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E6: Upper Llagas Creek Flood Protection*

About This Project

Preferred project: A federal-state-local partnership

This project continues a partnership with the U.S. Army Corps of Engineers (USACE) and the State of California to plan, design and construct improvements along 13.9 miles of channel. The project extends from Buena Vista Avenue to Llagas Road and includes West Little Llagas Creek in downtown Morgan Hill. The federally authorized preferred project protects the urban area of Morgan Hill from a 1% flood (100-year event) and reduces the frequency of flooding in surrounding areas. Construction includes channel modifications and replacement of road crossings. Valley Water continues to work with Congress to aggressively pursue federal funds to bring this project to full fruition.

Local-funding-only project

Construct flood protection improvements along Llagas Creek from Buena Vista Avenue to Highway 101 in San Martin (Reaches 4 and 5 (portion)), Monterey Road to Watsonville Road in Morgan Hill (Reach 7a), approximately W. Dunne Avenue to W. Main Avenue (a portion of Reach 8), and onsite compensatory mitigation at Lake Silveira.


*This project was voter approved as part of the Safe, Clean Water and Natural Flood Protection Program.

Upper Llagas Creek Project
On Target
Morgan Hill, San Martin and Gilroy
Start FY 2022 / Finish FY 2025
Safe, Clean Water Fund ($161.1); Watershed Stream Stewardship Fund; State of California; City of Morgan Hill
News and UpdatesNews and Updates
Reports and DocumentsReports and Documents
Environmental and Community BenefitsEnvironmental and Community Benefits
History and BackgroundHistory and Background
News & Updates

Upper Llagas Creek Flood Protection: Progress and next construction activities

Phase 1 of the Upper Llagas Creek Flood Protection Project began construction in September 2019 and is progressing ahead of schedule. This project is partially funded by the Safe, Clean Water Program, which helps Valley Water care for local waterways and provide flood protection to homes, schools, and businesses.

Phase 1 Project work completed to date includes completion of approximately 95% of the channel excavation, construction of the on-site compensatory mitigation, Lake Silveira wetlands, Masten Avenue Bridge concrete underpinning, Monterey Road Bridge concrete lining, installation of rock slope protection, storm drain outfall modifications, removal of concrete rubble, debris and legacy trash, and destruction of monitoring wells, installation of bat boxes, installation of approximately 50% of the  permanent fencing and gates, removal of 12.5 acres of invasive blackberry at Lake Silveira, and excavation to restore 2,000 linear feet of Llagas Creek from Lake Silveira towards Monterey Highway.

Valley Water created a video of the completed new wetlands and Llagas Creek restoration work. A story on this work is also available on our Valley Water News blog.   

In the early to late 1970s, Lake Silveira was an active quarry and presumably because of those operations, there was a significant amount of abandoned concrete rubble dispersed on and adjacent to Llagas Creek. Valley Water has removed the rubble and has constructed the wetlands, including construction of the side-weir inlet and outlet structure. Construction of the new wetland habitat at Lake Silveira included approximately 100,000 cubic yards of fill to create islands that will become habitat for birds, frogs, turtles, and other wildlife. Wetlands plant installation is underway and expected to be completed by mid-April 2021.

The Land Trust of Santa Clara Valley is Valley Water’s long-term land manager partner of the Lake Silveira Wetlands.

During the in-channel construction season of 2020 approximately 600,000 cubic yards of soil was excavated and removed from Upper Llagas Creek from Reaches 4, 5 and a portion of 7A to increase capacity of the creek channel during storm events. Rock slope protection was installed to protect the existing bridges. Approximately 75,000 CY of nutrient-rich topsoil was placed along the creek banks to help support the planting of native riparian vegetation where planting is underway. Instream complexities, such as coarse woody debris and rootwad-log structures, were installed along the creek’s bottom throughout Phase 1 to serve as future habitat for native wildlife.

