Earlier this year, Valley Water reached a milestone in our work to protect downtown Morgan Hill from a major flood event.
In May 2023, our agency completed the construction of a 2,300-foot-long tunnel underneath downtown Morgan Hill. Once all phases are complete, the tunnel will help protect downtown from a 100-year flood, which has a 1% chance of happening in any given year.
The tunnel is part of the Upper Llagas Creek Flood Protection Project, which consists of approximately 13.9 miles of flood protection improvements along portions of East Little Llagas Creek, West Little Llagas Creek and Llagas Creek. The project is located within Gilroy, Morgan Hill and the unincorporated area of San Martin.
Construction progress inside the 2,300-foot-long tunnel underneath downtown Morgan Hill. 
Contractors install walls and roof rebars required for a double reinforced concrete box culvert, which will connect to the tunnel and carry water underneath Morgan Hill during major storms. 
As part of the project, Valley Water built a structure known as a chute and pool on a section of Llagas Creek to facilitate fish passage for steelhead trout. 
Workers perform weed control to help establish newly planted native plants along Llagas Creek. 
The framework of a double reinforced concrete box culvert. 
A before, during and after view of Valley Water’s work to turn Lake Silveira into a new wetland.
During major storms, high water flows will be diverted from West Little Llagas Creek near Wright and Hale Avenues into the underground tunnel bypass. The high-water flows will rejoin West Little Llagas Creek downstream at Ciolino Avenue. These improvements will still allow West Little Llagas Creek to carry low flows through the downtown area while protecting it from flooding.
Once Valley Water completes all phases of construction, the project will help protect about 1,100 homes, 500 businesses, and more than 1,300 acres of agricultural land from a 100-year flood.
The project was divided into three phases. The tunnel is part of the Phase 2A flood protection improvements, which are anticipated to last until May 2024. Valley Water is currently working in partnership with the City of Morgan Hill to extend Hale Avenue and build a new four-way intersection.
The last phase of construction is anticipated to begin by the end of 2023 and take two years to complete. Valley Water is currently working to secure federal funding for this final project phase.
In May 2022, Valley Water completed the first phase of construction, which consisted of flood protection improvements along Llagas Creek from Buena Vista Avenue to Highway 101 and from Monterey Road to Watsonville Road. As part of this work, Valley Water restored a section of Llagas Creek and created a new wetland at Lake Silveira to provide environmental benefits.
Once the Federal Emergency Management Agency certifies the project improvements, South County residents and businesses within the floodplain will have the option to not purchase 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 program provides approximately $47 million annually for local projects that deliver safe, clean water, natural flood protection, and environmental stewardship in Santa Clara County.