Method of deepening a canal. A number of holes are drilled close together on bed and the spoil is put the barge accompanying the drilling rig. If current was not strong enough to level out the bed of the waterway, a scraper or drum was used to do the work. The process could also be carried out by two men (L) before canal was flooded. From Architecture Hydraulique by Bernard Forest de Belidor (Paris, 1737). Engraving.