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HomeMy WebLinkAboutPA2022-002_20220104_Coastal Hazards_11-8-21GeoSoils Inc. November 8, 2021 Helle McIain 8 Strands, 913 Balmoral 2 Praed Street London, UK W21JN SUBJECT: Coastal Hazard and Wave Runup Study, 2172 East Oceanfront, Newport Beach, California. Dear Helle McIain: At your request, GeoSoils, Inc. (GSI) is pleased to provide this coastal hazard and wave runup study for the property located at 2172 East Oceanfront, 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 latest CCC Sea-Level Rise (SLR) Guidance document (November 2018), a review of City of Newport Beach Municipal Code (NBMC) 21.30.15.E.2, a review of the site elevations, a discussion/review of the project plans, a site inspection, 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 years. It also provides conclusions and recommendations regarding the susceptibility of the property and the proposed new residential structure to wave attack. The analysis uses design storm conditions typical of January 18-19, 1988, the winters of 1982-83, and 1998 type storm waves and beach conditions. INTRODUCTION AND BACKGROUND The subject site is located at 2172 East Oceanfront, Newport Beach, California. It is an irregular shaped ocean front parcel with an existing residential structure. Figure 1 is a “Bird’s Eye” aerial photograph of the site taken in 2020 downloaded from the internet. The proposed development consists of the removal of the existing residence and construction of a new residence and other improvements. The site is fronted by a wide sandy beach and the Pacific Ocean. This shoreline is located between the Balboa Pier and the west jetty of Newport Harbor (at the jetty), in a coastal segment referred to as the Balboa 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). In general, the movement of sand along a shoreline depends upon the orientation 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. 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002 GeoSoils Inc.2 Figure 1. Subject site in 2020. Note the nearby dune areas and the very wide beach. USACOE (2002) contains historical beach profile and beach width data for the Newport Beach area. At the subject site, the beach width has changed little over the past 70 years as a result of beach nourishment in the 1930's with sand from Newport Harbor. The available photographic data shows that the actual beach width has increased since 1965. During typical winter beach conditions, the beach width may be reduced to about 550 feet. The narrowest beach width occurred in 1965 (approximately 500 feet). During typical summer beach conditions, the beach width is in excess of 600 feet. Measurements during our September 2021 site inspection indicate that the mean high tide line is ~650 feet from the site property line. Despite efforts to control the movement of sand along the Newport coast, the shoreline at this section of Newport Beach does experience short-term erosion. The erosion is temporary and is largely the result of an energetic winter. As stated before, there is no clear evidence of any long-term erosional trend (USACOE, 2002). The wide sandy beach in front of the subject site is normally over 600 feet wide and has provided more than adequate protection for the property over the last several decades. In the past, wave runup has not reached the site, and the site has not been subject to wave attack for at least the last 60 years. This includes the winter storms of 1982-83, January 1988, and 1998, which are considered the coastal engineering design storms for southern California. 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002 GeoSoils Inc.3 DATUM & DATA The datum used in this report is North American Vertical Datum of 1988 (NAVD88) which is 2.35 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). The NOAA Nautical Chart #18746 was used to determine bathymetry. Beach profile data was reviewed from USACOE (2002). Aerial photographs, taken from 1972 through 2020, were reviewed for shoreline changes. Site elevations relative to NAVD88 were taken from a site survey by Guida Surveying Inc, dated March, 2020. Development plans were provided by Graham Architecture, the project designer. 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 within 500 feet of the site since 1972. Figure 2, 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 what would be considered 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 3, taken in February 2021, shows what could be described as the normal beach width (over 600 feet). A review of the aerial vertical photographs over the last 45 years shows a very wide beach even though some of the photos were taken in the winter and spring, when the beach is seasonally the narrowest. None of the reviewed photographs show water reaching within 500 feet of the site. 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 70 years. The site has not flooded from ocean water or from surface drainage due to its elevation relative to the city street drainage paths. The adjacent city streets are lower than the lowest grade on site. In the future, wave runup will likely not reach the site under severely eroded beach conditions and extreme storms. 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002 GeoSoils Inc.4 Figure 2. Shoreline fronting the subject in January 1988 after the “400-year” wave event. Figure 3. Shoreline fronting the subject site in October 2020 (note the very wide beach). WAVE RUNUP AND OVERTOPPING Wave runup is defined as the vertical height above the still water level to which a wave will 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002 GeoSoils Inc.5 Figure 4. Wave runup terms from ACES analysis. 