Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Damsand provide regulation of the outlet works flow. Regulating gates and valves aredesigned to provide a wide range of operation from closed to fully open. Theclosure times for gates and valves should be closely evaluated to keep water hammerpressures within reasonable limits. Guard gates are designed to provide closure onlywhen the regulating gates become inoperable or when unwatering of the conduit isrequired to inspect or repair the section of conduit downstream of the guard gates orto inspect or repair the regulating gates. In some applications, an emergency gatemay be used in conjunction with or in lieu of a guard gate. An emergency gate istypically provided only as a standby or reserve gate and is used when the normalmeans of water control is not available for use. Generally, slots are provided forstoplogs or bulkheads to be installed at the conduit entrance to allow for unwateringand inspection of the conduit. In some cases, if stoplogs or bulkheads can be quicklyinstalled during an emergency, guard gates may not be required. However, stoplogsand bulkheads are not intended for emergency closure under unbalanced conditionsor when the outlet works is operating. Specially designed stoplogs and bulkheadswould be required.The control features should allow for complete inspection by man-entry or CCTV.Certain types of gates or valves (e.g., butterfly valves) can act as an obstruction andmay preclude the use of robotic camera-crawler equipment, since it may not be ableto pass under or around the gate or valve. Alternate access using manholes may berequired to provide access around the obstruction.An important consideration in any closed conduit design for an outlet works is theproper use of air venting. Air vents can permit air to enter the conduit to preventcollapse or to prevent the formation of low pressures within flowing water, whichcould lead to cavitation and its possible attendant damage. Air vents can also beused to bleed air from a conduit prior to operation. Figure 32 shows an example ofan air vent leading from the conduit that daylights onto the surface of theembankment dam. For guidance on the location, airflow rates, and structuralconsiderations of air vents, see Reclamation’s Air-Water Flow in Hydraulic Structures(1980).The location for the control of the outlet works can be placed at the upstream end ofthe conduit, at the downstream end, or at some intermediate point. For illustrativepurposes, four arrangements for locating the control features within the outlet workshave been adapted from Reclamation’s Design of Small Dams (1987a, p. 446):• Arrangement 1—Intermediate control with downstream access (figure 33)• Arrangement 2—Intermediate control without downstream access (figure 34)• Arrangement 3—Upstream control (figure 35)60
Chapter 3—Hydraulic Design of ConduitsFigure 32.—An air vent is required in closedconduits downstream from the controllinggate or valve to prevent collapse or theformation of low air pressures.• Arrangement 4—Downstream control (figure 36)These arrangements are discussed in the following sections. Figures 33 through 36illustrate the arrangement of control features only. The internal zoning of theembankment dam’s filters and drains are not shown in these figures.3.1.1.1 Arrangement 1—Intermediate control with downstream accessIn this type of arrangement (figure 33), a control gate or valve (i.e., guard or guardand regulating) is located at an intermediate point (typically at or upstream of theembankment dam centerline) between the intake and the terminal structures, withadditional regulatory gate(s) or valve(s) located downstream in a control house. Thespecific aspects of this arrangement are:• Flow conditions.—Pressure flow would exist upstream of the intermediatecontrol. Pressure flow could also exist downstream of the intermediate control,if the regulating gate in the control house is partially or fully closed.61
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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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Page 67 and 68: IntroductionThe “best practices
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Chapter 4—Structural Design of Co
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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 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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