McDaniel Slough Tidal Restoration in Janes Creek Watershed, Humboldt Bay, CA

Summer 2015 Ecesis, Volume 25, Issue 2

McDaniel Slough post-breach on December 1, 2013 showing tidal action. Photo by Dave Kenworthy. 

McDaniel Slough post-breach on December 1, 2013 showing tidal action. Photo by Dave Kenworthy. 

The City of Arcata’s environmental restoration projects began in the early 1980s with the creation of the Arcata Marsh and Wildlife Sanctuary. The original 75 acres of the Arcata Marsh and Wildlife Sanctuary, including 30 acres of freshwater wetlands, was completed in 1981. Since that time, the City has actively worked to enhance wetland and creek habitats within city limits. 

In the 1990s, the City of Arcata partnered with the California Department of Fish and Wildlife (CDFW) and the State Coastal Conservancy to plan to restore and enhance nearly 300 acres of coastal and riparian wetland habitats on the northern portion of Humboldt Bay. Humboldt Bay is second only to San Francisco Bay in terms of the numbers and diversity of migratory water birds that winter along California’s coastal Pacific Flyway. The McDaniel Slough project is significant — the site is not constrained by the railroad or Highway 101 which dikes off most of the Bay’s former tidelands — because it provides one of the best opportunities on Humboldt Bay to restore coastal landscape processes of former tidelands on the Bay and the McDaniel Slough estuary. In 2013, more than fifteen years later, the City and CDFW along with numerous funders celebrated the completion of the McDaniel Slough Restoration and Enhancement Project. 

The goal of Arcata’s restoration program is to modify disturbed ecosystems so that they more closely resemble a desired condition — usually one that is matched to a reference condition or by retrospective work looking at old historic maps and photos. Key to the success of habitat restoration efforts in Arcata is having a wealth of local expertise to draw upon as well as involvement of the citizenry. Participation in restoration projects helps bring the community together and create a social identity, sense of place and local pride in their community. Funding from the Coastal Conservancy, CDFW, Natural Resources Conservation Service, US Fish and Wildlife Service, Caltrans, Wildlife Conservation Board and many local non-profits and businesses made the McDaniel Slough project possible.

McDaniel Slough project objectives included (1) maximize restoration of a large area of tidal marsh habitat dominated by native vegetation; (2) provide unimpeded access for anadromous fish migration between Humboldt Bay, McDaniel Slough and Janes Creek; (3) create a tidal channel system that maximized estuarine fisheries habitat in large, high-order, sub-tidal channels; (4) provide connectivity of habitats using “eco-levees” to create a gradation between the salt marsh/mudflat habitats and uplands; (5) provide connectivity with existing habitats which also include palustrine freshwater, riparian, and brackish wetlands at the Arcata Marsh and Wildlife Sanctuary and CDFW’s Mad River Slough Wildlife Area; (6) alleviate rural and urban flooding due to tide gate restrictions and chronic channel aggradation; and (7) provide opportunities for public access, recreation and education.

Implementation of the McDaniel Slough project created a self-sustaining estuarine tidal marsh system through restoration of natural geomorphic and biologic processes. The project removed tide gates on McDaniel slough to provide access for anadromous fish between Humboldt Bay and Janes Creek. Design features included salt marsh, mudflat, tidal channels, brackish and freshwater habitats and uplands. Excavation to create or enhance brackish and freshwater habitats provided the fill for the levees that were constructed to protect adjacent non-project lands. Trails were constructed on the City-owned levees providing opportunities for public access, education, and recreation.  

Levee design included “eco-levees” with ten-to-one slopes on the bayward side to create a transition from low marsh to high salt marsh and upland habitat. Levee elevations of +9.0 feet NGVD accounted for sea-level rise and protection against the 100-year extreme tide. Heavy equipment (scrapers, excavators, backhoes) excavated and loaded material for levee construction and to build up the marsh plain. Excavation of tidal channels created or enhanced permanent and seasonal freshwater and brackish wetland habitats. The seasonal and brackish wetlands were excavated 12 to 18 inches to create optimal elevations for colonization by high salt marsh vegetation including rarer species such as Humboldt Bay owl’s clover and Point Reyes bird’s beak. 

Tidewater goby enhancements included US Fish and Wildlife Service designs for restored tidal channels. Drainage swales and tide gates were used to provide connectivity through seasonal fresh and brackish habitats to tidal areas. A water control structure between the seasonal fresh and brackish wetlands west of the levees insured freshwater wetlands could dry out during the summer season to prevent cattail growth and discourage mosquito breeding. 

When levee construction, channel enhancement, and culvert and tide gates work was completed in September of 2013, a full breach of McDaniel Slough occurred at low tide. The breach was done over a series of low tides excavating as much material as possible the first day while leaving enough to prevent overtopping by the intervening high tides. After three days of incremental excavation, the tide gates and culverts were removed and — for the first time in decades — McDaniel Slough flowed unimpeded to Humboldt Bay. Prior to the breach, monthly fish and water quality sampling was conducted to try to determine what resident/anadromous juvenile salmonids and other fish species utilized the estuary and lower watershed for rearing. Monitoring included water quality to make sure it was adequate to support juvenile salmonids. Pre-breach results showed poorer water quality and no fish utilization in the lower reaches of McDaniel slough. In the freshwater reaches of Janes Creek/McDaniel Slough, water quality was good with documented use by coastal cutthroat trout. Post-breach water quality improved throughout the system and monthly monitoring documented utilization by juvenile coho salmon, tidewater goby, Pacific staghorn sculpin, surf smelt, prickly sculpin and other marine species. Bird utilization of the area has also been monitored since 2009 with an increase in the number of species using to the area. CDFW’s 2015 monitoring found 35 species and total numbers of over 8,000 birds utilizing the restored area. 

The success of the ecosystem approach in restoring and enhancing Arcata’s aquatic resources depends upon the community’s interest and involvement as well as a degree of ecological awareness and understanding by the citizenry and elected officials. Even if not fully successful from an ecological perspective, the process of attempting to reverse past environmental impacts will have a lasting and profound impact on the people who choose to be involved and make the effort. For the McDaniel Slough project, the social dimensions of restoration are an important component to the overall project. — by Julie Neander, Environmental Programs Manager for the City of Arcata