Habitat Friendly Shoreline Structures at Sweetwater Channel and Memorandum of Understanding with the City of San Diego

Habitat Friendly Shoreline Structures at Sweetwater Channel and Memorandum of Understanding with the City of San Diego

The proposed project would involve the San Diego Unified Port District (District) entering into a Memorandum of Understanding (MOU) with the City of San Diego to replace portions of an existing riprap shoreline revetment along Sweetwater Channel with habitat-friendly shoreline structures that create ecological value and resiliency while maintaining the necessary structural protection currently in place. Through the District’s Blue Economy Incubator, in March 2021, the District successfully completed a nature-based climate solution, pilot project along Harbor Island using ECOncrete COASTALOCK interlocking tide pool units made from biologically enhanced concrete as an alternative solution to traditional armored shorelines. This project included the removal of approximately 160 linear feet of existing traditional riprap rock revetment with the installation of a hybrid solution that increased local biodiversity, productivity, and ecosystem services while continuing to provide the equivalent shoreline stabilization required for the area. Semiannual post-construction monitoring has occurred since installation and shows promising results exceeding initial expectations. Algae, shellfish and other marine life are creating a richer, diverse, and natural community with a lower ratio of invasive to native species among the COASTALOCK units compared to traditional riprap. In April 2020, higher than normal rainfall within a short period led to a failure in the City of San Diego’s (the City) wastewater collection system, resulting in a sanitary sewer overflow (SSO) discharge of 11.23 million gallons directly into the Sweetwater River connecting to San Diego Bay. The San Diego Regional Water Quality Control Board (Regional Board) determined that this discharge was in violation of Clean Water Act section 301 and Water Code section 13376, as well as a violation of the Statewide General Order and the Regional General Order. The City and the Regional Board reached a settlement agreement wherein the City will fund a Supplemental Environmental Project (SEP) that replaces approximately 1,000 linear feet of existing rock revetment along the Sweetwater Channel shoreline with an alternative sustainable shoreline that increases biodiversity and habitat value, improves water quality, and provides additional ecosystems services while maintaining the necessary structural protection currently in place. To facilitate the settlement agreement with the Regional Board, the City proposed a project for the installation of an eco-engineered sustainable shoreline along the Sweetwater Channel. The Sweetwater Channel Sustainable Shoreline SEP is informed by the success of the District’s prior ECOncrete COASTALOCK pilot project at Harbor Island. The proposed location within the Sweetwater Channel is in proximity to significant recreational uses including Pepper Park and Pier 32 marina, on the northern edge of the channel, and marsh habitat along the southern edge of the channel. The SEP scope of work includes the design, planning and environmental review, construction and two years of post-construction monitoring to evaluate biological establishment. To implement this project, staff is requesting the Board of Port Commissioners (Board) authorize the District to enter into a MOU, which details the responsibilities, budget, tasks, and deliverables necessary to complete the project. The City would fund the project for $2,600,000. The District shall not be required to incur any cost or spend any of its own funds to plan, design, permit, procure, construct, install, and/or monitor the Sustainable Shoreline, as the MOU includes the reimbursement of staff time. The MOU would be effective until September 30, 2027. The proposed project site is located along the existing armored shoreline of Sweetwater Channel in San Diego Bay. The proposed sustainable shoreline structures would be designed to create water retaining elements which are absent in most urban waterfronts. The proposed project, consisting of habitat-friendly shoreline structure units, would provide shoreline stabilization while simultaneously creating a well-defined local ecosystem that mimics natural rocky intertidal habitat, increasing local biodiversity and biological productivity. The site would consist of the replacement of approximately 1,000 linear feet of the existing riprap armored shoreline. A five-foot buffer would be provided in each direction of the installation site and included as part of the total project area. The installation site would be positioned to be intermittently submerged by the tide and, therefore, would not encroach into public park space. The production of the habitat-friendly structure units would be completed off-site. The removal of the existing riprap stones and the installation of the habitat-friendly shoreline structure units could be completed either waterside or landside. Installation of the tidal pool system would occur over several weeks within acceptable low tide windows. Work would occur five days per week and would require approximately seven (7) construction workers. If installed waterside, construction would likely involve a crane operated from a barge off the shoreline. The barge would avoid existing eelgrass and would be secured in place to avoid disturbance to the channel and not impede upon navigational rights. If installed landside, construction would likely involve a crane operated from the top of the existing shoreline slope with appropriate project limits demarcated with fencing. This may involve temporarily diverting public access during the installation period. Some temporary sidewalk detours may be provided to maintain public access during the installation period. The existing riprap stones within the footprint of the installation site would be removed likely by crane from either waterside or landside, with the exception of leaving a few stones in place to lock in and support the foundation of the newly-placed sustainable shoreline structures. The crane would likely remove the riprap using a clam bucket or grapple, as determined by the contractor. All removed riprap stones would be removed from the project area and transported off-site to an upland location. Upon removal of the existing riprap stones, the new sustainable shoreline structures would be placed within the shoreline footprint likely with the use of a lifting crane. Ecological and structural monitoring would take place every six months post-deployment for two years to evaluate the performance of the habitat friendly shoreline structures as an ecological armoring alternative to traditional riprap stones. The project requires a U.S. Army Corps of Engineers (ACOE) pre-certified Nationwide Permit #13 Bank Stabilization, and a Regional Water Quality Control Board Clean Water Act Section 401 Water Quality Certification, as part of the entitlement process. Additionally, the Applicant would be responsible for complying with all applicable federal, state, and local laws regulating construction and demolition debris, noise, and stormwater. No eelgrass resources are known to occur within the project area. If construction occurs waterside, all operations will require avoidance of eelgrass habitat and a pre-construction eelgrass survey would be completed prior to commencement of construction activities to identify potential eelgrass and unvegetated areas present in the nearshore adjacent to the shoreline, consistent with the ACOE Nationwide Permit requirements. This survey and on-site observations would be used to inform construction method and operations in order to avoid impacts to existing eelgrass that may be present in the nearshore outside the perimeter of the project area.

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