Saturday, August 02, 2014

Work is underway on a project to ease seasonal flooding on a stretch of U.S. Highway 101 south of Seaside. Heavy machinery from contractor Henderson LLC began removing a man-made berm surrounding property along the Necanicum River earlier this month. The work is expected to last into September.

The project is a joint effort of Clatsop County, the Oregon Department of Transportation and the North Coast Land Conservancy, as well as the Port of Astoria and local cities, designed to ease chronic wintertime flooding along a roughly one-mile stretch of the highway south of Seaside, while at the same time restore wetland habitat on a Conservancy-owned piece of property.

The $728,000 project is funded through the state's mitigation banking program, which pays for the restoration and preservation of wetlands and other sensitive natural resources. The work will open up to inundation about 110 acres of adjacent land within the Land Conservancy's Circle Creek habitat reserve, and contribute to the group's goal of re-establishing wetlands and riparian forests on the entire 364-acre site, which historically was used as pastureland for cattle.

To accomplish the restoration, crews are digging away all or parts of a berm built in the late 1960s that surrounds most of the Land Conservancy property. In total, as estimated 15,000 cubic yards of berm material will be excavated and spread over the adjacent land.

The project originated from a 2011 hydrological study funded by Clatsop County, ODOT, the Port of Astoria and cities of Astoria, Cannon Beach, Gearhart, Seaside and Warrenton that examined the almost yearly incidence of flooding. Heavy rains combine with high tides each winter to send water over the banks of the Necanicum and across the highway, and the flooding frequently leads to traffic restrictions and occasional closures of the roadway.

With the berm removed, it is projected that high water in the Necanicum will flow more easily into the Land Conservancy property, limiting the amount of flooding on the highway on the opposite side of the river.

Ben Brown, Clatsop County Public Works engineering technician and project manager, said the contractor, Henderson, has experience with environmentally sensitive projects. Care is taken to keep soil out of the adjacent river, erosion-control mats cover the excavated berm sites, and valuable trees and vegetation growing on the berms are preserved for replanting elsewhere on the project site.

Root wads and other woody debris will be placed around the site, and a berm on the western side of the property that runs through a marshy area will be replaced with supports for a future walking trail envisioned by the Land Conservancy.

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