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HomeMy WebLinkAboutPA2023-0169_20230921_Hazard Study dated 08-23-23Geotechnical 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 August 23, 2023 WO S8667 Lisa McGinnis 6400 West Oceanfront Newport Beach, CA 92662 SUBJECT: Coastal Hazard and Wave Runup Study, 4901 Seashore Drive, Newport Beach, California. Dear Ms. McGinnis: At your request, GeoSoils, Inc. (GSI) is pleased to provide this coastal hazard and wave runup study for the property located at 4901 Seashore Drive, 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 State of California Sea-Level Rise (SLR) document (adopted March 2018), the latest SLR science (NOAA, 2022), 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 preliminary new residence plans, 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 residence 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 4901 Seashore Drive, Newport Beach, California. The site is a rectangular shaped parcel, approximately 30 feet of ocean frontage by ~68 feet long, with an existing residential structure. Figure 1 is a 2022 Vexel Imaging aerial photograph of the site downloaded from the internet. The proposed development consists of removal of the existing residence and construction of a new residence. The proposed finished floor (FF) elevation is +13.76 feet NAVD88. The site is fronted by a sandy beach (~300 feet wide), and the Pacific Ocean. This site is located near the middle of the Newport Beach groin field and northwest of the Newport Pier, in a coastal segment described as the West Newport 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). The West Newport Beach shoreline segment stretches from the Newport Pier to the east jetty of the Santa Ana River, a distance of a little more than 2.3 miles. In general, the movement of sand along a shoreline depends upon the orientation 2 of the shoreline and the 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. 2022 aerial photograph of the subject site. Note the relatively wide beach. USACOE (2002) contains historical beach profile and beach width data for the beach near the site. The beach width has changed little over the past 60 years as a result of replenishment in the 1930's and 1980's with fill from Newport Harbor and the stabilizing effect of the nearby groins. The data shows that the actual beach width fronting the site has increased since 1965. Figure 2 is beach width survey data from the USACOE monitoring program. A beach width monitoring station near the project is station 741+31. During typical winter eroded beach conditions, the beach width may be about 300 feet. The narrowest the beach has been is about 250 feet in 1968, prior to a nourishment project. From 1972 to the present, the beach has been typically over 300 feet wide. In the long-term, the presence of the nearby groin field, a sand source (Santa Ana River), and future nourishment projects will continue to stabilize the shoreline fronting the site. 3 Figure 2. Mean sea level beach widths in the West Newport Beach area (USACOE 2002). Despite efforts to control the movement of sand along the shoreline, the shoreline at this section of the Newport Beach area does experience short-term erosion. The erosion is temporary, and usually the result of an energetic winter. As stated before, there is no clear evidence of any long-term erosional trend (USACOE 2002). The subject site is situated up coast from an active sand sink, the Newport Submarine Canyon. The site is somewhat sheltered from waves arriving from the south by canyon induced wave refraction (defocusing). This reduces the beach erosion potential by reducing the wave energy. The wide sandy beach in front of the subject site is normally about 300 feet wide and has provided more than adequate protection for the property over the last several decades. In the past, no wave runup has overtopped/reached the site. The site has not been subject to wave attack for at least the last 50 years. This includes the winter storms of 1982-83 and January 1988, 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 2.62 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). Beach profile data was reviewed from USACOE (2002). Aerial photographs, taken semi-annually from 1972 through 2022, were reviewed for shoreline changes. Site elevations relative to NAVD88 were taken from a site survey by RdM Surveying Inc., dated July 2023. Proposed preliminary plans by Eric Trabert and Associates, the project designer, were reviewed. The site is mapped in the FEMA shaded X Zone (map 06059C0377K, effective 3/21/2019). 4 SITE BEACH EROSION AND WAVE ATTACK In order to determine the potential for wave runup to reach the site, historical aerial oblique photographs dating back to 1972 were reviewed. None of the photographs showed that wave runup reached the site. Figure 3, taken in January 1988, shows a relatively wide beach in front of the property. The photo was taken after the January 19, 1988,“400-year” wave event and shows the eroded beach in front of the property. However, the beach did not erode back to the site and no water reached the site. Figure 4, taken April 2022, shows what could be described as the “normal” beach width (about 300 feet). A review of the annual aerial vertical photographs over the last 50 years shows a wide beach even though the photos 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 the site and allow direct wave attack on the existing or proposed development. Based upon interviews with long-term local residents, the subject site has not been subject to wave runup during the last 60 years. The existing residence has not flooded from ocean water or from surface drainage due to its elevation relative to the city street drainage paths. The adjacent city street is lower than the lowest grade on site. In the future, wave runup is unlikely to reach the site under severely eroded beach conditions and extreme storms. Figure 3. Shoreline fronting the subject in January 1988 after the “400-year” wave event. 5 Figure 4. Shoreline fronting the subject site in April 2022 (note the wide beach). 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 runup. 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 are 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 7 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. 