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Impounding action 138 



Delay in run-off I3g 



Duration of overflow 139 



Effect of under-drainage upon run-off and floods 140 



Statistics from hydrographs at Copperas Creek and LaGrange.. . 144 



The normal regimen 145 



High-water period 145 



Maximum flood 147 



June rise 147 



Low-water period 148 



Duration and stability 148 



Minor fluctuations 149 



Total movement and range in levels 1 50 



Instability of fluviatile environment 151 



Description of conditions at Havana in high water 151 



At low water 154 



The river as a unit of environment 156 



River gage-readings at Havana 157 



Monthly and yearly averages of gage-readings 163 



Hydrographic conditions 164 



In 1894 164 



In 1895 164 



In 1896 165 



In 1897 166 



In 1898 167 



In 1899 168 



Temperatures 168 



As a factor in the environment 169 



Temperature records 169 



Causes of fluctuations in temperature 169 



Annual and diurnal range 170 



Monthly and yearly averages 171 



Seasonal thermograph 172 



Comparison of thermographs of different years 173 



Surface and bottom temperatures 174 



Instability of temperature conditions in fluviatile environment 174 



Absence of thermocline 175 



The ice blockade in relation to plankton 175 



Ice conditions at Havana in 1895-1899 176 



Other Meteorological Factors 177 



Turbidity 1 79 



Method of determination 179 



Illinois River 179 



Spoon River 180 



Thompson's Lake 180 



Quiver Lake 180 



Dogfish Lake 181 



Flag Lake . 181 



