42 W. & L. E. GURLEY, TROY, NEW YORK 



WADING MEASUREMENTS 



M MMII. innits are made by wading (Fig. 18), wherever 

 the depth and velocity of the stream permit the hydrographer 

 to reach all measuring points and to hold the meter in position. 



To mark the points at which observations are taken, it is 

 customary to stretch a marking line across the stream. For 

 tlii> purpose a metallic tape may be stretched between iron rods 

 that have slits in their ends; when there is a little wind, or for 

 lengths not exceeding 200 feet, a braided silk fish line may 

 be used. The line should be prepared for such use by marking 

 it off while well stretched, into short lengths, say four feet each, 

 with black paint, using special marks every 20 feet. When put 

 in place for use the line is stretched until divisions are of the 

 correct length when checked with a steel tape. For greater 

 lengths a galvanized telephone wire, or a twisted smooth fence 

 wire, may be used, the size of the wire being properly propor- 

 tioned to the span. 



The tape or the fish line which forms part of the hydrog- 

 rapher's kit is kept stretched across the stream only during the 

 measurement, but wire markers are ordinarily left in place at 

 the station. 



Measurements should be made according to the condition 

 of roughness of the stream bed. Under ordinary conditions the 

 two-tenth and eight-tenth method should be used if the meter 

 can be properly submerged for the upper measurements. In 

 shallow water near the bank the six-tenth method may be used. 

 If a stream is very shallow and its bed rough, the position of 

 the thread of mean velocity may rise to one half of the depth. 

 The hydrographer using the wading method can get his sound- 

 ings accurately and can set his meter exactly at the proper posi- 

 tions. This method does not confine all measurements to a single 

 section, but permits the hydrographer to select the most suitable 

 section each time a measurement is made and is especially use- 

 ful on small streams or at low stages. See page 51. 



In making such measurements, the engineer should stand 

 below the tape line and to one side of the meter (Fig. 19), in 

 order that he may not disturb its action. 



