Salt River Restoration in the Lower Eel River Watershed

Summer 2015 Ecesis, Volume 25, Issue 2

Aerial view of the Riverside Ranch, immediately after completion of the Phase 1 excavation and construction, South Slough is in the foreground.

Aerial view of the Riverside Ranch, immediately after completion of the Phase 1 excavation and construction, South Slough is in the foreground.

The Eel River is the third largest watershed entirely within California and has a drainage area of approximately 3,700 square miles. The combination of the watershed’s geology, location and precipitation has resulted in two notable factoids. First, the watershed has the highest sediment yield per unit area of any watershed in the continental United States — only the Mississippi River delivers more sediment to the sea than Eel River, but it also has a much larger drainage area. Second, the lower Eel River is adjacent to the Mendocino Triple Junction, the convergence of three tectonic plates, including the northern terminus of the San Andreas Fault. The Eel River supports runs of Chinook salmon, coho salmon, steelhead, green sturgeon and Pacific lamprey. Tributaries near the mouth of the Eel River support the southernmost populations of coastal cutthroat trout. Historically, the Eel River had an extensive tidal estuary with numerous side channels, oxbows, sloughs, and perennial and seasonal wetlands. Approximately 5,500 acres of the Eel River’s wetlands were converted to agricultural lands as the lower Eel River was settled and populated in the late 1800s. 

The Salt River is a tidally influenced slough tributary to the Eel River estuary located in Humboldt County near Ferndale, California. Salinity in the Salt River varies with the interactions of tides, Eel River flows, and freshwater inflows from its tributaries (Williams, Francis, and Reas creeks). In the mid-1800s, the Salt River channel was sufficiently deep to support ship traffic several miles upstream to Port Kenyon; however, increased sediment delivered from the upper watershed and reduced tidal prism to flush sediment resulted in an aggraded channel with significantly reduced widths and depths. The frequency of flooding in Ferndale and the surrounding farmland progressively increased as the Salt River filled with sediment over the past century, and efforts to alleviate flooding have become a persistent issue. An intensive multi-stakeholder planning process was started in 1990 with a Coastal Conservancy grant that initiated studies on sedimentation, hydrology, and aquatic and avian biology. Stakeholders have included Ferndale residents and dairy farmers, as well as city, county, state, federal, and tribal entities. The culmination of this process was a multi-phase plan to restore the hydraulic and ecological function of the Salt River.

Near the Salt River mouth, the 420-acre Riverside Ranch was purchased from an interested seller and the title is now held by the California Department of Fish and Wildlife (CDFW). Phase 1 of the Salt River Restoration Program was focused on Riverside Ranch parcel. In 2013, the levee and tide gate at the Salt River’s confluence with the Eel River were removed and upstream slough channels were excavated to meet the following objectives: (1) increase hydrologic function to the lower 2.5 miles of the Salt River; (2) provide access for re-colonization of the lower Salt River by native fish species; and (3) improve habitat for waterfowl and other avian species. The interchange of flow between the Eel River estuary and the lower Salt River was restored in October of 2013 following completion of Phase 1 excavation and other construction activities. The purchase of the Riverside Ranch allowed the re-opening of two main sloughs and numerous secondary channels. Phase 2 was completed during the summer and fall of 2014, with another 1.8 miles of Salt River channel restored up to the Dillon Road Bridge. Phases 3 and 4 will eventually reconnect Francis and Williams creeks to the Salt River channel, for a total of seven miles of restored channel.

During the spring and summer of 2014, fish sampling was conducted in the lower Salt River by CDFW, the Humboldt County Resource Conservation District, and Humboldt State University to monitor the presence and distribution of fish within the recently restored main channel and sloughs located on the Riverside Ranch. This sampling captured fish with seine nets and minnow traps at 11 established sites distributed throughout the main channel and slough networks. All of the spring and summer sampling was conducted at low tide when water was concentrated in the channels. These initial sampling efforts documented numerous fish species utilizing the newly accessible habitat, including ESA-listed species such as coho salmon, tidewater goby and Chinook salmon.

The next phase of Salt River fish sampling occurred during the fall and winter of 2014-2015 and NOAA Fisheries requested that both low and high tide sampling were conducted. Ross Taylor and Associates (RTA) started this sampling effort in November of 2014 and sampled monthly through March of 2015. RTA conducted low tide sampling at the 11 sites established by CDFW, using methods consistent with those utilized by CDFW. RTA was also tasked with developing a high tide sampling protocol for the project. At high tide, increased water depths and channel widths in the Salt River’s main channel dictated using different sampling gear than wading with the 30 foot seine net. A kayak was used to set a 100-foot long seine net that was six feet tall and had ¼-inch mesh. Seventeen fish species were captured during the fall and winter sampling, including the first documentation of longfin smelt in the Salt River. The fall and winter sampling also confirmed overwintering use by coho salmon (see photo, page 1), with rapid growth and good condition factors. Fish sampling will continue in 2015 and 2016, extending farther upstream as subsequent Phases of the restoration project are completed.

Avian surveys have documented more than 100 species utilizing the restored habitat on the Riverside Ranch. The species diversity is greatest during the winter months when migratory birds are present, including cackling geese, Canadian geese, and 12 species of dabbling and diving ducks. The sloughs, side channels, and tidally flooded flats provide ample habitat for wading species. Resident raptors include northern harrier, white tailed kite, red tailed hawk, merlin and American kestrel. 

While the relatively immediate use of the restored estuary and wetland habitats by fish and avian species is encouraging, the long-term functionality of the restored Salt River channel to effectively transport sediment and reduce chronic flooding has yet to be determined. The channel’s low gradient, the watershed’s high sediment load, and the backwatering effect of high tides and periodic elevated Eel River flows are all factors being considered during project design as the program enters into its final phases.  — Ross Taylor, Ross Taylor & Associates