TM 5-850-1
CHAPTER 3
LAYOUT OF HARBOR FACILITIES
allowable current in the entrance channels is a function of
3-1. Harbor entrance.
the type of ship or ships to be accommodated. Except
under special circumstances, current is not to exceed 4
a. Location and orientation. The following factors
knots. The maximum velocity of the tidal current through
in the location and orientation of harbor entrances
the entrance channels may be estimated from equation (3-
should be considered:
1).
(1) Water depth. Locate the harbor entrances
4 π
A
in an area where the natural water depth is adequate for
V=
x
x
xH
(3-1)
passage of the largest ship.
5 T
S
(2) Sheltering. Locate on the lee side from
where
most severe storm waves, and between overlapping
V=
maximum velocity of the tidal current
breakwaters.
occurring
at the center of the
(3) Channeling
external
disturbances.
opening, feet per second
Location and orientation will direct any external wave
T=
period of the dice, seconds
disturbances to areas of the harbor remote from
A=
surface area of the harbor basin, square
locations of berthing and anchorage areas.
feet
(4) Navigation.
Navigation through the
S=
cross-sectional area of openings, square
entrance should be easily accomplished. In particular,
feet
locate so that there will be strong beam currents in the
H=
range of the tide, feet
harbor entrance at all tidal stages.
The tidal current in midchannel is about one-third stronger
(5) Littoral drift. Orientation should prevent the
than that at each side.
entrance of littoral drift into the harbor. Where possible,
(4) Discharge of upland drainage.
Entrance
the entrance will be located in an area relatively free of
widths must be adequate to discharge the accumulated
littoral drift.
upland drainage without exceeding the maximum
(6) Multiple entrance. Where possible, provide
permissible current value given in paragraph (3) above.
two entrances with different exposures, which can be
(a) The maximum velocity of the current
used as alternates depending on the direction of the
resulting from discharge of a given flow may be roughly
wind. Multiple entrances are advantageous in wartime,
estimated from equation (3-1) by substituting the rate of
since they make the harbor more difficult to block.
upland drainage to be discharged for the quantity AHIT.
Double entrances also reduce the velocities of the tidal
(b) The total current velocity in the entrance
currents because of the increased area.
due to tidal influence plus runoff may be obtained by
b. Channel entrance width.
Provide minimum
adding the value obtained from equation (3-1) and
channel entrance width consistent with navigation
corrected for quantity AH/T.
needs.
The approximate requirements of channel
(5) Reduction of incident wave height through
entrance width related to size of vessel to be
entrance. Although the model tests will give a more
accommodated are as follows:
accurate picture of wave conditions, the wave height within
Width of
the harbor can be approximated from the following
Harbor classification
entrance, ft
equation:
Medium Vessel
300 to 500
] (3-2)
[
b
b
)
( 1+
Large Vessels
600 to 1,000
- 0.02 4 D
h=H
(1) Entrance.
B
B
Except
in
unusual
circumstances, a width of 1,000 feet is ample for very
large container vessels, and under favorable conditions
h=
height of the wave at location 'X", feet
of entry, a width of 800 feet may be considered.
H=
height of the unrestricted wave at the har-
(2) Secondary entrances.
For secondary
bor entrance, feet
entrances, or those not to be used by large ships, a
b=
width of the entrance, feet
width of 300 feet may be considered, provided that
B=
breadth of the harbor at location "X", feet
entrance conditions are favorable.
(this being the length of the arc with its cen-
(3) Currents.
Entrance widths should be
ter at the harbor entrance center and radius
adequate to reduce currents to acceptable values. The
D)
maximum
D=
distance from harbor to location "X", feet
3-1
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