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<br />10
<br />
<br />TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS
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<br />Cross sections:
<br />Tagline
<br />Wading rod, old levell'Od
<br />Boat, Qars, motor, fuel
<br />Sounding line, weight, reel
<br />Boots
<br />Waders
<br />Metallic tape
<br />Photographs :
<br />Stereocamera
<br />CoI<>r film
<br />,LIght meter
<br />Tripod
<br />Miscellaneous :
<br />,Stream-gaging equipment
<br />Pacllllx>ard, knapsack
<br />Rope, string
<br />Two-way radios
<br />3-ft: carpenter's level
<br />Drinking-water container
<br />First-aid kit
<br />Life jacketls
<br />Ladder
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<br />Hints on surveying
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<br />In indirect-measurement work, the vertical
<br />survey requires a higher degree of precision
<br />than the horizontal. When setting up over a
<br />hub, a plumb bob is not ordinarily necessary as
<br />the instrument may he placed with snfficient ac-
<br />curacy by dropping a pebble. However, it is
<br />wise to use a plumb bob and tack at one hub, say
<br />the first, so that a resurvey can more readily be
<br />accomplished. Short sights in a large survey
<br />require plumbing and sighting to tack points on
<br />the two hubs. For levels involving only one in-
<br />strument position and run to arbitrary datum,
<br />an assumed OJ. of 99.99 has merit in that sub-
<br />traction of foresight is made very simple.
<br />When taking stadia readings, it is simpler to
<br />set the lower crosshair on the nearest footmark
<br />(with the telescope thumbscrew) than to at-
<br />tempt to subtract the lower reading from the
<br />upper while the telescope is level. To save time
<br />of releveling, note the reading of the middle
<br />crosshair before moving the telescope, then re-
<br />set to the same reading with the telescope
<br />thumbscrew after noting the stadia distance.
<br />Check the bubble; if level, the instrument must
<br />have remained level during readings.
<br />If part of a cross section is low enough for
<br />the top of the extended level rod to be below
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<br />the horizontal line of sight, hold the rod bottom
<br />at belt level or some other point on the body and
<br />add the distance from that point to the ground
<br />to the rod reading. This freqnently saves mak-
<br />ing an additional setup and is sufficiently ae-
<br />eurate on cross-section elevations which are
<br />being determined to the nearest 0.1 foot.
<br />In taking side shots to high-water marks, the
<br />transitman can save time by reading the rod for
<br />elevation and stadia, then waving the rodman on
<br />and reading the azimuth while the rodman is
<br />moving to the next high-water mark.
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<br />Ground plan
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<br />A plan sketch is needed showing all natural
<br />features of the site which are pertinent to the
<br />measurement. Show channel for some distance
<br />upstream and downstream from the actual
<br />reach, so that the flow pattern and its effect on
<br />the high-water profiles can be judged. Show
<br />direction of the flow in the channel with an ar-
<br />row. If the high-water lines do not define the
<br />channel alinement, as when a low-water chan-
<br />nel meanders in a flood plain, take some shots
<br />to locate the lower-water channel. Locate trib-
<br />utaries or any minor bypass channels. Indi-
<br />cate any high ground, ridges, riflles, or other
<br />features which would affeet the distribution or
<br />type of flow. Describe details of the ground
<br />cover, such as the extent of open fields, land un-
<br />der cultivation, brush, and wooded areas.
<br />Locate buildings, roads, fences, or other such
<br />manmade features for their relation to the
<br />problem, to identify the reach, or to help orient
<br />photographs of the site. On the sketch, show
<br />position and direction of the camera for each
<br />pieture.
<br />Always make a field sketch in the notes to
<br />show all the important items, both natural and
<br />eultural. Many of the features need not be
<br />located exactly by the survey. Make the field
<br />sketch carefully, because it may be a snfficient
<br />basis for transferring details, such as ground
<br />cover, extent of trees, and other features, onto
<br />the final plan. Show detailed dimensions of
<br />structures, such as bridges, culverts, and dams,
<br />by auxiliary sketches.
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