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HomeMy WebLinkAboutPA2022-025_20220127_Coastal Hazards Report_1-21-22• Geotechnical • Geologic • Coastal • Environmental 5741 Palmer Way • Carlsbad, California 92010 • (760) 438-3155 • FAX (760) 931 -0915 • www.geosoilsinc.com January 21 , 2022 Robert D. Olson RD Olson Development 520 Newport Center Drive, Suite 600 Newport Beach, CA 92660 WO S8275 SUBJECT: Engineering Assessment of Damage At and Adjacent to 925 Via Lido Saud, Newport Beach, CA, and Assessment of Support for a New Bulkhead. Dear Mr. Olson: At your request, GeoSoils Inc. (GSI) is pleased to present the following summary of the damage observed to the residential structures at and adjacent to 925 Via Lido Saud, Lido Isle, Newport Beach (the site), erosion condition on the site, and support for the installation of a new bulkhead at the site. Our scope of work included an inspection of the site, damage to the adjacent residences and other improvements, evaluation of the need for a bulkhead at the site to protect existing structures from erosion, and preparation of this letter report. SITE INSPECTION The subject site is located on the southeast corner of Lido Isle, in Newport Beach. The site is developed with a single family residence. There is no bulkhead fronting the site, which creates a gap in the almost continuous bulkheads fronting all the other properties in this area of Lido Ilse. Figure 1 shows a Bird's Eye View of the site and adjacent properties downloaded from the internet. The site inspection was performed by the undersigned on January 12, 2022. The site inspection included observations of conditions along the back shoreline at the site, and conditions of the foundations and flat work on the adjacent properties 921 Via Lido Soud and 929 Via Lido Soud . A summary of the observations, including photographs is provided after Figure 1. As noted above, Lido Island is generally protected by a seawall/bulkhead around its perimeter. Unlike the other 7 islands in Newport Harbor (Balboa, Little Balboa, Collins, Harbor, Bay, Linda, and Newport Islands) Lido Island bulkheads were not installed as a single continuous bulkhead. Rather, each property owner erected its own bulkhead subsequent to the subdivision of Lido Isle in the 1920's. Generally, the bulkheads followed the Federally designated "bulkhead line". PA2022-025 2 The site does not have a bulkhead. City policy encourages installation, maintenance and improvement of bulkheads to protect structures. (See, City LUP Policy 2.8.6-5) Filling existing gaps in Lido Island bulkheads is essential to the protection of the residential structures and the public infrastructure (streets, utilities, storm drains) which have been constructed over the past 100 years. Figure 1. Subject site, 925 Via Lido Sound and adjacent properties. 929 Via Lido Soud The property line wall between the site and 929 Via Lido Soud is, for the most part, obscured by landscaping hedges. However, the bayward ~10 feet of the wall was experiencing water damage (staining and finish bubbling) from bay waters coming thru the gap in the shore protection. The saturation of the site soils due to bay water intrusion weakens the sandy soils adjacent to the wall and the 929 Via Lido Saud residence foundation. Saturation is most prevalent in the periodic inundation of the sandy subsoils beneath the foundation at and during peak tides. The frequency and duration of such peak tides have increased over the past 100 years and can be expected to increase further in PA2022-025 3 the future. The 929 Via Lido Soud residence has a basement, which was inspected. The corner of the residence foundation wall directly adjacent to the site and nearest the bay showed signs of ongoing distress. The foundation wall was cracked and the crack geometry was such that it appears that the corner is settling towards the bay and slightly towards the property. Figure 2 shows the crack directly in the residence foundation. The settlement is likely caused by lateral spreading of the site soils away from the foundation and towards the bay when they are periodically inundated by the bay waters. Figure 2. Foundation cracks at 929 Via Lido Soud due to soil movement. PA2022-025 4 921 Via Lido Soud The residence at 921 Via Lido Saud is showing signs of foundation displacement shown in the patio settlement at the shared property line with the site. Like on 929 Via Lido Saud, lateral spreading of the soils adjacent to the foundation and the patio. This result in settlement of the residence and settlement of the patio along with distressed ( offset cracks) flat work. Figure 3 shows the foundation of 921 Via Lido Saud has settled about½ inch as a result of the sandy soils on the site moving away from the foundation and towards the bay. As noted above, the frequency and duration of this adverse soil saturation is project to increase in the future. Figure 3. Settlement of the foundation closest to the site property line and the bay. Note