Seaworthy | From The BoatUS Insurance Files
Danger In The New ShallowsBy Beth Leonard
Published: August/September 2013
With some inland lakes hitting unprecedented low water levels, boaters need to take extra precautions to keep their boats' bottoms clear of the bottom.
Where Has All The Water Gone?
The variation in water level on any inland lake over time is determined by simple addition and subtraction. Water enters the lake as precipitation, runoff from surrounding land, and inflow from other bodies of water. It leaves the lake as evaporation, in outflow to other bodies of water, or as diversions to supply water for drinking, irrigation, or other uses. The difference between what comes in and what goes out determines the current water level and how high or low it is relative to normal. Over the past few years, almost all of the factors in this equation have led to lower water levels on most inland lakes across the country.
On the inflow side, the first and most important ingredient is precipitation — rain, snow, sleet, hail — and there has been precious little of that in many parts of the country for more than two years. Both winter and summer precipitation levels were far below average for all of 2012. Last summer, according to the July 19, 2012 edition of the U.S. Drought Monitor, more than two-thirds of the lower 48 states were experiencing moderate to exceptional drought conditions, a record high for the 12-year history of Drought Monitor data. In Texas and other hard-hit areas, the drought has continued into 2013. Though this dry spell has not lasted as long as other major droughts such as the Dust Bowl in the 1930s, it is still ranked by the National Climatic Data Center as one of the top 10 most severe droughts in U.S. history in terms of extent and intensity. The lack of precipitation reduces inflow into any lake across the board because it also decreases runoff and inflow from other bodies of water.
On the outflow side, evaporation has also taken its toll on water levels across the country. Six of the warmest years on record occurred in the past decade. That heat lowers lake levels not only in the summer, but also in the winter by reducing or eliminating ice cover that would otherwise inhibit evaporation. According to NOAA, Lake Michigan had the second least ice cover on record during the 2011-2012 winter; only 2002 had less. This last winter, the first freeze of shallow bays on Lake Michigan didn't occur until January 23, far later than average.
All of that adds up to below-normal water levels in most lakes across the country. But Michigan-Huron water levels (the two lakes are actually one because they're connected at the Straits of Mackinaw) have also been impacted by an increasing outflow due to dredging in the St. Clair River over the past few decades. That dredging removed some harder rock that acted as a natural underwater dam and has led to extensive erosion of the channel, greatly increasing the outflow from the upper Great Lakes to the lower. Lake Michigan-Huron's water levels have been below average for 14 consecutive years, and below low-water datum continuously since September of last year. In February of this year, according to the Army Corps of Engineers, the lake reached its lowest level since recordkeeping began almost 100 years ago.
Which brings us back to that August night last summer on Lake St. Clair. When ongoing drought, lack of snow melt, and winter evaporation all combine to keep pushing lake levels lower and lower, boats find the ground even when their owners don't expect them to. When you only have a few inches below your keel, a windshift can be enough to leave you high and dry, and a log or rock you never found before can take out your lower unit.
An informal survey of TowBoatUS operators last summer revealed that dispatches due to groundings and striking submerged objects were up from 50 to 100 percent on most inland lakes. Insurance claims for groundings and related damage were up more than 50 percent on the Great Lakes.
It's difficult to say where lake levels will go in the second half of this boating season. A colder winter brought ice cover to many northern lakes, and enough snow pack to raise lake levels a foot or more in the Great Lakes this spring. But one normal season cannot make up for years of drought, and the Army Corps of Engineers is predicting low water levels by historical standards on most lakes through the end of the year.
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