After the deluge

Published 10:04 am Thursday, October 5, 2017

WINDSOR – As one commissioner said, “Let’s abandon the term of calling them 100-year floods!”

With three significant rising Cashie River water events in the last 17 years, that’s probably a good idea.

Determined to address the Cashie River flooding concerns both in the Town of Windsor, and in the surrounding area following Tropical Storm Julia and Hurricane Matthew in 2016, Bertie County was able to secure $72,207 in grant funding through the Golden Leaf Foundation to support the first of two studies of the Cashie River Basin.

Dr. Barbara Doll, with the NC Sea Grant & Biological & Agricultural Engineering Dept. at NC State University, was contracted by the county and is coordinating one of those studies: a research project entitled  the “Town of Windsor Flood Reduction Feasibility Study” which will identify engineering options and best management practices targeted at reducing runoff and surface flow reaching the Cashie River from the watershed and its tributaries, and for reducing the direct flow of water into the town during river flooding events.

Doll made her first presentation to the Bertie County Commissioners at their monthly meeting on Monday evening. Also in attendance to contribute were County Extension chairman Billy Barrow, along with Windsor Mayor James Hoggard and Town Manager Allen Castelloe.

”This is a work in progress,” Doll cautioned. “It is not a complete effort at all.”

Doll says the feasibility study her group is working on has four elements that would be engineering options: (1) to evaluate the engineered, structured flood prevention measures, as when the river rises and water spreads onto the flood plain and what can be done for prevention; (2) to evaluate land-use change that’s happening in the drainage area which comprises a 180-square mile watershed that drains into Windsor; (3) what is the potential to store water in the watershed to hold it back from hitting the town so quickly during major storms; and (4) to look at it from a water management-agricultural perspective.

“We’re ahead of schedule on some of the things that weren’t due until October,” she acknowledged. “So we hope to have our study completed in December, with the final report in January.”

Using FEMA maps and those provided by NC Emergency Management covering six miles of the Cashie River stretching though the town of Windsor, the researchers looked at river flow generated during 2016’s big storms.

Doll said her group looked at increasing the height of the King Street Bridge with two models: one, from 150-to-1600 feet, and another from 150-to-3750 feet.

“Theoretically, this would bring the river levels down,” she noted.

However, Doll stressed that initial results indicate that no appreciable benefit can be gained by increasing the capacity of the King Street Bridge.

“What we got (with the bridge restructuring) was just a foot of elevation change,” she stated. “That would be a tremendous bridge change for a lot of money.”

Asked if funding was available for such a bridge expansion, Castelloe said there was, but also said it wasn’t worth the expense for what little result it would produce.

East of the bridge area is a land mass the researchers called “Old Bertie”, which blocks off the flood plain and they then theorized if that area might be altered.

Another idea might be raising York St., Granville St., and Bianca St., along with old US-17 highway at their low points and outfitting these areas with tide gates and pumps to help reduce some structural flooding to properties. But they determined that solution would not be effective in the event of larger floods like Julia and Matthew and would not likely be certified under the National Flood Insurance Program.

“Because these are two areas where water really floods into the town,” she said.

“As you can see with Julia it shows about $1.2 million impacted by all the inundation at nine-and-a-half feet at King Street, then for Matthew a more substantial impact because once we reach that higher elevation of 11 feet on the river, we’re at almost $3 million of impact,” she explained.

Doll concluded the presentation surmising that Options 1 and 2 would be very expensive with little to no appreciable benefit. Implementing Options 3 and 4 would provide some level of protection from flooding, but not in the event of a major weather crisis on the scale of a hurricane or tropical storm.

“The Cashie River downstream of Windsor to the confluence with the Roanoke River is very flat, which is what exacerbates a lot of the flooding issue,” she said. “You just don’t have elevation change, and water just can’t get away.”

On the idea of land-use change, Doll said while forestry land had declined since 1999, agriculture had remained the same.

“Some of the question we have is did the removal of so many trees make for any improvements on the drainage on some of these properties, ditches and the like, and what impact does that have on the waters that are reaching Windsor on some of these storm events,” she reasoned.

One potential solution, she surmised, might be water storage – short-term – on some of the agriculture and timber properties.

“Controlled drainage during drier times actually helps the crops because it keeps the water tables en route,” she said, citing a Tidewater study.

Over time, Doll said her group found elevation varies across the 180 square-mile watershed and there had been no significant ditching or drainage enhancement done, and that one of the contributors to water control is the area were beaver dams are located.

“We built a model and looked at all of the areas where we could store water (old millponds),” she said. “Could some of these be retrofitted to provide temporary storage during some of these big events, holding the water back?”

She said finished research on water storage had not been done, but should be complete by the end of this month.

“This is very theoretical at this point, to see if we can get any benefit,” she emphasized. “We’re not going to put a structure out there in March.”

Commissioner Ron Wesson inquired if other flood-prone areas such as Hoggard’s Mill, the area around Powell and Stokes, NC Hwy 308, or Roquist Creek, had been studied.

“I know (these impoundments) keep water back from the town of Windsor, but is it going to help some of the other areas that have been damaged further back upstream,” he wondered.

Doll said no recommendation would be made in a particular area that might adversely worsen another.

Wesson further questioned if it was the flow of water, or other drainage issues further complicating the process.

“I don’t think it’s individual drainage issues as much as it’s the pure flow and magnitude of water coming down the whole system,” reasoned Castelloe.

Doll said it would have to be a managed engineered system (gate valves, temporary storage).

“That’s the main exercise,” she stated. “Will it benefit us if the water is held back, then we can have other conversations with more detail. I’m hoping we can get some benefit out of this and pursue bigger projects.”

The final report from NC State is due January 31, 2018.