Hardscape from development makes ‘1,000-year’ flood in Maryland worse

Ellicott City, Maryland suffered its second damaging “1,000-year” flood in two years last month.

The city is in a vulnerable location at the foot of a hill where river branches meet the Patapsco River. Another factor, a lot of impermeable concrete, exacerbated the flood.

Ellicott City has thrived in recent years with robust development. About one-third of the watershed that feeds into the historic community is now covered by roads, rooftops, sidewalks, and other hard surfaces.

Since the first major flood in 2016, the county has designed and engineered more stormwater retention facilities, but these projects will take time to implement. Across most of the U.S, impermeable surfaces make up just 1% percent of the land. In many cities, though, hardscapes account for 40% or more of the land area, leaving them vulnerable to floods.