Decades in the Making, Upper Llagas Creek Flood Protection Project Breaks Ground

Decades in the Making, Upper Llagas Creek Flood Protection Project Breaks Ground

For more than six decades, residents of Morgan Hill, California, have contended with severe flooding during major storm events. The rising waters of Llagas Creek currently affects more than 1,000 homes, 500 businesses, and more than 1,300 acres of agricultural land in southern Santa Clara County that are within the 100-year floodplain. In August 2019, the Santa Clara Valley Water District finally broke ground on a flood protection project that draws on modern tools and design, while also protecting and restoring vital habitat.

Federal funding for the project was initially approved by Congress in 1954. Issues with supplementary funding, property acquisition, and contention over the project’s execution delayed it until recent years, when voters in the community approved funding that set the stage for this groundbreaking. Woodard & Curran has provided a suite of services including project management and design for the project since 2010. 

Getting Here

For us, the groundbreaking ceremony in August 2019 celebrated our ongoing collaboration with the water district, dedicated subconsultants, and stakeholders ranging from local community members to federal regulators. This event marks much more for the local leaders who have spent countless hours setting the stage for this project.

Santa Clara County residents voted to enact the Safe, Clean Water and Natural Flood Protection Program in 2012, which provides $54.4 million in project funding. Morgan Hill is responsible for $3 million, and the remainder comes through numerous state and federal funding sources.

 

Representative Zoe Lofgren, D-Gilroy (above), started working with the water district and the U.S. Army Corps of Engineers to secure state and federal funds for the project in the late 1990s. Rich Constantine, currently mayor of Morgan Hill and a former city councilman has been working to ramp up local support and funding since 2010. Both manned shovels at the groundbreaking ceremony.

Phase 1 and Beyond

The groundbreaking ceremony kicked off Phase 1 of the project, which begins at the downstream end of the 13.6-mile stretch of Llagas Creek affected by the flood protection project. It is slated for completion in 2022. Phase 2A will kick off in fall 2020 and covers improvements that will convey flood waters around downtown Morgan Hill through a tunnel under Nob Hill. Phase 2B will include the remaining stretches of the project.

While the driving force behind this project is flood protection, our design sought reduce the project’s environmental impact by widening the creek on one side, thereby allowing swaths of native trees and habitat to remain. The team applied a modern geomorphologic analysis to the creek to determine the channel shape that would provide a more stable waterway, one that would not be prone to incising or depositing sediment. This approach is incorporated in both phases of the project.

 

Phase 1 includes the creation of 5 acres of wetlands at Lake Silveira, planting 105 acres of native vegetation, and restoring a remnant section of Llagas Creek for enhanced fish passage. Throughout the project, existing topsoil and streambed material will be harvested and stored during the widening phase, and placed in the new channel during the later phases of construction to support the proposed native revegetation mitigation plantings. By re-using topsoil, the natural nutrients and native bacteria will help restore the creek to a natural state.

The conservation elements of this project combine well with its main purpose. When completed, the Upper Llagas Creek Flood Protection Project will provide critical flood protection to the surrounding area and remove properties from the 100-year flood plain (thus eliminating the requirement for flood insurance), improving safety and peace of mind for residents, while maintaining critical habitat for local wildlife.

Author

Technical Practice Leader
Treatment Design

View All Posts

Share
Subscribe
Enter your email address below for industry news and updates about Woodard & Curran.