Lake. |Mean Tide.| Square| Square| Rain- |Evapo- | Dis-
| Feet. | Miles.| Miles.| fall. |ration.|charge.
| | | | | |
---------------+----------+-------+--------+-------+-------+-------
| | | | | |
Superior | 601.78 | 90,505| 38,875 |187,386| 34,495| 80,870
Huron and Mich.| 581.28 |121,941| 50,400 |262,964| 66,754|216,435
Erie | 572.86 | 40,298| 10,000 | 96,654| 13,870|235,578
Ontario | 246.61 | 31,558| 7,220 | 75,692| 10,568|272,095
| | | | | |
---------------+----------+-------+--------+-------+-------+-------

The average variation in level of the lakes is from 18 in. to 24 in.
during the year, and the range in evaporation from year to year is
also very considerable; thus the evaporation per second on Huron and
Michigan, as given in the table above, is nearly 67,000 ft., but the
figures for another year show nearly 89,000 ft. per second, which
would represent a difference of 6½ in. in water level. As a discharge
of 10,000 cubic feet a second into the new canal would lower the level
of these two lakes by 2.87 in. in a year, it follows that the
difference between a year of maximum and one of minimum evaporation is
more than twice as great as would be required for the canal, and even
under the most unfavorable conditions the volume taken from the whole
chain of lakes would not lower them an inch.

When the variations in level due to different causes--rain, wind, and
evaporation being the chief--are taken into consideration, the effect
of 10,000 cubic feet a second abstracted would probably not be
noticeable. That this would be so is the opinion, after careful
investigation, of many eminent American engineers. On the other hand