Redwood Creek Restoration at Muir Beach, Phase 5
|Sponsoring Agency||Golden Gate National Parks Conservancy|
|Watershed Tributary||Redwood Creek Watershed|
|Public or private land?||('Public',)|
|Location (lat/lon)||37.52, -122.35|
|Location Description||Big Lagoon, Muir Beach, Marin County The project area is bounded by Hwy 1 on the easterly side, the Pacific Ocean on the westerly side, Coastal hills to the south, and hillslopes occupied by residents of Muir Beach to the north.|
This project restores natural function to the mouth of the Redwood Creek Watershed at Muir Beach, in southern Marin County. It restores a natural creek alignment and floodplain connectivity along the last 3/4 of a mile of the creek, along with new backwaters, an expanded tidal lagoon, and extensive revegetation with native riparian and wetland plants. The project reduces flood elevations at private property and a public access road by removing and modifying poorly planned infrastructure. The new channel and floodplain connectivity create conditions to allow for natural sediment transport dynamics, including floodplain deposition. The extensive modifications enhance habitat for federally and state-listed coho salmon, as well as threatened steelhead trout and the threatened California red-legged frog.
The overall project will restore the lost natural function of lower Redwood Creek, its estuary, tidal lagoon, adjacent floodplain and associated wetland and dune habitats over a 46-acre area. Lower Redwood Creek has been degraded by a century of landscape modifications, and suffers from a lack of connectivity with its floodplain, severe channel aggradation and loss of habitat for federally listed coho and steelhead. Phase 5, or the last phase, of the project is proposed for IRWMP, which entails relocating the last 1,000 LF of the channel to its natural location when Marin County constructs a new vehicular bridge over the creek and its floodplain. The project is a partnership between the National Park Service, Marin County Dept. of Public Works, and the non-profit Golden Gate National Parks Conservancy.
Part 2 - Detail
The overall project restores the natural function to the creek, floodplain, wetlands and dunes in the 46-acre area at the mouth of the Redwood Creek. The restoration is accomplished by removing features constructed in the 20th Century which confine the creek, segregate it from its floodplain, constrict flows and obstruct sediment transport. Specifically, a 1,300 levee road across the center of the floodplain will be removed, a 500-LF visitor parking lot extending into the floodplain as a "dam" to restore the floodplain, and the undersized 25-foot-long Pacific Way Bridge, a county vehicular bridge, will be replaced with a 250-LF vehicular bridge across the creek and its newly connected floodplain. Along with these primary actions, numerous details are incorporated to provide enhanced winter habitat for federally and state endangered coho, such as an off-channel pond, backwaters and both large and small woody debris. About 240,000 people visit the site each year, so the modified visitor amenities must allow access while fully accommodating natural processes. A new 450-foot pedestrian bridge, with long spans between piers, will extend across the restored floodplain from the reconfigured floodplain. A new emergency access road was upgraded around the perimeter of the site, with rock drain lenses to allow natural drainage patterns, and a trail was rerouted in a subdrainage to better connect the micro-drainage with the creek and floodplain. When the natural processes function, the flood elevations during average and moderate winter events are lower, thereby reducing the threat to adjacent private property as well as access on the county road, Pacific Way.
The project is being implemented in 5 phases. IRWMP funding is requested for Phase 5, the last phase of the project. This entails the 1,000 LF of channel realignment to its natural location that must be conducted at the same time that Marin County Dept. of Public Works constructs its new 250-LF vehicular bridge. The bridge cannot be constructed without constructing the new channel alignment under it at the same time. This request does not include a request for the bridge, since Marin County is seeking other, transportation-related funds for that purpose. This request is focused on the channel construction, which will restore a alignment in the creek's natural topographic location and fully connect the creek with its floodplain both laterally and longitudinally. This phase of work also entails relocation of an AT&T utility box, excavation of natural gravel from the old creek bed, and abandonment of the old channel. About 12,000 CY of material will be moved for this work.
