Crews constructed a gravel cofferdam, about long upstream of the Edwards Dam. The restoration included reclaiming land beneath HMS "Alliance" using a cofferdam and backfill. With help of a cofferdam constructed earlier, foundation excavation was continued during flood season also. Behind the belt armor was a watertight internal cofferdam, filled with cellulose. A watertight internal cofferdam, filled with cellulose, stretched between these two decks. The upper cofferdam was high, and thick at its base, thicker than the dam itself. Construction also involved building a huge cofferdam to seal construction from water. The walkway sits atop the cofferdam necessary for the ship's repairs. A trenchlike cofferdam was built to facilitate construction. The west cofferdam was long, thick and was constructed above the bedrock. The initial main work was construction of a large cofferdam surrounding the worksite. The cofferdam was fixed by installing deep foundations made of gravel at the outermost cofferdam. The cofferdam is later replaced while the hull sections are welded together again. While under construction, a cofferdam at the west end burst. Her crew had to construct a cofferdam across the main deck to stop the flooding.