FLOOD03351

• County: Statewide
• Basin: Statewide
• Title: Engineering and Design Hydraulic Design of Flood Control Channels
• Date: 7/1/1991
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

transition to stabilize the hydr:wlic jump is iIluslrated in
USAED, Los Angeles (1961) and USAEWES (1962). A
typical example of this type of aransition is given in
Plate 25.

(c) USAED. Los Angeles (1958. 1961, 1962) has
designed and model tested a number of aransitions arans-
forming rapid flow in rectangular channels to aranquil
flow in lr:1peZOidal channels without the occurrence of an
abrupt hydraulic jump. The high-velocity jet from the
rectangular channel is expanded in the aransition by means
of lateral and boundary roughness control in such a man-
ner that an undular-type jump occurs in the downstre:lm
reach of the transition. Plate 26 illustrates a typical
design developed through model tests.

d. Transiti<Jn losses.

(1) Tranquil now. Transitions for aranquil flow are
designed to effect minimum energy losses consistent with
economy of consa-uction. Transition losses are normally
computed using the energy equation and are expressed in
terms of the change in velocity he:ld Ah., from upsa-eam
to downstre:lm of the transition. The head loss hI
between cross sections in the step computation may be
expressed as

hl = Cc&v

(2-29)

for conlraCtions and as

hl = Ce&v

(2-30)

where

C "contraction coefficient
c

C. = expansion coefficient

for expansions. Equations 2-29 and 2-30 have been
obtained and published (Chow 1959, Brater and King
1976, US Bureau of Reclamation (USBR) 1967). The
values in Table 2-3 are generally accepted for design
purposes.

EM 1110-2-1601
1 Jul 91

Tabla 2-3
Tranaition Los. Coefficienta

Transi-
tion

Type

C C Source
. .
0.10 0.20 Chow
1959.
Brale.
and King
1976
0.15 0.20 Chow
1959
0.30 0.50 USBR
1967
0.30 0.50 Chow
1959
0.30 0.75 Chow
1959

Warped

Cyfin-
dricaI
Quedtant

Wedge

Straight
Une

Square
End

(2) Rapid now. Transition losses may be estimated
for rapid-flow conditions from the information supplied in
(1) above. However, the effects of standing waves and
other factors discussed in c(2) above make exact determi-
nations of losses difficulL Model tests should be consid-
ered for important mpid-f!ow aransitions.

2.5. Flow In Curved Channels

a. General.

(1) The so-called centrifugal force caused by flow
around a curve results in a rise in the water surfxe on the
outside wall and a depression of the surface along the
inside wall. This phenomenon is called superelevation.
In addition, curved channels tend to create secondary
flows (helicoidal motion) that may persist for many chan-
nel widths downsa-e:un. The shifting of the maximum
velocity from the channel center line may cause a disturb-
ing innuence downStre:lm. The latter two phenomena
could lead to serious local scour and deposition or poor
petformance of a downstre:lIn sa-ucture. There may also
be a tendency toward separation near the inner wall., espe-
cially for very sharp bends. Because of the complicated

2-11