Duckett Dam Improvement Project

State Mandated Project Began in May 2012

Background

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The T. Howard Duckett Dam went into service in 1954 with the primary purpose of providing source drinking water for WSSC Water customers.  Located just off I-95 north of the Capital Beltway, it is clearly visible to those traveling to and from Baltimore. Spanning the Patuxent River between Prince George’s and Howard counties, it created the Duckett Reservoir (also known as Rocky Gorge). The reservoir holds approximately 5.5 billion gallons of source drinking water that is carried via underground pipe to WSSC Water’s Patuxent Water Filtration Plant for treatment. The Patuxent Plant produces approximately 30 percent of the drinking water for WSSC Water customers. 

While the dam is structurally sound, the Maryland Department of the Environment (MDE) requires WSSC Water to fortify the dam to meet updated standards. Under the requirements, Duckett must be able to withstand the new Probable Maximum Flood (PMF), which would be a 1-in-10,000-year storm. Such a storm would drop approximately 32 inches of rain over a 72-hour period. Obviously, a storm of that intensity would cause a tremendous amount of damage all across the region. Because a viable source of drinking water would be critical to regional recovery efforts, the integrity of the dam is paramount. Until the new project is complete, MDE technically has classified Duckett as “unsafe.” MDE inspects the dam regularly and has found that the dam is well maintained and structurally sound.

A comprehensive safety evaluation of Duckett Dam was conducted by URS Corporation’s Gaithersburg office, in cooperation with MDE’s Dam Safety Division. The evaluation found that Duckett required improvements to survive the new PMF. URS modeled the watershed to determine the rate and quantity of storm flow runoff that would result from such a storm. That analysis found that PMF flows would “overtop” the dam by almost 9.5 feet and also go over the side walls by 6.5 feet. The flood waters would erode earthen portions of the dam and water going over the top would scour the base of dam, eventually undermining the dam foundation – possibly causing failure.

The Project

The project will address the vulnerabilities highlighted by the safety evaluation, and take approximately three years to complete. Our contractors will fortify the dam by adding concrete walls along each side to hold back the theoretical flood waters. The walls will be 10 feet high at the dam and slowly taper to 6 feet high as the wall moves inland on both sides in Prince George’s and Howard counties. They also will construct thick concrete slabs on the downstream side of the dam to handle the force of water coming over the top and falling to the surface below. This will prevent erosion of the dam’s “footer.”

Community Impact

The community impact during the project is primarily truck traffic, some of which will pass through several neighborhoods in Laurel and on the Howard County side of the river. Work first began on the Prince George’s county side, and then work followed on the Howard County side. The concrete wall on the Prince George’s side extended along the tree line, across what is currently the left field fence, and was six feet high at that point. The high school was notified in advance and made other arrangements.