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The increased amount of impervious surfaces surrounding the watershed makes the area more susceptible to runoff, which contributes to the severity of flood impacts, though hydrologists have said development is not solely to blame.
In the wake of its second devastating flood in two years, Ellicott City, Maryland is once again facing the long haul of rebuilding. For some people, recovery is simply continuing work started after the 2016 flood. For others, it’s begun anew.
But much remains unclear, including what can be done differently—particularly whether the county will change future development, or mitigate ongoing projects, as a way to lessen the devastating impacts of flooding in the area. The notion is complicated, as floods are influenced by factors other than just increased watershed development, including climate change, Howard County Councilman Jon Weinstein said.
“Will this change the conversation about development? This changes the conversation about a lot of things,” Weinstein told Route Fifty in an interview about what has happened since the Memorial Day weekend flood. “One of the concerns I have about the super focus on development as a cause is that it diminishes the fact that this happened because of climate change. Development didn’t bring 8 to 10 inches of rain from the sky this time, and it didn’t bring the 6 inches of rain we got in 2016.”
But the increased amount of impervious surfaces surrounding the watershed makes the area more susceptible to runoff, which contributes to the severity of flood impacts. Community members have begun to question the decisions that led to those developments, said Nicholas Redding, executive director of Preservation Maryland.
“I have never seen before more of the general public begin to question development patterns and stormwater mitigation policy like I have after this, and that’s pretty wonky stuff,” Redding said. “A lot of people are talking about that now and beginning to question, ‘What have we done here? Did we create this?’ This wasn’t a natural phenomenon—humans had a hand in this.”
A history of flooding
To understand Ellicott City’s propensity for flooding, it’s necessary to understand its history.
The city’s topography, and its flood-prone nature, are key facets of its existence. Ellicott City sits in what’s sometimes called a “granite bowl,” where multiple streams and creeks converge and flow into the Patapsco River. The proximity to water was necessary to run the mills that operated there beginning in the mid-1700s.
“This is a town that was selected by the Ellicott brothers and designed to take waters from various tributaries, harness that water, and speed it up through town. It is a mill town,” Weinstein said. ”It’s a fact of topography, geography and design. What hasn’t kept pace is the impact we’re experiencing these last few years with the severity of storms.”
Even for the city’s founders, flooding was a concern almost immediately. In 1768, a flood destroyed a grist mill operated by James Hood, who settled in the city several years earlier.
Ellicott City has suffered 15 major floods since then. What’s changed is not the risk, but the type of flood, Redding said.
“Historically the floods would come when the Patapsco, after heavy rains, would sort of overflow its banks. It would be what’s considered an inundation flood, where the water slowly rises and everything gets soaked,” he said. “Time after time after time, that was the history and the standard type of flood Ellicott City had. Those aren’t good, but they’re slow—you know when they’re coming, particularly nowadays, and the damage, although everything gets wet, is not as ferocious as the types of floods that have happened recently.”
The last two floods were different, caused by heavy rainfall that gathered into rivers of angry water on the hill atop the town, then rushed down, tossing cars and debris into storm drains and culverts and devastating old buildings in the historic downtown area.
The development factor
Ongoing development above the downtown, which adds impervious surfaces that speed up rather than impede water flow, is a factor in those floods. Stormwater rules for developers in the watershed have only existed since the 1980s, and about 60 percent of the development there took place before 1991. It’s had an obvious impact, even with the town’s history of flooding, Redding said.
“You don’t have to be a hydrologist or climate scientist to recognize that when you have a lot more impervious services, water rushes off of it and has to go somewhere,” he said. “I think a lot of people, when they see the issue in Ellicott City, they think, ‘Well, this is a historic town, it’s always flooded, and that’s separate from the rest of the state and we shouldn’t have to worry about it or rebuild it because it’s always going to flood there.’ But our position is that this could happen anywhere, and it’s likely to happen more places.”
Both hydrologists and county officials have rejected the notion that development is entirely to blame for Ellicott City’s issues. A report commissioned by Howard County after the 2016 flood found that the area would be susceptible to flooding even if the surrounding area were entirely undeveloped, though it did stress that development can exacerbate stormwater runoff.
That’s not news to city and county officials, who have been discussing flood-control options since well before 2016. Some have been legislative changes, including a prohibition on waivers to allow development within the watershed to disturb steep slopes, streams or wetlands.
Others are proposals—some of them large-scale (reconfiguring the town by relocating buildings and digging up streets to create a stormwater channel); others smaller (encouraging homeowners to pursue micro projects, like rain gardens). Many have been revamped to take into consideration data and information generated by the 2016 flood, Weinstein said.
“We’re looking at doing an addendum to or using the data we have to advance additional scenarios. We had, for example, identified a couple of buildings that would obviously need to be relocated to redirect water through town, but now we have more opportunities and more people interested in having those conversations,” he said. “The study that was done provides us a very, very strong basis to do some additional thinking. We don’t have to start over again.”
But the next steps are still under consideration. Conversations are ongoing and it remains to be seen whether future development regulations will factor into the solutions, though Redding said the topic is unlikely to dissipate soon.
“I think if there’s ever an opportunity to develop the political will to begin to change the way in which counties develop, this is potentially going to prompt that,” he said.
Kate Elizabeth Queram is a Staff Correspondent for Government Executive’s Route Fifty and is based in Washington, D.C.