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Kankakee in which natural drainage channels have not as yet 
been opened, a fact which has a tendency to further moderate 
the run-off in the northern basin. 
The newer drift which covers the northern basin presents 
a great variation in its structure and consequent effect upon 
drainage. In general it is less compact than the older drift and 
offers greater opportunity for the storage of ground water, 
especially wherever extensive deposits of sand and gravel 
occur. Storage in such deposits tends to equalize the run-off 
throughout the year. 
The basins of the several tributaries present marked 
peculiarities which influence their contributions to the flood 
waters of the main stream. The basin of the Des Plaines 
River is largely underlaid by impermeable rock upon which 
the drift is twenty to one hundred feet in thickness. The 
lower end of the watershed alone contains deposits capable of 
affording considerable ground storage, while the upper end 
abounds in lakes, bogs, and swamps, which also have a tendency 
to retard and equalize the flow of the run-off. In spite of these 
equalizing factors the floods of the Des Plaines assume large 
proportions and, owing to the extent in latitude of the basin, 
they are often prolonged. A considerable portion of the 
flood water, under conditions prior to the construction of the 
drainage canal, escaped over the Ogden dam and through the 
Ogden-Wentworth ditch and the Chicago River to Lake Michi- 
gan, following what seems to have been a former channel of 
the Des Plaines. Cooley (’89) estimates that the discharge of 
the normal extreme flood at the junction of the river with the 
Kankakee is 12,000 cubic feet per second, and that this would 
be increased to 20,000 if all the water from the basin sought 
this outlet. This latter estimate is equivalent to the bank-full 
capacity of the [linois River at Copperas Creek dam, seventeen 
miles above Havana. High-water level at the junction is 15.7 
feet. above low water. The flow at low water is insignificant, 
amounting in 1887 to less than 163 cubic feet per second for a 
period of five months. The variations in the Des Plaines thus 