6 Figure 5. Wave runup terms from ACES analysis. Oceanographic Data The wave, wind, and water level data used as input for the ACES runup and overtopping application were taken from the historical data reported in USACOE (1986) and USACOE (2002), and updated as needed. 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 40th Street has experienced extreme storm wave erosion due to focusing of the waves by the canyon. The ACES analysis was modeled 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 Niño 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 is located at Los Angeles Harbor (Station 9410660). 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 is +7.72 feet NAVD88 on January 10, 2005. 7 Future Tide Levels Due to Sea Level Rise The November 2018 California Coastal Commission (CCC) SLR Guidance Update document recommends that a project designer determine the range of SLR using the “best available science.” The California Ocean Protection Council (COPC) adopted an update to the State’s Sea-Level Rise Guidance in March 2018 which the CCC has adopted in November 2018. These 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 Harbor, the closest SLR estimates to Newport Beach. 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 estimate to meet or exceed the 1991-2009 mean. Figure 6. Table from Kopp et al (2014) and COPC 2018, providing current SLR estimates and probabilities for the Los Angeles Harbor tide station. The CCC SLR Guidance (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 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” used by the CCC is 10 years old. The SLR models used as the basis for the COPC and CCCSLRG have been in place for over a decade. The accuracy of any model can be determined by comparing the measured SLR 8 (real data) to the model predicted SLR (model prediction). If the model cannot predict, with any accuracy, what will happen in the past, it is very unlikely that the model will increase in accuracy when predicting SLR over the next 75 years. Simply put, if the model is not accurate now, it will be even less accurate in the future. The National Oceanic and Atmospheric Administration (NOAA) has been measuring SLR globally and at Los Angeles Harbor. The NOAA Los Angeles Harbor SLR rate is 1.03 mm/yr. The rate can be used to calculate a sea level rise of 30.9 mm (0.1 ft) over the last 23 years and next 7 years (Jan 2000 to Jan 2030), a period of 30 years. NOAA also provides the latest SLR model curves and tables for the Los Angeles Harbor NOAA Station. Figure 7 provides the SLR model curves and tables for Los Angeles Harbor. Figure 7. Taken from the NOAA SLR program. Looking at the table in Figure 7, the SLR base value in the year 2000 is 2.70 feet. Adding 0.1 feet to the base SLR value yields the value 2.8 for the year 2030. The model that most closely predicts the currently measured SLR is the NOAA 2017 Low Model. This NOAA model predicts about 1.5 feet of SLR in the year 2100. Examining Figure 6 for the year 2030 and 0.1 feet of SLR, the closest probability category is the lower limits of the “Likely Range.” 9 The CCCSLRG document recommends that a project designer determine the range of SLR using the “best available science.” The NOAA 2022 information provided above is more current than the CCCSLRG. The checking of the models provides 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 a factor of about 4 as to the amount of the SLR in Los Angeles. Figure 6 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 and a 0.5% probability that SLR will be between 5 feet and 6 feet in the year 2098. The design historical water elevation at the for Newport Beach is elevation +7.7 feet NAVD88. This actual high water record period includes the 1982-83 severe El Niño, and the 1997 El Niño events, and is therefore consistent with the methodology outlined in the CCCSLRG document. The “likely” sea level rise range for the proposed project is 1.3 feet to 3.2 feet with a lower probability (~5%) of SLR of about 4.0 feet. This SLR range would account for future extreme water levels in the range of 9 feet NAVD88 (7.7 feet NAVD88 + 1.3 feet SLR) and 10.9 feet NAVD88 (7.7 feet NAVD88 + 3.2 feet SLR). There is a 0.5% probability that bay water will meet or exceed 13.7 feet NAVD88 (7.7 feet NAVD88 + 6 feet SLR). To be conservative, if 3.2 feet and 6.0 feet are added to this 7.7 feet NAVD88 elevation, then future design maximum water levels of 10.9 feet NAVD88 and 13.7 feet NAVD88 are the result. 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 depth is 10.4 feet, based upon a maximum scour depth at the toe of the beach slope of 0.5 feet NAVD88 and water elevation +10.9 feet NAVD88), then the design wave height (0.78xwater depth) will be about 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 6.0 feet SLR case will be considered with the elevation of the beach berm adjusted to +15 feet NAVD88. Table I, and Table II are the ACES output for these two SLR design conditions. 10 Table I Table II 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 15.0 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 6.0 feet with an overtopping rate of 15.0 ft3/s-ft, the water height h1= 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 11 Figure 8. Note the maximum wave runup in Newport Beach area is less than 2 meters. 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 300 feet away, so for the 6.0 feet of SLR case, the wave bore may travel about 100 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 extreme design conditions. TSUNAMI Tsunamis are waves generated by submarine earthquakes, landslides, or volcanic action. Lander, et al. (1993) discusses the frequency and magnitude of recorded or observed tsunamis 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. While this study is not specific to the east Newport Beach site, it provides a first order analysis for the area. Figure 8 shows the tsunami runup in the southern California bight, Legg, et al. (2002). The maximum tsunami runup in the east Newport area is less than 2 meters in height. Any wave, including a tsunami, that approaches the site in east Newport Beach will be refracted, modified, and reduced in height by the Newport Submarine Canyon. The Legg, et al. (2002) report determined a maximum open ocean tsunami height of less than 2 meters. Because of the wide beach, it is very unlikely that a 2-meter tsunami will be able to reach the site with sufficient energy to cause significant structural damage. 