Habitat Friendly Shoreline Structures at Harbor Island and Sweetwater Channel

Habitat Friendly Shoreline Structures at Harbor Island and Sweetwater Channel

The proposed project would involve the replacement of portions of an existing riprap shoreline revetment along Harbor Island and Sweetwater Channel with habitat-friendly shoreline structures that create ecological value and resiliency while maintaining the necessary structural protection currently in place. In March 2021, the District successfully completed a nature-based pilot project along the existing armored shoreline of Harbor Island using ECOncrete COASTALOCK interlocking tide pool units. Through material composition and design elements, the units provide an alternative solution to traditional armored shorelines that incorporates nature-based strategies into an urban context. The pilot project included the removal of approximately 160 linear feet of existing traditional riprap rock revetment and, in its place, 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. Since installation, semi-annual monitoring efforts have indicated the pilot project is exceeding performance expectations biologically and structurally. The units are creating a richer, diverse, and natural community with a lower ratio of invasive to native species compared to traditional rock revetment. The shoreline is expected to be more structurally sound in the long term than traditional riprap as biological growth over time further protects the units. For both sites, production of the habitat-friendly structural 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 units 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 units. 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. Although present in the nearshore adjacent to the project area, no eelgrass resources are known to occur within the project footprint. If construction occurs waterside, all operations will require avoidance of eelgrass habitat. 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. Harbor Island Site The District received funding for the proposed project at the Harbor Island site through the National Oceanic and Atmospheric Administration (NOAA) Community-based Restoration Program, and anticipates that installation would commence in spring or summer 2026. Informed by the success of the COASTALOCK pilot project, the District is now pursuing additional habitat-friendly structural shoreline alternatives. The proposed project site is located along the existing armored shoreline of Harbor Island in San Diego Bay in proximity to the existing COASTALOCK units installed in March 2021. The project scope consists of the removal of up to 450 linear feet of existing riprap rock revetment at two locations along Harbor Island, to be replaced with habitat-friendly structural shoreline units such as COASTALOCK or equivalent. The proposed habitat-friendly shoreline structures would be designed to incorporate water retaining elements which are absent in most urban waterfronts. The units will be placed between Mean Lower Low Water (MLLW) and Mean Higher High Water (MHHW) elevations within the footprint of the removed rock, as indicated in the attached construction plans. The expected area of impact is approximately 12 feet wide by 450 linear feet long, resulting in a total project area footprint of approximately 5,400 square feet distributed over the two locations. The proposed project would provide shoreline stabilization while simultaneously creating a well-defined local ecosystem that mimics natural rocky intertidal habitat, increasing local biodiversity and biological productivity. A five-foot buffer would be provided in each direction of the project site during installation. Since the project site would be intermittently submerged by the tide, it would not encroach into public park space. For the Harbor Island site, a temporary construction staging and laydown area for the proposed project would be located at Spanish Landing Park West, adjacent to Nimitz Bridge. This would involve the temporary use of the west parking lot, which is a paid lot and comprises 43 total spaces. Up to 28 spaces on the western end of this parking lot would be occupied by the staging and laydown area for a period not to exceed 180 days. The eastern end of this parking lot would continue to provide access to 15 parking spaces. The adjacent east parking lot would remain fully open, offering 56 spaces with 3 ADA-compliant spots. Sweetwater Channel Site In 2023, District entered 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. 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.

Chula Vista, San Diego

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