Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsFigure 39.—A drop inlet spillway conduit through an embankment dam.Ideally, the spillway should be designed to operate with crest control throughout theentire expected range of discharge. However, the range of expected discharge isbased on the current hydrologic data. Spillway flood flow rates may change due toupdated probable maximum precipitation quantities; changes in the basin runoffcharacteristics could vary significantly with time; and the project operation may berevised at a future date, which may result in an increase above the original spillwaydesign flow. Any of these factors, separately or in combination, could be sufficientto cause a spillway designed for crest control to shift to conduit control in the upperrange of expected discharge. The spillway conduit is considered a closed channeland generally takes the form of a vertical or inclined shaft connected to a horizontalor sloped conduit. In most cases, a spillway conduit is designed to flow partly fullthroughout the entire length. Another condition that could cause the control shift atessentially any discharge is partial plugging of the conduit. Plugging could occureither by external debris (i.e., logs or ice) or an internal problem resulting fromcavitation damage. To ensure free flow in the conduit, the ratio of flow depth toconduit diameter or height should be limited to about 75 percent or less. Some siteshave utilized log booms or specially designed trashracks that reduce surface currentsto prevent floating debris from entering the conduit. Additionally, air vents may berequired to ensure adequate air supply is provided to prevent unstable flow in theconduit. In areas where high velocity flow may occur, aeration of the flow may berequired to prevent cavitation damage.68
Chapter 3—Hydraulic Design of ConduitsFigure 40.—The riser structure for a principal spillway.Spillways utilizing conduits are not applicable to all sites, and an open channeloverflow spillway or tunnel may be preferable. The limitations of a spillway utilizinga conduit include:• The required flood discharge capacity may necessitate a large diameter conduitor multiple conduit barrels. The size and shape of the conduit can haveundesirable consequences, since it represents a discontinuity through theembankment dam.• Future increases in the size of the design flood are difficult to accommodatewith a spillway conduit.• Discharge capacity limitations of conduit may require the use of an auxiliary oremergency spillway to provide required flood control capability.3.3 Power conduitsPower conduits (also known as “penstocks”) are used to transport water from anintake structure located in the reservoir to a downstream facility for the generation ofpower. Figure 41 shows an example of penstocks extending through anembankment dam. The power conduit typically operates in a pressurized condition.The power conduit is usually constructed of steel pipe encased by reinforced69
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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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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 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 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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