subarea 6: estuary zone
This subarea captures most of the lower portions of the watersheds under tidal influence. The largest expanse of these areas is Clatskanie Flats, north of the City of Clatskanie. Clatskanie Flats area is drained by the Westport and Beaver Slough channels. Area also includes emergent marsh fringes along Columbia river shoreline and large mid-channel islands such as Wallace and Lord Island. Some of these islands have been shaped by the disposal of dredge material to maintain the federal navigation channel. Additional areas included in this area are Carr Slough near Prescott and Dibblee Beach. Most of the estuarine areas have been fragmented by flood control and road building activities shifting drainage patterns.
Contributing areas: Westport Slough, Beaver Slough, Randa Slough, Kelli Slough, Larson Slough, McLean Slough, Carr Slough, Wallace Island, Cooper Island, Crims Island,Gull Island, Lord Island, Walker Island, Rinearson Slough, Diblee Point
Survey data wasn’t collected for the estuarine sections of LC watersheds. Therefore, priorities weren’t determined from the GIS model described above. Several restoration projects have been completed in this area through the removal and/or manipulation of levee
material to re-establish tidal-estuarine hydrologic patterns. Consideration should be given to several criteria to screen range of estuarine opportunities in this area. They are listed here with descriptions as prioritization guidelines as estuary project opportunities are identified:
Size
Size is always a factor in determining priorities from several fronts. In simple terms, the larger the size the greater the capacity to support more fish and a variety of other species needs. The broader the expanse of the potential habitat “patch” the more likely it has the capacity to support a diversity of habitat types and diverse channel structures. Larger size habitats are general more resilient to bigger events such as storms, landslides, and flooding.
Proximity to tributary confluence area
Areas near transitional boundaries such as confluence area serves as important patches as aquatic species make their transition from freshwater stream systems to estuarine environments. Depending flow conditions from the estuary these areas may serve as cold-water
refugia from surrounding warmer water.
Proximity to reference site or completed restoration
project
Distance to functioning habitats may provide a synergistic effect in the availability of nutrients and resources to jump-start food web productivity for foraging needs of salmon and other aquatic species. An argument can also be made to developing a restoration project where there is no surrounding habitat, establish “steppingstones” to meet basic survival needs. Availability of these patches reduces stress and predation risk during estuary migration.
Potential habitat diversity
A site that has a variety of elevations may be considered high priority so that direct and indirect habitat patches can be made available for a variety of water level conditions. This can also bolster plant diversity that can facilitates prey resources available during different times of the year for range of juvenile salmonid life histories.