E6: Upper Llagas Creek Flood Protection*

Flooding History

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.

Project Background

The Upper Llagas Creek Flood Protection Project was initially part of the voter-approved Clean, Safe Creeks and Natural Flood Protection Plan (CSC Plan) that came into effect in Fiscal Year 2001-2002 (FY02).

The project entailed providing 1% flood protection for approximately 4.5 miles of the channel in the urban area of Morgan Hill; the remaining 9.4 miles of the channel within the rural areas would have approximately 10% level of flood protection.

Due to very little federal funding for the project, in 2009, the Valley Water Board and the City of Morgan Hill decided to proceed with the project using only local funding while still working with the U.S. Army Corps of Engineers to secure federal funding. The City of Morgan Hill agreed to contribute up to $3 million towards the project design. As part of the CSC Plan, planning and 65% project design was completed.  Upon certification of the Environmental Impact Report in June 2014, VW began acquisition of more than 100 parcels required for construction.

Phase 1: Complete

Phase 1 of the Upper Llagas Creek Flood Protection Project was completed ahead of schedule in April 2022. Phase 1 project work included 4.4 miles of channel excavation, construction of the on-site compensatory mitigation at Lake Silveira wetlands, Masten Avenue Bridge concrete underpinning, Monterey Road Bridge concrete lining with a low flow channel for fish passage, installation of rock slope protection, storm drain outfall modifications, removal of concrete rubble, debris, and legacy trash, destruction of monitoring wells, installation of bat boxes, installation of permanent fencing and gates, removal of 12.5 acres of invasive blackberry bushes at Lake Silveira, planting of approximately 45,000 new, native plants on approximately 50 acres of Valley Water project property, and restoration of 2,000 linear feet of Llagas Creek adjacent to Lake Silveira The three-year native plant establishment and maintenance period was completed in March 2025.  Phase 1 construction contract Notice of Completion was accepted by the Valley Water Board of Directors on June 10, 2025.

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

In the 1970s, Lake Silveira was an active quarry, and presumably, as a result of those operations, there was a significant amount of abandoned concrete rubble dispersed on and adjacent to Llagas Creek. Valley Water removed the rubble and created new wetlands. The wetland habitat at Lake Silveira included creating islands, constructing habitat features, constructing side-weir inlet and outlet structures, and planting thousands of native wetland and riparian plants that will become habitat for birds, frogs, turtles, and other wildlife. The Land Trust of Santa Clara Valley is Valley Water’s long-term land management partner of the Lake Silveira wetlands.

During the 2020 and 2021 in-channel construction seasons, approximately 600,000 cubic yards (CY) of soil was excavated and removed from Upper Llagas Creek from Reaches 4, 5, 7A, and a portion of Reach 6 to increase the capacity of the creek channel during storm events. Rock slope protection was placed at existing bridge abutments for erosion and scour protection. Approximately 75,000 CY of nutrient-rich topsoil was placed along the creek banks to help support the dozens of acres of newly planted native riparian vegetation. Instream complexities, such as coarse woody debris and rootwad-log structures, were installed along the creek bottom throughout Phase 1 to serve as future habitat for native wildlife.

Valley Water entered into a cost-sharing agreement with the City of Morgan Hill in October 2020 to construct a public trail within Reach 7A.  Valley Water completed the paved trail on behalf of the city. The city completed the construction of new pedestrian crosswalks at Middle Avenue and Watsonville Avenue. The project is an example of Valley Water’s commitment to restoring wildlife habitat and providing open space for public use.

Phase 2A: Complete

Phase 2A construction began in June 2021 in a portion of Reach 8 in downtown Morgan Hill. Phase 2A included approximately 2,300 linear feet of a horseshoe-shaped underground tunnel 14 x 12 feet and approximately 1,600 linear feet of 10 ft x 9 ft twin reinforced concrete box culverts upstream and downstream of the tunnel to carry high water flows. Low flows will remain within the existing creek that traverses through downtown Morgan Hill.  The Phase 2A construction contract Notice of Completion was accepted by the Valley Water Board of Directors on January 28, 2025.

Valley Water entered into a cost-sharing agreement with the City of Morgan Hill in April 2021 to construct an approximate 600-foot portion of the City’s Hale Avenue Extension Project, including a fully signalized intersection at West Main Avenue as part of Phase 2A. Valley Water utilized the City property as a staging area to construct the necessary flood protection improvements. Phase 2A is an example of the cooperation and commitment of Valley Water and the City to save public funds while minimizing impacts to the community.

Valley Water and Boy Scout Troop 730 
In May 2023, Morgan Hill Boy Scout Troop 730 constructed a bat roost adjacent to Lake Silveira. The construction was the culmination of many days of planning and preparation for the bat roost. Approximately 15 troop and community members helped at various stages of the project.

The bat roost is done and installed. THANK YOU!

Voters Approve 2012 Safe, Clean Water Program

In November 2012, voters approved the 15-year Safe, Clean Water and Natural Flood Protection Program (2012 Program), which replaced the CSC Plan. The project was carried forward into the 2012 Program with two key performance indicators (KPIs). The preferred project with federal and local funding entailed providing flood protection to 1,100 homes, 500 businesses, and 1,300 agricultural acres while improving stream habitat. The local-funding only project focused on providing 100-year flood protection for Reach 7 only (up to W. Dunne Avenue in Morgan Hill).

In 2020, the Valley Board modified the local-funding-only KPI #2 to “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.”

The modification increased the length of the locally funded project from approximately 2.9 miles to 4.9 miles in addition to constructing the onsite compensatory mitigation. Besides getting the most out of the available local dollars, this approach kept the project moving forward, shortening the construction window without inducing flooding downstream. This modification maximized the potential for external funding opportunities and also reflected improved collaboration with regulatory permitting agencies that require early mitigation for the project impacts. Details about the modification can be found at https://www.valleywater.org/sites/default/files/SCW_FY19%20ModificationsWithAttachments.pdf.

As part of the 2012 Program, Valley Water began Phase 1 construction in FY20 and Phase 2A in FY21.

Voters Approve the Renewed Safe, Clean Water Program

In November 2020, voters approved the renewed Safe, Clean Water and Natural Flood Protection Program (Safe, Clean Water Program), replacing the 2012 Program. The project has continued in the renewed Safe, Clean Water Program.

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.