extreme bay water level of 9.7 feet NAVD88 to 13.7 feet NAVD88. 3. Storm waves from a one hundred year event or storm that compares to the 1982/83 El Nino event; No ocean waves can reach the site. 4. An analysis of bluff stability; a quantitative slope stability analysis that shows either that the bluff currently possesses a factor of safety against sliding of all least 1.5 under static conditions, and 1.1 under seismic (pseudostatic conditions); or the distance from the bluff edge needed to achieve these factors of safety; and There is no bluff fronting the site. This condition does not occur at the site. 5. Demonstration that development will be sited such that it maintains a factor of safety against sliding of at least 1.5 under static conditions and 1.1 under seismic (pseudostatic) conditions for its economic life (generally 75 years). This generally means that the 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. This condition does not occur at the site. 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 The site bulkhead is in good condition (see following Bulkhead Condition Report) and can be increased in height to at least 14.4 feet NAVD88, if required in the future. The bulkhead is part of a continuous bulkhead system that protect several properties to either side of the site. The bulkhead is required for the existing development, the proposed development, the adjacent properties and the Linda Isle facilities (infrastructure). 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 10 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 project is safe from the coastal hazard of flooding by the proposed elevation of the finished floor 10.9 feet NAVD88, and the ability to additionally waterproof the building in the future, if necessary. It is important to point out that SLR will not impact this development alone. It will impact all of the Newport Bay low lying areas. The public streets throughout the Newport Beach coastal area, including the Lido Island, Balboa Peninsula and Balboa Island, will flood with lower SLR well before the residence floods. It is very likely that the area will soon adopt some of the SLR adaptation strategies that are currently being considered by the City of Newport Beach. These strategies involve raising, or adding/replacing the bulkheads, beaches and walkways that surround the bay, and waterproofing of the buildings. These are a site specific adaptation strategies. Bulkhead condition report shall include (NBMC 21.30.15.E.3): 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 44 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. Mr. Skelly has extensive experience in shoreline erosion, bluff erosion, soils engineering, and the design, permitting, and construction of shore protection devices. Projects include levee engineering and design in San Francisco Bay, seawall and marina engineering in Baja California Sur, coastal boardwalk design and protection in Pacifica, and seawall projects throughout southern California. ii. An analysis of the condition of any existing bulkhead including whether the top elevation meets current City standards, the conditions of the sheetpiles or panels, the condition of existing tiebacks and/or deadmen or similar, and any other relevant conditions; The site bulkhead has been maintained and is in good condition. The top of the bulkhead, at elevation +9.2 feet NAVD88, does not meet the current City’s top of bulkhead elevation requirement (10.9 feet NAVD88). It should be noted that very few bulkheads in the Newport Bay area meet this newer elevation requirement. The actual design (concrete panel with a restraining anchor) of the bulkhead does meet the City standard. 11 The bulkhead is in good condition and functioning as intended. Figures 5 and 6 shows the current visual appearance of the bulkhead. The bulkhead does not need any maintenance at this time. The panels are vertical with no signs of rotation, spalling, or cracking. The bulkhead can be additionally modified (increased in height) to adapt to sea level rise (SLR), as discussed in this report. The proposed residential development has an economic life of about 75 years. With maintenance, it is reasonable to assume that the bulkhead could last another 75 years. The bulkhead has tie-backs with deadman anchors. These components of the bulkhead cannot be observed without destruction of the existing flat work. Figure 5. Site bulkhead during site and bulkhead inspection. 