Restoration project
Adobe Creek Upper Reach 5
The purpose of the Adobe Creek Upper Reach 5 Restoration Project is to restore the creek by repairing the eroded channel, stabilizing banks, removing accumulated sediment, improving the channel conveyance capacity, and providing environmental benefits to the creek ecosystem.
Adobe Creek has a long history of flooding, with flood damages occurring in 1952, 1955, 1983, 1986, 1995 and 1998. The creek has problems such as localized flooding, creek-bank erosion, failing channel stabilization structures, sedimentation, barriers to fish passage and insufficient maintenance access.
In May 1999, water district staff prepared the Adobe Creek Watershed Planning Study, containing an Engineer's Report and Final Environmental Impact Report. A design for Adobe Creek Reach 5 was completed in 2002.
However, there was significant community opposition to the proposed creek design and also to the proposed use of Edith Park for the mitigation planting. In September 2003, the district, in partnership with local municipalities and the Adobe Creek Watershed Group, initiated a collaborative effort to revisit the goals and objectives of providing flood and erosion protection for Reach 5 of Adobe Creek.
The collaborative effort included district staff, Adobe Creek Watershed Group members, other creekside residents and citizens, and staff from the City of Los Altos, the Town of Los Altos Hills and various regulatory agencies.
Project contact
For more information about this project, contact: Tony Ndah, project manager, (408) 265-2607, ext. 2679.
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Project objectives
- Improve sediment transport
- Provide more channel capacity
- Improve fish passage through the reach
- Protect the eroded channel
- Restore the riparian corridor
Project elements
Project elements were developed and evaluated by the collaborative. The project elements were identified through the collaborative process, with decisions aimed at balancing the needs of all collaborative members.
The project consists of a modified natural geomorphic channel with a limited channel top width for 500 feet downstream (north) of West Edith Avenue and a geomorphic channel with “fish-passable” step pools for the following 200 feet, ending at the Robleda storm drain outlet. For 400 feet north of the Robleda storm drain outlet, the project consists of stabilizing the channel invert with "fish-passable" step pools along the channel bottom; placing rock from the channel toe to 3 feet up the bank; placing log slope protection at eroded channel banks up to the 10-percent water surface elevation, and reinforcing the existing cutoff walls at the toe of existing sacked concrete slope protection.
In addition to the project elements, the collaborative agreed on a channel capacity criterion of 1,100 cubic feet per second for the channel from West Edith Avenue downstream (north) to the Robleda storm drain outlet. The channel capacity is based on a stable channel configuration within the right-of-way limits provided by the creekside residents for the project.
The project that has evolved through the collaborative process is markedly improved from the design completed in 2002.
Highlights of the changes include:
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The proposed width of the improved channel varies from 40 feet to 50 feet instead of the 90-foot top width of the 1999 preferred alternative, thus yielding a much smaller footprint on properties adjacent to the creek.
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No rock gabions will be used in any section of the modified creek. The preferred alternative will reduce the amount of hardscape along channel banks.
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A natural channel will be installed for the first 500 feet of the channel downstream of West Edith Avenue bridge that will include an earthen bottom (no rock rip rap) in a geomorphically-derived bankfull (low-flow) channel, and a vegetated bench on either side.
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Step pools will be installed for the remaining 400 feet of channel improvements to accommodate the creek’s steep slope in a manner that will maintain the stability of the first 500 feet of channel but still allow for fish passage. Instead of gabion structures on either bank of the last 200 feet of the project, log slope protection will be provided only up to the 10-percent water surface elevation. Most existing bank slope protection will remain in place and natural bank areas will be revegetated to reduce erosion potential.
- Due to the smaller project footprint, fewer trees will be removed for the preferred alternative
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Project Status
- Prepared Problem Definition Report
- Evaluated feasible alternatives to meet project objectives
- Selected a preferred project alternative with the Adobe Creek Watershed Collaborative
- Prepared draft Engineer’s Report and draft Supplemental Environmental Impact Report
- Approved draft Engineer’s Report and draft Supplemental Environmental Impact Report for public circulation.
- Adopted final Engineer’s Report and certify final Supplemental Environmental Impact Report.
- Advertised contract documents for construction.
Project Timeline
- Award construction contract: March 2008
- Begin construction: May 2008
- Finish construction: December 2008
- Plant establishment period: January 2009 - December 2011
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Project history and background
Adobe Creek is located in the northwestern portion of Santa Clara County and lies within the district’s Lower Peninsula Watershed. Adobe Creek forms the boundary between the City of Los Altos (on the east bank) and the Town of Los Altos Hills (on the west bank). Adobe Creek Upper Reach 5 is located between Foothill Expressway and West Edith Avenue. The extent of the proposed project begins at West Edith Avenue and continues downstream (north) for approximately 1,100 feet.
In May 1999, staff prepared the Adobe Creek Watershed Planning Study, containing an Engineer's Report and Final Environmental Impact Report. As described in the 1999 Planning Study, the Adobe Creek Reach 5 channel improvements consisted of: a wider channel from an approximately 10-foot wide existing channel to an approximate 90-foot top width to convey the 1 percent flow. Gabions would line the City of Los Altos side of the creek to protect mature redwoods. Other modifications included a 10-foot wide low flow channel, a 10-foot wide vegetated mid-bank bench, and a 48-foot to 64-foot-wide high-flow bench. The mid-bank and high-flow benches were vegetated, but limited to groundcover and small shrubs to maintain high-flow functionality. The total length of the multi-level channel improvements proposed is approximately 700 lineal feet downstream of the West Edith Avenue bridge. For an additional 200 feet downstream of the 90-foot wide channel, the existing channel is widened from about a 10-foot width to a 20-foot width, with vertical rock gabions comprising the channel banks.
This design for Adobe Creek Reach 5, completed in 2002, was intended to provide for one-percent flood protection in the creek from the West Edith Avenue bridge to approximately 1,100 feet downstream. Construction of this stretch of creek required a certain acreage of mitigation planting, which the district proposed to install partly along the creek and partly in Edith Park, located just south of the West Edith Avenue bridge.
There was significant community opposition to the proposed creek design and also to the proposed use of Edith Park for mitigation planting. In April 2003, the Los Altos Hills Town Council voted to not grant the district two of the necessary easements to construct the project and install the mitigation planting for Adobe Creek Reach 5.
In September 2003, the district — in partnership with local municipalities and the Adobe Creek Watershed Group — initiated a collaborative effort to revisit the goals and objectives of providing flood and erosion protection for Reach 5 of Adobe Creek. The collaborative effort included district staff, Adobe Creek Watershed Group members, other creekside residents and citizens, and staff from the City of Los Altos, the Town of Los Altos Hills and various regulatory agencies.
Since September 2003, the district has held collaborative meetings almost monthly, as well as numerous steering committee meetings (the steering committee is comprised of the primary stakeholders of the Watershed Group) as a means of ongoing public outreach for the project. The meetings provided a forum to identify issues and concerns, develop project objectives, present alternatives and identify the preferred alternative for the project.
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