12 It should be noted that the site is mapped within the limits of the current 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 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 performance, 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 9 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 9. SAFRR tsunami modeling output for the site. 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, https://ourcoastourfuture.org/ . Using the modeling program the vulnerability of the site to 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 10 is the flooding risk output of the CoSMoS program. The modeling shows that the streets including the main arterial street, may flood during the 100 year event with ~4.9 feet of SLR. The site does not flood. The area flood waters will come from the bay and not from the ocean. The lowest existing FF is at 13.76 NAVD88 is above the adjacent street flow line of about 12 feet NAVD88. Figure 11 is the CoSMoS shoreline erosion risk output. The shoreline does not reach the site with 4.9 feet SLR. Figure 10. CoSMoS output for 4.9 feet SLR showing flooding from the low lying streets landward of the site. 14 Figure 11. CoSMoS output for 4.9 feet SLR showing the Mean High Water Shoreline not reaching the site. 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. Using the latest SLR science (NOAA, 2022) and the City of Newport Beach City Council SLR guidance, the range of estimate over the project design life that range in the year ~2098 is between 1.3 feet and 3.2 feet. In addition, the analysis herein considered a less than “likely” SLR of about 6.0 feet. This is the sea level rise range for the proposed project, 1.3 feet to 6.0 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 6.0 feet of SLR. The FF elevation of +13.76 feet NAVD88 is above the likely maximum future water elevation. 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 very conservative future erosion rate due to SLR of 1.4 ft/yr is used, then the shoreline will move about 100 15 feet over the life of the development. The site is over 300 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. 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 45 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 co-authored 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 coastal 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; 16 As discussed herein, due to the very wide beach, the site is safe from shoreline erosion, even factoring in SLR. The United States Geological Survey (USGS) provides the most a comprehensive assessment of shoreline change including this section of coastline. The USGS short-term erosion rate is calculated to be ~1.4 ft/yr or 100 feet over the 75 year life of the development. The site is currently 300 feet or more from the shoreline. If the beach retreats 100 feet in the next 75 years then the site will be 200 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 2. High tide conditions, combined with long-term (75 year) projections for sea level rise; Using the latest NOAA 2022 SLR guidance the range of SLR over the project design life that range in the year ~2098 is between 3.2 feet and 6.0 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 Niño and the 1997 El Niño 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 3.2 and 6.0 feet are added to this 7.7 feet NAVD88 elevation, then future design maximum water levels (“high tide conditions”) of 10.9 feet NAVD88 and 13.7 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 6.0 feet, the beach overtopping rate is 15.0 ft3/s-ft, the water height h1 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 300 feet away. So for the largest SLR case, the wave bore may travel about 100 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 17 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 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 6.0 feet of SLR. The existing finished floor elevation of +13.76 feet NAVD88 is safe for all reasonable estimates of SLR. Site drainage from non-ocean waters is provided by the project civil engineer. If a future erosion rate due to SLR of 1.4 ft/yr is used, then the shoreline will move about 100 feet over the life of the development. The site is about 300 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 decades before the residence will be impacted by SLR. The shoreline fronting the site is stable and an increase in the water elevation will 18 likely not increase shoreline erosion. The proposed project is safe from shoreline erosion due to the setback of the development to the potential future Mean High Tide (MHT) line in consideration of SLR. 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 wide (>300 feet) sandy beach in front of the property 99.99% of the time. •A review of aerial photographs over the last five decades 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 very conservative FUTURE retreat rate of 1.4 feet/year is used, it would account for about 100 feet of retreat over the life of the structure. This conservative retreat rate will not reduce the beach to less than 200 feet in nominal width (200 feet width of beach is recognized by coastal engineers as a sufficiently wide beach to provide back-shore protection). •The existing finished first floor (FF) elevation for the structure is above the street flow line (landward of the residence). CoSMoS modeling with 4.9 feet of SLR show no flooding of the site. •The current mean high tide line is over 300 feet from the site and it is unlikely that over the life of the structure, the MHT line will reach within 200 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 the 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. 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). 20 REFERENCES Coastal Engineering Manual 2004, US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, US Government Printing Office, Washington, DC. FEMA Website, 2022 https://msc.fema.gov/portal/home 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 NOAA, 2023, Web Site, 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 Shore Protection Manual, 1984, 4th ed. 2 Vols, US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, US Government Printing Office, Washington, DC. 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. 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