The demolition of Bloede Dam finally got under way Tuesday, as explosives blew a hole in the long-dormant hydroelectric facility blocking the Patapsco River west of Baltimore. Explosives blew up a section of Bloede Dam on Maryland's Patapsco River on Tuesday, launching a demolition process that will open upstream habitat to migrating fish and eels. (MD Dept. of Natural Resources)

Kiewit, the Nebraska-based contractor handling the removal of the state-owned dam, had been waiting for the river’s rain-swollen flow to subside before triggering the blast to make it easier for heavy equipment to work in the channel.

But Hurricane Florence’s imminent East Coast landfall prompted a decision to get on with it, according to Amy Kober, spokeswoman for the nonprofit conservation group American Rivers. The yearlong preparatory work for the dam’s demolition already had suffered disruption and delay earlier this year because of severe flash flooding on Memorial Day weekend. Now, there’s a chance the tropical storm expected to hit the Carolinas later this week could produce more heavy rain and potentially disruptive flooding in central Maryland.

Video of the Bloede Dam detonation by Jack Hardway, Elevated Media Concepts, Inc.

Bloede has limited the access of spawning fish to the lower nine miles of the Patapsco since it was completed in 1907. Originally built to supply electricity to the nearby communities of Catonsville and Ellicott City, the dam became superfluous before long and ceased generating power in the 1930s. But it has continued to prevent fish and eels from getting upriver while also posing a safety hazard. Situated in one of Maryland’s more popular state parks, the dam has proven to be a dangerous attraction — there have been nine deaths from drowning there since the 1980s, according to the state Department of Natural Resources.

Bloede is the third large fish barrier on the Patapsco to be removed. Union Dam was taken out in 2010, followed by Simkins Dam in 2011. This $17 million project, mostly underwritten with federal funds, will open up 65 miles upriver for the annual springtime spawning runs of migratory river herring and American shad, authorities said. It will also make even more of the watershed accessible to American eels.

The initial blast was planned to open up one end of the dam, drawing the river’s flow through the breach so that heavy equipment could move into the channel and take out the rest of the reinforced concrete structure. Removal is expected to take several months, followed by the restoration of the portion of the riverbank that has been cleared and graded to provide access for heavy equipment. That area of Patapsco Valley State Park, closed to the public since last year, is expected to reopen in 2019.

The removal of Bloede Dam is likely to have short-term impact on fish habitat in the lower Patapsco, because it will release more than 300,000 cubic yards of sediment that have accumulated behind the dam. Analysis of the sediment buildup found it to be mostly sand and gravel, and less than a third silt, and without significant toxic contaminants. The DNR has said that fishing success could decline for a year or two as sand and gravel wash downriver, but habitat is expected to recover afterward.