Technical Manual: Conduits through Embankment Dams (FEMA 484)

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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
Chapter 3—Hydraulic Design of ConduitsFigure 42.—Typical outlet works intake structure.Figure 43.—Typical outlet works terminal structure.The type of intake structure selected should be based on several factors: thefunctions it must serve, the range in reservoir head under which it must operate,the discharge it must handle, the frequency of reservoir drawdown, the trashand debris conditions in the reservoir (which will determine the need for or thefrequency of cleaning of the trashracks), reservoir ice conditions or wave actionthat could affect the stability, and other similar considerations. Depending onits function, an intake structure may be either submerged or extended in theform of a tower above the maximum reservoir water surface. A tower must beprovided if the controls are placed at the intake, or if an operating platform isneeded for trash removal, maintaining and cleaning fishscreens, or installingstoplogs. Where the structure serves only as an entrance to the conduit and71
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Technical Manual:Conduits throughEm
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PrefaceTens of thousands of conduit
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Prefacecondition. The hazard classi
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PrefaceLakeLine MagazineMaryland Da
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Conduits through Embankment Dams11.
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Contents23 Precast concrete pipe be
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Contents81 On first filling, a high
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Contents117 This conduit was severe
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Contents158 An example of a histori
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ContentsFigures in the AppendicesNo
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ContentsB-33 Aerial view of Como Da
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ContentsB-81 Cross section of Wiste
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ContentsMASW, multichannel analysis
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Symbolsc, cohesionE', modulus of so
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ContentsD 3350D 4221D 4253D 4254D 4
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IntroductionConduits convey water f
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IntroductionFigure 3.—A 15-inch d
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Introductionunstable. When seepage
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IntroductionAn embankment dam with
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A vortex may form at the location w
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IntroductionWater from the reservoi
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IntroductionFlowing water from the
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IntroductionThe process of dislodgi
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Introductionbe observable at the su
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Page 67 and 68: IntroductionThe “best practices
Page 69 and 70: Chapter 1GeneralConduits have been
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Page 75 and 76: Chapter 1—Generalmeans the condui
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Page 79 and 80: Chapter 2Conduit MaterialsVarious m
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Page 113 and 114: Chapter 4Structural Design of Condu
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Page 151 and 152: Chapter 5Foundation and Embankment
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Chapter 5—Foundation and Embankme
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Chapter 6Filter ZonesZones of desig
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Chapter 6—Filter Zonesseepage or
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Chapter 6—Filter ZonesFigure 87.
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Chapter 6—Filter Zones3. Upstream
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Chapter 6—Filter Zonesbedrock sur
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Chapter 6—Filter Zoneszones, and
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Chapter 6—Filter Zonesfiltering t
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Chapter 6—Filter Zonessoil. This
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Chapter 6—Filter Zones6.8 Specifi
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Chapter 6—Filter ZonesVarious deg
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Chapter 6—Filter Zones• For pre
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Chapter 7Potential Failure Modes As
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Chapter 7—Potential Failure Modes
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Chapter 8Potential Defects Associat
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Chapter 8—Potential Defects Assoc
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Chapter 9Inspection and Assessment
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Chapter 9—Inspection and Assessme
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Chapter 10Evaluation by Geophysical
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Chapter 10—Evaluation by Geophysi
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Chapter 11Appropriate Emergency Act
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Chapter 11—Appropriate Emergency
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Table 11.2.—Potential problems an
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Chapter 12Renovation of ConduitsThe
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Chapter 12—Renovation of Conduits
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Chapter 13Replacement of ConduitsGe
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Chapter 13—Replacement of Conduit
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Chapter 14Repair and Abandonment of
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Chapter 14—Repair and Abandonment
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ReferencesThe following references
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ReferencesBureau of Reclamation, De
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ReferencesCooper, Chuck, E. Wesley
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ReferencesJacobsen, S., “Buckling
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ReferencesNatural Resources Conserv
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ReferencesU.S. Army Corps of Engine
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ReferencesWooten, R. Lee, Peter S.
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Additional ReadingThe following ref
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Additional ReadingCarter, Brent H.,
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Additional ReadingJohnson, Brian, J
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Additional ReadingNatural Resources
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Additional ReadingU.S. Army Corps o
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Additional ReadingVan Aller, Hal, R
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GlossaryThe terms defined in this g
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Glossary• Backward erosion piping
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GlossaryCathodic protection system
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GlossaryConsequences (FEMA, 2004):
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Glossarymalfunction or abnormality
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GlossaryDrawdown (FEMA, 2004): The
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GlossaryFailure mode (FEMA, 2004):
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GlossaryGate chamber: An outlet wor
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GlossaryImpervious: Not permeable;
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GlossaryLeakage (FEMA, 2004): Uncon
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GlossaryOpen cut: An excavation thr
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GlossaryPolyvinyl chloride (PVC): A
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GlossaryResistivity: A measure of t
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GlossarySettlement (FEMA, 2004): Th
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GlossaryStandard Proctor compaction
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GlossaryThermoset (ASTM F 412, 2001
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GlossaryReferencesAmerican Concrete
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IndexAAbandonment of conduits, 225,
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IndexCompaction of backfill, 6, 10,
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IndexDDamembankment, 113-130, 333-3
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IndexExisting conduit, 23, 31, 45-5
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IndexHydraulic fracture, 4-11, 17,
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IndexMechanical caliper, 246Metal c
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IndexPressure flow, see Conduit, pr
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IndexSliplining, 39, 45-47, 51, 164
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IndexUUltrasonic pulse-echo, 245, 2
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Appendix AHistory of Antiseep Colla
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Appendix A—History of Antiseep Co
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Appendix BCase HistoriesIndexDam Lo
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Appendix B—Case HistoriesDam Loca
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Appendix B—Case HistoriesProject
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Appendix B—Case HistoriesFigure B
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Appendix B—Case Historiesproject,
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Appendix B—Case Historieswatersto
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Appendix B—Case HistoriesLessons
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Appendix B—Case HistoriesThe cond
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Appendix B—Case Historiesroadway.
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Appendix B—Case Historiesentire c
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Appendix B—Case Historieshauled i
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Appendix B—Case Historiescoal tar
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Appendix B—Case Historiespipe. Du
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Appendix B—Case Historiesinvert o
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Appendix B—Case Historiesdownstre
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Appendix B—Case Historiesof sever
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Appendix B—Case HistoriesThe down
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Appendix B—Case Historieshose and
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Appendix B—Case HistoriesADownstr
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Technical Manual: Conduits through Embankment Dams (FEMA 484)

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