Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsFigure 44.—No intake structure exists for this outlet works. Thisconduit is prone to plugging with trash and debris.Figure 45.—No terminal structure or erosion protection exists for thisoutlet works. The embankment around the exit portal has experiencedsignificant erosion.72
Chapter 3—Hydraulic Design of Conduitswhere trash cleaning is ordinarily not required, a submerged structure may beappropriate.The conduit entrance may be placed vertically, inclined, or horizontally,depending on intake requirements. Where a sill level higher than the conduitlevel is desired, the entrance can be a drop intake similar to the entrance of adrop inlet spillway. A vertical entrance is usually provided for intakes at theconduit level. In certain instances, an inclined intake structure may be placedalong the upstream slope of the dam or along the reservoir bank upstream ofthe dam.The designer should exercise caution in the design of the trashracks for the intakestructure. As releases are made through the intake structure, debris can accumulateon the trashracks. Continued accumulation of debris will gradually begin to clog thetrashracks to a point where the internal and external hydrostatic pressures on theintake structure and conduit are no longer balanced. Unless these structures havebeen properly designed to resist this type of loading, the pressure differential maycause a collapse of the structures. Another concern the designer should be aware ofis the accumulation of sediment and debris in the reservoir. Severe storms can washtree stumps and other large debris (e.g., logs) into the reservoir. Also, if a forest fireoccurs in the watershed, this can cause mud, ash, and debris to enter the reservoir.For trashracked intake structures, this debris can accumulate on the trashracks andclog them. For intake structures without trashracks, this can result in plugging of theconduit. The lack of regular testing of gates and valves and reservoir flushing cancontribute to this situation. For flood control conduits, the clogging or plugging canresult in loss of discharge capacity, which could lead to overtopping of theembankment dam. Clogging and plugging can also affect the operation ofdownstream turbines (ICOLD, 1994a).Reclamation’s Design of Small Dams (1987a, p. 452) provides a good source ofinformation concerning terminal structures. The following has been adapted fromthat reference:Terminal structures.—The discharge from a conduit, whether it be pressure orfree flow, will emerge at a high velocity, usually in a nearly horizontal direction.If erosion-resistant bedrock exists at shallow depths, the flow may bedischarged directly into the river. Otherwise, it should be directed away fromthe toe of the embankment dam by a deflector. Where erosion could be apotential problem, a plunge basin may be excavated and lined with riprap orconcrete.When more energy dissipation is required, the hydraulic jump basin is mostoften used for energy dissipation of discharges. However, flow that emerges inthe form of a free jet, as is the case for valve-controlled outlets of pressure73
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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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IntroductionFigure 11.—Example of
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Page 61 and 62: Introduction• Conduits within lev
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Page 65 and 66: Introductionmore recent practiced h
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
Page 81 and 82: Chapter 2—Conduit MaterialsFigure
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Page 89 and 90: Chapter 2—Conduit MaterialsSteel
Page 91 and 92: Chapter 2—Conduit Materials2.3.2
Page 95 and 96: Chapter 3Hydraulic Design of Condui
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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 Historieshistory
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Appendix B—Case Historiesarea, a
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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 HistoriesThe caus
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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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