FLOOD06380

• County: Statewide
• Community: Adams/Arapahoe/Denver/Broomfield/Douglas/Jeffco
• Basin: Statewide
• Title: Urban Storm Drainage, Criteria Manual Volume 2
• Date: 6/1/2001
• Prepared By: Wright Water Engineers, Inc.
• Floodplain - Doc Type: Educational/Technical/Reference Information

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DRAINAGE CRITERIA MANUAL (V. 2)

HYDRAULIC STRUCTURES

g = acceleration of gravity = 32.2 ftIsec'

For hydraulic conditions at a point immediately downstream of where the nappe hits the basin
floor, the following variables are defined as illustrated in Figure HS-10:

~ = 4.3Do27
y n
f

Y
--E... = l.ODO.22
Y n
f

~ = O.54Do425
y n
f

2i = l.66Do.27
y n
f

in which:

Yf= effective fall height from the crest to the basin floor (ft)

La = length from the crest wall to the point of impingement of the jet on the floor or the nappe
length (ft)

Yp = pool depth under the nappe just downstream of the crest (ft)

Y1 = flow depth on the basin floor just below where the nappe contacts the basin (ft)

Y, = tailwater depth (sequent depth) required to cause the jump to form at the point evaluated
(ft)

In the case where the tailwater does not provide a depth equivalent to or greater than Y20 the jet
will wash downstream as supercritical flow until its specific force is sufficiently reduced to allow
the jump to occur. Determination of the distance to the hydraulic jump, Dj' requires a separate
water surface profile analysis for the main and low-flow zones as described herein for sloping
drops. Any change in tailwater affects the stability of the jump in both locations.

2. The hydraulic jump length, Lj, is approximated as 6 times the sequent depth, Y2. The design
basin length, Lb, includes nappe length, La, the distance to the jump, Dj, and 60% of the jump
length, Lj. (The subscripts "m" and "t" in Equations HS-11 and HS-12 refer to the main and trickle
channel zones, respectively.)

06/2001
Urban Drainage & Flood Control District

HS-27