Union soldiers started building the main dam on April 30, 1864. By May 6, the water had risen 4 feet. By May 8, the water had risen up 5 feet 4 inches. The dam was working! Hundreds gathered from the city to watch the spectacle. Four of the lighter vessels crossed the upper rapids at this time, and waited behind the dam. Yet, as the water level behind the dam rose, so too did the pressure on it.
The next day, the dam burst from the strain. Two of the four barges forming the middle section of the dam moved out of place, opening a hole. Water began gushing through. Seizing the opportunity, Porter ordered one of the four waiting boats to go through the gap. Ten thousand
spectators watched the gunboat Lexington steer toward the opening in the dam. The water was running wildly through the gap. Porter feared the Lexington would be destroyed. The gunboat struggled to maintain control.
To everyone’s amazement, the ship made it through the dam and past the lower rapids. Onlookers cheered in awe. Bailey had succeeded! The three other waiting vessels also went through the gap before the water got too low. After more dam building at the upper rapids, the water rose again. The largest remaining gunboat, Mound City, ran the gap in the main dam on May 12. By the next day, all the gunboats had passed over the rapids.
Porter's fleet passing the dam at Alexandria. From Harper's Pictorial History of the Civil War, c1894. Courtesy of the Library of Congress LC-USZ62-39604.
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