12 Figure 6. Close up of the top of the bulkhead. Note the shallow depth at the toe of the wall. iii. Recommendations regarding the need for repair, augmentation or replacement of the bulkhead or any parts thereof; Augmentation of the site bulkhead as part of the residential development project will be necessary to meet the City of Newport Beach bulkhead elevation requirements. The existing bulkhead needs to be increased in height. The project proposes a replacement concrete deck on top of the bulkhead. The deck can be constructed with a low height concrete perimeter wall to meet the City elevation standard. It will also be necessary for this low height wall to be capable of being augmented and increased to a height of 14.4 feet NAVD88, as required by the City. The increase in height is an SLR adaptation strategy. iv. If augmentation or replacement in the existing alignment is necessary, recommendations that will avoid seaward encroachment of the bulkhead; The added height of the bulkhead/deck will be located within the current 13 bulkhead/deck footprint. No encroachment into Newport Bay (Linda Isle lagoon) is necessary. v. If replacement is necessary and the existing bulkhead is not in alignment with adjacent bulkheads, recommended alternatives that will relocate the bulkhead in as much in alignment with adjacent bulkheads and as far landward, as possible. Bulkhead replacement is not necessary. CONCLUSIONS •The proposed residential development with the implementation of the SLR adaptation strategies such as the design of the building for future waterproofing above the FF elevation of 10.9 feet NAVD88, the ability to add waterproofing to about elevation +14.4 feet NAVD88, if needed, and the increase in height of the existing bulkhead to elevation 10.9 feet NAVD88) will not be adversely impacted by potential coastal hazards including sea level rise over the next 75 years. Finally, the site will be part of a community wide response to mitigate SLR hazards. •An augmented site bulkhead is currently needed to conform with the City’s minimum bulkhead elevation requirement for new development. The condition of the site bulkhead tie-back and deadman anchor system cannot be verified at this time. However, there are no indications of distress to the bulkhead and it components. •For the most part, in the remainder of the Newport Bay area, including the Balboa Peninsula, and other developed islands within the bay, flooding with a lower SLR is likely to occur. Such flooding will occur well before any part of the proposed residential development will flood. It only requires a few of the protective bulkheads around Newport Bay to remain at low levels to allow flooding of the streets. •Provided the recommendations of this report are implemented during the project construction, no site specific protective devices will be necessary to protect the proposed development from any existing or anticipated future coastal hazards for the next 75 years or more. RECOMMENDATIONS During the project construction the landward side of the bulkhead should be exposed and inspected by the engineer. While unlikely, tie-back rod or deadman deterioration may require replacement. Based upon the analysis and discussion herein, the proposed development is reasonably safe from coastal hazards for the next 75 years including shoreline movement, waves and wave runup, and flooding with future SLR for the next 75 14 years. It should be noted that future flooding hazards due to SLR are shared by all development around Newport Bay. The roads on Linda Isle may be impassable due to ocean flooding long before the flood water level approaches the FF elevation of the development. SLR impacts will be a regional problem and only solved by a regional management plan. The proposed City of Newport Beach bulkhead modification/replacement plan will likely mitigate many SLR impacts on the project. The proposed development will neither create nor contribute significantly to erosion, geologic instability, or destruction of the site or adjacent area. The opportunity to be of service is sincerely appreciated. If you should have any questions, please do not hesitate to contact me. Respectfully submitted, GeoSoils, Inc. David W. Skelly MS, PE RCE#47857 15 REFERENCES 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 Newport Beach, “Waterfront Project Guidelines and Standards, Harbor Design Criteria Commercial & Residential Facilities,” Revised 2021 Edition NASA, 2023, https://sealevel.nasa.gov NOAA, 2023, Web Sites, Maps http://anchor.ncd.noaa.gov/states/ca.htm Tidal Datums http://www.opsd.nos.noaa.gov/cgi-bin/websql/ftp/query_new.pl N O A A 2 0 2 2 , S e a L e v e l R i s e R e p o r t e m a i l l i n k . https://oceanservice.noaa.gov/hazards/sealevelrise/sealevelrise-tech-report.html State of California, County of Orange, 2009, “Tsunami Inundation Map for Emergency Planning, Newport Beach Quadrangle,” 1:24,000 scale, dated June 1. State of California Sea Level Rise Guidance 2018 Update, by Ocean Protection Council, dated in March 2018.