In some areas of the world, railway bridges parallel highway bridges.
They should not be overlooked as possible bypasses.
The symbol used is
similar to that of highway bridges, with two major exceptions.
Above the
symbol is placed the letters "RL." The line indicating the location of the
bridge indicates whether its use as a bypass would be easy or difficult.
Use easy is if an engineer platoon could prepare it in less than four hours
for highway use. If it would take longer, it is considered use difficult.
Use easy is indicated by drawing a straight line to the bridge location.
Use difficult is indicated by drawing a jagged line to the bridge location.
Whenever you cannot determine bypass information, it is indicated by
placing a question mark where the bypass information would be.
l.
Fords.
Most modern military vehicles have a built-in stream
crossing capability. This allows greater use of fords. Many vehicles have
the capability to "swim" certain streams. Fords have, therefore, taken on a
much greater significance than ever before. You must include fords on your
overlay. There are several factors that apply to fording operations. These
include stream depth, width, approaches, velocities, and natural and man-
made obstacles.
(1) Depth.
Stream depths can usually be determined by using
such expedients as measured poles or weighted ropes.
Depth readings are
normally taken every three meters.
In determining depths, you must be
careful that unusual conditions do not exist that might affect the depth.
These might include a dam or lock upstream that is open or closed. There
may have been a recent heavy rainfall, or a long dry spell.
Where such
conditions might affect your depth readings, they should be noted
separately.
(2) Width.
MP normally use one of two methods to determine
stream width. Where the distance between the banks is relatively short: a
tape measure or rope may be used. One member of the team holds the rope on
the near shore while a second member crosses the stream with the other end.
The rope is then stretched taut and marked.
The distance can then be
measure on the rope. A second method is to use a compass (Figure 24). Use
the compass to take an azimuth from a point on the near shore to one on the
far shore.
On the near shore, establish another point that is on a
line and at a right angle to the azimuth. The azimuth from the second point
should be at about a 45 degree angle from the first azimuth. Measure the
distance between the two points on the near shore. This distance is equal
to the distance across the stream.
(3) Velocity.
The velocity of a stream is measured in either
feet or meters per minute.
On your overlays you should use meters.
The
velocity of the current varies in different parts of the stream.
It is
usually slower near the shore and swifter in the main channel. It also is
slower whenever the channel widens.
To determine the velocity of the
current, measure a
MP1028
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