148 
but appears occasionally (nine times in twenty-one years) in 
the annual ones as a well-defined flood. In the. majority of 
years, however, it appears as a slight interruption in the decline 
of the earlier spring flood. In a few cases these fluctuations 
occur late in May or early in July. The fact that this June 
rise is so little felt in the Illinois, while it is so prominent in 
other streams of the state, is explained by the fact that it often 
occurs within the period of overflow, when large accessions of 
water produce relatively slight rises of river levels. A compar- 
ison of the hydrographs of 1889 and 1892 will illustrate the 
points in question, the June rise of the latter year appearing as 
a slight fluctuation in the declining flood, while in the former 
year it stands out as a well-marked rise, owing simply to the 
previous low water. 
As compared with Leverett’s normal regimen for an I]linois 
stream, we find in the case of the Illinois River that the high- 
water period exhibits a considerable range; that it extends over 
a much longer time; and that the phenomenon of the June rise 
is less pronounced,—all of which deviations may be explained 
by the impounding action of the slightly developed flood-plain 
of the Illinois. 
Following the period of high water comes an equally pro- 
nounced period of low water, extending through the summer 
months until the late autumnal or winter rise. As shown by 
the averages, this low-water period (below four feet) extends 
from August to November, inclusive. It varies, however, with 
the high-water period, appearing even in May, as it did in 1895, 
and frequently continuing through the fall and winter till late 
in February, as it did in 1891, 1893, and 1894. The average 
time during which the water was below 4 feet for the 21 years at 
' Copperas Creek is 1384.1 days, two days more than the high- 
water period. This low-water stage is quite variable in its du- 
ration, ranging from 260 days in 1895 to 5 in 1885. The low- 
water period, which Leverett estimates as continuing at least 
ten months in normal Illinois streams, is thus much shortened 
in the Illinois River. The lowest levels of the year are reached 
