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Civil Engineering Magazine THE MAGAZINE OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS

Keeping the Water at Bay

By T.R. Witcher

Alexandria, Virginia, is preparing to beautify its historic waterfront while it protects its shores from floods.

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The proposed reimagining of the Alexandria waterfront will tuck improved greenery and pedestrian spaces behind a flood wall. © OLIN

April 14, 2015—When Hurricane Isabel hit Alexandria, Virginia, in September 2003, it rocked the historic city that fronts the Potomac River, flooding streets and destroying trees. But it spurred city leaders to begin considering how to both protect near-shore development from future flood events while at the same time reconnecting the waterfront to the city's historic Old Town district

The city first hired the San Francisco-based engineering firm URS to conduct a multiyear small-area plan (SAP) for redeveloping the waterfront. URS, which has since been acquired by Los Angeles-based AECOM, was then hired along with the Philadelphia-based landscape architecture firm Olin to develop a schematic design that would integrate flood mitigation with the goals and vision established in the SAP.

The SAP and the schematic design focused on approximately 1.5 mi of the waterfront, from Harborside Park on the south to Tide Lock Park on the north, encompassing $120 million in public improvements. Because the scope of the project was too large for the city to build all at once, the city council decided this past January to prioritize the flood mitigation aspects. "The idea is for this to be a major overhaul, a reinvention of the waterfront," says Tony Gammon, P.E., the acting deputy director of Alexandria's Department of Project Implementation. "One of the primary elements of the small-area plan was to incorporate continuous pedestrian connectivity along the waterfront."

Olin worked closely with URS and the city to gain a better understanding of the area's flood history; the city experiences more than 100 nuisance flood events each year. "It's that frequent," says Skip Graffam, ASLA, LEED AP BD +C, a partner of Olin and the firm's director of research. "It's just enough to create havoc with traffic and business at the foot of King Street," one of the main thoroughfares leading from the city proper to the Old Town section, which is popular with tourists and residents alike. Water has reached one to two blocks beyond the shore, Graffam says, noting, "It's slowly damaging some of the historic structures." Television footage of people canoeing around Union Street, one long block from the waterfront, is not uncommon during larger flood events. The central portion of the waterfront, along the Strand, currently experiences flooding approximately one to two times each month. 

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The relocation of the Old Dominion Boat Club to a position further down the waterfront will create space for a flexible plaza, Fitzgerald Square, at the base of King Street. © OLIN

While floodwalls in nearby Georgetown extend straight out of the ground, city officials in Alexandria told the engineers that tourism, recreation, and maintaining the beauty of the site were incredibly important. "They didn't want to ruin that," says AECOM's Mary Roman, P.E., who at the time was a manager with URS and now serves as a water resources engineer for AECOM.

The solution that AECOM devised is a floodwall that will rise to what is known as elevation 6, roughly 3 to 4 ft higher than the existing ground in most places. "When we first broached the subject, it was not what they originally envisioned for the area," Roman says. "The proposed solution would not protect against a storm at the level of Isabel." But it will, she explains, "mitigate frequent flooding and significantly reduce flood damages. The majority of the damages, in terms of cost, occur due to frequent flooding. To put something up that will protect everybody from every storm is not cost effective," Roman says. While AECOM's solution "functions as a floodwall," Roman says, "in my mind what it looks like is a bulkhead that comes above the ground and has a walkway on top of it. It's a waterproof wall to elevation six."

To protect against much higher and less-frequent floods would have changed the character of Old Town. "We would have had to go to ten and a half feet to protect [against] the hundred-year flood," says Graffam. "But if you go up that high, you're basically building a giant wall between you and the water, which no one wanted. So the city determined that a financially responsible compromise between waterfront views, accessibility, and nuisance flood relief was at elevation six, which allowed us to create a really nice pedestrian promenade all along the edge of the water that served as that nuisance flood mitigation."

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A proposed jet fountain in Fitzgerald Square could be turned on or off for events. © OLIN

In addition to the floodwall itself, the project will include storm drain diversions and a pair of pump stations to divert any drainage around the floodwall. According to Graffam, these pumps will remove the water that would collect in areas behind the flood mitigation line at elevations lower than 6 ft.

But the new waterfront has to work aesthetically as well, drawing people down to a beautified area along the water and making it easy for them to move along the waterfront. Graffam says the guiding principle for the plan wasn't to replace what was there before, but to create a waterfront that fit the scale and character of Old Town. "We're not dropping NYC in here," he explains. "We're enhancing what's great and we're thoughtfully reimagining spaces that aren't so nice into one, contiguous, wonderful, outdoor public space."

The shoreline in some places is not in great shape, with leftover debris of concrete and sheet piling from previous projects. And parts of the waterfront are cut off by fences and parking lots. The new waterfront will remove the impediments, beautify the shoreline, and reconnect streets to the water. 

The focus of activity will be at the foot of King Street, which will feature a plaza for events and an arrival point for boats and water taxis. The waterfront will grow quieter and more parklike as it moves in either direction of that central point.

The privately owned Old Dominion Boat Club (ODBC), which had disrupted the free flow of pedestrians along the water at the foot of King Street, has agreed to relocate to the site of a former waterfront restaurant. The city will purchase the property, demolish the building and its parking lot, and transform the site as part of the full buildout of the waterfront plan.  

The new promenade that will be created will be slightly wider that the walkway there now, but Olin's plan retains all of the existing trees, which will have their canopies lifted to create safe sightlines and better views. Scrubby underbrush will be pruned or removed to further beautify the space. Graffam notes that Fitzgerald Square, the new paved plaza at the foot of King Street, will become primarily a flexible open space suitable for a range of activities, including a farmer's market, movies, and concerts-it may even sport an ice rink. Olin is also proposing a flush-jet fountain in Fitzgerald Square which can be turned on or off for events.

Two other long-standing obstructions on the waterfront, the north and south Robinson Terminal buildings, are set to be redeveloped and integrated into the pedestrian fabric of the waterfront, as well.

The schematic design of the SAP was adopted by the city in June 2014. Currently, says Gammon, the city is developing a request for proposals (RFP) from engineering consultants, which will be asked to develop the final flood mitigation design and construction documents. The city's proposed budget for fiscal years 2016 through 2025 includes $60 million in capital improvement funds for the project. The plan is to start the multiyear preliminary design and permitting process immediately following the RFP and the design contract award, which is anticipated to be within 4-6 months. Gammon adds that the initial infrastructure construction is anticipated to begin in summer 2018, and flood mitigation construction should begin by summer 2021.

"It was a challenging project," Roman says, "and I am really glad we came up with a workable and cost-effective solution for the city."

 

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