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Great Lakes Levels Are at Record Low Point URING the past year or two D the waters of the Great Lakes have receded to stages lower than even the oldest inhabitant could remember, and the causes, extent and effects of this lowering have been the subject of much discussion in our lake cities, not only by the ship- ping and riparian interests who were materially affected, but also by the man on the street. His interest in the matter has been twofold: on the one hand, he fears he may be in- directly disadvantaged, and on _ the other, the breaking of a _ record— whether it be by mere man or by Mother Nature—always arouses the curiosity of the American citizen. In this case there can be no doubt that such record as we have has been broken in recent years for all the lakes except Ontario. The corps of engineers of the army, the govern- ment agency having charge of river and harbor improvements on the Great Lakes and their connecting water- ways, has kept a careful and accurate record of changes in lake levels for the past 66 years. We have scattered records of levels prior to 1860, but little is known concerning the ac- curacy of these early figures. It is safest to confine this discussion of lake levels to the fairly wide range of 66 years regarding which we have reliable data. At the time this is written the latest available reports are for the month of August, 1926. These show that the mean stage for that month for Lake Superior was 0.54 foot be- low the lowest August stage pre- viously recorded—that of a year ago— while Lakes Michigan and Huron were 0.15 foot higher, and Lake Erie was 0.22 foot higher than their pre- viously recorded August lows, which were in 1925. Lake Ontario, on the other hand, was 0.64 foot above its lowest August stage made in 1895. Just what these figures mean will perhaps be more clearly ap- preciated from the following table: Below highest August stage ever recorded Below average August stage of last 10 years Lake Superior 1.47 ft. 2.95 ft. (in 1876) Lakes Michigan- Huron 1.96 ft. 4,92 ft. (in 1876) Lake Erie 1.16 ft. 2.81 ft. (in 1876) Lake Ontario 1.30 ft. 3.27 ft. (in 1862) It will be observed that in all these BY COL. SPENCER COSBY Corps of Engineers, United States Army cases comparison is made with the corresponding month (August) of other years. This is the fairest meth- od since it eliminates the seasonal variation to which, as will be ex- plained later, the levels of all the lakes are subject. However, to show the greatest recorded variations in monthly mean lake stages, the fol- lowing table has been compiled: Highest recorded monthly mean stage Lake Superior Sept., 1869 6 Ween nena eeeeeeeneesesenenerenese Lake Michigan 188 Lake Huron , 1876 TiQKG PIL ICS (ecseiiivsvesscssexsies 1876 Lake Ontario 1870 Lowest recorded monthly mean stage Lake Superior Apr., 1926 Lake Michigan Jan., 1926 WAKO ELUPON =. savidisvescsenrtsvese Feb., 1926 Dinka cM yi: coe ae ssereretevvvseons Feb., 1926 Lake Ontario Novy., 1895 Difference THAMES. F SUPCHIOP: | ccs ces chesecaeckscensdockducnesseeestee 3.96 ft. Joalse Mich oain © isc scvcdetevicncsscoscssavencesnenen 6.22. ft Lake Huron Lake Erie Lake Ontario Prreee errr e etree To prevent misunderstanding, it may be stated here that there have been many occasions on which the dif- ferent lakes have, at particular localities, reached elevations several feet lower or higher than the monthly means, but these abnormal changes were for short periods only (often only a few hours) and were due to temporary causes, chiefly to strong winds blowing for some time in the same direction. Causes of Change in Levels It is manifest from what has al- ready been stated that the levels of the Great Lakes are in a constant state of fluctuation, that some of the changes are gradual, some _ sudden, some amount to only a few inches and others to. several feet. For changes of such varying character there must be varying causes. These may be conveniently divided into six general classes. 1. The first and most important cause is the amount of rainfall over the drainage basins of the Great Lakes, especially over that of Lake Superior, the largest of all (80,700 square miles) whose discharge directly affects the water surface of every other lake. It has been estimated that the aver- The author, Colonel Cosby. is engineer in charge of the Great Lakes district. 59 age annual precipitation over ‘the watershed of the lake system above Niagara Falls is about 80 inches, and that the net supply to the lakes, tak- ing into account rainfall, run-off and evaporation, amounts to about 36 inches in depth over the lake sur- faces. The chain of Great Lakes are con- tinuously discharging a huge stream of water over Niagara falls and down the St. Lawrence into the Atlantic. to conpensate for this loss rivers -and streams innumerable are gather- ing and pouring into the lakes the water that falls as rain or. snow on their watersheds. If this pre- cipitation decreases and continues be- low normal for’ several successive years, the inflow will be less than the outflow and the levels of the lakes. will fall more or less steadily during that period. This lowering will take place very gradually how- ever as the water areas involved are enormous and the relation be- tween them and the discharge ca- pacities of their outlets is such as to make a fair degree of stability by natural regulation. From 1917 to 1926 there was a deficiency of rain- fall over the whole drainage basin of the Great Lakes, and _ this is the primary and principal cause of the low levels during recent years. The records show that a major rise or fall in lake levels. due to pre- cipitation changes usually continues, when once started, over a period of several years, but the duration of these periods or cycles is very ir- regular and the rise or ‘fall is often subject to minor interruptions, Taking Lake Erie as an example and disregarding these minor interrup- tions there were, roughly, nine highs between 1860 and 1925, both years inclusive; the length of time from one high to the next varied from 4 years to 15 years. For Lake Huron during the same period there were also nine highs, the length of time from one high to the next varying from 5 years to 13 years. 2. A second cause of what may. be termed lasting and general, as op- posed to temporary and local, changes in lake levels is the amount of water (Continued on Page 75)