Hydraulic Design of Energy Dissipators for Culverts and Channels Hydraulic Engineering Circular Number 14, Third Edition
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Acknowledgments
First Edition
The first edition of this Circular was prepared in 1975 as an integral part of Demonstration Project No. 31, "Hydraulic Design of Energy Dissipators for Culverts and Channels," sponsored by Region 15. Mr. Philip L. Thompson of Region 15 and Mr. Murray L. Corry of the Hydraulics Branch wrote sections, coordinated, and edited the Circular. Dr. F. J. Watts of the University of Idaho (on a year assignment with Hydraulics Branch), Mr. Dennis L. Richards of the Hydraulics Branch, Mr. J. Sterling Jones of the Office of Research, and Mr. Joseph N. Bradley, Consultant to the Hydraulics Branch, contributed substantially by writing sections of the Circular. Mr. Frank L. Johnson, Chief, Hydraulics Branch, and Mr. Gene Fiala, Region 10 Hydraulics Engineer, supported the authors by reviewing and discussing the drafts of the Circular. Mr. John Morris, Region 4 Hydraulics Engineer, collected research results and assembled a preliminary manual that was used as an outline for the first draft. Mrs. Linda L. Gregory and Mrs. Silvia M. Rodriguez of the Region 15 Word Processing center and Mrs. Willy Rudolph of the Hydraulics Branch aided in manual preparation. The authors wish to express their gratitude to the many individuals and organizations whose research and designs are incorporated into this Circular.
Second Edition
Mr. Philip Thompson and Mr. Dennis Richards updated the first edition in 1983 so that HEC 14 could be reprinted and distributed as a part of Demonstration Project 73. The 1983 edition did not add any new dissipators, but did correct all the identified errors in the first edition. A substantial revision for Chapter 5, Estimating Erosion at Culvert Outlets, was accomplished using material that was published by Dr. Steven Abt, Dr. James Ruff, and Dr. A Shaikh in 1980. The second edition was prepared in U.S. customary units.
Third Edition
Mr. Philip Thompson and Mr. Roger Kilgore prepared this third edition of the Circular with the assistance of Dr. Rollin Hotchkiss. This edition retains all of the dissipators featured in the second edition, except the Forest Service (metal), USBR Type II stilling basin, and the Manifold stilling basin. The following dissipators have been added: USBR Type IX baffled apron, riprap aprons, brokenback culverts, outlet weir, and outlet drop followed by a weir. This edition is in both U.S. customary and System International (SI) units. A previous SI unit version of HEC 14 was published in 2000 as a part of the FHWA Hydraulics Library on CDROM, FHWAIF00022.
Table of Contents
List of Tables
List of Figures
 1.1 Energy Dissipator Design Procedure
 3.1 Outlet Control Flow Types
 3.2 Definition Sketch for Brink Depth
 3.3 Dimensionless Rating Curves for the Outlets of Rectangular Culverts on Horizontal and Mild Slopes (Simons, 1970)
 3.4 Dimensionless Rating Curves for the Outlets of Circular Culverts on Horizontal and Mild Slopes (Simons, 1970)
 3.5 Inlet Control Flow Types
 4.1 Transition Types
 4.2 Dimensionless Water Surface Contours (Watts, 1968)
 4.3 Average Depth for Abrupt Expansion Below Rectangular Culvert Outlet
 4.4 Average Depth for Abrupt Expansion Below Circular Culvert Outlet
 4.5 Subcritical Flow Transition
 4.6 Supercritical Inlet Transition for Rectangular Channel (USACE, 1994)
 6.1 Hydraulic Jump
 6.2 Jump Forms Related to Froude Number (USBR, 1987)
 6.3 Hydraulic Jump in a Horizontal Channel
 6.4 Hydraulic Jump  Horizontal, Rectangular Channel
 6.5 Length of Jump for a Rectangular Channel
 6.6 Hydraulic Jump  Horizontal, Circular Channel (actual depth)
 6.7 Hydraulic Jump  Horizontal, Circular Channel (hydraulic depth)
 6.8 Jump Length Circular Channel with y_{2} < D