Construction activities beginning in May 2021:

  • Continued excavation and placement of topsoil within the Reach 7A diversion channel;
  • Construction of a low-flow invert channel to facilitate fish passage;
  • Installation of aggregate base maintenance roads on both sides along the top of the creek banks;
  • Construction of a Reach 7A asphalt concrete public trail on behalf of the City of Morgan Hill; and
  • Completion of the installation of permanent fencing and gates.

Valley Water has collaborated with the City of Morgan Hill and recently enter into a cost sharing agreement with the City to construct a Reach 7A public trail during the summer of 2021. The Project is an example of Valley Water’s commitment to restore wildlife habitat and provide open space for the public.

Valley Water Begins Project Construction (from September 2019)

In September 2019, Valley Water began construction of Phase 1 (Reaches 4 and 7a, portion of Reach 5, and Lake Silveira). Work for this phase consists of channel widening and deepening, instream improvements for wildlife and habitat, and revegetation.

The project will be constructed in several phases with each phase having specific sections (referred to as reaches on the map) where the proposed improvements will occur. With the completion of both Phase 1 and Phase 2, the project will provide 100-year level of flood protection to urban areas of Morgan Hill in Reaches 7 and 8, 10-year for Reach 14, and no induced flooding due to creek modifications on Reaches 4, 5, and 6. For a 100-year level of flood protection, this means Llagas Creek should be able to withstand flooding in the event of a large and rare storm event which has a one-in-100 (1 percent) chance of occurring in any given year.

Phase 2A: (portion of Reach 8) Construct approximately 2,300 linear feet of a horseshoe-shaped underground tunnel 14-foot x 10 foot and approximately 1,600 linear feet of 10 ft x 9 ft twin Reinforced Concrete Box Culverts (RCBs) upstream and downstream of the proposed tunnel to carry high water flows. Low flows will remain within the existing creek that winds through downtown Morgan Hill in Reach 8. Construction is expected to take 2.5 years and will include traffic control, detours, utility coordination and relocation, and public outreach. Phase 2A was advertised for construction in January 2021 with construction anticipated to begin in May 2021.

Phase 2B: (portion of Reach 5, Reach 6, Reach 7b, portion of Reach 8, Reach 14) Construct improvements on approximately 8 miles of Upper Llagas Creek, from US 101 to Llagas Road, to provide an increased level of flood protection with adequate freeboard. Construction will include creek widening and deepening, bridge/culvert construction, traffic control, utility coordination and relocation, construction of maintenance roads, and stable channel, with habitat enhancements. Construction is expected to take 2.5 years, followed by a 3-year plant establishment period. Phase 2B will be advertised for construction when funding is determined.

The Project requires purchasing approximately 105 parcels (76 permanent, 29 temporary) from private or public agency owners. Approximately 100 of these permanent acquisitions have been acquired to date with the remaining parcels required for Phase 2B construction, including temporary construction rights, to be acquired by December 2021.

The latest Upper Llagas Creek project mailer is available for viewing.

Project brochure and inserts for Phase 1:

Brochure   Insert 1   Insert 2

Updated April 2021 

For more information:


Reports & Documents

Pursuant to the California Environmental Quality Act, Valley Water, as the lead agency for the Project, has prepared a Final Environmental Impact Report (FEIR) to evaluate environmental impacts of the proposed Project

Additional reports related to the Project can be found by clicking on the link below:

  1. Geotechnical Report (2006)
     - Part 1
     - Part 2
  2. Site Characterization Report (2012)
  3. Reach 4 and 5 Limited Phase II ESA (2003)
  4. Reach 4, 5, 6, and 7B – Phase I ESA Vol 1 (2003)
  5. Reach 4, 5, 6, and 7B – Phase I ESA Vol 2 (2003)
     - Part 1
     - Part 2
  6. Reach 5 and 6 – Phase I ESA (2002)
  7. Reach 8 – Phase I ESA (2003)
  8. Reach 14 – Phase I ESA(2005)
Environmental & Community Benefits

FY22-36 Key Performance Indicator for the Safe, Clean Water Program 

  1. Preferred project with federal and local funding: Plan, design and construct flood protection improvements along 13.9 miles of Upper Llagas Creek from Buena Vista Avenue to Llagas Road to provide flood protection to 1,100 homes, 500 businesses, and 1,300 agricultural acres, while improving stream habitat.