The phase 5 channel would be the upstream-most channel restoration in the project, with its most upstream point at about 3,200 LF upstream of the confluence with the ocean. Phases 1 through 3 of the project were completed from 2009 to 2011 and included realignment and restoration of the channel and new backwaters along the lower 2,200 LF of the project area. The levee road was removed, and a portion of the parking lot was removed and replaced with the first half of a 450-LF pedestrian bridge over the floodplain. Phase 4 is expected to be constructed in 2013 and will consist of reconfiguring the visitor parking lot to expand the full floodplain. The second leg of the new pedestrian bridge (an additional 225 LF) will also be constructed in Phase 4.
Since the new channel and floodplain processes directly benefit coho salmon and since the coho population in Redwood Creek is the southern-most viable population of coho, this project meets regional priorities identified by the National Marine Fisheries Service and the California Dept. of Fish and Game to enhance habitat for the California Central Coast Evoluntionarily Significant Unit.
For general Project Information and Photos, see: http://www.nps.gov/goga/naturescience/muir-beach.htm
for videos of restoration in progress for Phases 1 to 3, see: http://www.nps.gov/goga/naturescience/muir-beach.htm
Project Meets Multiple Recommendations in NMFS Recovery Plan:
National Marine Fisheries Service, March 2010. Public Draft Recovery Plan for the Central California Coast Coho Salmon (Oncorhynchus kisutch) Evolutionarily Significant Unit, Southwest Regional Office. (See Chapter 10, Redwood Creek).
Project Fulfills High Priorities in Watershed Plan:
Stillwater Sciences. January 2009. Redwood Creek Watershed Assessment. Final Draft. Prepared by Stillwater Sciences, Berkeley, California for Golden Gate National Recreation Area, San Francisco, California.
Jones and Stokes Associates, 2007. Final Environmental Impact Statement/Environmental Impact Report for the Wetland and Creek Restoration at Big Lagoon, Muir Beach. Prepared for the National Park Service and the Marin County Community Development Agency.
Moffatt and Nichol, with Jeff Anderson and Associates, January 2009. Geomorphic and Hydraulic Design Report, Redwood Creek Restoration at Muir Beach. Prepared for the Golden Gate National Recreation Area.
Moffatt and Nichol, with Jeff Anderson and Associates, September 2009. Final Construction Drawings for the Redwood Creek Restoration at Muir Beach. Prepared for the Golden Gate National Recreation Area. 30 Sheets. (This includes 100% designs for the Phase 5 channel relocation proposed for IRWMP. We show designs above at 90%, however, because we expect to refine designs for the upstream reach slightly prior to construction.)
Philip Williams & Associates (PWA) with Stillwater Sciences, John Northmore Roberts & Associates, and the Point Reyes Bird Observatory, 2003. Big Lagoon Wetland and Creek Restoration Project, Muir Beach, California. Part I. Site Analysis Report. PWA Ref. # 1664.02. San Francisco, CA. Prepared for the National Park Service.
Philip Williams & Associates (PWA) with Stillwater Sciences, and John Northmore Roberts & Associates, 2004. Big Lagoon Wetland and Creek Restoration Project: Part II. Feasibility Analysis Report. Prepared for the National Park Service. February. San Francisco, CA.
Reichmuth, M., Fong, D., and Press, D. 2006. Long-Term Coho Salmon and Steelhead Trout Monitoring Program in Coastal Marin County – Redwood Creek Summer Basinwide Monitoring Report. Unpublished report prepared for California Department of Fish and Game, Point Reyes Seashore Association, and San Francisco Area Network Inventory and Monitoring Program, National Park Service.
Smith, J.J. December 31, 2000. Distribution and abundance of juvenile coho and steelhead in Redwood Creek in fall 2000. Unpublished report for the Golden Gate National Recreation area, National Park Service. 8 pp.
Stillwater Sciences. 2004. Sediment Budget for Redwood Creek Watershed, Marin County, California. Berkeley, CA.
Stillwater Sciences, March 2009. Assessment of Winter Habitat for Juvenile Coho Salmon in Lower Redwood Creek under Existing and Proposed Conditions. Technical Memo prepared by Ethan Bell for the National Park Service. 9 pp.
Redwood Creek Watershed (8.9 square miles)
Green Gulch Tributary (flows into Redwood Creek in the project area and gains habitat function as a result of this project)
High flows will be choked by the undersized Pacific Way Bridge.
Sediment transport will be obstructed, causing the upstream channel to fill more rapidly with sediment and reducing its conveyance capacity.
