Biennial report of the State Board of Irrigation to the Governor of Nebraska Volume 1

 
9781130770407: Biennial report of the State Board of Irrigation to the Governor of Nebraska Volume 1
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1807 Excerpt: ...of from three inches to ten or twelve feet, in streams of moderate velocity. The price of this instrument is $50.00. A rough approximation of the velocity may be obtained by throwing a floating body in the stream and noting the time of passage over a known distance. About.8 of the maximum surface velocity will represent the mean velocity of the water. This, however, is only applicable to ditches and canals and small streams of uniform cross-section. In wide and shallow streams no constant relation exists between the maximum surface velocity and the mean velocity of the water. In order to get a continuous record of the discharge, an observer is engaged at each gauging station who makes daily observations of the height of water on the rod. Once a month or oftener an actual measurement of the discharge is made, at the same time noting the river height on the rod. After a series of measurements have been made at various river heights comprising high and low water and intermediate stages, a table of discharges corresponding to the river height can be computed, it being considered that a recurrence of the same river height corresponds to the same discharge. This assumption would be practically true if the bed of the stream always remained constant, but this condition does not exist in any of the important streams of this state. At times sand and silt are deposited, and at other times scouring takes place, thus decreasing and increasing the area of the cross-section, and consequently the discharge, especially during and after floods. Therefore it has often been difficult to determine the correct relation between gauge height and discharge. But although the discharge given in the tables for any particular day may vary considerably from the truth, the average for an...

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