Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsFigure 41.—Penstocks extending through an embankment dam.cast-in-place concrete. Power conduits are often combined with the outlet worksconduit by the use of a wye branch to the powerplant. Power conduits are normallydesigned and constructed with the same criteria used for outlet works conduitsthrough embankment dams.3.4 Entrance and terminal structuresEntrance and terminal structures are placed at the upstream and downstream ends ofconduits, respectively. Entrance structures are often referred to as intake structuresfor outlet works and inlet structures for spillways. Properly designed entrance andterminal structures are important to the safe operation of the conduit. Figures 42and 43 show typical intake and terminal structures for an outlet works conduit.Figures 44 and 45 show examples of outlet works where no entrance and terminalstructures have been provided. In both of the situations shown in figures 44 and 45,serious dam safety deficiencies exist, since the upstream entrance could becomeplugged or the downstream toe of the embankment dam could erode. Reclamation’sDesign of Small Dams (1987a, p. 451) provides a good source of informationconcerning purpose and design considerations for entrance and terminal structures.The following has been adapted from that reference:Intake structures.—In addition to forming the entrance to the conduit, anintake structure may accommodate control devices, support necessary auxiliaryappurtenances (such as trashracks, fishscreens, and bypass devices), and includetemporary diversion openings and provisions for installation of bulkhead orstoplog closure devices.70