a8 THE IMPROVEMENT OF RIVERS. 



a flag so rigged that the steersman can raise or lower it instantaneously. When the 

 boat passes the cross-section line going up stream, this flag is raised and the transit- 

 men bring their instruments to bear upon it, keeping their vertical wires upon the 

 mast as near its intersection with the deck as possible. The boat continues up stream 

 until the flagman on shore signals to sound. It is then allowed to drift astern, the 

 leadsman heaving the lead as soon as the headway is 1 >: ', and raising or lowering the 

 lead so as to have it on the bottom and to keep the line plumb. An instant before the 

 boat crosses the line going down stream the flagman on shore signals; the recorder 

 calls out ' Sound ' ; the leadsman gives the reading on his line ; the steersman lets the 

 flag drop, and the transit-men read their angles. 



"For longitudinal soundings two additional ranges are located at each base,, one 

 1000 feet above, and the other the same distance below the middle range. At the 

 middle of each base oblique ranges are laid off to intersect the uppermost of the new 

 ranges in ten selected positions. 



"The positions assigned to the party are the same as in the cross-section surveys, 

 with the exception of the flagman on shore, whose duty consists in changing the flags 

 on the oblique ranges and in signaling the boat when it approaches and when it crosses 

 the middle range. 



"Soundings are taken mainly from the skiff, and while it is drifting astern, the 

 velocity being so regulated that the lead-line can be kept plumb. The boat having 

 been run into position, obtained by the steersman from the intersection of the range- 

 signals, is rowed up stream a sufficient distance to obtain a vertical sounding by the 

 time it has drifted back to the upper or zero range. As soon as the boat is in position 

 the flag is raised, and when the uppermost range is crossed going down stream it is 

 dropped. Between ranges the flag is raised at every fifth and dropped at every tenth 

 sounding. As the boat approaches one of the old cross-section lines, the steersman 

 is signaled and raises the flag; when the leadsman is on the line he is again signaled 

 and drops it. At each end of the base this is determined by the observer setting his 

 instrument on line and giving the requisite signals, and at the middle range "by the 

 flagman 'lining in.' The paths of the boat are located from the same base as was 

 used in cross-section surveys. The shore flags are placed and located as before, thus 

 giving cross-sections of twelve located soundings. 



"By Range-poles. As it may be necessary to measure the cross-section after 

 every rise of considerable extent on rivers having shifting beds, because of changes of 

 form and elevation in the river bottom, it will be well to fix certain range-points by 

 which this work can be done with less instrumental work, and accuracy in finding the 

 same positions secured. Two poles should be placed on each side of the river on the 

 section-line produced. Then points above or below on either or both sides of the river 

 may be selected from which angles will be turned to the section-line and ranges set up 

 on these lines. Thus the observations can thereafter be taken without the use of a 

 transit, all the points having been previously fixed and a diagram made." 



