Santa Clara County, CA

Valley Water's Upper Llagas Creek Flood Protection

The city of Morgan Hill is situated at the southern tip of California’s Silicon Valley, sandwiched between the Santa Cruz and Diablo mountains. Bisecting the valley, Llagas Creek flows south through the city to Gilroy. More than 1,000 homes, 500 businesses, and 1,300 acres of agricultural land that sit within the floodplain of the perennial creek and its tributaries have experienced several destructive flood events. The effort to protect residents and businesses from 100-year floods has long been underway with federal funding for the project initially approved in 1954.

Woodard & Curran’s partnership with Valley Water began in 1999, providing project management and design, among other engineering services. In 2010, our stormwater and flood resiliency experts continued this partnership by providing project management, design, and engineering services for the Upper Llagas Creek Flood Protection Project, which spans 13.6 miles along East Little Llagas Creek, West Little Llagas Creek and Llagas Creek in Morgan Hill, Gilroy, and unincorporated areas in Santa Clara County. Our team is collaborating with 17 subconsultants to develop a design that improves resiliency in the area, while also meeting Morgan Hill’s vision for downtown redevelopment, following the goals and objectives of Clean Safe Creeks, adhering to the U.S. Army Corps of Engineers and Vally Water’s design standards, strategizing to reduce costs, and producing a design that can be efficiently implemented.

Wet weather conditions in January 2017.

The project included a 2,000-foot tunnel.

Overlooking the dry creek bed.

Overcoming the Funding and Voter Approval

Though the project began in the mid-1950s with federal funding, it was met with supplementary funding issues, property acquisition challenges, and contention over the execution. The Upper Llagas Creek Flood Protection Project was later included in the voter-approved Clean, Safe Creeks and Natural Flood Protection Plan (CSC Plan) during fiscal year 2001-2002, but funding remained an issue. In 2009, Valley Water and Morgan Hill in collaboration with the U.S. Army Corps of Engineers proceeded with the project, leveraging local funds, including $3 million from the city for project design. The CSC Plan was replaced in 2012 when Santa Clara County residents voted to enact the Safe, Clean Water and Natural Flood Protection Program, which provided $54.4 million for the Upper Llagas Creek Flood Protection Project. Valley Water has secured the remainder of funding through numerous state and federal sources.

Woodard & Curran’s team rose to the challenge of managing the project delivery based on available funding. Initially planned as a two-phase construction period, the project team further subdivided the work into three phases. By being flexible in the approach, we were able to keep the complex project moving and position Valley Water to receive substantial grants for the work.

Phased Construction Underway

Valley Water was able to acquire more than 100 parcels to make way for construction, which broke ground in 2019. Several local, regional, and state officials who had already spent countless hours setting the stage for this project were in attendance to celebrate.

The design Woodard & Curran produced will provide protection from the 100-year storm event within Morgan Hill by widening and deepening the creek channel, adding a high-water flow bypass tunnel, replacing box culverts, relocating utilities, revegetating streamside habitat, and improving instream habitat for wildlife. The project has also been carefully designed to avoid inducing floods in downstream reaches. In addition to increasing capacity for stormwater flows, the project produces multiple benefits, such as the creation of wetlands, habitat restoration, reduced environmental impacts and maintenance, and integration with the Morgan Hill trail system. The project also includes conversion of an abandoned quarry and produce processing facility to tiered wetlands and wildlife habitat, with avoidance of high-value trees such as native sycamores and excavation of only one bank where possible. By applying geomorphological science, Woodard & Curran integrated stable channels and profiles into the design, which reduces the need for future sediment removal and bank stabilization. Additional considerations for maintenance requirements and environmental impacts were made by accounting for future vegetation growth and minimal maintenance between the top of banks.

Project area map depicting phases of construction.

The project is being executed with a high flow bypass consisting of double box culverts in Morgan Hill and a tunnel under Nob Hill, which will reduce impact to residents and businesses downtown. When the three phases of construction are complete, homes and businesses within Morgan Hill will no longer be in the 100-year floodplain, reducing the financial burden on property owners and allowing downtown to be reimagined without the threat of consistent flooding.

Mulit-Beneficial Flood Resiliency Project

Watch Video

The Upper Llagas Creek Flood Protection Project included creating a new wetland habitat at Lake Silveira, with water flowing in this section of restored creek for the first time in more than 40 years. Watch the video Valley Water created to educate residents on the benefits project brings.


Project Team

David White PE, CFM National Practice Leader Stormwater & Flood Resiliency
Xavier Irias PE Senior Technical Practice Leader Water Resources
Glenn Hermanson PE Senior Delivery Leader Water Resources
David Liu PE Project Engineer Water Resources
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