U.S. Army Corps of Engineers
Lake Level Report: April 7, 2014
For the first time since 1998, the mean water level of Lake Superior is above long-term average.
After more than 15 years of low levels, the Big Lake has reached its long-term average level, thanks in part – yes, thanks – to the long and hard winter.
This March, the Lake's monthly mean was 1 cm (0.4 inches) above average and 13 inches above the level recorded a year ago.
The Lake had been below long-term average since April 1998, a record-long stretch of low water. But since the levels dropped to more than a foot below normal in March 2013, we’ve seen a dramatic reversal.
The hard-hitting and late-leaving winter of 2013 contributed to a 23-inch seasonal rise from March through September, says Keith Kompoltowicz, a hydrologist with the U.S. Army Corps of Engineers. “That’s almost twice the seasonal rise you would normally see.”
Heavy snowfall last April made May 2013 one of the wettest months on record for the Lake Superior basin, and the net water supply was above average the rest of the year, too. For some perspective on how wet 2013 was, consider that raising Lake Superior’s level by just an inch takes 551 billion gallons of water.
Because of heavy snow and extreme cold this winter, levels could climb farther above average in the coming months as the snow and ice melts.
In addition to precipitation, evaporation has a major influence on the levels. The Lake almost completely iced over this year – by far the most ice we’ve seen since 2008 – which has both immediate and long-term benefits for the levels.
Of the five feet of water that Lake Superior naturally loses throughout the year, evaporation accounts for two. (The rest flows out the St. Marys River into Lake Huron.) Ice cover cuts off evaporation, but more importantly, it will keep the water cooler the rest of the year, delaying and shortening the peak evaporation season – and keeping more water in the Lake. Evaporation rates are highest when there’s a large difference between the air and water temperatures, as in the fall and early winter.
The recovering levels are welcome news for ships large and small. Commercial vessels can carry more on each run: an extra inch of draft on a 1,000-foot laker equals an additional 270 tons of cargo. When the water is near average, recreational boaters can again use shallow harbors and docks that had become inaccessible or dangerous to navigate. The higher water also obviates some harbor dredging projects that drain local budgets.
The levels of the other Great Lakes remained below average in March.