“Spanish Moss just below No. 82. This is a beautiful right hand bend forming three-fourths of a regular circle of about eight miles in length.
“The left had shore around this bend is clothed with willows and sand bars. Near the lower end of the bend the river in its highest state become much crowded together, not being more than a third of a mile in breadth, consequently very deep and rapid, and full of boils or swells, but no way dangerous.
“This settlement, of four small cabins, occupied by one Indian, one French, and two American families, having as many corn patches of three or four acres to each house, is at the right hand point immediately below the Spanish Moss bend, and a little above the head of No. 83. The bank here is pretty high, but I fear the overflowings of 1813 have destroyed all present attempts to continue the settlement. The peach tree leaves were green here on the 21st of December 1812, through the fall had been unusually cold and early, and the winter afterwards more severe than had been witnessed in 20 years.
“Just above the settlement you run nearly east, and three miles below it as nearly west.” –Zadok Cramer, 1814[i]
On Monday, August 20 a barge ran aground on the Lower Mississippi south of Greenville, Mississippi. The U.S. Coast Guard closed the river to barge traffic, but reopened it 12 hours later to slow-moving southbound traffic, alternating with slow-moving north bound traffic, with the Coasties acting as traffic cop. There is history behind these problems at Greenville.
In the wake of the Flood of 1927, which drowned the Lower Mississippi alluvial valley from wall to wall, Congress authorized the Mississippi River and Tributaries Project in the Flood Control Act of 1927. The project standardized and raised the levees between Cape Girardeau, Missouri and Venice, Louisiana. It allowed reservoirs on the headwater tributaries of the Mississippi (Table Rock Lake on the White, Clearwater Lake on the Black, Wappello Lake on the St. Francis, all in Missouri; Arkabutla Lake on the Coldwater, Grenada Lake on the Yazoo, Sardis Lake on the Little Tallachatchie, and Enid Lake on the Tallachatchie, all in Mississippi) to retain flood waters in the uplands until the Mississippi could hold them. On the other hand, water released from the reservoirs during a drought can raise the level of the river. It created the New Madrid, Atchafalaya and Bonnet Carre Floodways (all used during last years flood) to siphon off floodwater, and in the case of the Atchafalaya and Bonnet Carre carry it to the Gulf of Mexico without ever returning it to the Mississippi. Finally, it authorized cutoffs across point bars to shorten the river and speed floodwater downstream. Therein lie our current problems on the Mississippi near Greenville.
The grey line follows the old Greenville Bends.
From the Mississippi: A Visual Biography Draft: Rowdy Bend, Miller Bend, Spanish Moss Bend, and Bachelor Bend: the river zigged and zagged between Arkansas City and Greenville, Mississippi. River pilots called them the Greenville Bends. They were shallow and meandered through erosion-resistant and cohesive clay. The Corps of Engineers worked for years to prevent the river from cutting new channels across the point bars that formed them, only to have General Harley Ferguson include them in his cutoffs to shorten the river and speed floods downstream.
Follow the thin blue line to understand the Greenville Bends and Point Bars across which General Ferguson made his cutoffs.
A meandering river works hard to maintain a fairly constant length. Natural cutoffs are its means. When the river becomes too long and its slope too flat, its searches out a steeper, more efficient slope. It makes a cutoff across the narrow neck of a point bar or by forming a chute across a wider part of the point bar. Once the river makes a cutoff, the speed and the slope of the river above the cutoff increase, it erodes its banks and its bed, adding to the load of sediment it carries. Below the cutoff the river remains unchanged. It moves slowly down a shallow slope, forcing the river speeding through the cutoff to slow down and deposit its sediment downstream of the cutoff, creating a new sand bar, around which the river will meander, restoring its length. In its natural state the Lower Mississippi made a cutoff once every seven to ten years. After it made a cutoff, the river took thirty to eighty years to recover and regain its width, its bar sequence, and its flow regimen.
Before Ferguson made his cutoffs, the average length of the Lower Mississippi River was about 1080 miles. It varied up and down as the river made cutoffs and created bars, but it always came back to the average. Ferguson lopped off 116 miles off the average in the 330 miles between the mouth of the Arkansas and the mouth of the Red River.
It was a mere fifteen land miles between the head of Rowdy Bend, the first Greenville bend, and the toe of Bachelor Bend, the last, but fifty miles by river. After 1880 the river added seven miles in the bends as it shaved sediment off the concave bends, deposited it on the head of the point bars, and threatened to chew away the levees on both banks. The Corps spent much time and money building revetments to stop the river’s meander at Rowdy Bend and Bachelor Bend. And, as Cramer noted, the river slowed and pooled in the bends at flood time, acting like a dam. Floodwaters back up to Arkansas City. In Ferguson’s view the bends had to go. Bachelor Bend, on which the City of Greenville is located, volunteered to go first. That was not Ferguson’s plan.[ii]
Bachelor Bend and Point Chicot aka Lake Ferguson north of Greenville
Ferguson only planned two cutoffs at the Greenville Bends and Bachelor Bend was not one of them. The bendway wrapped itself around Point Chicot. In 1882 the distance across the neck of the point was 5,500 feet, just over a mile. Within twenty years the distance had narrowed to 3,500. The Corps of Engineers constructed a protective dike, 6,250 feet long, across the axis of the neck. The Mississippi continued to scour the neck, reducing the distance across it to 2,600 feet by 1910. The Corps extended the dike a half mile. The Floods of 1922, 1927, and 1929 scoured a trench across the neck. The Corps responded with a mile-long permeable dike. The river broke through the new dike on July 8, 1933, deepened the trench, and forced Ferguson to move up his plans to take out the Greenville Bends by two years.
