BLANKET (OF A DAM)

A portion of the physical structure of a dam designed to affect the dams hydrologic characteristics, particularly its seepage and strength characteristics. Types of dam blankets include: (1) Drainage Blanket: A drainage layer placed directly over the dam's foundation material; (2) Grout Blanket: The injection of grout to consolidate a layer of the foundation, resulting in greater impermeability and/or strength; and (3) Upstream Blanket: An impervious layer placed on the reservoir floor upstream of a dam; in the case of an Embankment Dam, the blanket may be connected to the impermeable element in the dam itself.