From Clatsop County: Consultant Report Offers Solution To South Seaside Highway Flooding

Friday, July 15, 2011

Consultants hired to research possible remedies to the chronic flooding problem on U.S. Highway 101 south of Seaside have presented a potential fix.
Northwest Hydraulic Consultants of Seattle last week presented a plan that recommends the removal of some berms and construction of others along an approximately one-mile stretch of the highway near Beerman Creek.
The study was spearheaded by Clatsop County with support from local cities, the Port of Astoria and Oregon Department of Transportation. The project aims to find a solution to annual wintertime flooding from the nearby Necanicum River, when heavy rainfall combines with high tides to send water over portions of the highway, resulting in traffic restrictions on low-profile cars and occasional complete closures.
As part of the study the consultants held meetings with affected landowners and other stakeholders, and installed gauges at several points around the highway and river to gather flow data during high-water periods.
The study’s recommended first step is the removal of a berm on the west bank of the Necanicum. The berm, built in the 1960s, confines the river during high water and prevents excess flow from spilling out onto lower ground to the west. Removing the structure could reduce floodwater levels on the highway up to seven inches, according to the study’s modeling, and would result in fewer occurrences of flooding.
The Phase 1 project alone may be sufficient to eliminate most of the flooding problem, the consultants say. In addition, the adjacent land is owned by the North Coast Land Conservancy, and removal of the berm would fit in with the organization’s restoration strategy, the study notes.
In the event flooding remains a problem after the berm’s removal, the study offers as a second step the construction of a one- to two-foot berm around the Circle Creek Campground, located on the west side of Highway 101. Much of the water that overtops the roadway comes from overflow from the Necanicum that washes through the campground, according to the consultants.
Additional remedies offered by the study include the construction of three new berms or floodwalls along the highway itself. But the consultants warn that additional data on water flows must be collected before embarking on those projects, due to the uncertainty over whether these protective barriers might increase the risk of flooding farther north.
The study states that the options with the most certain results involve elevating the roadway at the two most flood-prone locations and replacing the Dooley bridge and Beerman Creek culvert with larger structures, but notes these are the most costly alternatives. Removal of the existing Necanicum River berm is estimated to cost $500,000, and construction of the four new berms $520,000. Elevating the roadway and installing new bridges has a projected price tag of $5 million.
The consultants recommend continued monitoring, including another winter season’s worth of data, with additional gauges installed at key points.
The county will convene a meeting of the stakeholders in the next few weeks to review the recommendations and seek consensus on a solution, according to Ed Wegner, Clatsop County Transportation and Development Services Director. The next step will be to seek funding opportunities, he said.
Clatsop County contributed $31,437 from its video lottery and road department funds to the study’s $126,151 total cost – ODOT, the port, and the cities of Cannon Beach, Gearhart, Seaside and Warrenton covered the rest.