Deer Lagoon Restoration Assessment

The hydrodynamic processes within the Deer Lagoon estuary, in Island County, western Washington State,  are dominated by tidal currents and sediment deposition from the tide gate. A series of dikes and tide gates has reduced tidal influence in the western lobe of Deer Lagoon, limiting its value as habitat for juvenile salmon. These dikes have resulted in the loss of over 450 acres of potential salt marsh and mudflat habitat. These dikes have also degraded ~100 acres of existing salt marsh on their seaward side. These barriers have led to the increase of sediment in both the opening of the lagoon and the remnant marsh.

The primary objective of this project was to increase the amount and quality of salt marsh habitats available to juvenile salmon in Admiralty Inlet. Wild Fish Conservancy (WFC) evaluated the feasibility and impact of multiple habitat restoration strategies. Restoration strategies were assessed using hydrodynamic models that simulate water surface elevations and erosion/deposition. These models then provided WFC with an analytical tool that became a major component of local community and stakeholder outreach effort. Based on the results of the modeling and public outreach effort, WFC worked with Island County to develop a design for restoration.

The recommended restoration is a new tide gate, which could be designed to keep the water level within the western part of the lagoon at a specific elevation which could provide some protection from flooding to homeowners. Additionally, a new tide gate would result in a larger area that would be flooded during low tide than would naturally occur with any of the levee breach alternatives. However, it would be important to understand the contributions of other hydrologic inputs into the western lobe if the new tide gate were to be designed to limit maximum water level in the western lobe. This restoration alternative would achieve all of the project goals, both biological and hydrological.