Spanish Moss Bend and Carter Point
While the river, in 1933, did not develop a new channel across Point Chicot, its elevation was three and a half feet higher on the upstream side of the point than the downstream side. The next flood could ream an uncontrolled cutoff through the point. That the river chose the place for the cut across Point Chicot and not the general added to his worries. Therefore, to align the cut across Tarpley Neck to eliminate Spanish Moss Bend, and the cut across Ashbrook Point to eliminate Rowdy Bend with the river’s cut at Point Chicot, and to incorporate Miller Bend between the two artificial cuts, Ferguson had to redraw his plans.
Lake Ferguson Marina. Greenville’s Casino floats on Lake Ferguson, but goes no where.
Ferguson and his engineers finished the work the river had started across Point Chicot and aligned it properly in 1933, leaving Greenville on the shores of Lake Ferguson, old Bachelor Bend. When they finished the new channel, called the Leland Cutoff, carried fifty percent of the flow during the low-water season in 1933.
The Mississippi south of Greenville at the Leland Cutoff
The Corps started work on the lower end of Tarpley Cutoff in January 1935 directly opposite the head of the Leland Cutoff and completed it on Easter Sunday in April just as the crest of the 1935 flood streamed past Greenville. The cut, through sandy soil, was 13,000 long, 250 to 300 feet wide, and forty feet deep. Its slope was five times greater than the slope around Spanish Moss Bend. The new channel developed rapidly, but because the slope was steep and the soil sandy, the river flowed in a braided pattern and deposited many sandbars at the foot of Tarpley Cutoff.
The sinuosity of the old Greenville Bends allowed the Mississippi fifty-three miles to negotiate the steep grade between the top of Askbrook Cutoff and the foot of Leland Cutoff. The meandering channel gave the river a place to deposit its sediment: on Ashbrook Point, Point Comfort, Carter Point, and Point Chicot. Ferguson made his cutoffs and created a relatively straight, wide channel, but the steep grade remained and caused all kinds of problems for the engineers.
Tarpley Cutoff above Greenville
Almost as soon as it opened up, a sand bar formed at the mouth of the Tarpley Cutoff. The Corps dredged it away with a pump dredge only to have it form again two years later. Year in and year out the Corps dredged from the top of Ashbrook Cutoff to the foot of Leland Cutoff, but could not create a reliable navigation channel. The steep grade and the clay bed never allowed the river to adjust its slope or scour a deep channel. Nor could the river manage its sediment load through the wide channel that had a constant slope of a half-foot per mile.
Beginning in 1963 the Corps laid revetments on the banks to discourage scour and built training dikes to catch sediment and lock in the channel, reducing the need for so much dredging. But, still the river deposited sediment in the navigation channel, which shifted constantly, leading one potamologist to suggest the solution to the Greenville Bends was to use the training structures to create a sinuous channel that would allow the river to meander and handle its sediment the old way, by shaving it off the concave bends and depositing it on the convex bends.[iii]
Thus during the drought of 2012, when the river ran very low, barges ran aground and traffic backed up on the Lower Mississippi south of the Leland Cutoff at Greenville, Mississippi.
[ii] Winkley, Brian R., Man-made Cutoffs on the Lower Mississippi River, Conception, Construction, and River Response, Potamology Investigations, Report 300-2, Vicksburg: U.S. Army Corps of Engineers, 1977, 3-10; Camillo and Pearcy, Chapter 11, Chapter 12, http://www.mvd.usace.army.mil/mrc/Upon_There_Shoulders/Chapter11.htm.
[iii] Winkley, Brien R., Man-made Cutoffs on the Lower Mississippi River, Conception, Construction, and River Response, Potamology Investigations, Report 300-2, Vicksburg: U.S. Army Corps of Engineers, 1977, 50-69; Schumm, Stanley, and Brinkley, Brien T., “The Variability of Large Alluvial Rivers, New York: American Society of Civil Engineers, 1994, 66-70; Smith, Lawson M., and Winkley, Brien R., “The Response of the Lower Mississippi River to River Engineering,” Engineering Geology, 1996, 441-442.
Filed under: Mississippi River, Photography, U.S. Army Corps of Engineers | Tagged: Arkabutla Lake, barge traffic, Drought of 2012, Enid Lake, Flood of 1927, General Harley Ferguson, Greenville, Greenville Mississippi, Grenada Lake, Mississippi, Mississippi closed, Mississippi River and Tributaries Project, Sardis Lake, United States Coast Guard | Leave a comment »