Geotechnical C Geologic C Coastal C Environmental

5741 Palmer W ay C Carlsbad, California 92010 C (760) 438-3155 C FAX (760) 931-0915 C www.geosoilsinc.com

November 27, 2017 WO S7309-SC

Pacifica States Capital Corp.PO Box 7602Menlo Park, CA 94026

Attention: Mr. John Hansen

Subject: Coastal Hazard Discussion 1567 Beach Blvd and Inspection of City ofPacifica Shore Protection Fronting 1567 Beach Blvd, Pacifica, San MateoCounty, California.

Dear Mr. Hansen:

At your request, GeoSoils, Inc. (GSI) is pleased to provide the following coastal hazardsand shore protection condition report for the subject site. The analysis is based upon oursite and shore protection inspection, existing published reports concerning the local coastalprocesses, site elevations, and knowledge of local coastal conditions. The analysis utilizesthe criteria guidelines in the California Coastal Commission (CCC) Sea-Level Rise (SLR)Policy Guidance document, adopted in August 2015. This report constitutes aninvestigation of the wave and water level conditions expected at the site in consequenceof extreme storm and wave action. The purpose of this report is to provide the necessarycoastal engineering permit information to support the project. It also provides conclusionsand recommendations regarding the susceptibility of the property to wave attack, andmethods for controlling wave overtopping and ocean flooding on the property.

INTRODUCTION

The proposed project is consists of at most 7 attached two and three story town homes,built at finished grade, and all within the 35 feet height limit. The project includes a 20 feetsetback from the Beach Blvd right of way. The Beach Blvd right of way at the property is50 feet behind the existing City of Pacific shore protection. The residential structures willbe at least 70 feet behind the shore protection. Parking will be traditional two car attachedgarages. Preliminary plans for the project, including site elevations, have been reviewedby this office. Our most recent site and shore protection inspection was performed onNovember 8, 2017. Figure 1 is an aerial photograph, downloaded with permission fromGoogle Earth, showing the site, the adjacent properties, the public street, and the shoreprotection fronting them, taken on November 2, 2016.

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Figure 1. Subject site, adjacent properties, Beach Blvd, and the shore protection.

SHORE PROTECTION INSPECTION

Beach Blvd, fronting the site, is protected by shore protection that consists of a reinforcedearth (RE) wall and a quarry stone revetment. The quarry stone revetment was subject tomajor maintenance and reconstruction in the Fall of 2002. The maintenance wasperformed under the supervision of this office. The slope of the face of the revetment isabout 2:1 (horizontal:vertical). The top of the revetment is at about +18 feet NAVD88. Thetop of the RE wall is about +25.3 feet NAVD88. GSI has observed the shore protectionalong Beach Blvd periodically over the last 15 years. In addition, GSI has inspected theshore protection fronting this site regularly since 2004. A comparison of aerialphotographs available on the Coastal Records website shows little, if any, change in overrevetment geometry and the relative positions of the stones fronting the RE wall.

This particular section of the Beach Blvd shore protection has not been subject to anydamage to the vertical RE wall. In 2016 there was some damage to the RE wall locatedabout 500 feet to the south of the subject site. The build up of sand at this section of theBeach Blvd seawall likely contributed to the direct wave runup attack on the vertical seawalland piping out of fill soils behind the wall. An important point is that there was no damageto the residences on the landward side of Beach Blvd behind the damaged section. Finally,there was no damage to the seawall fronting the subject site. The City has performedmaintenance to the shore protection fronting the site in the form of adding more quarry

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stone, in about 2010. In addition, the City recently commissioned an investigation toidentify voids behind the seawall along the promenade and Beach Blvd proper. Therewere NO voids detected fronting the subject site.

HAZARD ANALYSIS

Moffat & Nichol (M&N) in 2016 prepared a coastal hazards study for a City of PacificaBeach Blvd ocean front site to the south of the subject site. Relevant (oceanographic andcoastal processes) information will be taken from that report and supplemented herein asnecessary.

COASTAL PROCESSES

The City of Pacifica is in the northern part of San Mateo County about 4 miles south of SanFrancisco. The city lies within what the US Army Corps of Engineers (1972) has termedthe San Francisco littoral cell. A littoral cell is a coastal compartment that contains acomplete cycle of littoral sedimentation including sources, transport pathways andsediment sinks. This overall cell extends from San Francisco Bay to Point San Pedro justsouth of Pacifica a total distance of about 16 miles. The San Andreas Fault essentiallybisects this littoral cell at the area known as Mussel Rock. There is some indication fromanalysis of beach sand mineralogy that there is little transport of sand from the northernhalf of the cell, Ocean Beach, to the southern half of the cell, Pacifica.

