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HomeMy WebLinkAboutItem 6d. Authorize On-Call Engineering Professional Services for the Design of Stilling Basin ImprovementsCity of San Luis Obispo, Title, Subtitle Whale Rock Commission Report Whale Rock Commission Meeting – May 28, 2026 Agenda Item 6d – Authorize On-call Engineering Professional Services for the Design of Stilling Basin Improvements FROM: Shawna Scott, Assistant Director of Utilities PREPARED BY: Noah Evans, Whale Rock Reservoir Supervisor SUBJECT: AUTHORIZE ON-CALL ENGINEERING PROFESSIONAL SERVICES FOR THE DESIGN OF STILLING BASIN IMPROVEMENTS RECOMMENDATION Authorize selection of a consultant from the City of San Luis Obispo’s Qualified Civil Engineering On-Call Consultant List to provide engineering professional services consisting of the design of stilling basin improvements, and issuance of a purchase order, and any subsequent change orders, in an amount not to exceed the total authorized budget of $120,000. DISCUSSION Background Whale Rock Dam’s stilling basin is located at the base of the concrete spillways and is designed to dissipate the energy of high- velocity water and prevent scouring and structural erosion that could damage the spillway or the dam. In recent years, the Reservoir has spilled twice, releasing water through the stilling basin. When the Reservoir was spilling, staff observed water backing up in the stilling basin before flowing downstream. During the 2025 Stilling Basin Drain, Clean, and Inspect project, the basin was drained, exposing significant sediment and vegetation just downstream of the structure's end. When Whale Rock Reservoir releases water, flows are slowed by vegetation and sediment, leading to high water levels and erosion below the stilling basin. To restore downstream water flows, sediment and vegetation need to be removed downstream of the stilling basin, restoring the stilling basin to its designed discharge capacity. SPILLWAY AND STILLING BASIN DURING HIGH FLOWS Page 25 of 103 City of San Luis Obispo, Title, Subtitle Whale Rock Commission Report Whale Rock Commission Meeting – May 28, 2026 Agenda Item 6d – Authorize On-call Engineering Professional Services for the Design of Stilling Basin Improvements Based on review by the Utilities Branch’s Engineering and Planning team, staff recommend retaining an engineering consultant to design a project to restore the stream bed's original condition and topography below the stilling basin. The effort will remove obstructions in the stream bed to improve water flow and add riprap or boulders to prevent future erosion of the structure. ENVIRONMENTAL REVIEW The proposed action is limited to design only at this phase. Once designed, the City will retain an environmental consultant to prepare the California Environmental Quality Act (CEQA) analysis and determination for the Project. The previously mentioned Stilling Basin Drain, Clean, and Inspect project included adoption of an Initial Study Mitigated Negative Declaration, and permits and authorizations from regulatory agencies. While no special-status species were observed during implementation of the Project, it is anticipated that implementation of the restoration project may result in impacts to wetland and riparian habitat, and may potentially impact special-status species, cultural and tribal cultural resources, and water quality. Prior to implementation of the project, staff will prepare analysis and documentation in compliance with CEQA, and obtain all required regulatory permits and authorizations. The Whale Rock Commission’s approval to move forward with the project design does not commit the Commission to implementation of the Project, and the Whale Rock Commission will be required to consider the pending CEQA determination prior to approving and authorizing implementation of the Project. SEDIMENT AND VEGETATION BELOW THE STILLING BASIN Page 26 of 103 City of San Luis Obispo, Title, Subtitle Whale Rock Commission Report Whale Rock Commission Meeting – May 28, 2026 Agenda Item 6d – Authorize On-call Engineering Professional Services for the Design of Stilling Basin Improvements FISCAL IMPACT Design of Stilling Basin Maintenance Funding Category Contribution Source Amount Budgeted Amount Spent Capital Asset Expense 2026-27 CIP Contributions $120,000 $0 ALTERNATIVES The Commission may direct staff not to use the City of San Luis Obispo’s Qualified Civil Engineering On-Call Consultant List and to release an RFP. Firms on the Qualified Civil Engineering on-Call Consultant List have been selected through a competitive qualifications-based bidding process. Staff would determine the appropriate consultant from the On-Call list based on their specific experience successfully performing studies and designing projects for dam spillway and stilling basins, and demonstration of their expertise and knowledge of the Whale Rock Reservoir facility. Attachments: No attachments. Page 27 of 103 Page 28 of 103