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 is 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 4 is a diagram showing the analysis terms. Oceanographic Data The wave, wind, and water level data used as input to the ACES runup and overtopping application were taken from the historical data reported in USACOE (1986) and USACOE (2002). 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 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 "v h s PA2022-002 GeoSoils Inc.6 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 performed 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 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, the 2011 Everest International Consultants Inc. (EICI, 2011) reported that the elevation of 7.71 feet NAVD88 is the 1% water elevation. For this analysis the design historical highest water elevation will be +7.7 feet NAVD88. 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 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002 GeoSoils Inc.7 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 5 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 5. 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 about 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 (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. 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 LOW Medium -High Extreme Risk Aversion Risk Aversion 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 PA2022-002 GeoSoils Inc.8 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 21.5 years and next 8.5 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 6 provides the SLR model curves and tables for Los Angeles Harbor. Figure 6. Taken from the USACOE SLR curve calculator program. Looking at the table in Figure 6, 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 5 for the year 2030 and 0.1 feet of SLR, the closest probability category is the lower limits of the “Likely Range.” 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 ro (X) 0 j 14 12 10 8 6 NOAA et al. 2017 Relative Sea Level Change Scenarios for: LOS ANGELES 2010 2020 2030 2040 2050 2060 Year Huntington Hart>oi. Scenarios for LOS ANG COLES NOAA.2017 VlM: -0.00328 feet/)'I" All val!RS are expressed in ieet Year NOAA2017 NOAA.2017 NOAA2017 NOAA2017 NOAA2017 VLM Low Int-Low Intermediate Int-High 2000 2.70 2.70 2 70 2.70 2.70 2010 267 2n 2n 283 290 2020 2.63 283 290 3.00 309 2030 260 293 303 316 336 2040 2.57 3 03 313 342 3.72 2050 2.54 3 13 329 372 4 24 2060 2.50 323 342 4.08 480 2070 2.47 3.32 359 4.44 546 2080 2.44 3.42 372 4.90 6-24 2090 2 40 3.49 3 85 5.36 710 2100 2.37 3.52 398 5.88 815 2070 NOAA.2017 High 2.70 293 3 16 352 4.08 483 5.69 6.67 7.82 9 13 10.61 2080 NOAA2017 Extreme 2.70 2.93 3.23 365 4.37 526 6.37 7.65 9.10 10.67 12.61 2090 __, NOAA2017 Extreme __, NOAA2017 High -.-f-lOAA2017 Int-High --. f-lOAA2017 lntermedia1e .-NOAA2017 lnt-lo\V -+-NOAA2017 low _.... f.fOAA2017 VU/1 2100 PA2022-002 GeoSoils Inc.9 The CCCSLRG document recommends that a project designer determine the range of SLR using the “best available science.” The 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 5 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 2096. 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. 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002 GeoSoils Inc.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 15.6 ft3/s-ft. For the calculated overtopping rate (Q=q), the height of water and the velocity of this water can be calculated using the 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 feet with an overtopping rate of 15.6 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 Manual (CEM) 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 q ACES I t'ode : Single Case I Funct iona l Area: Wave -Structure Interaction App I icat ion: Wave Runup and Overtopping on l111perireable Structures Item Unit Value I Sroooth SI ope I Runup and Incident Wave Height Hi: ft 8.500 Overtopp i ng Wave Period T: sec 15 .oc:o COTAN of Nearshore Slope COT("): 80.0C:O 2172 East Water Depth at Structure Toe ds: ft 10 .900 COTAN of Structure Slope COTCeJ: 12 .oc:o Oceanfront Structure Height Above Toe hs: ft 12 .500 Wave Runup H: ft 8 .263 New port Onshore Wind Uelocity U: ft/sec 16 .878 Beach Deepwater Wave Height H0: ft 5 .818 Relati.....e Height ds/H0: 1.861 Wave Steepness H0/CgT'2l: 0.000808 Overtopping Coefficient "' 0.070000 3.2 FT SLR Overtopping Coefficient Qstar0: 0.070000 Overtopping Rate Q: ftA3/s-ft 11.575 I ACES I t'ode : Single Case I Functional Area: Wave -Structure Interaction Application: Wave Runup and Overtopp i ng on Impermeable Structures Item Unit Va lue I Sroooth Slope Runup and Incident Wa1,,.,1e Height Hi f t 10.0C:O 01,,.,1ertopp i ng Wa1Je Period T sec 15.0C:O CO TAN of Nearshore SI ope COT(") 80.0C:O 2172 East Water Depth at Structure Toe ds f t 12.300 CO TAN of Structure SI ope COTCel 12.0C:O Oceanfront Structure Height Abo1Je Toe hs ft 11.0C:O Wa1,,.,1e Runup Onshore Wind Velocity Deepwater Wa1,,.,1e Height Relati1,,.,1e Height Wa1,,.,1e Steepness 01,,.,1ertopping Coefficient 01,,.,1ertopping Coefficient 01,,.,1ertopp i ng Rate f:: 3/2 0.5443,v .i-; ,h1 H u H0 ds/H0 H0/CgT'2l " Qstar0 Q ft 8 .962 Newport ft/sec 16.878 ft 7.077 1.738 Beach 0.000978 0.070000 6.0 FT SLR 0.070000 ftA3/s-ft 15.607 V e PA2022-002 GeoSoils Inc.11 states as a wave bore travels across a sand beach, the height of the bore is reduced. Based upon observations, this is about 1-foot reduction in bore height every 25 to 50 feet. The site is over 600 feet away, so for the 6 feet of SLR case, the wave bore may travel about 150 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. 