Water Supply and Irrigation Papers of the United States Geological Survey (1910) (14579357118)

Identifier: watersupplyirrig250unit (find matches)
Title: Water Supply and Irrigation Papers of the United States Geological Survey
Year: 1910 (1910s)
Authors: United States Geological Survey
Subjects:
Publisher:
Contributing Library: Clemson University Libraries
Digitizing Sponsor: LYRASIS Members and Sloan Foundation



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it holds nearly as wellfor ice-covered rivers. It is very extensively used in the regularpractice of the United States Geological Survey. The single-point method consists in holding the meter either at thedepth of the thread of mean velocity or at an arbitrary depth forwhich the coefficient for reducing to mean velocity has been deter-mined or must be assumed. Extensive experiments by means of vertical velocity curves showthat the thread of mean velocity generally occurs between 0.5 and0.7 total depth. In general practice the thread of mean velocity isconsidered to be at 0.6 depth, and at this point the meter is held inmost of the measurements made by the single-point method. Alarge number of vertical velocity curve measurements, taken onmany streams and under varying conditions, show that the averagecoefficient for reducing the velocity obtained at 0.6 depth to meanvelocity is practically unity. The variation of the coefficient from U. S. GEOLOGICAL SURVEY MTER-SUPPLY PAPER 250 PLATE
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PRICE PENTA-RECORDING CURRENT METERS INTRODUCTION; 19 unity in individual cases is, however, greater than in the 0.2 and0.8 methods and the general results are not as satisfactory. In the other principal single-point method the meter is held nearthe surface, usually 1 foot below, or low enough to be out of the effectof the wind or other disturbing influences. This is known as the sub-surface method. The coefficient for reducing the velocity taken atthe subsurface to the mean has been found to be in general fromabout 0.85 to 0.95, depending on the stage, velocity, and channelconditions. The higher the stage the larger the coefficient. Thismethod is especially adapted for flood measurements, or when thevelocity is so great that the meter can not be kept in the correctposition for the other methods. The vertical-integration method consists in moving the meter at aslow, uniform speed from the surface to the bottom and back againto the surface and noting the number of revolutions and the t