在战斗中应对海平面上升,of Norfolk, Va., finds itself on the front lines. The city, which officials say is the urban area most at risk from the looming threats of rising sea levels on the East Coast, is going beyond just conducting studies of future impacts and is taking action. In the Ohio Creek Watershed project, the city is employing a multi-layered approach to mitigating current and future flooding concerns. Design started on the $122-million project in 2016, and construction is expected to be completed in January. It aims to help mitigate both regular nuisance flooding and storm-surge flooding in the historic Chesterfield Heights neighborhood. The strategies deployed will offer city officials valuable insight for future planning while creating best practices that other flood-threatened urban centers can follow.

“By bringing all of these strategies together into one neighborhood, we are providing a test bed in Norfolk that they can work with for decades to come,” says Edgar Westerhof, U.S. flood risk and resiliency lead at Arcadis, which led the project’s design team.

切斯特菲尔德高地（Chesterfield Heights）沿着伊丽莎白河（Elizabeth River）的支流沿俄亥俄州克里克（Ohio Creek）的边缘，近几十年来看到波浪动作和风暴潮越来越侵蚀其海岸线。此外，暴风雨会定期在邻里街道上引起令人讨厌的洪水，因为衰老的基础设施无法有效处理雨水。

Flooding also raises safety concerns. The neighborhood, which is partly cut off from the rest of the city by Interstate 264, can only be accessed by two streets. During flooding events, those roads may be impassable.

Given the city’s growing need for solutions, the state in 2017 was able to secure a $112-million resiliency grant through the Dept. of Housing and Urban Development’s National Disaster Resilience Competition. As part of conceptual design, the city and designers worked with the community to devise a strategy that would not only address flooding concerns and make the neighborhood more resilient, but also provide other improvements for the community.

“During our dialogue with the community, we toured around the neighborhood and you felt how deep their connection with the water goes,” Westerhof says. “That’s not something you want to take away with a big wall. We wanted them to stay connected.”

设计师解决方案

The final design concept called for a mix of hard infrastructure and natural solutions. Near the shoreline, crews would construct more than 1,000 linear ft of floodwall, along with more than 2,000 linear ft of living shoreline. Based on National Oceanic and Atmospheric Administration sea-level rise projections, an earth berm was built to an elevation of 12 ft. It extends from the floodwall, across the shoreline and into the neighborhood. The combination of floodwall and berm create a continuous coastal defense system for the entire community.

Strong Defense |Norfolk planners stepped into action to combat sea-level rise by constructing 4,200 linear ft of living shoreline; infrastructure upgrades that included raised roadways, permeable pavers and pump stations; and community parks and green spaces that serve as shallow stormwater retention areas following a flood event. (Click the image for greater detail)
Map courtesy of VHB

VHB环境科学家金伯利·布洛斯（Kimberly Blossom）说，护堤的街道高达5英尺，但并没有完全脱离社区的水景。

“The design team brought in hay bales and stacked them so they could demonstrate the height to the community,” she says. “What we found is that the porches on most homes are at about 5 feet [above street level], so most could still see well over the berm. It helped them understand things better and calmed some nerves.”

At the foot of the berm along Ohio Creek, the team designed a living shoreline to provide a natural buffer against wave action and surge. Blossom says the design was largely based on studies of wave energy.

沿最接近伊丽莎白河的一侧，使用了一种硬化的方法，并结合了大面积的Rip-Rap石头来装甲。在较少的波动作用的区域中，安装了植被的海岸线。牡蛎礁也是在某些区域填充的区域中创建的，这是仅在海上提供的小型防波堤。

Although the living shoreline is located on the other side of the berm from the neighborhood, the community can walk along the berm or gain access to a new fishing pier to better experience the new shoreline.

Designers added a tide gate to the floodwall that can be operated by city staff, as needed, in the event of a storm. As part of that project, VHB also enhanced an existing marsh on the neighborhood side of the gate, where water will be able to move in and out as needed.

Although walls can keep water out, they can also keep water in, Westerhof notes. As a result, numerous solutions were designed to help alleviate flooding, including two large pump stations. Stormwater systems were also improved in the neighborhoods, with new large-diameter drainpipes installed along streets that are already prone to nuisance flooding. Planted bioswales and permeable pavers were also added to help convey stormwater.

为了解决访问问题,roadways that regularly flood were raised. Because the neighborhood had limited access to begin with, existing roads needed to be kept open while construction crews built raised roadways on new alignments, including a new 30-ft span precast concrete bridge.

