Thursday, December 8, 2022

Washed-out 421 exposes water supply vulnerability, to be turned (back) into a bridge

Fixing the washout on Highway 421 is at least a $10.2 million project. Besides travel concerns, the region's main water supply transmission is now susceptible to damage, triggering an emergency plan for if it fails during bridge construction.

During Hurricane Florence, flooded waters from Fishing Creek, a tributary of the Cape Fear River, washed out a four-lane portion of road on Highway 421 north of Wilmington. (Port City Daily photo/Courtesy North Carolina Department of Transportation)
During Hurricane Florence, flooded waters from Fishing Creek, a tributary of the Cape Fear River, washed out a four-lane portion of road on Highway 421 north of Wilmington. (Port City Daily photo/Courtesy North Carolina Department of Transportation)

NEW HANOVER COUNTY — When the Cape Fear River Crested at 31 feet in late September, eastbound waters wiped out an entire portion of Highway 421’s four-lane road.

Just north of Wilmington, the compromised section of Highway 421 is getting transformed back into a bridge — right next to the region’s water supply transmission line.

RELATED: CFPUA concerned about Army Corps seeking to back out of managing regional dams

After Hurricane Florence, North Carolina Department of Transportation temporarily patched the washed out highway near Fishing Creek with a two-lane road, a $2.2 million fix.

But the washout also unveiled a vulnerability bigger than travel in and out of Wilmington: the water supply for every Cape Fear Utility Authority (CFPUA) customer in New Hanover County.

Lower Cape Fear Water and Sewer Authority (LCFWSA) supplies raw water to Pender, Brunswick and New Hanover County, and two companies, Praxair and Invista on Highway 421. A 48-inch water main carries the region’s raw water supply from Bladen County under Highway 421, approximately 75 feet south of the damaged road.

The washout physically exposed the water transmission but did not damage it.

Now, LCFWSA is developing an emergency plan if the water main fails while the North Carolina Department of Transporation (NCDOT) performs work to build two new bridges.

Bridged again

This won’t be the first time a bridge has connected Highway 421 over Fishing Creek. According to Lauren Haviland, an NCDOT spokesperson, the highway was just two lanes in the 1950s.

That portion used to be connected by a 500-foot bridge, Haviland said. But in the ’70s, when Highway 421 was widened to four lanes, the bridge was replaced with a pipe.

During Hurricane Florence, mother nature had its way. The 78-inch culvert crumbled under the pressure of Fishing Creek’s waters, with the breach nearly in line with the old ’50s bridge, Haviland said.

Construction on two new north and southbound bridges over the location will begin early next month. An approximately $8 million project, the bridges will replace the temporary $2.2 million two-lane road by the end of 2019, Haviland said.

“The Department felt the decision to bridge this location again would ensure the integrity of this route for the future, as an alternate for I-40 if there were another catastrophic event,” Haviland wrote in an email.

Water supply concerns

While crews work to deconstruct the temporary road and install the bridge in 2019, an engineer hired by LCFWSA will be on the scene for at least two hours a week.

For $40,500, LCFWSA hired McKim & Creed, a Wilmington-based engineering firm, to prepare an emergency plan in case the water main fails next year. The plan includes continued monitoring and an alternative bypass location for the water main.

During construction, NCDOT will take precautions to eliminate conflicts with the line, its spokesperson said. The department understands the importance of the supply line, Haviland said, and will work with LCFWSA and other utilities in the state’s right-of-way.

“We have been and will continue to work with LCFWSA to protect this line as we do with all utilities within NCDOT right-of-way,” Haviland said. “LCFWSA also has responsibility within NCDOT right-of-way, to ensure the integrity of their line.”

As part of its proposed emergency plan, initiated last week, LCFWSA will look at the cost of permanently relocating the pipe away from the bridge. The plan will also evaluate contingency plans for each of CFPUA’s customers, serving over 200,000 people.

About 23 miles upstream from Wilmington, the region’s intake source, has also been compromised. The Bladen Bluffs Water Treatment Plant water intake line, just south of Lock and Dam No. 1 in Riegelwood, was subject to erosion after the storm.

Dam releases in Jordan Lake last month, the source water for the river, also contributed to erosion around the plant, LCFWSA’s engineering scope of services contract states.

At the release’s peak, 4.5 million gallons per minute were released downstream the Cape Fear River.

Now, intake piping and air backwash piping are exposed. As part of the emergency plan contract, engineers will conduct site visits and recommend river bank restoration options.

Also in that area, CFPUA raised concerns Monday about a U.S. Army Corps of Engineers disposition study that could end federal maintenance of the Cape Fear River’s dams.

Check out footage of Highway 241 in September after the road gave way to Fishing Creek.


Send tips and comments to Johanna Ferebee at johanna@localvoicemedia.com

Related Articles