The first phase of the dam project was the construction of the navigation lock on the Georgia side of the Savannah River. The coffer dams were built to redirect the river so workers could construct the lock and dam on a drier surface. Workers filled these temporary dams with granite, rock, and dirt to stop the river’s water.
Coffer dams are watertight enclosures that are constructed so workers can build on surfaces that are normally underwater.
After workers completed the lock, they opened it, and the river flooded the lock and rerouted through it. Workers then constructed another coffer dam on the South Carolina side of the river to build the pylons and lift gates of the dam.