City considers approaches to wind-driven flooding; memo casts doubt on ideas that have support from Knight

A driver braves a flooded street in Ashville Park after Hurrican Matthew in 2016. [John-Henry Doucette/The Princess Anne Independent News]
Ed. — This story originally ran in the Sept. 28 print edition.


COURTHOUSE — Information from preliminary study about wind tides arrived this fall amid the threat of a hurricane that ultimately landed well south of here but was followed by widespread flooding that has become too familiar to residents of southern Virginian Beach, especially near the waters around Back Bay.

Among other things, a city memo, which was delivered with some background information from the city’s studies of sea level rise and flooding, cast doubt on whether changes to the operations of the Great Bridge Lock could alleviate water levels in Back Bay or the North Landing River.

There would be little solved by such a step, according to information provided to the City Council, and some other approaches, such as creating an inlet or spillway between the bay and ocean, might come with prohibitive costs. Those ideas were reported this past year by The Independent News.

Regarding the lock, Deputy City Manager Tom Leahy in September wrote the “answer is ‘no’ because inflow from Back Bay’s watershed, and more importantly inflow from the Currituck Sound, have far more capacity to replace any water lost through the canal.” 

Dewberry, a city consultant, is studying sea level rise and recurrent flooding issues, and the city is mapping its stormwater system as part of a wider approach to address flooding that is expected to be delivered to the City Council for discussion. 

Dewberry used a hydrodynamic model of the locks to simulate changes to water levels in the bodies to test the lock theory, which was among ideas presented to the city last year by state Del. Barry Knight, R-81st District. Additionally, Leahy and his staff made calculations to double-check the consultant’s assessment about the lock.

“The results indicated that opening the locks would have a minimal effect upon wind tides along the North Landing River and no effect on wind tide elevations in Back Bay,” Leahy wrote. “These results did not come as a surprise.” 

The city agreed to look at suggestions raised by the delegate last year, though officials including Leahy at the time noted the likelihood of high costs and little chance of a return. Creating a means of pumping water from the bay to the ocean, or moving it by creating an inlet also were among ideas suggested. So the city looked at that, too, and the findings raise a number of challenges that make those ideas longshots. 

Last year, one official from the U.S. Army Corps of Engineers said high water is often on the Chesapeake side of the locks. Then, Leahy said there might be some impact on the river but the likelihood of changes in the bay were remote – essentially what results now suggest.

“There’s just simply no way water moving through that lock can compete with the wind driven water,” Leahy said this past week.

Yet Knight said he isn’t giving up on the idea. In late August, the delegate wrote to U.S. Reps. Scott Taylor and Don McEachin about a way to alleviate severe flooding locally.

“The reason for my letter to you both is to request you explore removing the Great Bridge Locks in Chesapeake, which were originally wooden locks installed in the late 1800s,” Knight wrote. “Then, in the early 1900s, the present locks were installed through an act of Congress. Therefore, an act of Congress is required to remove them.”

Deputy City Manager Tom Leahy speaks with reporters at the municipal center during a forum on Wednesday, Aug. 2, 2017, about stormwater and flooding issues in the Princess Anne District, which includes the southern area of Virginia Beach. [John-Henry Doucette/The Princess Anne Independent News]
Southerly winds can wreak havoc in Virginia Beach’s rural communities and near neighborhoods such as Sandbridge, which suffered significant flooding following the anticipated arrival of Hurricane Florence. For Virginia Beach, the hurricane itself was a miss, but winds from the south in the following days pushed water to the bay, leading to a number of street closures in Creeds, Back Bay, Blackwater and Pungo. There also was flooding in Knotts Island, N.C., connected by a causeway to Virginia Beach’s southern communities and consequently reliant upon city roads. 

Flooding swamped Sandbridge Road, leading to the opening of the amphibious base to allow an alternate route for local traffic to the residential resort community that faced evacuation a week earlier for Florence. 

As officials have noted in numerous forums and meetings, wind-driven flooding is not the only challenge here. Sea level rise, over the coming decades, may impact southern Virginia Beach disproportionately compared to others areas of the city.