The source of for the littoral cell includes sands transported south from the San Franciscotidal bar and Ocean Beach, sediments delivered by the local streams (San Pedro Creek,alluvium from Laguna Salada, Big Inch Creek, Milagra Creek, and others), and erosion ofthe bluffs. The shoreline from Mussel Rock to Mori Point is characterized by bluffs thatrange in height from 40 to 150 feet. The beaches are characteristically narrow along thissection of shoreline. Beach Blvd is located along this stretch of coastline. The actualquantities of sand, that are derived from each source, have not been determined, and thecontribution of each source will vary with rainfall and wave activity.

The energy that moves the beach sands on and offshore, and along the shore is derivedfrom waves. Waves reach the Pacifica shoreline from the southwest through the northwestdeepwater wave directions. The US Army Corps of Engineers produced a draft report in1972 that used wave refraction diagrams to determine the predominate direction of littoraltransport. The final report and data are not available from the Corps’ San FranciscoDistrict Office. However, the report concluded that “sand transport in both directionsbetween Mussel Rock and Mori Point is known to occur, depending upon the time of yearand direction of wave attack, the net longshore movement is negligible.” Using Battalio(1996) one can assume that annual longshore sediment transport rates are on the orderof 100,000 cubic yards. Moffatt & Nichol 2016 provide a wave and period rose in AppendixA that justifies a 11.5 feet analysis wave height and a 17 second design wave period ofwave overtopping analysis.

The sinks for sediment in the Pacifica area have not been clearly identified. Most likelysome beach sediment is transported north past Mussel Rock, and some sediment is lost

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offshore trying to move south around San Pedro Point. There is also some potential lossof beach sands offshore along the entire cell. However, the US Army Corps of Engineers(1972) determined that “beach profiles show that during winter months sand is removedfrom the beach and during summer months is returned with very little net loss.” The reportdoes not quantify this net loss other than to say it is very little or in others words notsignificant. The Corps report gives an estimated average annual erosion rate of about 2feet along this area. Again, it is important to point out that the Corps study does not includethe last few decades of El Niño storms.

In 2006 the US Geologic Survey (USGS) published a comprehensive report aboutshoreline change for the coast of California (Hapke, et al, 2006). This report uses datafrom the late 1800s to the early 2000s and covers the section of shoreline that the subjectsite is in. Using Figure 25 from the report and the ruler/path tool on Google Earth thedistance from the site to the San Francisco Bay is 18 kilometers. A portion of Figure 25from the USGS report is reproduced below as Figure 2 to show the short-term and long-term erosion rates at the site. The short term and long term erosion rates at the site areessentially equal and scale to be 0.42 m/yr = 1.38 ft/yr.

Figure 2. Short-term and Long-term shoreline movement rate at the site (USGS 2006).

Despite the fact that natural cliffs along the coastline of Pacifica are recently experiencingincreased bluff retreat, the shore protection fronting the site prevents erosion at the subjectsite. M&N (2016) concluded in section 3.4 that “Beach Boulevard prevents erosion at theproject site. Bluff retreat is not estimated to be a direct hazard to development of the 2212Beach Boulevard property.” We are in general agreement with M&N and their conclusionsapply to the subject site.

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DESIGN WATER LEVEL SEA LEVEL RISE

The maximum water elevation recorded near the site is ~+8.72 feet NAVD88 (M&N, 2016).This sea level includes short-term effects that would increase sea level, such as wave setup and El Niño. The CCC SLR Policy Guidance document was approved in August 2015. The CCC has adopted the National Research Council (NRC) 2012 SLR estimates of 16.56inches to 65.76 inches over the time period from 2000 to 2100. Using the CCC guidancethe range of projected sea level rise is between 1.27 feet and 4.8 feet in the year 2092 (75years from 2017). The ranges provided in the CCC SLR Guidance provide no probabilityof occurrence. That is to say that it is not clear as to the likelihood of any given SLR in theyear 2092. The 1.27 feet of SLR may be more likely than the 4.8 feet SLR, or vice versa.The April 2017 “Rising Seas in California” by the California Ocean Protection Council(COPC) provides more current SLR estimates within a “likelihood” frame work. The COPCprovides SLR estimates based upon emission scenarios known as a “representativeconcentration pathway” or RCP. TABLE I below is from the 2017 COPC document (page27) for San Francisco, and is applicable to the site.

