31
6.3
Nomenclature for Free Surface Flow
Name
Symbol Units Definition
Velocity of gravity wave in still
shallow water
c
ms
-1
(sometimes called
celerity)
Coefficient of contraction
C
c
-
Coefficient of discharge
C
d
-
Coefficient of velocity
C
v
-
0.95<C
v
<1.0
Specific energy head (total energy
head measured relative to channel
bed)
E
m
E = y + V
2
/2g
Note
: If
the datum is the channel
bed then E = H (z = 0)
Force of a stream
F
N
F =
ρ
gby
2
/2 +
ρ
Q
2
/by
Height of water surface above a
weir crest
y
c
m
Total energy head or total head
(height of energy line (e) above a
datum)
H
m
H = y + V
2
/2g + z
Loss of total head between
specified sections
∆
H
m
Pressure at height y above channel
bed
p
Nm
2
Measured
Height of weir crest above
channel bed
h
m
Measured
Height of water surface above the
bed at position x
y
x
m
Measured
Critical depth
y
crit
m
Depth at which specific
energy of flow is at a
minimum.
Height of sluice gate opening
y
g
m
Measured
Height of siphon throat
y
t
m
Measured
Slope of energy line (for uniform
flow assumed to be the same slope
as the channel bed and the surface
of the water)
S
°
Sin
θ