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. Legg, et al. (2002) examined the potential tsunami wave runup in southern California. 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 will be refracted, modified, and reduced in height by the Newport jetties, as it travels into the bay, or over the development land seaward of the site. Due to the infrequent nature and the relatively low 500-year recurrence interval tsunami wave height, setback from the ocean, 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 tsunami innundation map, Newport Beach Quadrangle (State of California 2009). 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. 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002 GeoSoils Inc.12 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 7 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 7. SAFRR tsunami modeling output for the site. SHORELINE EROSION WITH FUTURE SLR The California Coastal Commission (CCC) Sea Level Rise (SLR) Guidance suggests the use of the highest erosion rate available for the predication of the future shoreline erosion due to SLR (Appendix B, page 237). The United States Geological Survey (USGS, 2006) performed a comprehensive assessment of shoreline change including this section of coastline. Figure 8 is portion of a figure from USGS 2006 (Figure 39, page 62) and shows shoreline change at the subject site. There is no long-term (purple) or short-term erosion rate at the site. Even if a short-term rate of 1 ft/yr was used as the long-term rate (this would be very conservative analysis), the retreat would be 75 feet over the 75 year life of the development. The site is currently over 600 feet from the shoreline. If the beach retreats 75 feet in the next 75 years then the site will be ~525 feet from the shoreline. A 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 ~~~,~ \, - \\ -D ' ' ' ' \\ \ Plult \ \ \\ ........ , PA2022-002 GeoSoils Inc.13 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. Figure 8. Shoreline change rate in meters per year from USGS 2006. 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 three different SLR scenarios with shoreline erosion 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. 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 hica State each 2m/ r 'E Hun ti gton "" 40 + * .. a ,. . a • ;; .., e ;; ~ .. z l! C SITE WestH wportBea h -• " ., 0 50 • • u D .;i * ! , Q • ~ ccrer on E 1sion PA2022-002 GeoSoils Inc.14 Figure 9 is the output of the CoSMoS program. The modeling shows that the shoreline does not erode to even near the site, that the streets including East Balboa, the main arterial street, will flood during the 100 year event with 175 cm (~5.7 feet) of SLR. The road near site may flood slightly. However, the area flooding will come from the bay and not from the ocean. The lowest finished floor is above + 13.5 feet NAVD88 and well above the adjacent flow line in the alley at ~+11.4 feet NAVD88. Based upon the CoSMoS modeling, the development is reasonably safe from flooding over the design life of the development due to the proposed elevation of the finished floor and setback from the ocean. Figure 9. Output for USGS CoSMoS vulnerability modeling. 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 CCC SLR guidance, the SLR estimate over the project design life the “likely” range in the year ~2096 is 3.0 feet to 3.2 feet. In addition, the analysis herein considered a less than “likely” SLR of 6.0 feet. This is the sea level rise range for the proposed project, 3.2 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. 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 Mean High Water Shorelin1 Max Wave Runup during Rood 175an SlR + Wave 100 50 cm {8.2 ft) S00 cm 06.4 ft) 7S0 cm {24.6 ft) PA2022-002 GeoSoils Inc.15 The analysis herein shows that it is unlikely that wave runup will reach the site even with 6.0 feet of SLR. The lowest habitable finished floor elevation will be at or above elevation 13.5 feet NAVD88. Site drainage from non-ocean waters is provided by the project civil engineer. The CCCSLRG 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 CCCSLRG document provides very little means or methods for predicating shoreline erosion due to SLR. If a conservative future erosion rate due to SLR of 1 ft/yr, then the shoreline will move about 75 feet over the life of the development under 6 feet SLR. The site is currently over 600 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. For SLR greater than 6 feet, which will not likely occur for many decades, waterproofing of the lower portions of the structure can be added to mitigate potential flooding impacts. It is important to point out that SLR will not impact this property alone. It will impact all of the Newport Bay low lying areas. The public streets on Balboa Island, and Balboa Peninsula will flood with lower SLR well before the subject site floods. 