EM 1110-2-1100 (Part II)
30 Apr 02
EXAMPLE PROBLEM II-6-3
FIND:
The width of the ebb jet and its maximum velocity along the centerline 2,000 m seaward from shore.
GIVEN:
The inlet channel width where the ebb jet exits the inlet is 200 m and the channel depth is 8 m. A flat
bottom and Mannings n = 0.02 are assumed. The maximum average velocity in the channel is 1.5 m/sec.
SOLUTION:
The friction factor (from zsy and nlata (1982)) is calculated as
g bo n 2
(9.8) (100) (0.02) 2
'
' 0.08
'
0.75
(8) 0.75
ho
where bo = half-width of channel = 200 m / 2 = 100 m and the dimensionless distance offshore parameter is
x
ξ'
bo
with x, the distance offshore, equal to 2000 m. Calculating these parameters, = 0.08 and ξ = 20. Using
Figures II-6-32 and II-6-33, and interpolating for , the results are
b
Y
ξ ' 18.5
b ' 100 (18.5) ' 1850 m
bo
and
uc
Y
(ξ) ' 0.2
uc ' 0.2 (1.5) ' 0.3 m/s
uo
Therefore, for a flat bottom, the half-width of the jet expands from 200 m to 1,850 m and the center-line
velocity of the jet decreases from 1.5 m/s at the inlet to 0.3 m/s 2,000 m from shore.
Hydrodynamics of Tidal Inlets
II-6-41
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