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Permanente Creek Flood Protection*

About This Project

This project provides flood protection to thousands of homes and businesses in Mountain View and Los Altos, created recreational opportunities and enhanced the environment. The project spanned 10.6 miles of Permanente Creek, from San Francisco Bay’s southwest shoreline through Mountain View to Foothill Expressway in Los Altos. A natural flood protection approach to prevent potential flooding damages in excess of $48 million (1999 value) was used for many of the key project elements. The project includes multiple elements: channel improvements; flood detention area and recreational improvements at City of Mountain View’s McKelvey Park; and flood detention areas, recreational improvements and enhanced habitat at County of Santa Clara’s Rancho San Antonio Park.

*This project was funded by the voter-approved 2012 Safe, Clean Water and Natural Flood Protection Program

McKelvey Ball Park big field completed
Completed 2021
Mountain View and Los Altos
Completed 2021
Safe, Clean Water Fund ($81.7 million); Watershed Stream Stewardship Fund
News and UpdatesNews and Updates
Reports and DocumentsReports and Documents
Environmental and Community BenefitsEnvironmental and Community Benefits
History and BackgroundHistory and Background
News & Updates

Permanente Creek Flood Protection Project (all elements completed)

This project was completed with funding from the voter-approved 2012 Safe, Clean Water Program and included four flood protection elements at different parts of Permanente Creek. See below for specific information about the flood detention basins at the county's Rancho San Antonio Park and Mountain View's McKelvey Park and the channel improvement elements. 

Letter of Map Revision (LOMR) Update
All of the flood protection measures for the Permanente Creek Project are complete. Valley Water started the federal application process, known as Letter of Map Revision (LOMR), to revise the Flood Insurance Rate Maps (FIRM) maintained by the Federal Emergency Management Agency (FEMA) to reflect the flood protection provided by the project. These maps are part of the National Flood Insurance Program and are used to establish Special Flood Hazard Areas (i.e., FEMA’s 100-year floodplain), determine flood insurance rates, and help the community with floodplain management.

Valley Water and FEMA are in the final stage of finalizing the LOMR and expect FEMA to issue a letter of approval by end of February 2024. Valley Water is reviewing FEMA’s draft floodplain maps, prior to receiving the approval letter. Once the letter is issued, a 4 to 5-month public review and appeals period will begin. Assuming no appeals are filed, the LOMR becomes effective at the end of the review period. At that time, Valley Water will notify property owners of the flood zone designation change and the proposed date when the maps would become effective.

FEMA’s LOMR Process

FEMA’s process is thorough to ensure that completed projects meet all flood protection and safety standards. The process takes 1-2 years to complete. Valley Water does everything possible to keep the process moving and responds promptly to FEMA’s comments.

Here is the process that results in Flood Insurance Rate Maps (FIRM):

  • Review, comments, and responses between FEMA and Valley Water:
    • Each round of comments takes 180 days: 90 days for FEMA review, and 90 days for Valley Water to respond.
    • There may be additional rounds of comments, typically, there are two to six rounds.
  • After the review period, the public is notified of an upcoming appeals period:
    • Notices are published in the Federal Register and local newspapers twice (typically 2-3 weeks).
    • The required appeals period lasts 4 to 5 months.
    • If no appeals are filed, the LOMR becomes effective after the appeals period closes. If appeals are filed, the process will take longer, depending on the nature of the appeals.

Valley Water will provide updates as it moves through the process. Visit FEMA’s website to learn more about the LOMR process.

Aerial Project Video
Valley Water developed a video of the completed Permanente Creek Flood Protection Project with aerial images of all the project elements. Click here to see the video. 

Rancho San Antonio Detention Basin (completed)

This detention basin element was completed in June 2021. Valley Water held a zoom event to celebrate the completion of the Rancho San Antonio Detention Basin, the last element of the Project. To view the event video or the aerial video of the 10-mile stretch of the project, click on the hyperlinks.

McKelvey Park Detention Basin (completed)

This detention basin element was completed in February 2020. View more information about this completed project element.

Channel Improvements Elements: Levees/Floodwalls and Channel widening elements (completed)

The construction of these elements was completed in December 2018. View more information about these completed project elements.

January 2024


For more information: 

Environmental & Community Benefits

Key Performance Indicator for the Safe, Clean Water Program

  1. Provide flood protection to 1,664 parcels downstream of El Camino Real, including Middlefield Road and Central Expressway.


  • Provides flood protection to a minimum of 1,664 parcels (1,378 homes, 160 businesses and 4 schools/institutions) downstream of El Camino Real from a 1% (or 100-year) flood

  • Prevent flooding of Middlefield Road and Central Expressway

  • Minimize the future cost for maintenance

  • Provide opportunities for environmental enhancements and trail extension

Geographic Area of Benefit

Mountain View and Los Altos

History & Background

Flooding History and Project Background 

Permanente Creek has a history of flooding, having experienced major flooding in 1862, 1911, 1940, 1950, 1952, 1955, 1958, 1963, 1968, 1995 and 1998. Flooding can result in millions of dollars in damage to homes, businesses and schools. In addition, disruption to businesses and transportation networks can result in significant loss of productivity and revenue. One of the project’s goals is to avoid utility and transportation shutdowns and prevent potential damages that could exceed $48 million (1999 value).

Each winter, thousands of households, schools and businesses in Mountain View and Los Altos are susceptible to flooding from Permanente Creek during a major storm. The Santa Clara Valley Water District has initiated planning of a flood-protection project along 10.6 miles of Permanente Creek, from San Francisco Bay’s southwest shoreline through Mountain View to Foothill Expressway in Los Altos.

The Permanente Creek Flood Protection Project offers a tremendous opportunity for a multi-purpose project to improve flood protection, create recreational opportunities and enhance the environment. The District worked with the cities and the community to design the most suitable alternative. 

About the Safe, Clean Water and Natural Flood Protection Program

In November 2012 the voters of Santa Clara County overwhelmingly approved Measure B, the Safe, Clean Water and Natural Flood Protection Program, as a countywide special parcel tax for 15 years with a sunset date of June 30, 2028. This Program replaced the Clean, Safe Creeks and Natural Flood Protection Plan, which voters approved in November 2000.

The Safe, Clean Water Program was developed with input from more than 16,000 residents and stakeholders and was created to match the community’s needs and values. The voters of Santa Clara County identified five priorities:

Priority A: Ensure a Safe, Reliable Water Supply

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

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

Priority D: Restore Wildlife Habitat and Provide Open Space

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

Other: Six projects from the Clean, Safe, Creeks Plan have been carried forward into the Safe, Clean Water Program.  

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.

In addition, the Program requires three independent audits, the first of which was conducted in FY 2017.

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