Vll 



PAGE. 



Tributaries 103 



Course 104 



Distribution of tributaries 105 



The Illinois River Botto?ns 106 



Alluvial deposits 106 



Elevation of flood-plain 107 



Area and subdivisions 107 



Bank height 108 



Connections with backwaters 109 



The Illinois River Proper no 



Direct course and undeveloped flood-plain no 



Relation to river levels in the Mississippi River no 



Dams and their relation to river levels at Havana in 



Fall 114 



Current 115 



Velocity at LaGrange 115 



Testimony of steamboat men 116 



Tests at Havana 116 



Rate of flood movement 117 



Relation of current to plankton 118 



Comparison with current of Great Lakes 119 



Re-statement of Schroeder's law 120 



Discharge 121 



Rainfall 121 



Boundaries of watershed 121 



Statistics for Illinois 122 



Periodicity of rainfall 124 



Correlation between rainfall and hydrograph 125 



Seasonal distribution of rainfall 126 



Run-off 127 



Situation of plankton station in relation to storm-tracks 127 



Relation of flood movements to plankton 127 



Slope of watershed 128 



Drainage lines and storage basins of tributaries 129 



Volume discharged 131 



Average flow 132 



Measurements 132 



Comparison with other streams 133 



Maximum flood discharge 133 



Minimum discharge 134 



Regimen of the Illinois River 134 



Leverett's statement , . . 135 



Hydrographs at Copperas Creek and LaGrange 135 



Comparisons 135 



Effect of dams upon Havana hydrograph at low levels 136 



Transit of floods 137 



Floods and impounding action of the bottom-lands 137 



Bank height ( and bank-full capacity 137 



