44 BULLETIN 832, U. S. DEPARTMENT OF AGRICULTURE. 



channel for the two sets of measurements. In Table 4 are given the 

 values of n obtained for the years 1916 and 1917, respectively. From 

 this table it is seen that the values of n obtained for the low stages 

 during 1916 are lower than those obtained for the higher stages during 

 1917. This is due to the fact that the upper portion of the channel is 

 irregular and covered with growth, as may be seen from the view of 

 of the channel. During the gaugings and slope measurements the water 

 was not as fully laden with silt as in the case of the ditches in the vicin- 

 ity of the Missouri Valley, nor were the sides of the channel so well 

 coated with mud. The bed and the flatter portions of the sides of 

 the channel were covered with silt, varying in depth from \ to 1 \ feet. 

 (See fig. 7 E for average cross section of channel.) 



LITTLE SIOUX RIVER CUT-OFF. 



Gaugings of the Little Sioux River were made from the highway 

 bridge on the Onawa-Turin road, about one-half mile from Turin. 

 Values of n for the channel were obtained during 1916 and 1917. Views 

 of the slope course taken during June, 1916, and June, 1917, are shown 

 in Plates XV, figures 1 and 2. The length of the slope course for the 

 measurements made in 1916 was 1, 212 feet, and for those made in 

 1917 was 1,654 feet. The slope course was located on the straight 

 stretch of channel above the gauging station at the highway bridge. 

 The soil in the upper part of the channel is a dark silty loam, while in 

 the lower part it is a heavy firm clay. There was practically no silt 

 in the bed of the channel during the time that the experiments were 

 made. The channel during 1916 was fairly uniform in section, and 

 the left bank, which is shown on the right-hand side of the view (PI. 

 XV, fig. 1), was quite regular. The right bank was somewhat irregu- 

 lar, due to caving. (See fig. 7 F, for average cross sections of the 

 channel.) There was some vegetation on both side slopes of the chan- 

 nel, as may be seen from the view. The values of n obtained for this 

 channel, shown in Table 4, are about what would be expected for a 

 channel hi its condition. 



Plate XV, figure 2, shows the condition of the same channel in June, 

 1917. The right bank, which in 1916 was covered with trees, has 

 caved into the channel, and the left bank is considerably rougher 

 than it was in June, 1916. The two values of n obtained, 0.075 and 

 0.076, are considerably higher than those obtained in 1916. This may 

 readily be ascribed to the caving of the right bank, which carried into 

 the channel large trees and other obstructions. The water during the 

 experiments was not laden with silt, as in the case of the ditches near 

 Missouri Valley, and the channel was not coated with mud after the 

 subsidence of the water. 