Winter habitat for coho and steelhead in that reach of the creek will continue to have dysfunctional connections between the creek and floodplain.
Management actions at the county bridge are likely to be needed.
Residents of Muir Beach will continue to have periods during average and moderate winter of events where the road to their homes is unpassable.
The downstream reaches of the channel restored in Phases 1 to 3, in 2009 to 2011, already provide significant flow and habitat benefits, but they were designed and constructed for the long term downstream with the added conveyance capacity of the restored upstream reach. The area restored in the lower 2,200 LF is subject to a function related to flows and sediment transport that is different than designed if the upper reach is not constructed.
i. Water Supply (conservation, recycled water, groundwater recharge, surface storage, etc.)
The project removes the constraints to natural groundwater dynamics with the channel and associated off-channel ponds and backwaters. A levee across the floodplain is removed and the channel is located at a natural location in the floodplain. Groundwater recharge will function naturally. An extensive network of groundwater wells has been installed at the site to document exactly how groundwater elevations function in relation to creek water surface elevations. Models projected that groundwater elevations would drop about 1 foot when the confining features (eg: the levee road and parking lot) were removed; data being collected is testing that theory. However, please note that even a possible decline in groundwater elevations was considered for new plant communities. In many areas, a surface layer of fill has been removed, creating wetlands with better groundwater connection for native plants.
A very minor component of the overall project includes a feasibility analysis to identify ways to increase groundwater storage about a mile upstream of the project area (in Franks Valley). The purpose of increased groundwater storage is to protect instream flows to benefit summer habitat for coho and steelhead. We would look at ways that drainages from the hillslopes could direct water to wetlands in the floodplain instead of draining directly into the channel in winter events.
ii. Water Quality
...Water quality benefits of this project pertain primarily to turbidity and sediment loading. The project will allow more natural sediment transport dynamics as well as more natural areas for deposition on the floodplain, which may benefit salmonids.
iii. Flood and Stormwater Management
...By removing the constraints to floodflows and reconnecting the floodplain, hydraulic models have shown up to a 1 foot decrease in water surface elevations of overbank flows in the vicinity of private residences and a local private business near the new creek reach proposed for Phase 5 funding. In addition, the local road, Pacific Way, would never be flooded since the bridge would span the 100-year event; therefore residents and visitors would never be stranded due to flooding on the road. In the pre-restoration condition, stranding occurred on average about once per year due to flooding on the road.
iv. Resource Stewardship (watershed management, habitat protection and restoration, recreation, open space, etc.)
... This project entails extensive resource stewardship management for volunteers and participation by school groups, conservation groups, neighborhood groups and others. So far, we have clocked about 3,000 hours of volunteer participation each year in this project. We grow about 30,000 native plants each year in a watershed nursery. One nursery manager works with volunteers and interns throughout the year to collect these propagules of riparian and wetland species and grow them. A stewardship coordinator then manages volunteer work groups one to two times per week - or sometimes more - to plants these. Additional stewardship activities include detailed work to create suitable cover for coho while the riparian vegetation becomes reestablished and removing non-native weeds.
An analysis by Stillwater Sciences (2009) showed project actions would double suitable winter habitat for coho, which has been identified as a limiting factor for their survival in Redwood Creek.
Hydraulic modelling conducted for the EIS/EIR (Jones and Stokes Associates, Philip Williams Associates) and for construction designs (Northern Hydrology and Engineering) showed the 3,200 LF of channel relocated to its natural location and reconnected with the floodplain over 46 acres would provide floodplain connectivity for fish, sustain riparian and emergent wetland habitat, and allow long-term natural variability in the creek system without the need for on-going management.
Benefits already observed as a result of implementing Phases 1 through 3 corroborate the data used as a basis of design, with well-functioning floodplains, inundation under average events, extensive connectivity and options for fish to return to the creek, self-recruiting riparian species among the almost 90,000 native plants grown and planted, and a population of California Red-Legged Frogs now inhabiting two ponds created for their use.
Indeed, observations of channel function after implementing Phases 1 through 3 demonstrate that opening up the lower floodplain already reduces flood elevations on Pacific Way; however, it is important to recognize that full benefits willl not be achieved without implementation of the upstream reach in Phase 5.