HY8:Energy Dissipators

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Hydraulic Engineering Circular No. 14 (HEC-14) describes several energy dissipating structures that can be used with culverts. HEC-14 describes procedures that can be used to compute scour hole sizes and design internal and external dissipators. It outlines the following steps that can be used when designing a culvert:


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HEC-14 also describes the energy dissipators and their limitations as follows:

Chapter Dissipator Type Froude Number[1] (Fr) Allowable Debris[2] Tailwater (TW)
Silt/Sand Boulders Floating
4 Flow transitions na H H H Desirable
5 Scour hole na H H H Desirable
6 Hydraulic jump > 1 H H H Required
7 Tumbling flow[3] > 1 M L L Not needed
7 Increased resistance[4] na M L L Not needed
7 USSBR Type IX baffled apron < 1 M L L Not needed
7 Broken-back culvert > 1 M L L Desirable
7 Outlet weir 2 to 7 M L M Not needed
7 Outlet drop/weir 3.5 to 6 M L M Not needed
8 USBR Type II stilling basin 4.5 to 17 M L M Required
8 USBR Type IV stilling basin 2.5 to 4.5 M L M Required
8 SAF stilling basin 1.7 to 17 M L M Required
9 CSU rigid boundary basin < 3 M L M Not needed
9 Contra Costa basin < 3 H M M < 0.5D
9 Hook basin 1.8 to 3 H M M Not needed
9 USBR Type VI impact basin[5] na M L L Desirable
10 Riprap basin < 3 H H H Not needed
10 Riprap apron[6] na M L L Desirable
11 Straight drop structure[7] < 1 H L M Required
11 Box inlet drop structure[8] < 1 H L M Required
12 USACE stilling well na M L N Desirable


  1. ^ At release point from culvert or channel
  2. ^ Debris notes: N = none, L = low, M = moderate, H = heavy
  3. ^ Bed slope must be in the range 4% < So < 25%
  4. ^ Check headwater for outlet control
  5. ^ Discharge, Q < 11 m3/s (400 ft3/s) and Velocity, V < 15 m/s (50 ft/s)
  6. ^ Culvert rise less than or equal to 1500 mm (60 in)
  7. ^ Drop < 4.6 m (15 ft)
  8. ^ Drop < 3.7 m (12 ft)
na = not applicable.