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|Title:||Symposium on channel stabilization problems|
|Authors:||United States. Army. Corps of Engineers. Committee on Channel Stabilization|
Asphalt bank protection
|Publisher:||United States. Army. Corps of Engineers. Committee on Channel Stabilization|
Engineer Research and Development Center (U.S.)
INTRODUCTION: In discussing channel stabilization work in the Vicksburg District it is interesting to look back at the tools which have been used in the past before looking ahead toward an eventual goal and the tools now being used to attain that goal. In the beginning, and for many years thereafter, channel stabilization in the Vicksburg District was dictated by the urgent need to protect levee locations threatened by caving banks. Efforts to protect the levees were largely successful, but while “putting out the fires” there was little room left in which to maneuver and plan ahead for overall stabilization of the river. During the 1930’s thirteen cutoffs were made within what is now the geographical limits of the Vicksburg District. The cutoff program, which was completed in 1937, was quite beneficial in that it shortened the river by 115 miles in 332 miles, resulting in substantially reduced flood heights. For instance, flood heights at Arkansas City (about 20 miles above Greenville, Miss.) were lowered by as much as 12-1/2 ft for comparable discharges. An interesting sidelight concerning the cutoff program is illustrated in fig. 1, which shows what is known locally as the “Famous Greenville Bends.” Here, within 40 miles of river length, three cutoffs, constructed across Ashbrook, Tarpley, and Leland Necks, resulted in a net shortening of the river by 30 miles. It is said that in the early days, prior to the cutoffs, travelers desiring to go north, or upstream from Greenville, could embark there, paddle downstream and portage north across Leland Neck, paddle downstream and portage north across Tarpley Neck, paddle downstream and portage north across Linwood Neck, paddle downstream and portage north across Ashbrook Neck and thus, by making four portages and paddling downstream all the way, find themselves 40 miles upstream. The cutoffs intensified channel stabilization problems, since they caused an increase in surface slope. The increased surface slope, due to the same fall in a stretch of river now only two-thirds its former length, produced violent changes in velocity, and upset the equilibrium of the river. The increased current velocities accelerated the erosion of unprotected banks but did not appreciably deepen the channel until assisted by dredging. This charnel rectification and deepening required extensive use of dredges and pump barges. At the same time, stabilization of the banks of the river was continued with various types of revetment, and some channel contraction was attempted with triangular frame retards and, to a very limited extent, with pile dikes.
|Appears in Collections:||Committee on Channel Stabilization|