The easiest way for me to understand the impact of melting snow, is to watch the data provided by the Wisconsin River gages at Merrill and Rothschild. (http://waterdata.usgs.gov/WI/nwis/current/?) Merrill is considered the southern end of the Upper Wisconsin River Watershed. The Upper Wisconsin River Watershed covers roughly 2760 square miles, and contains 34% of Wisconsin's 15,057 lakes in addition to 17 tributary river watersheds like the Prairie, Spirit, and Tomahawk Rivers. The Merrill gage helps me better understand what's headed in our direction. The Rothschild location watershed area increases to 4020 square miles with the addition of the Rib, Eau Claire, and Trappe Rivers to name a few, and helps me better understand what may happen to areas South of Wausau. The USGS uses square miles to describe the watershed area, making it a little difficult to understand. The acreage and square foot equivalents are hard to comprehend as well, but in order to get the point across I'll give you the numbers. 4020 square miles is equivalent to 2.6 million acres, or twice the size of Delaware. The square foot comparison is even more mind boggling at 112 billion square feet. This means with a liquid equivalent of 4" on average across the watershed area, we are looking at more than 37 billion cubic feet of liquid (5 billion gallons), which is roughly 18-20% higher than normal.
These gages typically record gage height in feet and discharge in cubic feet per second. Right now, the gage in Merrill is frozen and not displaying information, however, the gage height in Rothschild is recording 13.72 feet with a discharge of 2580 cubic feet per second. If you look at the historical data for the past 100 years, you begin to see an increase in flow rates starting around March 10th, with highest average flow in the middle of April, and they finally return to average numbers near the end of June. So what is average? At its highest point in the middle of April, the Rothschild location averages 8700 cubic feet per second, which typically equates to a gage height of approximately 17.8 feet. That sounds like a big difference from the 13.72 feet we have currently, but the National Weather Service defines Action or Bank-Full stage at 18 feet, and lowland flooding begins to occur when you get to 20.5 feet. If this spring season is similar to historic average, even with the 20% increase in moisture, the maximum discharge in April would be around 10,000 cubic feet per second. This equates to about 18.5 feet at the gage. Still below flood stages. Where the real concern lies, is in the rate of snow melt. The approximate 100 day melt cycle would be ideal, but if it were to shorten due to prolonged increases in temperature or increased rainfall in March and April we may have some validated concerns. The National Weather Service is currently predicting a 50% chance of flooding this spring in our area. So, it's essentially a coin toss at this point. Either way it is something to watch, especially if you are a paddler or fisherman waiting to get on the water this spring.
"We must build dikes of courage to hold back the flood of fear." Martin Luther King Jr.