Valley Water outlines plan to reconnect creeks to Alviso salt ponds as part of larger Bay restoration effort

Sunnyvale (Virtual) — Santa Clara Valley Water District (Valley Water) on Tuesday detailed the Calabasas–San Tomas Creek Marsh Connection Project, a feasibility-stage plan to reconnect local creeks to former salt ponds in the Alviso Complex to restore tidal marsh, improve sediment delivery and provide adaptable flood protection for Sunnyvale and neighboring communities.

Valley Water project manager Judy Nam said the effort would convert parts of Pond A8 and Pond A4 and portions of Harvey Marsh toward tidal marsh and transitional habitats while improving public access, particularly for historically disadvantaged neighborhoods in Alviso. "The intent is to establish tidal marshes before significant sea level rise becomes a critical challenge," Nam said.

The project matters because restored tidal wetlands can attenuate waves, trap sediment that builds elevation, and improve water quality — functions that planners say support both natural ecosystems and built infrastructure under rising sea levels. Christina Toms, an ecological engineer at the San Francisco Bay Regional Water Quality Control Board, told attendees the Bay historically held about 200,000 acres of tidal wetlands but now supports roughly 54,000 acres and that the region needs a landscape-scale, nature-based approach to regain resilience.

Valley Water summarized a multi-stage planning process that began with 20 initial alternatives and, after public input and technical screening, narrowed to five alternatives for modeling. Alternatives vary by the number and location of pond breaches, direct creek-to-pond connections, changes in creek alignment through Harvey Marsh and inclusion of habitat islands and ecotone (horizontal) levees. Nam said the project area includes about 1,500 acres of Pond A8 (US Fish and Wildlife Service), 300 acres of Pond A4 (Valley Water), and roughly 50 acres of Harvey Marsh (Caltrans), plus lower reaches of Guadalupe River, San Tomas Aquino Creek and Calabasas Creek.

Modeling focused on sediment accretion and where creek-delivered sediment would settle. Nam said the modeling showed Alternative 6 had the greatest potential to deliver creek sediment to Pond A8, while Alternative 5 caused sediment to settle in Harvey Marsh rather than in targeted ponds. "This slide clearly demonstrates the critical role of modeling and testing various restoration elements," she said.

Project objectives listed by Valley Water include restoring tidal and freshwater marsh, providing resilient flood protection that adapts to projected sea level rise, reducing maintenance needs for creeks, and improving public trails and access. The team noted grant funding already secured for planning and modeling (including Measure AA, Prop 1 and an EPA San Francisco Bay Water Quality Improvement Funds award) but said construction funding has not yet been secured. Nam said staff expect to summarize a staff-recommended alternative in the final planning study report scheduled for late this year or early next year and that construction timing could fall in the 2028–2030 range, contingent on funding.

The project also includes a proposed pilot study to use a portion of an ecotone (horizontal) levee at Pond A4 to treat reverse osmosis concentrate, wastewater or stormwater; that pilot is supported by coordination with regulators, Valley Water’s recycled water unit, a UC Berkeley professor and the San Francisco Estuary Institute. Nam said agencies have given positive regulatory feedback to date.

Presenters stressed regional coordination: Toms and Judy Nam highlighted the South Bay Salt Pond Restoration Project and the Don Edwards San Francisco Bay National Wildlife Refuge as partners; they named coordinating bodies and funds such as the San Francisco Bay Restoration Authority (Measure AA), the Bay Restoration Regulatory Integration Team (BRIT) and the San Francisco Estuary Wetlands Regional Monitoring Program as key to aligning permitting, funding and science across jurisdictions.

On technical details, Toms described observed Bay trends and constraints: roughly eight inches of sea level rise in the last century, about a 36% decrease in suspended sediment since the 1990s, and broad subsidence where diked and drained marshes oxidized and compacted. She described nature-based options — living shorelines, beach enhancement, beneficial reuse of dredged sediment, horizontal levees, and migration-space restoration — and emphasized phased, trigger-based adaptation rather than fixed calendar dates.

During the audience Q&A, presenters answered questions on sediment placement methods and invasive-species management. Toms said beneficial reuse projects have used "thin lift" sediment placements for ecotone slopes (maximum about 2 feet in the examples cited) and up to 4-foot deposits to form levy cores, and that tidal marsh plants can grow through sediment deposits. Nam said invasive-species removal and coordination with the State Coastal Conservancy and other nonprofit partners are planned as part of project preparation and construction. Both speakers described volunteer and nonprofit roles for post‑project maintenance and planting.

What’s next: Valley Water will finalize the staff-recommended alternative in a final planning study report, continue permitting coordination and pursue construction funding. Project proponents said the work will be phased and adaptive; no construction schedule is yet set and key implementation elements remain contingent on funding and regulatory approvals.