Sidewalks and paths were also added to expand transportation options, helping to improve access to a light rail station located just outside the neighborhood.

Green space was converted to “stormwater parks,” which also help capture runoff and lessen flooding. The strategy provides a public amenity, too. The largest of the parks is an area adjacent to a school, which has been converted to play fields once the area was graded to alleviate standing water and help better direct runoff.

Funding the problem

HUD funds made the project possible, but they came with stipulations that added early challenges. The National Environmental Policy Act process had to be completed for the project to be eligible for funding. That meant the project needed to be well into design by that point. HUD also required that the funds be spent within a five-year period.

The city contracted with MEB in 2018 as the construction manager at-risk for the project. At that point, however, Arcadis was deep into designs. “[Arcadis was] well past the conceptual phase when we got involved,” says Tim Griffin, project executive at MEB. “They knew where berms and concrete walls were going. They had narrowed down the scope to two pump stations. We didn’t have the ability to impact the design much.”

MEB joined the project as material and labor costs were increasing significantly. As a result, MEB’s guaranteed maximum price came in over budget and the team needed to conduct a six-month value engineering process. “In hindsight, having the construction team completely separate from the design team cost the project some time,” says Kyle Spencer, acting chief resilience officer for the city of Norfolk. “Right as we reached 100% design and release of funds from HUD, steel tariffs took effect. We had huge cost differences.”

The pump stations proved some of the best opportunities to trim the budget. The foundation system was originally designed with piles, but the team was able to redesign it as a mat slab system.

“The buoyant factor of the pump station and the depth underground allows you to not have piles under structures like that in this area,” Griffin says. “We put geotechnical fabric down and then 2 feet of stone underneath.”

而是由han结构采用现浇concrete, and above grade, the stations are masonry structures, he says.

To construct the pump stations, crews excavated roughly 30 ft down. Because the project was located at the water table, Griffin says the team installed interlocking sheeted cofferdams to keep work areas dry. “With the soils here, there is a sandy layer between 5 and 10 feet down,” he explains. “Then after 10 feet, you get into some heavy clay materials. Water does not move through that well.”

MEB还通过自我绩效泵站的大部18luck.cub分建设来节省了成本，同时遵守其建筑经理处于高风险合同的规定。MEB机组人员自我施加了现场混凝土工作以及泵站的机械和地下管道。

One station, now complete, features three pumps, each with a capacity of 50 million gallons per day. The other station houses four pumps—one redundant—each with a capacity of 11 million gallons per day.

Logistically, Griffin says that installing new stormwater infrastructure under neighborhood streets provided the greatest challenge, particularly once the schedule had to be compressed following the lengthy value engineering process. “A lot of this job is about being respectful of the residents while getting the job done,” he says.

Griffin says extensive water and sewer relocation was required so crews could install new storm pipes. Griffin says crews had to work up and down streets multiple times to relocate and install new water mains and sewer mains. After those were relocated, crews went back in to install the new 54-in. storm drain. At various locations, crews also installed bioswales and permeable pavers. All of this was done while trying to maintain traffic flow and residents’ access to their homes.

他说：“这就是推动附近时间表的原因。”“在某些情况下，我们可以一次进行街道的一侧，但这是一个紧密的街区，您有一个54英寸的雨水排水管在道路中间。因此，您一次要关闭一个街区，同时确保在工作区域周围的弯路路线上没有其他施工。”

Walk in the Park |The Grandy Village stormwater park is one of the project’s green spaces that serve as shallow stormwater retention areas following a flood event.
Photo by MEB

Beyond community benefits for Chesterfield Heights, Spencer says the city of Norfolk anticipates using the Ohio Creek project as a proving ground for sea-level rise strategies that could be deployed in other parts of the city.

“It’s a good opportunity to see what’s replicable,” he says. “It shows the art of possible.”

Spencer adds, “For the neighborhood, it’s about staying on top of how it’s performing. We just don’t want to walk away when we’re done. We want to check back in and see if there are issues. That’s something we’ll keep track of as it moves forward.”

In the big picture, Westerhof sees the impact of Ohio Creek resonating far beyond southeastern Virginia as other communities advance from studies and planning to developing infrastructure. “Norfolk has stepped up early on to get shovels in the ground,” he says. “That is so vital. You can study anything you want, but eventually this is about quality of life and doing the right thing for communities under stress. This neighborhood is already seeing a higher level of protection. That’s exactly what we need.”