the cracked and displaced tiles(flat work) in the fore ground. The return wall from the 921 Via Lido Saud bulkhead, along the site shared property line, is just a retaining wall with a traditional wall footing (not deepened). It is not designed like a bulkhead, which extends down several feet. The saturation of the site soils by bay water, and the lateral spreading of the soils adjacent to the return wall has resulted in the distress to both the patio flat work (differential cracks) and rotation of the return wall towards the site. Figure 4 shows this distress observed during the site inspection. PA2022-025 5 Figure 4. Bulkhead return wall at 921 Via Lido Saud rotation and damage in the form of settlement and cracking of the patio behind the bulkhead and adjacent to the return. 925 Via Lido Soud The intrusion of the bay waters onto the site has resulted in a bayward movement of sand. The soils next to the foundation of the adjacent residences become saturated and spread laterally away for the foundation due to the foundation loading. The innundation is evidence by the landscaping that was died from salt water. The sand on the site has moved bayward as shown in Figure 5. Over the 90+ years since the subdivision of Lido Isle for residential purposes, sea level rise has increased the duration and frequency of the soil saturation events, which lead to damage to the structures at 921, 925 and 929 Via Lido Saud. The Coastal Commission Sea Level Rise Guidance advises that this sea level rise will accelerate in the future, further increasing the duration and frequency of soil saturation. PA2022-025 6 Without a bulkhead at 925 Via Lido Soud, foundation displacement as described above will further damage the structures eventually to the point of foundation failure. Figure 5. Photograph showing the damaged areas at 921 Via Lido Sound and the site. ADDITIONAL INFORMATION The majority of Lido Isle is protected by private bulkheads. In the site area all of the residences are protected by bulkheads with the exception of the site. Other areas without a bulkhead proper are protected by retaining walls that exclude the bay waters. These areas include behind the public boardwalk on the north west side of the island and some street ends. These bulkheads and walls are essentially to prevent flooding of the island during King Tides. The City of Newport Beach produced a Public Trust Lands Sea Level Rise Vulnerability Assessment in 2019. Currently, the City is working on increasing the height of the city owned seawall around Balboa Island. Balboa Island street and residence elevations are a few feet lower than Lido Isle streets and residences . While the City may incorporate other sea level rise (SLR) adaptation strategies such as planned retreat and beach nourishment for other parts of the community, it appears that at this time the City is using the "hold the line" SLR adaptation strategy for the island communities. This makes sense for the 8 island communities within Newport Bay. On Lido Isle the bulkheads PA2022-025 7 are privately owned so increasing them in height to adapt to SLR will not involve public money. The installation of a bulkhead/seawall at the site, paid by the property owner, is consistent with the overall City SLR resiliency efforts at this time. One of the important aspects of construction of a bulkhead at the subject site is that the work can be performed entirely from the private property. The work would take place well above the Mean High Tide. No equipment will need to be on public lands. The proposed new bulkhead is a "deadman" restrained pile design with a concrete cap top than can be adapted to SLR. The seawall is designed to protect the low lying portions of Lido Ilse behind it including public roads and infrastructure (utilities). CONCLUSIONS A new bulkhead/seawall is needed at the subject site to stop the ongoing and increasing distress to the adjacent residence foundations and other improvements (deck and patio). The damage to these adjacent residences is from lateral spreading of unconfined soils on the subject site. The proposed bulkhead is necessary to protect these existing structures threatened by natural hazards and is in alignment with the bulkheads on the adjacent properties. A new bulkhead will confine the site soils and stop the progression of the damage to the residence foundations. A new bulkhead will provide protection of Lido Isle in consideration of SLR and is consistent with the SLR adaptation strategy for Newport Bay island communities. Finally, the construction of the bulkhead will be entirely on and accomplished from private property. Based upon our review of the proposed plans the bulkhead meets the current requirements for new bulkheads in the City of Newport Beach. We appreciate this opportunity to be of service. Should you have any questions, please do not hesitate to contact the undersigned at (760) 438-3155. Respectfully submitted, GeoSoils, Inc. David W. Skelly MS RCE#47857 PA2022-025