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. This is a regional adaptation strategy. The project design is suitable for a site specific SLR future adaptation strategy to waterproof the structure(s) up to an elevation above the impact of SLR. In addition, there are currently several very effective temporary flood control systems such as Quick Dams or even sand bagging that can be used in the future. 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): 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002 GeoSoils Inc.16 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 40 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 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 costal 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; As discussed herein, due to the very wide beach, the site is safe from shoreline erosion, including factoring in SLR of up to 6 feet. If a conservative future erosion rate due to SLR of 1 ft/yr, then the shoreline will move about 75 feet over the life of the development. The site is currently over 600 feet from the shoreline. If the beach retreats 75 feet in the next 75 years then the site will be ~525 feet or more 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 CCC SLR guidance, the “likely” SLR estimate over the project design life in the year ~2096 is 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, 3.2 feet to 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 CCCSLRG document. Per the Guidance, this elevation includes all short-term oceanographic effects 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002 GeoSoils Inc.17 on sea level, but not the long-term sea level rise prediction. If 3.2 feet and 6 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 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 feet, the beach overtopping rate is 15.6 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 currently over 600 feet away, so for the largest SLR case, the wave bore may travel about 150 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 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. 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 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002 GeoSoils Inc.18 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 feet of SLR. The habitable finished floor elevation at or above elevation +13.5 feet NAVD88 is reasonably safe for over 6 feet of SLR. Site drainage from non-ocean waters is provided by the project civil engineer. If a conservative future erosion rate due to SLR of 1 ft/yr, then the shoreline will move about 75 feet over the life of the development with 6 feet SLR. The site is currently over 600 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 long before the residence will be impacted by SLR. The shoreline fronting the site is stable and an increase in the water elevation will likely not increase shoreline erosion. The proposed project is reasonably safe from shoreline erosion due to the setback of the development to the potential future MHT line in consideration of SLR. Finally, in the future if necessary, the residence can be retrofitted with waterproofing to an elevation above the flooding potential elevation along with flood shields and other flood proofing techniques. 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 very wide (>600 feet) sandy beach in front of the property 99.99% of the time. 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002 GeoSoils Inc.19 • 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. • There is no long-term shoreline erosion. If a very conservative FUTURE retreat rate of 1 feet/year is used, it would account for about 75 feet of retreat over the life of the structure. This conservative retreat rate will not reduce the beach to less than 300 feet in nominal width (200 feet width of beach is recognized by coastal engineers as a sufficiently wide enough beach to provide back-shore protection). • The site has not been subject to any wave overtopping in the past. • The finished first floor elevation for the structure is above the street flow line (landward of the residence). • The current mean high tide line is over 640 feet from the site and it is unlikely that over the life of the structure that the mean high tide 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 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. 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). 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002 GeoSoils Inc. REFERENCES Coastal Engineering Manual 2004, US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, US Government Printing Office, Washington, DC. 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. FEMA Website, 2021 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 Legg, Mark R., Borrero, Jose C., and Synolakis, Costas E., Evaluation of tsunami risk to southern California coastal cities, in The 2002 NEHRP Professional Fellowship Report. NOAA, 2021, 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 Shore Protection Manual, 1984, 4th ed. 2 Vols, US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, US Government Printing Office, Washington, DC. State of California, County of San Diego, 2009, “Tsunami Inundation Map for Emergency Planning, Newport Beach Quadrangle,” 1:24,000 scale, dated June 1. 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. USGS 2006, “National Assessment of Shoreline Change Part 3: Historical Shoreline Change and Associated Coastal Land Loss Along Sandy Shorelines of the California Coast”, Open File Report 2006-1219, 5741 Palmer Way, Suite D, Carlsbad CA 92010 760-438-3155 PA2022-002