Why Do Rivers Crest Long After Heavy Rain Ends

Posted at 3:13 PM, Apr 20, 2013
and last updated 2013-04-20 15:56:46-04

WEST MICHIGAN – With the six to nine inches of rain we’ve seen over the past several days, I noticed many people always wonder why it takes so long for the rivers to crest (go to their highest point) long after the heavy rains have ended.

It’s no secret! Several millions of gallons of water fell across the West Michigan basin (some may call it the Grand River basin). By the time that water tries to percolate in to the ground (which is already saturated), it takes a fair amount of time to runoff into creeks, streams, and tributaries that dump out and feed in to the larger basins like the Grand River. In fact, a good three or four days AFTER heavy rain is typical before rivers start to crest.

Of course we need to realize that a river like the Grand will typically crest at its beginning (far upstream), then that crest will likely take another day or two to travel downstream before dumping out in to Lake Michigan. That’s why the National Weather Service has river point gauges in several different locations. It’s also important to note that what may be high water in one area or location, may not create an issue somewhere else. It’s all about the surrounding area (riverbanks, topography, urbanization, etc.). The attached photo was submitted by Jan Ladegast around the location of West River Drive and Northland Drive in the Rockford/Northview area.

Several counties remain under flood warnings because of high rivers. One of the largest, most important flows is down the Grand. Ionia is expecting major flooding, Lowell is expecting major flooding, Ada is bracing for record flooding, and Comstock Park along the Grand River has just been upgraded from major to record severity. Record flooding is also occurring and is forecast for the Grand River in downtown GR, and major flooding as well along the Grand in Ottawa County in Robinson Township. Minor to moderate flooding is likely along the Rogue River below Rockford.

These are the worst areas. Make sure to click here for the hydrology page from the National Weather Service to get the latest river level and crest forecast in your location. As always, you can get the West Michigan forecast by going to Dry weather is expected through Monday!