. Farrow's manual of military training . anchorageand be free from snags, bowlders, and other obstructions. Thevelocity of current can be measured by timing the passage of afloating object over a measured length of stream. If not in excessof 3 or 4 feet per second no special difficulty need be expected;with greater velocities it will be necessary to use precautions such 622 MILITARY TRAINING as extra anchors or guy ropes leading to points on the banks up-stream. The reconnaissance should furnish information as to theliability of freshets and their probable height, the rise and fall intidal str
. Farrow's manual of military training . anchorageand be free from snags, bowlders, and other obstructions. Thevelocity of current can be measured by timing the passage of afloating object over a measured length of stream. If not in excessof 3 or 4 feet per second no special difficulty need be expected;with greater velocities it will be necessary to use precautions such 622 MILITARY TRAINING as extra anchors or guy ropes leading to points on the banks up-stream. The reconnaissance should furnish information as to theliability of freshets and their probable height, the rise and fall intidal streams, the width and depth of the stream, the presence orabsence of navigation, the nature of existing facilities such as roadsor fords, and the presence of bridge material such as timber, rope,or wire. The depth can be measured by sounding with a pole or asounding line. The width should be measured as accurately aspracticable. Narrow streams can be measured by stretching aline across. Wider streams can be measured by triangulation from. BRIDGE-HEAD FLANKED BY TWO REDOUBTS. a base line, using the most accurate instrument at hand. Tributarystreams near the site, especially if concealed from the view ofthe enemy, are advantageous, as they may be used for storage ofmaterial or the construction of parts of the bridge which are after-wards floated into place. An island may facilitate crossing byreducing the length of bridge required or affording secureanchorage for a bridge built below the island. The approachesare important. An easy exit is particularly essential. A bridgeeasy of access and difficult of exit will cause crowding, accidents,and delay. Where possible, the approaches should be straight andin line with the bridge for at least 20 yards next to the bridge; BRIDGES AND PONTOONS 623 the grades should not be steeper than 1 on 10 if possible, and inno case steeper than 1 on 7. Kinds of Bridges.—The kind of bridge to be built dependson the nature of the obstacle to be crossed
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