· The working costs of Risdon dredges in California are stated to be in certain cases about 4 cents per cubic yard of gravel, but are generally from 6 to 8 cents. Crane and Bucket Dredges. In these dredges a single large bucket or shovel, with a capacity of 1 or 2 cubic yards, is filled with gravel and hoisted on board a barge by some form of ...