There’s also the pollution. “Every bit of dirt that we have to take off the site and throw away is expensive, because it’s contaminated with metals and other things,” says the environmental scientist Justin Reel of RK&K, who leads mitigation and hydrological planning for the project. “But for the low-level type of human interaction we’re proposing, with a fairly thin cover we can use it on the site effectively. If you don’t have frequent, regular, intended exposure, these contaminants aren’t super bad. Where we do anticipate frequent soil contact, like our upland islands, we are planning for a cover over top of any native soil.”
A single strategy
But resolving the polluted soil problem will be complex. “It’s one thing to clean up an area for humans. But if you’re bringing burrowing animals in, or shellfish,” a more stringent standard might be required, says Marian Young, the president of the remediation consultancy BrightFields. Scarfone quips, “For the amount of remediation we need, all the earthworms in the world aren’t going to be able to do.” Normally, he says, “for projects like this, you cap it. But here, we want to re-create a functioning system.”
This spring, the future park was cleared of dense Phragmites. The resulting open, savanna-like vista gave a delightful hint of how it might eventually look—or feel, anyway, because it has yet to be sculpted and engineered.
Added water storage capacity and created habitats that can resist recruitment of invasives like Phragmites will both be achieved with a single strategy, lowering the site to alter the hydrology and establish “a different water regime than we have right now, which is very irregular and storm driven,” Reel says.
When there is a flush of stormwater from the residential neighborhood, it will collect in a forebay, to let sediment settle, and then will cross the site through a winding network of channels and ponds. These eventually converge on a short, straight connection from the park to the river that is partly open ditch and partly pipe.
At the river, the flow, as it is currently, will be controlled by a self-regulating tidegate. An open flow to the Christina and its tides was considered. That would promote the wetland’s naturalization and its connection to fisheries. But properties surrounding and contiguous to the park are low-lying.
The park “could be potentially completely full of tidal inundation,” Reel says, “and flood all our neighbors around the edges of the site.” But the tide gate creates other problems. Young explains that when stormwater is filling the park while simultaneously “the river is high, the gate will be closed and make a big lake. You have to have the stormwater holding, but the plants can only stand it for a certain amount of hours.”
Meanwhile, enticing fish to travel in from the river through the pipe, to populate the new habitat, is also a problem, but maybe illumination inside the pipe will attract them. The ditch and pipe connection, however, doesn’t even belong to the city. “Where it outfalls back into the wetland is probably the most contaminated part of the project,”—a PCB dump, Scarfone called it. “It’s a point source. Every time water flushes over here and back into the river, it picks up some of that.”
Remediation is obligatory, “which requires destabilizing some of these edges, and they’re owned by other people.” There’s a gas station on one side and a property development company’s offices on the other. “It’s one challenge after the other that fascinates you and makes a project super exciting.”
Reel says, “I’m normally engaged in wetland habitat creation and restoration as a compensatory project for some permit. In those situations, we try to find the nicest, most natural site we can get our hands on. I don’t normally do it in the middle of an urban situation, right next to a neighborhood, or incorporate urban stormwater into the site.”
The economic reverberations of new parks are well documented. “When government spends in an area, it sends a message,” says Jeffrey Flynn, Wilmington’s director of economic development. “We’re hoping this $40 million investment drives private in vestment” in housing and new commercial activity—specifically “space that is not a junkyard…something that requires employees.”
His office has informally calculated that within 10 to 15 years, improvement of underdeveloped parcels in a 100-acre zone of influence surrounding the park could bring in $5 to $7 million annually in additional property tax revenue. That may seem slight, but property tax accounts for about a third of the city’s $150 million budget.
That’s aside from “revenues you can’t measure. It’s going to psycho logically have a great impact for a historically disadvantaged community and residents who may not have been exposed to a natural feature like this.” The Nature Conservancy, which has recently focused its energy on nature based solutions for urban problems, is participating in the project.
They’ve helped the city purchase some of the land, for example, and are helping navigate the project’s regulatory hurdles. This model of an engineered wetland as both stormwater separation infrastructure and civic space, with all the potential knock-on benefits, can be replicated, says Richard Jones, the organization’s Delaware state director.
Agreat deal of new housing is being built on empty land
“Cities tend to have a fair amount of space that is degraded, or has been overlooked. If you have nature there already and can improve it and make it work for you, that’s fantastic. But what if you don’t? What if it’s parking lots? Can you still make use of that? The answer is yes.” A new amenity like a park often drives up nearby property values, leading to the displacement of long time residents. This seems less inevitable in South Wilmington.
Property taxes there only go up if the millage rate is raised, which is rare, or improvements are made on a specific property that raise its individual assessment. They are not adjusted for every owner as a result of changes in the market. “People come in and start doing infill housing? The assessed value of the surrounding properties doesn’t change,” Flynn says. And Wilmington speculators and landlords have little motive to force rents up.
While the trend for central-city living does express itself there, and the new park should make this part of town more desirable, a great deal of new housing is being built on empty land that was cleared at midcentury for urban renewal or was formerly industrial, in both downtown and along the riverfront.
Wilmington seems insulated from the housing shortages and price inflation occurring in many cities. What it is not insulated from is climate change.
As with any adaptation project, this is the unknowable: How fast and how far will the water rise? “Our tidal connectivity goes away in about a two-foot sea-level-rise scenario,” because gravity will no longer drain the park into the river, Reel explains. “The wetland complex and habitat we created would remain, and we would still have our resiliency and stormwater storage for the neighborhood. But we would have to get that water out, and be ready for the next storm, through a pumping system.”
In the longer run, he suggests that the wetland might need to be expanded, and that additional pumping systems and perhaps revetments be built in the larger South Wilmington area. “We certainly don’t want to make this level of investment for a 20-year life span, or a 50-year life span. So what’s our 100-year life span, or our 200 year life span?” he asks. “That long term approach is bigger than the one adaptation for this system.”