According to Frank Quinn, Ph.D, a NOAA Senior Research Hydrologist, water levels are expected to drop to within inches of mean low water which represents the water depths found on nautical charts. This plunge has been more than usual according to Quinn. Lake Michigan dropped 1.6 feet in the last year- the third largest recorded drop in over a century; the other drops followed the droughts of 1977 and 1931. Although this rate of descent is unusual, lake level fluctuations are not. Water levels can range from as little as 2-1/2 feet to as much as 6-1/2 feet during high and low periods over a extended period.

The major natural processes affecting Lake Michigan water levels include inflows from upper Lakes (Huron), run off from land draining into the Lake, evaporation, and direct precipitation. Of these, precipitation is the primary source of water input for the Great Lakes basin. The average annual precipitation over the basin is 32 inches. Observers say, however, last summer’s dry conditions, combined with low precipitation last fall and winter have caused the lake’s water level to drop below average to its lowest level in nine years. Fortunately, above average precipitation during July and August have prevented the lake from plunging even further.

Accompanying these short-term fluctuations are long-term fluctuations which usually take several years to manifest themselves, and often as many years to correct. They are the result of persistent low or high water supply conditions within the basin, which culminate in extremely low levels, such as were recorded in the mid-1960s, or in extreme high levels such as those of the early to mid-1970s and mid-1980s. The intervals between periods of high and low levels, and the lengths of such periods vary widely. More than 100 years of water level records on the Great lakes indicates that there is no regular, predictable cycle for long-term fluctuations.

Because of the vast size of the Great Lakes and the limited discharge capacity of their outflow rivers, extremely high or low levels and flows can exist for a considerable time after the factors which caused them have changed, or ceased contributing to the situation.

On the other hand, seasonal fluctuations reflect the annual hydrologic cycle which is nothing more than a circulation and distribution of water during seasonal cycle. In early spring, as a result of snowbelt, heavier rains and reduced evaporation over the basin due to lower temperatures, the water levels begin to rise from their winter lows. This trend continues until the lakes peak, usually sometime in August. During the summer, when the lakes are their warmest, persistent winds and drier air intensify evaporation, and runoff and groundwater flow into the lake reaching their lowest values. This can be seen in the many creeks and small streams that in early spring carried lake feed and now lie bone dry. As the water supplied to the lakes become less than the outflows, mainly through evaporation, the water levels begin their downward trend toward the winter minimums.

According to Quinn, water levels could drop in September to a low equaling the September 1966 lows. The good news: above average expected snowfall this winter could help to reverse the situation. We’ll see.

But for now, caution should be the order of the day. Especially in those areas where shoals run parallel along Lake Michigan’s eastern shore line. As the seasonal hydrologic cycle moves into the fall, water levels drop and navigable shoals now become hazards. And in those areas where rocks lie just beneath the surface, as near the mouth of the Plate River outlet, special caution is advised. And so too, with the many lakes that connect to Michigan: many of these lakes share a great lumber history that now lies silent just beneath the surface. More than once, I have evacuated people off boats that have run aground onto under-water slabs and piers. Remember, telltale bands along sea walls ripraps and piers tell their own story . Boat Smart: read them wisely.

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Boat Smart is now on the Internet: www.boatsmart.net (includes Lake Michigan water temperatures and local weather).

Use channel 16 for emergencies, and channel 9 for calling fellow boaters.