Four Mile Run is not a popular jogging event, but a stream on the Arlington-Alexandria line that has sent residents running for high ground more than 80 times in the past 15 years.

The controversial -- and long-delayed -- project to tame Four Mile Run is now virtually complete.

Last week, the U.S. Army Corps of Engineers finished work on seven bridges that cross Four Mile Run at the Potomac Railroad Yards, Rte. 1 and the George Washington Memorial Parkway. The engineers also opened a pedestrian and bicycle path along the stream beneath the bridges -- the first Washington-area bridges to include full-width bike trails in their construction. The bike path under the bridges connects to the existing George Washington Parkway bike path south of National Airport.

When the 45-acre Four Mile Run Park and Bike Trail are completed sometime this spring, they will link up with the Washington area's longest bike trail, now also under construction, the 42-mile Washington and Old Dominion Trail.

The flood control project is expected to cost $63 million -- four times the original estimate of $16.6 million made when the project was approved in 1970.

Arlandria, a low-lying neighborhood west of Rte. 1, has been flooded so many times by Four Mile Run that it had almost become an aquarium. Until the channel-widening project got under way in 1974, residents were evacuated an average of seven times a year. The dozen major floods in Arlandria caused more than $40 million in damage.

The seven bridges opened over the run last week replace three, three-foot wide pipes, which carried water from Four Mile Run under the railroad yards and Rte. 1 for more than 50 years.

Until the 1930s and 1940s, the pipes along, with the natural drainage system of surrounding farmland acted as flood controls in the area. But as developers moved into the area, one of those controls -- farmland -- began to be replaced with streets, parking lots and buildings. Rainstorms caused flash floods when water running into the stream backed up at the three drainage pipes like a dam.

By the early 1970s, when Arlandria's most severe floods occurred, more than 80 percent of the stream's 16-square-mile watershed had been paved over by developers.

In the early 1960s, as flood problems began increasing, Alexandrians urged a federal flood control project to protect the area.

But the Army Corps of Engineers advised against such a project, noting that it was "not economically feasible" and would be less expensive to buy the houses and businesses in the flood plain than to protect them.

That view was backed by several congressman as late as 1973, three years after actual approval of the project and just a year after Tropical Storm Agnes hit the area, causing more $14 million damage in Arlandria.

When construction finally began in 1974, cost estimates had doubled from the 1970 figure to $32.4 million, with most of the increase in the federal share. Of the final cost estimate of $63 million, the federal government is paying $50.8 million. Of the remaining costs, Alexandria is paying about $8 million, said Dayton Cook, director of the city's Department of Transportation and Environmental Services, Arlington is paying about $5 million and the Richmond, Fredericksburg & Potomac Railroad, about $500,000.

In approving the flood-control project, Congress set two requirements:

That Alexandria waterproof buildings still within in the flood plain when the project is complete. The city must waterproof 19 buildings, according to Cook, at a cost estimated at $300,000 to $400,000.

That action be taken to prevent additional run-off from future development in the 16-square-mile watershed, which extends beyond Alexandria and Arlington into Falls Church and Fairfax County. The four jurisdictions already have spent more than $250,000 in monitoring all construction in the watershed. "We've actually reduced water run-off," Cook said, largely through "requiring holding tanks and ponds in new developments."

The final cost-benefit ratio, despite the project's cost overruns, is 1.5, according to the Corps of Engineers -- or $1.50 in benefits for every $1 spent on the project.