The floodplain is flat. If you spill a glass of water it can spread for miles before being challenged by verticality.
Add to that the fact that it flows north. Unlike most rivers where the melt starts on the lower reaches and progresses toward the higher latitudes, the Red's melt starts at the headwaters sending the water into colder territory.
Where it can run into ice dams. And overflow it's banks. And head for the Rockies.
( kidding on that last bit but just barely)
Here's the National Oceanic and Atmospheric Administration*:
March 17, 2011U.S. Spring Flood Risk Map for 2011.
Download here (Credit: NOAA)
With spring flooding already underway over portions of the U.S., NOAA forecasters are warning the worst is yet to come. Almost half the country – from the North Central U.S. through the Midwest and the Northeast – has an above-average risk of flooding over the next few weeks, according to the annual spring outlook released today by NOAA’s National Weather Service. This week is also national Flood Safety Awareness Week, and NOAA has partnered with FEMA to encourage residents to prepare for this imminent threat.
The highest spring flood risk areas include the Red River of the North, which forms the state line between eastern North Dakota and northwest Minnesota, the Milk River in eastern Montana, the James and Big Sioux Rivers in South Dakota, the Minnesota River, the upper Mississippi River basin from Minneapolis southward to St. Louis, and a portion of lower New York, eastern Pennsylvania and northern New Jersey. Many metropolitan areas have a greater than 95 percent chance of major flooding, including Fargo, Grand Forks, St. Paul, Davenport, Rock Island, Sioux Falls and Huron. Devils Lake in North Dakota has an 80 percent chance of reaching two feet above last year’s record of 1452.1 feet....MORE*I get a kick out of the closing paragraph on NOAA press releases:
NOAA’s mission is to understand and predict changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and to conserve and manage our coastal and marine resources. Find us on Facebook.