cut-off

When a flooding river is powerful enough, it may force its way across the neck of a meander and erode a more direct channel, which is called a cut-off. The gradient of a cut-off is necessarily steeper than that of the meander it replaces, which results in an increase in the river’s energy. The river may in turn dissipate this energy by forming a new meander, which ultimately it will bypass with a new cut-off, as the self-reinforcing cycle continues. Not all cut-offs form naturally. According to Mark Twain in Life on the Mississippi, little excavation was required to make a cut-off on the Lower Mississippi. “When the river is rising fast, some scoundrel whose plantation is back in the country and therefore of inferior value, has only to watch his chance, cut a little gutter across the narrow neck of land some dark night, and turn the water into it, and in a wonderfully short time a miracle has happened: to wit, the whole Mississippi has taken possession of that little ditch, and placed the countryman’s plantation at its bank.” Twain also reported that many cut-offs were made for the sake of shortening the distance riverboats and other craft had to travel, so much so that between 1706 and 1882 the length of the Mississippi from Cairo, Illinois, to New Orleans, Louisiana, shortened from 1,215 to 973 miles. Never one to shy from the absurd, Twain extrapolated that rate of change into the distant future, concluding that “seven hundred and forty-two years from now, the Lower Mississippi will be only a mile and three-quarters long, and Cairo and New Orleans will have joined their streets together, and be plodding comfortably along under a single mayor and a mutual board of aldermen.”

William deBuys