“The walking trail at Nob Hill Park may have potential intermittent closures during the proposed tunnel construction.”

Lake Silveira, a former quarry site where a portion of the lake will be converted to wetland habitat with islands (September 2019)

By John Varela

John Varela

Although Santa Clara County is facing a drought, flooding remains a threat to many of our communities. The last drought was followed by one of the wettest winters on record. Climate change has made extreme weather the new normal.

Valley Water remains committed to keeping residents, schools and businesses safe through our flood protection projects and programs. On June 21, Valley Water began construction on the next phase of the Upper Llagas Creek Flood Protection Project.

The entire project consists of about 13.9 miles of flood protection improvements along East Little Llagas Creek, West Little Llagas Creek and Llagas Creek within Gilroy, Morgan Hill and the unincorporated area of San Martin. Once we complete all phases of construction, the project will provide flood protection for about 1,100 homes, 500 businesses, and more than 1,300 acres of agricultural land in South County.

Our next section of work, Phase 2A, involves building an underground bypass tunnel about one-half mile in length and underground reinforced concrete box culverts roughly 1,600-feet long. During major storms, high flows will be diverted from West Little Llagas Creek into the underground bypass tunnel, thus protecting the downtown area of Morgan Hill from a 100-year flood event. These improvements will allow West Little Llagas Creek to carry low flows through Morgan Hill’s downtown area.

You can expect the following activities to take place during the construction of Phase 2A:

  • Underground tunneling and related work from about Warren Avenue to near the intersection of West Dunne and Del Monte avenues
  • Utility relocations
  • Construction of underground box culverts near West Main Avenue and Hale Avenue to Warren Avenue
  • Construction of underground box culverts from about West Dunne Avenue along Del Monte Avenue to Ciolino Avenue
  • Temporary closure of shoulder parking, some driveways and sidewalks

While there will be an increase in truck traffic, noise and dust, Valley Water and contracted crews will do our best to minimize such impacts, including implementing extensive traffic control measures to ensure vehicle traffic safely flows during construction.

Also, the walking trail at Nob Hill Park may have potential intermittent closures during the proposed tunnel construction. Signs will be placed to inform the public should such temporary closures occur.

We expect the work on Phase 2A to last until May 2024, with required intermittent traffic control implemented along portions of Hale, West Main, Del Monte, West Dunne and Ciolino avenues.

Last year, Valley Water restored a section of Llagas Creek and created a new wetland habitat to provide environmental benefits that mitigate the impacts of the flood protection work along Llagas Creek.

The last construction phase, Phase 2B, is anticipated to begin sometime in 2022 and last two to three years. We anticipate completing it in late 2025.

Once the project improvements are certified by the Federal Emergency Management Agency, South County residents and businesses within the floodplain will no longer be required to buy flood insurance. Currently, those residents and business owners are mandated to purchase flood insurance.

The voter-approved Safe Clean Water and Natural Flood Protection Program is partially funding this project. The Safe, Clean Water Program provides about $47 million annually for local projects that deliver safe, clean water, natural flood protection, and environmental stewardship in Santa Clara County.

John Varela is the District 1 director on Valley Water’s board.