A photo of the breach at Pawtucket Dam, July 23, 1915

As the water dropped and the extent of the damage became clear, the Locks and Canals Company began repair efforts. On July 17, the river had dropped enough for repair work to begin. The first job was to build a coffer dam, a temporary dam made largely of sandbags, just above the existing dam to allow workers access to the damaged area. A derrick crane at the left of the picture was installed to move the heavy stones. During the repair project, about 150 granite blocks were recovered from the riverbed, moved to the riverbank, cleaned and bored for pins. In addition to the holes for flashboard rods, each stone in the dam had holes for dowel rods on the top and bottom of the stone to anchor it to the stones above and below.

• Keywords: Lowell; engineering; Merrimack River