Necanicum River Wetland Mitigation Bank

ElkPastureHENDERSON design-build professionals worked with Clatsop County, the North Coast Land Conservancy (NCLC), and the Oregon Department of Transportation in the construction of the approximately 300-acre Necanicum River Wetland Mitigation Bank.  The County, NCLC, and ODOT entered into an agreement to cooperatively develop the mitigation bank to offset unavoidable impacts from ODOT’s highway maintenance and repair work in the northern Oregon coast region.  Necanicum River flows in this location are constricted between the prism shoulder of US Highway 101 and earthen berms historically constructed to prevent flooding of the project site.  As a result of this constriction, peak seasonal flows in the Necanicum River exceed their embankments and flood Highway 101 causing periodic closure of this vital transportation corridor.

 HENDERSON crews re-connected the Necanicum River’s historic floodplain, breaching sections of the earthen berm along the river bank, removing nearly 16,000 cubic yards of material.  Approximately 570 pieces of large woody debris were placed in the graded pasture and river bank as habitat enhancement.  Other floodplain restrictions were removed including a decommissioned railway bed and flood-control levees along the Circle Creek tributary.  Areas of the pasture lands that were not re-graded were disked and stabilized prior to hydroseeding with native seeds for reestablishment of coastal wetland and riparian vegetation communities.

Restoration of this Necanicum River stream habitat is critical for enhancing coastal juvenile salmon and steelhead rearing.  The Necanicum River mitigation site also includes a mature Sitka spruce swamp, a forested wetland type that has largely been eliminated from Oregon, emergent wetlands, and seasonally-flooded pastures that provide important habitat for wintering waterfowl and other migratory birds.  Two herds of elk use the open fields almost daily during the spring and winter.  Protection and restoration of these habitats provide an ecological link between existing conservation lands on the Necanicum River and the upland forests of Ecola State Park.

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