  2. With local funding only: Construct flood protection improvements along Llagas Creek from Buena Vista Avenue to Highway 101 in San Martin (Reaches 4 and 5 (portion)), Monterey Road to Watsonville Road in Morgan Hill (Reach 7a), approximately W. Dunne Avenue to W. Main Avenue (portion of Reach 8), and onsite compensatory mitigation at Lake Silveira.


  • Provides 1% flood capacity for four (4) miles along West Little Llagas Creek within downtown Morgan Hill, protecting approximately 1,100 homes and 500 businesses

  • Provides 10% (10-year event) flood protection to approximately 1,300 agricultural acres in Morgan Hill, Gilroy and San Martin

  • Locally funded project provides improved flood protection for a limited number of homes and businesses in Morgan Hill

  • Improves stream habitat and fisheries

  • Creates additional wetlands

  • Improves stream water quality

  • Identifies opportunities to integrate recreation improvements with the City of Morgan Hill and others as appropriate

  • Addresses climate change

Geographic Area of Benefit

Morgan Hill, San Martin and Gilroy 

History & Background

Flooding History and Project Background

The area sustained damage in 1937, 1955, 1958, 1962, 1963, 1969, 1982, 1986, 1996, 1997, 1998, 2002, 2004, 2008, 2009, and 2011. In 2009, many businesses and residences in downtown Morgan Hill were flooded under 1 foot of water. The project builds on the planning, design and property acquisition initiated under the Clean, Safe Creeks plan of 2000.

In September 2019, Valley Water began construction on the locally funded Reaches 4, 7a, a portion of Reach 5 and Lake Silveira, which is expected to be completed in 2022. Construction of the approximately 2,300 linear feet of a horseshoe-shaped underground tunnel and approximately 1,600 linear feet of twin reinforced concrete box culverts upstream and downstream of the tunnel to carry high water flows is scheduled to begin in November 2020. Construction is expected to take 2.5 years.

About the Safe, Clean Water and Natural Flood Protection Program

In November 2020, voters in Santa Clara County overwhelmingly approved Measure S, a renewal of Valley Water’s Safe, Clean Water and Natural Flood Protection Program.

The program was first passed by voters in 2000 as the Clean, Safe Creeks and Natural Flood Protection Plan, then again in 2012 as the Safe, Clean Water and Natural Flood Protection Program. The renewal of the Safe, Clean Water Program will continue to provide approximately $47 million annually for local projects that deliver safe, clean water, natural flood protection, and environmental stewardship to all the communities we serve in Santa Clara County.

While evaluating ways to improve the 2012 program, Valley Water gathered feedback from more than 21,000 community members. That helped Valley Water create the six priorities for the renewed Safe, Clean Water Program, which are:

Priority A: Ensure a Safe, Reliable Water Supply

Priority B: Reduce Toxins, Hazards and Contaminants in our Waterways

Priority C: Protect our Water Supply and Dams from Earthquakes and Other Natural Disasters

Priority D: Restore Wildlife Habitat and Provide Open Space

Priority E: Provide Flood Protection to Homes, Businesses, Schools, Streets and Highways

Priority F: Support Public Health and Public Safety for Our Community

Each year, Valley Water prepares a report providing a progress update for each of these program priorities, along with fiscal year accomplishments.

To ensure transparency and accountability to the voters, the ballot measure also created an Independent Monitoring Committee, appointed by the Santa Clara Valley Water District Board of Directors. The Independent Monitoring Committee annually reviews the program’s progress to ensure the outcomes are achieved in a cost-efficient manner and reports its findings to the Board. Additionally, the IMC also reviews each proposed 5-year implementation plan prior to its submittal for Board approval.

In addition, the program requires three independent audits.

View the Safe, Clean Water Program’s annual reports, annual IMC audit reports, and independent audits, including a staff response, on the Valley Water website.