Redwood Creek Restoration at Muir Beach

Golden Gate National Recreation Area, CA

Golden Gate National Parks Conservancy, in partnership with the National Park Service 2009 - 2011

In July 2009 Hanford ARC began a three year project with the Golden Gate National Parks Conservancy (GGNPC) to restore Lower Redwood Creek and Big Lagoon in the Golden Gate National Recreation Area (GGNRA).  Redwood Creek, which flows to the ocean at Muir Beach, was restricted through historical development for ranching and recreation.  Impacts included levees, lagoon filling, and channel relocation.  Work included lagoon expansion, fill removal, channel realignment and bridge replacement.  The primary goal of the project is to increase rearing habitat for the federally listed coho salmon and steelhead populations that have historically used the watershed.  In addition, the project will increase habitat for the California red-legged frog, also a federally listed species.

Our scope for 2009 was defined by the need to provide immediate improvements for the dwindling population of Coho Salmon that rely on Redwood Creek for spawning and rearing habitat.  We substantially increased the size of the existing tidal lagoon by excavating an off-stream tidal basin, and constructed seven log structures at the perimeter of the lagoon.  The basin is fully connected to the existing lagoon, and will capture flood flows from Redwood Creek.

We restored the floodplain on the right bank of Redwood Creek upstream of the tidal lagoon.  This work involved removing the end of the beach parking lot, including relocating restrooms and fencing.  This was considered an interim solution, with the long-term solution being full realignment of the parking lot in a future phase.

The 2009 work included a mitigation component as well.  California red legged frog have historically inhabited the project area.  To offset temporary impacts to the riparian habitat and to encourage potential reestablishment of red legged frog in the area, we constructed a frog pond on the east side of the historic lagoon and future channel alignment.  This work included excavation and berm construction.

Other notable components of 2009 included native sod salvage and replanting, screening approximately 1,000 CY of sand for weed removal, working with archeological and historically significant features, and routing public access to minimize impacts to recreational users on this very popular beach.

The 2010 phase consisted of construction of 650 feet of the new Redwood Creek alignment and three tributary channels, installation of log structures, harvest and replacement of 1,500 CY of native streambed gravel, and construction of a red-legged frog pond.

The native gravel harvest was a substantial portion of the 2010 work.  It required dewatering of approximately 2,000 LF of the existing stream channel and removal of an average of 2’ of streambed gravel.  We reconstructed a new channel bed and low flow channel within the existing channel to minimize impacts to spawning fish during the winter of 2010/2011.

We completed approximately half of the project scope, the final of the three phases, in 2011.  This phase included constructing an upstream and downstream segment of realigned channel, tying the new channel to the old channel, backfilling the old channel, a backwater channel and frog pond, removal of a levee and construction of a 215’ pedestrian bridge set on torque-down piles and pile caps.

The schedule was accelerated based on permit constraints from multiple agencies, including NMFS, RWQCB and USFWS, and required simultaneous channel construction and bridge construction activities to be carefully coordinated.  Part of the project included removal of a levee which also served as the primary access route, and intersected the new channel alignment.  We established an extensive, 24-hour bypass system to capture water in the main stem and tributaries, and a 24-hour site dewatering system to maintain dry work areas below the water table.  Much of the work in the new channel was below the higher-high tide elevation.

Backfill and interception of the existing channel included sheetpile, a rock revetment, and a vegetated soil lift structure.  The new channel included a series of log structures that provided cover and bank stabilization both upstream and downstream of the 2010 channel segment.  We worked closely with the design team to locate and set the log structures.

In addition we harvested approximately 600 tons, and imported approximately 1,400 tons of streambed gravel to augment the channel bed with a 1-2 foot layer of gravel.  The harvested gravel was removed from the existing channel prior to backfill.

The 215-foot pedestrian bridge included three pile clusters and pile caps, and one abutment.  We installed torque-down piles, driven up to 55’.  The bridge itself is an aluminum welded structure, with wood decking.  We set the bridge in two 90’ sections and one 45’ section with a 200’ crane.  We also constructed a landing and new trail section on the south approach, including gravel paving and visitor amenities.

For all three phases of work we used our GPS system for layout and as-built records.  This involved establishing a permanent base station and calibration using a series of surveyed points at the perimeter of the project.  NPS will use data from our records as a baseline for monitoring sediment transport and channel migration.