Box 23, Folder 6: Geographical and Topographical Description of Wisconsin 1855, Third Edition

36.

The second system of changes of level is occasioned by the annual change of seasons. The lakes may be regarded as portions of a great river subject to annual rise and fall of its waters precisely as other rivers are. But being spread over a vast expanse of surface, the quantity of water that would rise the Ohio rivers for instance twenty or thirty feet would rise these lakes only a few inches.

During the winter when the fountain springs are closed with ice, and when the [atmospheric] waters precipitated from the atmosphere are retained on the surface where it falls in the form of snow, the lakes gradually fall until they reach their greatest depression in the spring. The breaking up of winter then causes the waters of the lake to rise; but the process is so slow that they do not reach their maximum height until the middle of the summer.

37.

The nature of the third class of changes in the level of the lakes, which is supposed to have a regular period of fourteen years has been the subject of much discussion. That the waters continue to rise for a series of years, and then to fall for another term of years there can be no doubt; but it is not believed that this periodical change is at all regular, or measured by any definite time. As all large rivers occasionally rise to an unwanted height and as often fall to an unusually low stage, so the great river passing through these lakes has its [periodical] occasional changes.

A wet season will cause a rise of the waters, not only [to] in convergence of the increased quantity of rain, but the diminution of evaporation; and a succession of such seasons may cause a continuance of the rise of the waters for several years. On the other hand a dry season, or several dry seasons together may, in consequence of the diminished amount of falling water, and the increased evaporation cause a corresponding depression in the surface of the lakes.

38.

It is estimated that the water which passes out of Lake Erie is the surplus or drainage of an area of 335,515 square miles; and by recent measurement, which appears to have been made with sufficient regard for accuracy, it is ascertained that the quantity of water passing into the Niagara river at Black Rock, is 22,440,000 cubic feet per minute,* or about eighty and one eight cubic miles per annum. This is equivalent to fifteen inches perpendicular depth of water spread over the whole area of the country drained; and therefore something less than half the annual quantity of rain in this portion of the country. From these data, it results that an increase of three inches in the quantity of rain in a year (or circumstances being the same) would cause an increase of 4,488,000 cubic feet per minute at Black Rock, or an annual amount of 2,358,892,800,000 cubic feet, and requiring an increased depth of channel at that place, of about five feet, to pass this excess of water.

*See Silliman's Journal, for January, 1844.

We know, from observations made with care, that such variations in the annual quantity of rain do often occur. Need we therefore wonder that there is a periodical rise and fall of the surface of these lakes?

So far it appears that the changes of level of the lakes are occasioned by meteoric causes alone, and they are consequently as variable and as uncertain as the weather!

39.

The fourth and last kind of change of level is a regular linear tide similar to that of the ocean. I deem it right to present here the observations carefully made each hour night and day for the space of two months [upon] which [is founded the] confirmed announcement of the real fully existence of such tide in the waters of Lake Michigan.

The following table shows the height of the water in feet and decimal parts of a foot above the zero of levels established for grades of streets in Milwaukee. The same zero place has been used in running various lines of canals, plank roads, & rail roads leading from the city; and is the low water of the spring of the year 1836. The figure in heavy face type show those observations that [were] fall nearest to the time when the moon [is] was south.

Made in public papers (Sentinel & Gazette (Milwaukee) Sept. 3, 1849 base don observations made in August of that year.

40. 1852 Tide Data Table.