DESCRIPTION
Snohomish County will enlarge existing dike breaches and construct new breaches on Mid-Spencer Island. Project elements include the following components: (1) increase the size, quantity, and diversity of breaches, (2) increase connectivity between Steamboat Slough and other sloughs, and (3) restore natural tidal exchange processes. The proposed project site is located in the Snohomish River estuary, east of Everett, Washington, and is owned and managed by Snohomish County for conservation purposes. Historically, the project site was diked and farmed, but in the late 1960's it was abandoned. Since that time, the site has remained unused, and dikes along Steamboat Slough have naturally breached at several locations. However, the breaches are generally limited in width and much less numerous than at intact reference sites (e.g., Otter Island). These undersized and infrequent natural breaches prevent full tidal exchange, limit fish access, and hinder full site restoration.
Snohomish County enhanced natural tidal exchange processes on Mid-Spencer Island by improving connectivity along approximately 0.75 mile of Steamboat Slough (eastern shoreline) and 0.75 mile of Union Slough (western shoreline). Mid-Spencer Island is centrally located east of Everett, WA in the Snohomish River estuary where the tidal slough channel network links the few naturally intact islands to large newly restored areas. This project created immediate improvements to site access and habitat for fish by enhancing connectivity for the neighboring Smith Island restoration site (located across Union Slough) and creating conditions that allow for natural restoration of tidal influences and floodplain connection over the long-term. Project elements included:
- breaching 16 sections of remnant dike to connect naturally developing interior channels to the main slough;
- removing 43 historic pilings from the new tidal channel openings.
- removing ~35 spruce trees (planted 17 years ago) from the remnant dike and re-purposing for channel edge complexity and interior fill to create a complex organic base for a diverse aquatic and terrestrial insect community;
- excavating approximately 1,095 feet of interior channels;
- adding 15 vertical wood arrays in the interior of the island to encourage natural racking, aggrade the marsh, and provide nurse material for native vegetation to accelerate the rate of native vegetation diversity and succession to forested scrub shrub wetlands;
- creating 8 bird perches using spruces removed from the remnant dike and drift logs with rootwads.
The interior of Mid-Spencer Island is now accessible to young salmon, providing critical rearing habitat and food sources. Without these areas of refuge, the river currents are too fast and channels too barren for juvenile fish to feed and hide. The newly created habitat and increased tidal channel accessibility will increase the estuary's carrying capacity for juvenile salmon. The new connections decreased the previous fish travel distances to the interior tidal wetland channel habitat by a total of 9352’ (1.77 miles). Increasing the juvenile salmon out migration survival rate and improving early conditioning will help increase the number of returning adult salmon. The estuary rearing is particularly important for Chinook salmon whose well being is linked to the survival of the Southern Resident Killer Whales, as well as Snohomish County citizens' cultural, recreational, and economic interests.