 6.9 Relative Energy Loss for Various Channel Shapes
 6.10 Hydraulic Jump Types Sloping Channels (Bradley, 1961)
 7.1 Definition Sketch for Tumbling Flow in a Culvert
 7.2a Tumbling Flow in a Box Culvert or Open Chute: Recommended Configuration
 7.2b Tumbling Flow in a Box Culvert or Open Chute: Alternative Configuration
 7.3 Definition Sketch for Slotted Roughness Elements
 7.4 Definition Sketch for Tumbling Flow in Circular Culverts
 7.5 Definition Sketch for Flow in Circular Pipes
 7.6 Flow Regimes in Rough Pipes
 7.7 Conceptual Sketch of Roughness Elements to Increase Resistance
 7.8 Transition Curves between Flow and Regimes
 7.9 USBR Type IX Baffled Apron (Peterka, 1978)
 7.10 Elevation view of (a) Double and (b) Single Brokenback Culvert
 7.11 Weir Placed near Outlet of Box Culvert
 7.12 Drop followed by Weir
 8.1 Definition Sketch for Stilling Basin
 8.2 Length of Hydraulic Jump on a Horizontal Floor
 8.3 USBR Type III Stilling Basin
 8.4 USBR Type IV Stilling Basin
 8.5 SAF Stilling Basin (Blaisdell, 1959)
 9.1 CSU Rigid Boundary Basin
 9.2 Definition Sketch for the Momentum Equation
 9.3 Roughness Configurations Tested
 9.4 Energy and Momentum Coefficients (Simons, 1970)
 9.5 Splash Shield
 9.6 Contra Costa Basin
 9.7 Hook Basin with Warped Wingwalls
 9.8 Hook for Warped Wingwall Basin
 9.9 Velocity Ratio for Hook Basin With Warped Wingwalls
 9.10 Hook Basin with Uniform Trapezoidal Channel
 9.11 Hook for Uniform Trapezoidal Channel Basin
 9.12 Velocity Ratio for Hook Basin With Uniform Trapezoidal Channel
 9.13 USBR Type VI Impact Basin
 9.14 Design Curve for USBR Type VI Impact Basin
 9.15 Energy Loss of USBR Type VI Impact Basin versus Hydraulic Jump
 10.1 Profile of Riprap Basin
 10.2 Half Plan of Riprap Basin
 10.3 Distribution of Centerline Velocity for Flow from Submerged Outlets
 10.4 Placed Riprap at Culverts (Central Federal Lands Highway Division)
 11.1 Flow Geometry of a Straight Drop Spillway
 11.2 Drop Structure with Grate
 11.3 Straight Drop Structure (Rand, 1955)
 11.4 Box Inlet Drop Structure
 11.5 Discharge Coefficients/Correction for Head with Control at Box Inlet Crest
 11.6 Correction for Box Inlet Shape with Control at Box Inlet Crest
 11.7 Correction for Approach Channel Width with Control at Box Inlet Crest
 11.8 Coefficient of Discharge with Control at Headwall Opening
 11.9 Relative Head Correction with Control at Headwall Opening
 11.10.. Relative Head Correction for h_{o}/W_{2} >1/4 with Control at Headwall Opening
 12.1 US Army Corps of Engineers' Stilling Well (USACE, 1963)
 12.2 (SI) Stilling Well Diameter, D_{W} (USACE, 1963)
 12.2 (CU) Stilling Well Diameter, D_{W} (USACE, 1963)
 12.3 Depth of Stilling Well Below Invert (USACE, 1963)
 B.1 (SI) Critical Depth Rectangular Section (Normann, et al., 2001)
 B.1 (CU) Critical Depth Rectangular Section (Normann, et al., 2001)
 B.2 (SI) Critical Depth of Circular Pipe
 B.2 CU)Critical Depth of Circular Pipe
 B.3 (SI) Critical Depth Oval Concrete Pipe Long Axis Horizontal
 B.3 CU) Critical Depth Oval Concrete Pipe Long Axis Horizontal
 B.4 (SI) Critical Depth Oval Concrete Pipe Long Axis Vertical
 B.4 (CU) Critical Depth Oval Concrete Pipe Long Axis Vertical
 B.5 (SI) Critical Depth Standard C.M. PipeArch
 B.5 (CU) Critical Depth Standard C.M. PipeArch
 B.6 (SI) Critical Depth Structural Plate C.M. PipeArch
 B.6 (CU) Critical Depth Structural Plate C.M. PipeArch
 C.1. Forces Acting on a Roughness Element
 D.1. D_{50} versus Outlet Velocity
 D.2. D_{50} versus Discharge Intensity
 D.3. D_{50} versus Relative Tailwater Depth
List of Symbols
 a = Acceleration, m/s^{2} (ft/s^{2})
 A = Area of flow, m^{2} (ft^{2})
 A_{o} = Area of flow at culvert outlet, m^{2} (ft^{2})
 B = Width of rectangular culvert barrel, m (ft)
 D = Diameter or height of culvert barrel, m (ft)
 D_{50} = Particle size of gradation, of which 50 percent, of the mixture is finer by weight, m (ft)
