[Illustration: Portion of the tree dam exposed during the low water in August 1984.]
Together, the crib and tree dam sections did not cross the entire 758-foot riverbed. A 150-foot gap existed between the two dams. To close this gap, four coal barges were used. While the remains of these barges were not found in the archaeological excavations, historical photographs provide a fairly detailed picture of their appearance. These 24-by-170-foot barges were sunk in the gap, lying lengthwise with the current, and more stones, brick, and iron rails were used to anchor them. Braces and ropes, anchored to the riverbanks, were also needed to secure the barges against the rising water pressure.
Bailey directed that the second barge from the Alexandria side be only partially filled with anchoring materials. This was the barge that he hoped either to ram or blast out of the way, creating a flood that the gunboats would ride like kayaks. As it turned out, Bailey’s idea worked, but not exactly as he would have liked.
[Illustration: Building the Red River Dam. Courtesy of the Library of Congress.]
To the amazement of practically everybody except Bailey, the dam complex was working. By May 6, the water held by the dam had risen 4 feet. By May 8, the water level was up 5 feet 4 inches. Three of the lighter vessels even crossed the upper rapids and now waited behind the dam for the heavier gunboats. As the soldiers worked to finish the dam, the water continued to build until the pressure against the dam became tremendous. General Banks feared the pressure would soon burst the dam, and the next day, at around 5:30 in the morning, one officer “heard a great crashing in the direction of the dam. Jumping out of the blankets and slipping on my coat, cap, and boots, I ran down to the bank. The water was rushing through at a great rate” (Tyson May 9, 1864).
Two of the barges used in the dam had broken loose, and the water was gushing through. Porter, seeing the crisis, quickly ordered the gunboat _Lexington_ to run the gap:
[Illustration: Porter’s fleet passing through Colonel Bailey’s Dam above Alexandria, May 1864. From _Frank Leslie’s Illustrated Newspaper_, July 16, 1864. Courtesy of the Library of Congress.]