The Snohomish is one of the largest river delta sites in Puget Sound. It is one of the site being managed under the Snohomish Coordinated Investment Network. Recovery of historical wetland area is a target of Salmon Recovery in the Snohomish Watershed. The lower delta is being modified under a series of large scale restoration projects including Qwuloolt Restoration, Smith Island Restoration, and Blue Heron Mitigation Bank among others. These projects are reestablishing a large area of tidal inundation in the saline mixing zone. Upstream, freshwater tidal lands are in agricultural production, divided into diking districts such as Marshlands and Ebey Island, and depend on diking and pumping to lower water tables. There is controversy over the loss of agricultural lands as Snohomish County works to increase Snohomish Agricultural Resilience. Sea Level Rise effects may be important to long term planning.
Nearshore Strategies Data Report
Cereghino et al 2012 completed a soundwide analysis to identify and describe river delta sites in Puget Sounds as part of a nearshore ecosystem restoration strategy (using remote sensing data c. 2000-2006). The following narrative of this delta site was developed to support distribution and use of analysis results:
- The Snohomish Delta in the Whidbey sub-basin historically contained 18,706 acres of vegetated wetland along a 95 km shoreline. The delta receives flow from a 465,216 square kilometer watershed. These characteristics make this system the 2nd largest delta out of 16 systems in Puget Sound.
- Simenstad et al 2011 found that this system had lost 90% of its vegetated tidal wetlands, and 37% of its shoreline length. Of the remaining shoreline, 87% shows some evidence of infrastructure development. In the surrounding uplands, 55% of land is estimated to have greater than 10% impervious surface. Across the watershed, 32% of land is estimated to have greater than 10% impervious surface. Based on these paramters, the site was given a degradation score of 54 out of 100, making it the 4th most degraded delta in Puget Sound. It faces a medium risk of future development locally, and a low risk of development across the watershed. Approximately 53 percent of the watershed is currently impounded behind dams.
- Ecology TMDL for ammonia and BOD. The estuary has been listed as impaired for water quality violations. The study included load allocations for Quilceda, Allen, Woods Creek, and the Sultan and Pilchuck River watersheds, which drain into the mainstem Snohomish River, as well as four drainage systems controlled by pumping stations: French Creek, the Marshland, Deadwater Slough, and Swan Trail Slough.
- French Creek Watershed, Pilchuck River Watershed, and Marshlands systems all drain into the freshwater tidal zone of the delta.
- Quilceda Creek Watershed and the Jones and Allen Creek Watershed are the largest creeks flowing into the lower estuary from the north.
- SBSRF 2005 defines salmon recovery goals, including a 10 year objective for estuary restoration.
Snohomish Delta Workgroup
Snohomish County, NOAA, Ecology, and WDFW are collaborating in the delta, facilitated by Morgan Ruff (Tulalip Tribes). Efforts are focused on restoration of salmon habitats in the lower delta. There is unresolved controversy around continued conversion of farmland to tidal marsh. Sea level rise is anticipated to affect long range planning. This working group does not have a charter vision or a workplan.