138 
per second, while the bank-full capacity is estimated at double 
this amount. In either case complete overflow stages appear 
more readily than they do in the majority of streams. 
The impounding action of the bottom-lands, on the other 
hand, begins with every rise af the river, for as the water rises 
large amounts are drawn off from the main stream by the 
adjacent lakes and bayous, many of which retain their connec- 
BANK-FULL CAPACITY OF LOWER ILLINOIS RIVER. 
Distance Bank Height Cubic feet | 
Locality | from Utica (feet) per Remarks 
(miles) Av. Range second . 
Peru Paral 6.2 10.4 8—13 | 18,000 —22,000|Measured in 1889. Varia- 
tion according as river 
is rising or falling 
leleibinids | Sea 33.2 9.4 Q—II | 20,000—22,000/Very tentative estimates 
from dam and prison 
Copperas Very tentative estimates 
Creek .... 92.7 13.7 | 12—15 | 18,000—20,000] from dam and prison 
Havana .... 109.5 10 7—16 
LaGrange .. 152.2 II.5 8—15 | 30,000 Measured in 1889 
Kampsville.. 197.8 11.8 8—15_ | 40,000 Estimated from measure- 
ments in 1889 
tion with the river even at the lowest stage. In the vicinity 
of Havana, for example (see Plate II.), Quiver, Thompson’s, and 
Matanzas lakes respond at all times to fluctuations in the river. 
Flag Lake is invaded at about the stage of 3 feet, and at 5 to 6 
feet the water begins to overflow the bottom-lands between Flag 
and Thompson’s lakes. It is not, however, until the river has 
reached a stage of 8 to 9 feet that the water enters Phelps Lake. 
The wooded bottom-lands to the east of Flag Lake are not en- 
tirely submerged until the gage reads 12 feet, while those below 
Spoon River and adjacent to the main stream do not disappear 
until the water has reached 16 feet. Thus the impounding 
action of the bottoms is at its greatest as soon as the water 
reaches the condition of complete overflow, though it begins 
at the first stages of a rise above low water. 
In his discussion of this subject Cooley (91), speaking of 
