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Rancho San Antonio County Park detention basin

Permanente Creek Flood Protection Project

Updated June 30, 2017

New south parking lot completed and open for use

The new south parking lot was completed on June 1 and is now open for use. The new paved parking area is approximately double the capacity of the previous paved parking area, and the new unpaved parking area will also have 25 designated spaces, making for a total of 80 marked vehicle spaces, three handicap spaces, and two or three equestrian spaces.

The new parking area was designated to be as large as possible within the limits of the habitat area of the federally listed threatened California red-legged frog. We worked closely with County Parks and Midpeninsula Regional Open Space District to determine the design of the new parking area and to balance the vehicular users with the equestrian users within the limited footprint.

The new restrooms are being built and expected to be completed this fall. This summer, work on the detention basin area will begin , along with the continued long-term closure of the Hammond-Snyder loop trail.

The water district and its contractors are working with the County of Santa Clara and Midpeninsula Regional Open Space District to minimize impacts to the park as much as practical.

We will continue to share new information on the website and with the email subscriber list.


Project summary

After years of planning and design, the Santa Clara Valley Water District is preparing to construct flood protection improvements along Permanente Creek. Once completed, the Permanente Creek Flood Protection Project will provide natural flood protection for at least 2,200 properties in Mountain View and Los Altos, create recreational opportunities and enhance the environment.

The Rancho San Antonio County Park detention basin is the first project element to begin construction. Construction is expected to begin in December 2016 and last for approximately two years.

Project highlights


  • A 15-foot deep depression to collect peak storm flows from Permanente Creek
  • Planting of native trees
  • Removal of non-native trees that compete with native species
  • Replacement of existing maintenance bridge
  • New restroom facilities
  • New enlarged paved parking area with designated equestrian spaces


  • Enhances many acres of wildlife habitat
  • Provides flood protection for thousands of homes and businesses in Mountain View and Los Altos, saving residents thousands of dollars on flood insurance each year
  • Reduces construction impacts to downstream residential and business areas
  • Reduces flow rates, allowing for potential riparian restoration downstream

Project construction schedule

The following schedule is the expected sequence and duration of the work. However, the schedule may change as construction progresses and may be updated.

Expected construction activityEstimated date

Parking lot preparation and construction

December 2016 to May 2017             

Well construction August 2017
Basins construction August 2017 to December 2018
New bridge and inlet structure May to October 2018
Trail constructionOctober 2018
Site restoration October to December 2018

What to expect during construction

The Santa Clara Valley Water District, Santa Clara County Parks and MidPeninsula Regional Open Space District are working together to minimize construction impacts as much as practical and in accordance with local ordinances. We appreciate your understanding and cooperation as we embark on this important flood protection project.

  • Regular construction work hours are 8 a.m. to 5 p.m. Work is scheduled Monday through Friday, excluding legal holidays.
  • The South Meadow parking lot will be open throughout construction. The new, expanded parking lot and restroom will be built first, slightly north of the existing parking lot. Upon completion of the new facilities, the existing parking lot will be closed.
  • Various parts of the South Meadow and Hammond-Snyder Loop Trails will be closed during construction. Trail accessibility signage will be installed at least two weeks in advance of any closures.
  • A large amount of dirt will be removed from the site. The contractor will construct a 15-foot wide road behind the Gate of Heaven Cemetery for the haul trucks. The trucks will drive on the Hammond-Snyder trail to Stevens Creek Boulevard, to Foothill Boulevard, then onto I-280 (to avoid Cristo Rey Drive).
  • A visual screening fence will be installed around the construction areas.
  • Hundreds of native trees and removal of non-native trees that compete with native species along the creek.
  • Safety of the community and our employees is a priority. Barricades, railings, lights, fences and other warning devices will be used for public safety and convenience.

What is a flood detention area?  

Flood protection methods can include berms around buildings, widening channels, raising floodwalls, elevating structures and roadways, and/or constructing a bypass channel. In areas where development limits widening the creek or raising floodwalls, flood storage basins are used to temporarily divert and store floodwaters until a major storm passes.

The Rancho San Antonio detention areas will be approximately 12 acres in size and 15 feet deep with mild side slopes, contoured to the surrounding area and replaced with native trees and grass. Flood flows would inundate the site very rarely and quickly drain away. A 25-year flood, which has a 4 percent chance of occurring in any given year, would result in about one foot of water in the detention area that would drain away in hours. A 100-year storm, which has a 1 percent chance of occurring in any given year, would fill the area and drain in one to four days.

Use Access Valley Water to submit questions, complaints or compliments directly from your computer or smart phone to a water district staff person who can help you.




Project Quick Look

Construction StartDecember 2016
Construction FinishDecember 2018
Location Cupertino

Reference Documents

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