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F3: Flood Risk Assessment Studies*

About This Project

This project is to enable Valley Water scientists to update custom software models of local creeks for the most current and accurate understanding of potential flood risks in high priority flood-prone areas and then develop options for managing those risks. Existing models will be verified, updated and recalibrated as conditions change. Updating our knowledge-base will lead to more effective creek management and maintenance. Valley Water will also convey this information to the community and partner cities.

When creek conditions necessitate rehabilitation to preserve flood protection, this project also funds preliminary engineering studies to isolate problem areas and explore potential solutions.

Under the 2012 Safe, Clean Water Program, Valley Water completed engineering studies on five (5) reaches of creeks as part of the Flood Risk Assessment Studies project. These were on Coyote Creek (Bay to Anderson Dam, including Rock Springs Neighborhood); Adobe and Barron creeks tidal flood protection (Highway 101 to Middlefield Road in Palo Alto); Alamitos Creek (upstream of Almaden Lake in San José); and Ross Creek (Guadalupe River to Blossom Hill Road in San José). The Coyote Creek study completed under this project was utilized to develop the short-term interim projects that Valley Water built to help reduce the risk of flooding along Coyote Creek (See Project E1 - Coyote Creek Flood Protection Project). These include the installation of an interim floodwall and embankment along the creek to protect the Rock Springs community from a flood event equivalent to the February 2017 flood. Valley Water also updated the Alamitos Creek 2-D hydraulic (HEC-RAS) model of the 1% (100-year event) floodplain and shared the information with the City of San José.

Revising flood models on a regular basis enables Valley Water to keep pace with changes in rainfall patterns and intensity as our climate changes. An up-to-date understanding of flood risks allows us to work toward preventing future flooding.

 

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

Needles Dr between Senter Rd and Welch Ave
Datapoints
Status
On Target
Location
Countywide
Schedule
Start FY 2022 / Finish FY 2036
Funding
Safe, Clean Water Fund ($21.9 million)
News and UpdatesNews and Updates
Reports and DocumentsReports and Documents
Environmental and Community BenefitsEnvironmental and Community Benefits
History and BackgroundHistory and Background
News & Updates

See Environmental & Community Benefits section for complete description of Key Performance Indicators (KPIs).

KPI #1: (Engineering studies)

The South Babb Creek alternatives analysis was completed in Q2 of FY22. 

  • The study incorporates refined hydraulic modeling and analyses to identify potential flood mitigation and 100-year flood protection projects on South Babb Creek for the area.
  • The study explores the feasibility, constructability and costs of the proposed alternative solutions.
  • The engineering study on South Babb Creek has been leveraged for a capital project which is still ongoing.

KPI #2: (Floodplain maps)

Llagas Creek Watershed Floodplain Model – 25 and 100 Year Floodplains

At the end of FY22, Valley Water began a new floodplain study for the Llagas Creek Watershed, located in southern Santa Clara County. An existing 1D, steady-state Hec Ras hydraulic model of Llagas Creek and its many tributaries is being converted to a 1D/2D Hec Ras unsteady hydraulic model that will be used to map out the floodplain for different flow events. Two tributaries were added to the model. The model includes Llagas Creek, Madrone Channel, Tennant Creek, West Little Llagas Creek, West Little Llagas Bypass, and East Little Llagas Creek.  This work will feed directly into Valley Water’s One Water Plan.

As of October 2022, the draft model has been completed and reviewed.

West Branch Llagas Creek Floodplain Model

Valley Water started work on a new, unsteady 1D/2D Hec Ras model for the West Branch Llagas Creek in Q1 of FY23.  The model will be run as “rain on grid”.  This method will generate the hydrology for the watershed as well as floodplain mapping. This model will also be used for Valley Water’s One Water Plan.

As of October 2022, Model 1D geometry for West Branch Llagas Creek has been developed and the model is being stabilized.

October 2022

For more information:

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Environmental & Community Benefits

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

  1. Complete engineering studies on three (3) creek reaches to address 1% (100-year) flood risk.

  2. Annually, update floodplain maps on a minimum of three (3) creek reaches in accordance with new FEMA standards.

Benefits

  • Provides more current and accurate mapping of areas at risk of flooding

  • Provides the technical basis for developing future flood protection plans, and for potential funding partnerships

  • Identifies, in a timely manner, the needs to prevent creek deterioration

  • Identifies the need for flood mitigation or creek rehabilitation projects

  • Facilitates communication with partner cities on evolving flood risks and possible solutions

  • Addresses climate change

Geographic Area of Benefit

Countywide

History & Background

Engineering studies history and project background

Under the 2012 Safe, Clean Water Program, Valley Water completed engineering studies on five (5) reaches of creeks as part of the Flood Risk Assessment Studies project. These were on Coyote Creek (Bay to Anderson Dam, including Rock Springs Neighborhood); Adobe and Barron creeks tidal flood protection (Highway 101 to Middlefield Road in Palo Alto); Alamitos Creek (upstream of Almaden Lake in San José); and Ross Creek (Guadalupe River to Blossom Hill Road in San José). The Coyote Creek study completed under this project was utilized to develop the short-term interim projects that Valley Water built to help reduce the risk of flooding along Coyote Creek (See Project E1 - Coyote Creek Flood Protection Project). These include the installation of an interim floodwall and embankment along the creek to protect the Rock Springs community from a flood event equivalent to the February 2017 flood. Valley Water also updated the Alamitos Creek 2-D hydraulic (HEC-RAS) model of the 1% (100-year event) floodplain and shared the information with the City of San José.

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.