“The problem down in the southern watershed dwarfs everything else in the city because the rest of the city is considerably higher than the southern half,” Leahy said in an interview. “It’s just a much bigger issue.”

The city is working on a sea level rise and flooding study, and has defined impacts of sea level rise of 1.5 feet and three feet, with the staff looking at strategies. The city also is working on a stormwater modeling and master planning study, in which it is modeling 31 subwatersheds, with recommendations expected to come in 2019. The studies are interrelated, Leahy told the City Council in September.

And sea level rise threatens losses for coastal communities, though Leahy noted that the projections are spread over time. Potential average losses per year today are about $26 million per year, but it could be $87 million at 1.5 feet of sea level rise or $375 million at three feet. In the southern watershed, potential losses become a greater percentage costs to the city over time as sea level rise worsens.

That change has sobering potential for the southern city, including the transition area between suburban and rural Virginia Beach in which some development is allowed. The floodplain at three feet of sea level could include “practically everything east of Princess Anne Road” in the transition area, according to Leahy’s briefing to the City Council. In rural communities, where significant flooding issues already exist, there could be “severe impacts to infrastructure, residences and agriculture,” he said.

Wind tides, different from flooding conditions than other areas of the city, drive water from the Albermarle, Currituck and Pamlico sounds, pushing the water against low-lying lands, according to a city summary. 

“The last round of flooding is terrible, but it has shown the ability of Currituck to provide a phenomenal amount of water,” Leahy said.

“The Oregon Inlet is the closest inlet we have, and so the water has to all go all the way down to the Oregon Inlet to get out,” City Councilmember Barbara Henley said during a recent meeting. “So it’s just bottled up here.”

As the sea level rises, potential impacts of flooding could worsen during significant rains and when wind drives water into the bay.

“Increases in sea level are the main factor that increase flooding for lands next to Back Bay and North Landing River,” according to a city information sheet that accompanied Leahy’s memorandum.

Following May 2017 wind tide flooding, which increased water levels in the bay by about 2.5 feet, Dewberry conducted simulations of 10 days worth of southerly winds with locks open and locks closed. The simulation showed levels in the canal differed by about a 10th of a foot, with no effect upon the bay, according to the city.

Dewberry also looked at the possibility that lowering the dune line or barrier islands between the bay and ocean could reduce water levels in the bay during flooding events, but found that the bay water level “only exceeds the ocean water level during the highest peak of the event and during the daily ocean low tides.”

At other times, the ocean water level is higher, and flood elevation levels are higher on the ocean side during storm events. This suggests “an inlet that conveys ocean water into the bay could lead to more frequent flooding with higher flood waters.”

This sort of approach could be costly, and creating an inlet could lead to salinity changes in the bay, according to the consultant. There would be significant regulatory hurdles because much of the barrier system is federal land. There are also state and local regulatory issues that could govern feasibility.

A gated waterway or inlet between the bay or ocean would also face challenges due to differences in ocean and bay water levels, and the structure would face regulatory hurdles that likely would include dealing with North Carolina, as well.

State Del. Barry Knight [The Independent News]
Knight is not swayed by arguments against ideas he took to the city. In an interview in late September, Knight discussed the history of the bay, going back hundreds of years to show how inlets between bay and ocean formed, plugged and reformed, and the former Wash Woods community was a site where ocean water passed over the land to the bay. He discussed the manmade dune lines along the ocean, a 1930s works program that made a greater barrier.

“It just looks like Back Bay has always wanted to ebb and flow,” Knight said.

Regarding the lock, Knight said there doesn’t seem to be the same conditions in place now that led to its placement. Justification for the lock at Great Bridge was to help keep waste from Norfolk out of Back Bay and help barge traffic, he wrote in his letter to McEachin and Taylor. They are no longer needed, he added.

He wants them removed but understands the likely pushback to such an idea. “Undoubtedly, there [will] be some bureaucrats and other officials who will assert the necessity of the locks, but those views are biased to preserve their jobs,” Knight wrote.

Knight said even a small return could help prevent flooding. He suggested testing whether changing lock operations would make a difference over a period of months.

