Four factors make the Red River Valley prone to flooding (the factors are related to
physical geography):
Synchrony of Discharge with Spring Thaw: The Red River flows northward. The spring thaw also proceeds gradually northward. As a result, runoff from the southern portion of the valley gradually joins the fresh melt-off waters from northerly areas along the Red River. In the northern part of the Valley, this can result in devastating floods if the effects occur at the same time.
Ice Jams: These are also produced because of the northward-flowing river system. Ice is moving from the southern Valley and freshly-broken ice is moving from the central and northern Valley. These two meet steadily; as a result, ice concentration in this system builds and causes delay of water flow.
Glacial Lake Plain: The floor of Glacial Lake Agassiz is one of the flattest expanses of land in the world. Here, the Red River has cut a shallow, winding valley. As a result of this, when the river floods on this plain, a devastating event can occur. The areal coverage of the waters can become dramatic. Being approximately 9,300 years old, the Red River has not yet carved a large valley-floodplain systems on the surrounding geography. Thus, the large lake plain becomes the floodplain to the Red River. The Lake Agassiz glacial lake plain extends around 100 miles from east to west, end to end, between northeastern North Dakota and northwestern Minnesota.
Decrease in Gradient Downstream: The gradient, or slope, of the Red River averages 5 inches per mile of length. In the region of Drayton-Pembina, the gradient is only 1.5 inches per mile. The water tends to pool in this area during flood season. The region can become a massive, shallow lake. ==See also==