To re-establish freshwater flow in the Old Channel of the Stillaguamish River, a low-restriction tidegate structure would be installed to capture tidal inflows from Hatt Slough. At present, whenever main channel levels are low in July-October, fresh water enters the Old Channel from Hatt Slough only during flood tide. Little or no net downstream flow is produced, however, because the tides enter from both ends, they ebb back the way they came. Stagnation results with dissolved oxygen (DO) levels as low as 4.4 mg/l, high conductivity and elevated temperatures. Hydraulic data indicate that a tidegate facility installed near the Old Channel entrance at Hatt Slough would capture the flood-tide inflow and force downstream an averaged daily freshwater volume of roughly 1.5 million cubic feet. The project combines this infusion of clean water (90-95% DO, zero salinity) with restoration or enhancement of approximately 85 acres or riparian vegetation along the length of the Old Channel, which meanders 81/2 river miles from Hatt Slough, past Stanwood, to Port Susan and Skagit Bay. Phase 1 - Clarify projected impact on water quality Develop the revegetation plan and the design for the tidegate facility. Phase 2 - Construct tidegate facility (partly funded by COE), implement the reveg plan, and initiate monitoring.