TABLE I

This table illustrates that SLR in the year 2100 could be any where between 1.6 feet and6.9 feet. The likely range for the most onerous RCP is 1.6 feet to 3.4 feet, with a 5%probability that SLR meets or exceeds 4.4 feet. Based upon M&N (2016)a reasonableestimate of SLR over the 75 year design life is 3 feet. The design still water elevation willbe the maximum water elevation of 8.72 NAVD88 plus 3 feet of SLR or +11.7 feetNAVD88.

OVERTOPPING ANALYSIS

The Coastal Engineering Manual (CEM) provides wave overtopping analysis methodology

sfor irregular waves that are dependent upon the significant wave height, H , and the mean

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omwave period, T . For this analysis CEM Equation VI-5-23 is used. The first step is to

s omdetermine H and T for the Beach Boulevard site. There is much wave data that hasbeen collected by the Coastal Data Information Program (CDIP) at the Scripps Institutionof Oceanography. CDIP data is available on line from several wave buoys and arrays.GSI relied on the M&N (2016), Appendix A, CDIP wave data. The wave rose shows a

ssignificant wave height, H , of 11.5 is reasonable for the CEM wave overtopping analysis.

omThe period rose shows that a wave period, T , of 17 second is reasonable for the CEMovertopping analysis.

Table VI-5-9 from the CEM provides the equation and coefficients, along with the

s omcalculations. The H and T are taken from the historical wave data and M&N (2016). Thecalculation was done for the revetment slope ½, up to elevation +18 feet NAVD88, andwith a crown wall (the RE wall) to elevation +25.3 feet NAVD88, with the design ocean levelat 11.7 feet NAVD88. Figure 3 is taken from the CEM Table VI-5-9.

Figure 3. Overtopping figure from the CEM for Beach Blvd.

For the revetment the overtopping rate equals 1.18 ft /s-ft. For the calculated overtopping3

rate (Q=q), the height of water can be calculated using the following empirical formulasprovided by the USACOE (Protection Alternatives for Levees and Floodwalls in SoutheastLouisiana, May 2006, equation 3.1). For the calculated overtopping rate (Q=q), the heightof water and the velocity of this water can be calculated using the following empiricalformulas provided by the USACOE (Protection Alternatives for Levees and Floodwalls inSoutheast Louisiana, May 2006, equation 3.1).

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For SLR of 3 feet, with an overtopping rate of 1.18 ft /s-ft at the crest of the seawall, the3

bore height is ~0.5 feet. The result of this overtopping calculation is in good agreementwith the results of M&N (2016) as shown in their Figure 9. M&N Figure 9 shows that theovertopping bore dissipates in about 40 feet from the top of the shore protection. Theproposed project is over 70 feet from the top of the shore protection fronting Beach Blvd.

An available internet tool for site hazard determination (used by the California CoastalCommission) is the USGS model called the Coastal Storm Modeling System (CoSMoS)for assessment of the vulnerability of coastal areas to SLR and the 100-year storm,http://walrus.wr.usgs.gov/coastal_processes/cosmos/. Using the modeling programCoSMoS 3.0, the vulnerability of the site to different SLR scenarios and the 100 yearextreme waves can be assessed. The model output includes wave runup and flooding. The output of the CoSMoS provides an additional validation of the conclusions andrecommendations of this report. The program output provides a third party analysis for anysite specific independent coastal engineering analysis. Figure 4 is the output for theCoSMoS for the Beach Blvd Pacifica site. It should be noted that under 150 cm (4.9 feet)of SLR and the 100 year wave event, the site is not in the flooding or inundation zone.

Figure 4. CoSMoS output for the subject site for 4.9 feet of SLR and the 100-year storm.

TSUNAMIS

The site is mapped within the limits of the California Office of Emergency Services tsunamiinnundation map, San Francisco South Quadrangle (State of California 2009). The tsunamiinundation maps are very specific as to their use. Their use is for evacuation planningonly. The limitation on the use of the maps is clearly stated in the PURPOSE OF THISMAP on every quadrangle of California coastline. In addition, the following twoparagraphs were taken from the CalOES Local Planning Guidance on Tsunami Responseconcerning the use of the tsunami inundation maps.

