115 



CURRENT. 



The effect of this low gradient is seen in the slight current 

 found in the Illinois, a current so insignificant that Mississippi 

 River steamboat men are wont to refer contemptuously to the 

 Illinois River as a "frog pond." The current is further im- 

 peded, especially when the water level is below eight feet, by 

 the presence of the four dams, which at low water convert the 

 river into a series of slack-water pools. 



Discharge Observations on Illinois River at LaGrange Lock, 1887-1890. 

 (Gage referred to low water of 1879; Price current meter used in 1888-89.) 



*Computed. tBackwater from the Mississippi River. 



As shown in the above table, the mean velocity per second 

 of the current at LaGrange, forty-three miles below Havana, has 

 been determined by the IT. S. Army Engineers (see Marshall '90, 

 p. 2443) to range from .409 of a mile per hour at low water to 

 1.754 miles at 12.8 foot stage — 1.8 feet above bank height at that 

 point. The velocity, in miles, per hour and the time required to 

 move from Utica to the mouth at this rate are given in the 

 table, having been computed from the data in the second col- 

 umn, quoted from Captain Marshall's Report. It will be noted 

 that in a general way the velocity of the current increases as 

 the river rises. This increase is, however, modified by the rel- 

 ative heights of the water in different parts of the stream ; thus 



