4 BULLETIN 832 5 U. S. DEPARTMENT OF AGRICULTURE. 



with a level to the nearest two or three thousandths of a foot -and 

 were carefully checked after every high stage in the stream to detect 

 any possible changes due to the disturbance of the posts. The posts, 

 however, were set in such a substantial manner, that very seldom 

 were any changes found. The vertical measurements from the points 

 on the arms to the water surface were made with a hook-gauge measur- 

 ing rod. In some instances a stilling box arrangement was employed 

 in connection with the hook gauge. These measurements were made 

 either before or after the gauging was made, and often both before 

 and after. They were made simultaneously by observers at either 

 end of the course, or by one observer who first read at the end of the 

 course nearer the gauging station, then at the other end, and then 

 repeated the first measurement, the average of the first and third 

 measurements being used. This method is based upon the assump- 

 tion that the same time elapses between the first and second measure- 

 ments as between the second and third measurements; hence errors 

 due to a rising or falling stage are practically eliminated. Realizing 

 that the accuracy of the results depended largely upon a correct 

 determination of the slope, the utmost care was taken to secure accu- 

 rate and dependable slope measurements. 



CROSS SECTIONS. 



The length of the slope course was carefully measured along one 

 bank of the stream and stakes were placed at intervals of 50 or 100 

 feet to mark the points where the cross sections were to be taken. 

 Where the channel was regular the cross sections were taken at 

 intervals of 100 feet. Where the channel was irregular they were 

 taken 50 feet apart, or at such irregular intervals as to represent as 

 nearly as possible the true average cross section of the course. In 

 making the cross-sectional measurements, distances across the channel 

 were measured from the stakes to the nearest tenth of a foot. For 

 the smaller channels, where wading was possible, elevations on the 

 bottom and side slopes of the channels were taken with a level and 

 rod to the nearest tenth of a foot, and were taken at intervals of 5 

 feet across the channel and at all points where a change in slope 

 occurred. For the larger channels the measurements in the water 

 section were generally taken from a boat attached to a rope stretched 

 across the stream and fastened securely on both sides. 



COMPUTATIONS. 



In the experimental determination of the value of n in Kutter's 

 formula, 



„, _ , 1.811 , 0.00281 



1+Ml . 6 + «- 0U2m " 



S 