“It may be a half inch, but a half inch could be the difference between your house flooding or not,” Knight said during the interview. “If it’s not going to hurt anything, why don’t we open these locks for a test period and leave them open?”

Knight also said creating an outlet between the bay and ocean would face regulatory challenges and many other issues, but it should be studied in detail. The location should be at False Cape, he said.

“What is the cost of putting in an outfall opposed to the value of the property that is being damaged?” he asked.

Knight has met with state officials about challenges in his district, and, in early August, he wrote to Virginia Natural Resources Secretary Matt Strickler about using False Cape as the location to create an outlet, spillway or floodgates.

“There are many, many reasons to explore this option and to make it happen,” Knight wrote in a letter, asking to gather affected agencies together to consider the idea.

The delegate told The Independent News that he had seen the memo from Leahy.

“I think the city needs to think big,” Knight said. “Nothing will be done if nobody tries to do anything.”

Pumping water from Back Bay to the ocean appeared to have some support in the city information, but the costs would be high. “It would probably be a pumping operation, not a tide gate operation,” Leahy said.

A large pumping station might operate for about half a day to make a half-foot difference in the bay in ideal conditions, and such pumps, similar in scope to a project in New Orleans, could cost more than $300 million. 

Reintroduction of aquatic grasses in the bay, which declined in the last century, could be among a number of other measures to address flooding in the southern watershed, but changing salinity in the bay would not necessarily mean vegetation returns. Virginia Beach pumped saltwater into Back Bay from the 1960s to the 1980s, but “this did not result in the anticipated water quality improvements,” according to the city. 

In the coming months, Virginia Beach will unveil its findings from studies of sea level rise, recurrent flooding and drainage. Infrastructure improvements and approaches these reports will suggest may include the following: 

  • Seawalls and levees, including raised roadways that serve as levees
  • Tide gates and blackflow prevention with drainage improvements
  • Elevated homes
  • The restoration of marshes and submerged aquatic vegetation
  • Marsh terraces to impede water
  • Shoreline stabilization with hybrid living shorelines

Henley said it was important for citizens to follow the issues the city is navigating and become involved in discussions about recommendations.

“We still have to keep this conversation going in some fashion,” she said. “It’s just important to have the dialogue so it’s not hitting everyone cold.”

Among the items for discussion would be green infrastructure ideas, she said, as well as possibly tweaking the agricultural reserve program, which buys development rights to farmland, to bring in and preserve some properties that might not be eligible now.

Henley also said solutions must be approached with care and an understanding of effects elsewhere within the community.

“When we do one thing, there’s going to be a reaction somewhere else,” she said.

The city is installing gauges in the watershed to track rain, wind and water levels, as well as constructing detailed computer models, according to a statement released by the city.

During a Tuesday, Sept. 18, City Council informal session, City Manager Dave Hansen called dealing with sea level rise and recurrent flooding the city’s largest engineering challenge since the Lake Gaston project. 

“If we can precede engineering decisions with good scientific decisions or information, then our decisions will probably have greater value,” Hansen said. “We are faced in Virginia Beach with probably the greatest challenge that this city has ever had, and that is how do we remain a preferred coastal city on the East Coast of the United States?”

The city is working on a sea level rise and flooding study, and has defined impacts of sea level rise of 1.5 feet and three feet, with the staff looking at alternatives and strategies. The city also is working on a stormwater modeling and master planning study, in which it is modeling 31 subwatersheds, with developing recommended projects expected to come in 2019. Again, the studies are interrelated.

In a presentation to the City Council that afternoon, Leahy described two years of work to study the issue and a schedule of upcoming steps, including releasing information and recommendations to the public.

He talked about the data showing that the seas are rising effectively an inch every four or five years, or about a foot every 50 years. Inland and ground water levels are coming up, too, and data shows the city has faced more rainfall in recent years, including a sharp increase since 2000, and storms may come more frequently.

“The question everyone would ask is, is this an anomaly or is this the new normal?” Leahy said during the meeting. 

It might take years to determine.

© 2018 Pungo Publishing Co., LLC

Related Posts

Leave a Reply

Your email address will not be published. Required fields are marked *