In order to avoid the conflict over tsunami origin, inundation projections arebased on worst-case scenarios. Since the inundation projections are intended for

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emergency and evacuation planning, flooding is based on the highest projectionof inundation regardless of the tsunami origin. As such, projections are not anassessment of the probability of reaching the projected height (probabilistichazard assessment) but only a planning tool.Inundation projections and resulting planning maps are to be used for emergencyplanning purposes only. They are not based on a specific earthquake and tsunami.Areas actually inundated by a specific tsunami can vary from those predicted. Theinundation maps are not a prediction of the performance, in an earthquake ortsunami, of any structure within or outside of the projected inundation area.

The City of Pacifica receives immediate notice from NOAA Pacific Tsunami WarningCenter if there is any indication of potential tsunami hazard. The City adheres to the SanMateo County protocol for tsunami watches and warnings and provides residents andbusiness owners within potential inundation areas with multiple forms of notification of thehazard. Evacaution routes are clearing marked int eh coastal areas.

M&N (2016) provides a discussion of tsunami impacts on the City of Pacifica property thatis very similar to the subject site. The City property is landward of shore protection, andBeach Blvd, and at a similar distance and elevation from the ocean as the subject site.M&N (2016) stated that the CalOES maps model the inundation of a tsunami with anapproximate 1,000 year recurrence interval. M&N determined that the inundation extentreaches up to about elevation +36 feet NAVD88. The Science Application for RiskReduction (SAFRR) tsunami study headed by USGS investigated a tsunami scenario witha 200-240 year recurrence interval. Figure 5 shows the SAFRR model output for the site.The site is only partially in the SAFRR inundation zone. M&N (2016) concluded that themore probable SAFRR will impact the City site with less than 1 feet of water. Thisconclusion and bore height (1 feet) logically apply to the subject site. The larger CalOESmodel has a low probability due to the concurrence of several low occurrence probabilityearthquake events.

Figure 5. SAFRR tsunami modeling output for the subject site showing that only a smallportion of the site is in the inundation zone.

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CONCLUSION

The proposed project is reasonably safe from coastal hazards for the following reasons.

• The project is setback from the shoreline and at an elevation such that wave runupwill not reach the development. The finished floor elevation is above elevation +31feet NAVD88.

• The presence of the shore protection and the continued maintenance of the shoreprotection prevents erosion and site flooding.

• Rare and infrequent impacts from tsunamis are mitigated by the design of the oceanfacing portion of the development. The structure is protected by a ~3 high blockwall along the ocean facing potions of the development, which will resist thepotential forces of a 1 feet high tsunami bore coming over the shore protection.

The recommendations of this report should be used by the design team to minimize risksfrom flooding. The proposed development is entirely on private property and well abovethe mean high tide line, so it will not impact lateral public access or visual resources alongthe shoreline. As designed the proposed project will not impact the adjacent properties orcontribute to geologic instability of the adjacent sites. It is unlikely that any additional shoreprotection will be needed over the 75 year life of the development. The final plans shouldbe reviewed and approved by this office with regard to compliance with the wave runup andcoastal hazard recommendations.

The opportunity to be of service is sincerely appreciated. If you should have anyquestions, please do not hesitate to contact our office.

Respectfully submitted,

David W. Skelly MS, PERCE #47857GeoSoils Inc.

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REFERENCES

Battalio, R.T. and Dilip Trivedi, 1996, “Sediment Transport Processes at Ocean Beach, San Francisco,” California, ASCE Coastal Engineering Proceedings Vol 3 Chapter208.

Hapke, Cheryl J.; Reid, David; Richmond, Bruce M.; Ruggiero, Peter; and List, Jeff; 2006,National assessment of shoreline change part 3: historical shoreline change andassociated coastal land loss along sandy shorelines of the California coast:U.S.Geological Survey Open-File Report 2006-1219.

Lajoie, K.R., and Mathieson, S.A., 1998, 1982-1983 El Niño coastal erosion, San MateoCounty, CA: U.S. Geological Survey Open-File Report 98-041, 61p.

Moffatt & Nichol, 2016, “Coastal Hazards Study, 2212 Beach Boulevard, Pacifica,”prepared for the City of Pacifica, dated June.

USACOE, 1972, “(Draft) Beach Erosion Control Report on the Shores of the City of Pacifica, California.”

USACOE, 2004, Coastal Engineering Manual.