PCWA-L 467.pdf - PCWA Middle Fork American River Project ...

110 MEASUREMENT OF STAGE AND DISCHARGE
read correctly at an appropriate average depth determined by other
means.
WlDTH·MEASURING EQUIPMENT
The distance to any point in a cross section is measured from an
initial point on the bank. Cableways and bridges used regularly for
making discharge measurements aTe commonly marked at 2-, 5-, 10-,
or 20-ft (0.61-, 1.52-,3.05-, or 6.10-m) intervals by paint marks. Distance
between markings is estimated, or measured with a rule or
pocket tape.
For measurements made by wading, from boats, or from unmarked
bridges, steel or metallic tapes or tag lines are used. Tag lines aTe
made of 1/32-, 1116-, 3132-, or ll8-in (0.79-, 1.59-, 2.38-, or 3.18-mm)diameter
galvanized steel aircraft cord having solder heads at measured
intervals to indicate distances. The standard arrangement of
solder beads or tags used by the U.S. Geological Survey is as follows:
one tag every 2 ft for the first 50 ft of tag line;
one tag every 5 ft for stations between 50 and 150 ft on the tag
line;
one tag every 10 ft for stations between 150 ft and the end of the
tag line.
For identifying the stationing ofthe tags, an additional tag (total of
two tags) is used at stations 0, 10,20,30,40,50, 150,250,350, and
450 ft. Two additional tags (total of three tags) are used at stations
100, 200, 300, 400, and 500 ft.
The standard lengths of tag line are 300, 400 and 500 ft (91.4, 122,
and 152m), but other sizes are available.
Three types of tag-line reels in use are Lee-Au, Pakron, and Columbus
type A (fig. 66). Larger reels designed particularly for use
with boats are described on page 120. It is practically impossible to
string a tag line for discharge measurements from a boat when the
width of the stream is greater than 2,500 ft 050 m). The methods
used to determine width at such sites are described on pages 156-157.
EQUIPMENT ASSEMBUES
Special equipment is necessary for each type of current-meter
measurement. The meters, weights, and reels used have already been
described. The additional equipment needed is described in this section.
The special equipment assemblies have been divided into five basic
groups: cableway, bridge, boat, ice, and velocity-azimuth-depth assembly
(VADAI equipment.
CABLEWAY l:QUiP\IE.;\l-r
The cableway provides a track for the operation of a cable car from
which the hydrographer makes a current-meter measurement. Cable