THE FLOW OF WATER IN IRRIGATION CHANNELS. 11 
each other. Through these holes a well-oiled fishline formed a four- 
tie suspension for a perforated disk. The hole in the disk was a 
trifle larger than the punch which passed through it, so that when 
held truly vertical the disk acted as a plumb bob) not touching the 
punch at any point. A very slight leaning of the punch caused the 
disk to touch, which of course warned the operator that the punch 
must be plumbed. 
In concrete-lined sections and in wooden flumes it was not prac- 
ticable to use the above device, so a thin headed wire nail was driven 
horizontally into the side at the water surface. In many cases it 
was not possible to use a stilling box with such a mark, but it is 
believed that very little error results where the same operator sets 
all the marks with the same relation to top and bottom of whatever 
surface fluctuations exist. Wherever the velocity is sufficient to 
cause much doubt in the mind of the operator as to the accuracy 
of the mark, then the total fall between the two ends of the reach 
tested is so great that any error of a few thousandths is but a very 
small percentage of the total fall. 
Stilling box. — A tin salve box about 3 inches in diameter made a 
very good stilling box. A hole about three-eighths inch in diameter 
was made in the center of the bottom. After the nail had been started 
in the top of the stake in the canal, the box was set over the stake, 
with the nail projecting through the hole. When the box rested on 
top of the stake water entered and withdrew slowly and quietly, so 
that a quiet, definite surface was maintained in the box, and the top 
of the nail was driven to this surface. 
Trimming canal section for measurement. — Where it was necessary 
to make a current- meter measurement for discharge in a canal and 
grass or moss was liable to clog the meter and make inaccurate the 
measurement, or the bottom was slightly uneven, the sides and 
bottom were neatly trimmed, and all interfering growths removed 
by means of a sharp short-handled hoe. 
FIELD METHODS. 
The general method used by the writer in conducting the measure- 
ments for the field data was as follows: Minor changes were some- 
times necessary for various reasons. 
A length or reach of the canal to be tested was chosen. The dis- 
charge measurement was started immediately, preferably at the 
center of the reach chosen. While the measurement was progressing, 
the length of the reach was carefully chained, the final length being 
determined by actual position of the two nails driven to the water 
surface at the ends of the reach. The upstream nail was always set 
first, so that the party walked downstream with any slight change 
in volume of the discharge rather than have this change pass them, 
