Though workers have completed part of a $2 million project to dredge parts of a city stream and replace a weir, Alexandria remains at risk from storms, staff told the City Council this week.

“All the efforts so far are getting back to pre- [summer 2006] flood conditions,” Rich Baier, director of Alexandria's Transportation and Environmental Services department, said Thursday.

City employees began dredging a second 1.5-mile stretch of Cameron Run this week. They also have to replace a weir on Eisenhower Avenue, which burst during the storm. Weirs are used to reduce the velocity of running water in a stream, said Craig Perl, a city hydraulic engineer. The Federal Emergency Management Agency is providing matching funds for the work.

“The main reason flood levels were higher than expected” on the left bank of Cameron Run by the Beltway was because outdated data, some 40 years old, was used to determine what property was at risk from 100-year magnitude storms, according to a summary of the draft investigation prepared by the Army Corps of Engineers. The old data do not account for current sedimentation and development, Baier said.

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Sedimentation, or accumulated dirt that makes a channel shallower, contributed to flooding around the Beltway bridge that crosses Cameron Run. If the channel was as deep as it was in 1965, the floodwater could have been about 3 feet lower, according to the report.

Modifying the bridge might reduce future flooding, the report suggested. If the area for water to pass through was larger, the floodwaters could have been almost 2 feet shallower.

Two culverts were too small to handle the 2006 storm, resulting in flooding on Janneys Lane and in the basements of several homes between Glendale Avenue and Summers Drive, according to the report.

It is not yet known what measures besides dredging will be taken, Baier and Perl said. The Corps’ draft report also suggests flood walls and other techniques. Cost estimates to replace the culverts or perform other work aren’t known.

mhegstad@dcexaminer.com