Unwatering Akosombo Cofferdams

A high and almost completely submerged rockfill and cofferdam was sealed by inducing artificial silting on its water face. First, the rockfill was placed by dumping, and carefully selected transition zone material was then placed on the slope of the rockfill. The water outside the cofferdam was rendered muddy by pumping clay and silt from the river bottom and discharging it near and along the water face of the cofferdam. At the same time, water was pumped from within the cofferdam, creating a differential head on the rockfill and the transition zone. Under the influence of this head, the suspended clay and silt penetrated the transition and made it watertight. The cofferdam was sealed and unwatered at an appreciable saving of time and money.