Technical Manual: Conduits through Embankment Dams (FEMA 484)

IntroductionConduits convey water from a reservoir through, under, or around an embankmentdam in a controlled manner. Conduits through embankment dams serve a variety ofpurposes. Conduits typically convey releases for:• Releasing stored waters to meet downstream requirements• Providing emergency reservoir evacuation• Flood control regulation to release waters temporarily stored in flood controlspace• Diverting flow into canals or pipelines• Providing flows for power generation• Satisfying a combination of multipurpose requirements• Stream diversion during constructionMost conduits through embankment dams are part of outlet works systems.However, some conduits act as either primary or service spillways; auxiliary orsecondary spillways to assist the primary spillway structure in passing floods; orpower conduits (penstocks) used for the generation of power. Conduits can beclassified as either:• Nonpressurized flow.—Open channel flow at atmospheric pressure for part or allof the conduit length (figure 1). This type of flow is also referred to as “freeflow.”• Pressure flow.—Pressurized flow throughout the conduit length to the point ofregulation or control or terminal structure (figure 2)Many types of materials have been used for conduits over the years, such asreinforced cast-in-place and precast concrete, thermoplastic and thermoset plastic,cast and ductile iron, welded steel, corrugated metal, and aluminum. Some earlybuilders of conduits used whatever materials were readily available, such as wood(figure 3) and hand-placed rubble masonry (figure 4). Regardless of the material use,a conduit represents a discontinuity through an embankment dam and its foundation.