BOARD AGENDA MEMORANDUM
Government Code § 84308 Applies: Yes ☐ No ☒
(If “YES” Complete Attachment A - Gov. Code § 84308)
SUBJECT:
Title
Approve the Modified Palo Alto Flood Basin Tide Gate Structure Replacement Project, Project No. 10394001 (Palo Alto, District 7).
End
RECOMMENDATION:
Recommendation
A. Consider the First Addendum to the Final Mitigated Negative Declaration for the Palo Alto Flood Basin Tide Gate Structure Replacement Project (PATG Replacement Project); and
B. Approve the Modified Palo Alto Tide Gate Structure Replacement Project.
Body
SUMMARY:
The primary objective of the Palo Alto Flood Basin Tide Gate Structure (PATG) is to continue to protect residents from coastal flooding and control the downstream water levels for Matadero, Adobe and Barron Creeks, which all drain to the Palo Alto Flood Basin. Originally built in 1957, the PATG has exceeded its 50-year design life, and the surface of the concrete structure has degraded due to harsh conditions near the San Francisco Bay (Bay). The existing structure is also vulnerable to a large earthquake since seismic codes have changed significantly since 1957.
A California Environmental Quality Act (CEQA) document was prepared in 2021 for a project to build a replacement tide gate structure and the Board adopted a Mitigated Negative Declaration on April 27, 2021 (MND for PATG Replacement Project) before approving the project. However, following project approval the construction cost estimate increased significantly due to dewatering needs and the narrow construction window to avoid impacts to the Ridgeway’s Rail bird species, which annually breeds and nests between February and August. In FY 2024, as part of Santa Clara Valley Water District’s (Valley Water) Capital Improvement Program FY2025-2029 Five-Year Plan development process, the Valley Water Board approved staff’s recommendation to pursue development of a revised capital project within the funding constraints. Subsequently, staff was able to develop a design plan to seismically retrofit and rehabilitate the existing structure. An Addendum to the MND for PATG Replacement Project was prepared to evaluate environmental effects of the revised project to seismically retrofit and rehabilitate the existing structure. The revised project plan is subject to approval by the City of Palo Alto (City) through adoption of a Park Improvement Ordinance in accordance with the City’s Municipal Code. Valley Water would be advertising for construction bids once the City’s approval is obtained. Staff plans to recommend approval of the contract documents and advertise for construction bidding at the March 25, 2025 Board meeting.
Project Background
The PATG Project is located along the Bay shoreline in the City of Palo Alto (City), east of the Palo Alto Municipal Airport and Palo Alto Baylands Nature Preserve. The PATG and the levees connected to PATG were constructed in 1957 by Valley Water with support from the City to prevent flooding in the lower creek reaches and avoid coastal flooding and future loss in the level of service of flood protection. The PATG is regularly inspected and maintained by Valley Water, and the motorized sluice gate is regularly inspected and maintained by the City.
In 2011, the City and Valley Water discovered that water was flowing beneath the structure, undermining the function of the tide gates and, potentially, its structural stability. Emergency repairs to arrest flow were completed in 2012 and continue to be effective at holding the leak.
Efforts have continued over the next decade in evaluating shoreline protection plans for the region, through the PATG Replacement Project which was approved by Valley Water Board in April 2021 as discussed above, the South San Francisco Bay Shoreline Project - Phase II (Shoreline Phase II Project), led by the United States Army Corps of Engineers (USACE) in partnership with Valley Water, as well as through the Strategy to Advance Flood protection, Ecosystems and Recreation (SAFER) Bay Project. The SAFER Bay Project is a multi-benefit, multi-jurisdictional, public-private collaboration that will protect critical infrastructures, provide community resilience to current tidal flooding and projected sea level rise, and improve recreational access, using both engineered structures and nature-based flood protection.
In late 2022, the USACE determined that the economic damages from shoreline flooding would not justify a federal investment in a Shoreline Phase II Project until the year 2060. At the same time, design development on the PATG Replacement Project resulted in a significant increase of estimated construction costs due to the complex dewatering efforts needed for construction as well as the environmental requirements of the project. The cost estimates far exceeded Valley Water’s available funds for the project.
On January 10, 2023, the Board put on hold indefinitely further development of the PATG Replacement Project following the USACE’s decision not to progress the Shoreline Phase II Project.
First Addendum to the Final Mitigated Negative Declaration
In response to the escalated costs as well as the longer-term outlook for the Shoreline Phase II project and pursuant to the adopted FY2025-29 CIP Five-Year Plan, staff conducted an evaluation to potentially pursue and implement a lesser scope for the PATG in the short term to address seismic vulnerabilities and extend the existing structure’s service life while the long-term shoreline protection efforts advance. As a result, a modified project consisting of seismically retrofitting and rehabilitating the existing structure was developed. As the larger shoreline protection efforts proceed, a long-term structure replacement of the tide gate will be evaluated to ensure alignment and sea level rise compatibility with shoreline protection.
Staff has prepared a First Addendum to the MND for PATG Replacement Project to evaluate the environmental impacts associated with the modified project comprising PATG seismic retrofit and rehabilitation work (Attachment 2).
The seismic retrofit and rehabilitation work has a reduced duration of a 5-month construction period compared to the 43-month construction period for the previous replacement project. In addition, the project area would be reduced to 3-acres surrounding the existing tide gate structure compared to 8.9-acres for the replacement project. The seismic retrofit and rehabilitation project would not require dewatering or in-channel work.
The First Addendum describes changes to the PATG Replacement Project, evaluates the potential impacts, and concludes that the PATG Replacement Project modifications, which focus on the seismic retrofit and rehabilitation work, would not result in any new significant environmental impacts, or substantially increase the severity of significant impacts beyond those identified in the adopted MND for PATG Replacement Project, approved by the Valley Water Board on April 27, 2021.
ENVIRONMENTAL JUSTICE AND EQUITY IMPACT:
There are no Environmental Justice impacts associated with this item.
FINANCIAL IMPACT:
There is no financial impact associated with this item. After advertising the project for construction bids, staff will make a recommendation to award the construction contract to the lowest responsive and responsible bidder. The financial impact of staff’s recommendation will be the costs of the lowest responsive and responsible bid and the recommended contingency funds.
CEQA:
On April 27, 2021, the Board adopted the Final MND and Mitigation Monitoring and Reporting Program (MMRP) for the PATG Replacement Project before approving the Project.
A First Addendum to the adopted MND to PATG Replacement Project has been prepared and is before the Board for consideration. Pursuant to CEQA Guidelines Section 15164(d), the decisionmaker should consider an addendum along with the adopted MND before taking further discretionary action of a project. A link to the Final MND is provided here: <https://www.valleywater.org/sites/default/files/PATG_FinalMND_body_WEB.pdf>
ATTACHMENTS:
Attachment 1: Map
Attachment 2: First Addendum
UNCLASSIFIED MANAGER:
Manager
Bhavani Yerrapotu, 408-630-2735