 E = Energy, m (ft)
 f = DarcyWeisbach resistance coefficient
 F = Force, N (lb)
 Fr = Froude number, ratio of inertial forces to gravitational force in a system
 g = gravitational acceleration, m/s^{2 }(ft/s^{2})
 H_{L} = Head loss (total), m (ft)
 H_{f} = Friction head loss, m (ft)
 n = Manning's flow roughness coefficient
 P = Wetted perimeter of flow prism, m (ft)
 q = Discharge per unit width, m^{2}/s (ft^{2}/s)
 Q = Discharge, m^{3}/s (ft^{3}/s)
 r = Radius
 R = Hydraulic radius, A/P, m (ft)
 R_{e} = Reynolds number
 S = Slope, m/m (ft/ft)
 S_{f} = Slope of the energy grade line, m/m (ft/ft)
 S_{o} = Slope of the bed, m/m (ft/ft)
 S_{w} = Slope of the water surface, m/m (ft/ft)
 T = Top width of water surface, m (ft)
 TW = Tailwater depth, m (ft)
 V = Mean Velocity, m/s (ft/s)
 V_{n} = Velocity at normal depth, m/s (ft/s)
 y = Depth of flow, m (ft)
 y_{e} = Equivalent depth (A/2)^{1/2}, m (ft)
 y_{m} = Hydraulic depth (A/T), m (ft)
 y_{n} = Normal depth, m (ft)
 y_{c} = Critical depth, m (ft)
 y_{o} = Outlet depth, m (ft)
 Z = Side slope, sometimes expressed as 1:Z (Vertical:Horizontal)
 α = Unit conversion coefficient (varies with application)
 α = Kinetic energy coefficient; inclination angle
 β = Velocity (momentum) coefficient; wave front angle
 γ = Unit Weight of water, N/m^{3 }(lb/ft^{3})
 θ = Angle: inclination, contraction, central
 μ = Dynamic viscosity, N·s/m^{2} (lb·s/ft^{2})
 ν = Kinematic viscosity, m^{2}/s (ft^{2}/s)
 ρ = Mass density of fluid, kg/m^{3} (slugs/ft^{3})
 τ = Shear stress, N/m^{2} (lb/ft^{2})
Glossary
 Basin: Depressed or partially enclosed space.
 Customary Units (CU): Footpound system of units also referred to as English units.
 Depth of Flow: Vertical distance from the bed of a channel to the water surface.
 Design Discharge: Peak flow at a specific location defined by an appropriate return period to be used for design purposes.
 Freeboard: Vertical distance from the water surface to the top of the channel at design condition.
 Hydraulic Radius: Flow area divided by wetted perimeter.
 Hydraulic Roughness: Channel boundary characteristic contributing to energy losses, commonly described by Manning's n.
 Normal Depth: Depth of uniform flow in a channel or culvert.
 Riprap: Broken rock, cobbles, or boulders placed on side slopes or in channels for protection against the action of water.
 System International (SI): Meterkilogramsecond system of units often referred to as metric units.
 Uniform flow: Hydraulic condition in a prismatic channel where both the energy (friction) slope and the water surface slope are equal to the bed slope.
 Velocity, Mean: Discharge divided by the area of flow.
Listing of Updates and Corrections (errata & corrigenda)
Date 
Action 
By 
13 Aug 2012  Page 42, first paragraph: text should have parentheses around the '3Fr' quantity:" ... if the tanθ is greater than 1/(3Fr), ..."
 JSK 
1 Oct 2012  Page 42 Figure 4.2 Blaisdell's (1/3Fr) should be Blaisdell's (1/(3Fr))  CLN 
13 Aug 2012  Page 44, Equation 4.3 should be:
"θ = tan1(1/(3Fr))"
 JSK 
13 Aug 2012  Page 44, third paragraph: text should have parentheses around the '3Fr' quantity:
"... flaring the wingwall more than 1/(3Fr) (for example 45°) ..."
 JSK 
13 Aug 2012  Page 45, Step 3: equation should depict:
"tanθ = 1/(3Fr) = 1/(3(1.52)) = 0.22"
 JSK 
1 Oct 2012  Page 46, Alternative 2 ... tanθ = 1/3Fr should be tanθ = 1/(3Fr)  CLN 
13 Aug 2012  Page 47, Step 3: equation should depict:
"tanθ = 1/(3Fr) = 1/(3(1.52)) = 0.22"
 JSK 
1 Oct 2012  age 48, Alternative 2 ... tanθ = 1/3Fr should be tanθ = 1/(3Fr)  CLN 
This list includes all known items as of Monday 1 October 2012
Notes:
 No update to the publication is planned at this time.
 FHWA does not have any printed copies of this document. NHI allows purchase of some FHWA documents. See the FHWA Hydraulics website to report any additional errata and corrigenda.

