Crib Dam

a wooden or, sometimes, reinforced-concrete water-retaining structure whose basic load-bearing elements are cribs. Crib dams usually withstand pressures to 10–15 m (sometimes up to 20 m). Despite the limited durability of wood, crib dams made out of such material are very economical, especially in heavily forested regions. In reinforced-concrete crib dams both the upstream and downstream faces are solid reinforced-concrete slabs; the space between the slabs is filled with ballast (earth, stones). Considerably less concrete is used in a reinforced-concrete crib dam than in a large gravity dam. Crib dams are erected, as a rule, directly on rocky foundations and other foundations in which it is impossible to drive pilings. In some crib dams, however, the cribs are supported by piles.