Thursday, August 18, 2011

Dredging helps restore Mississippi River channel

Dredge Potter
The St.Louis District is authorized to maintain a minimum 9-foot deep, 300-foot wide navigation channel on 300 miles of the Mississippi River from Saverton, Mo. to Cairo, Ill., the lower 80 miles of the Illinois River and on the lower 36 miles of the Kaskaskia River.

This mission is accomplished in several ways. The channel patrol boat, MV Pathfinder, identifies possible dredging locations by performing channel reconnaissance surveys. MV Pathfinder also assists the Coast Guard with buoy positioning on the navigable waterways within the St. Louis District boundaries.

Another method used by our Engineering Hydraulics Branch is designing and building structures in the river, such as dikes and revetments that maintain sufficient depths in the waterway. Locks and dams also play a vital role in maintaining navigation on the upper Mississippi River.

Water management and dredging round out the tools used to maintain the channel.

Dredging in the St. Louis District is accomplished by using hydraulic pipeline dredges, -- Dredge Potter and Dredge America. A hydraulic dredge mixes large quantities of water with the excavated material (almost always sand in the St. Louis District) to create a slurry which is then pumped out of the navigable channel.

Dredge Potter is a dustpan dredge, a type of dredge specifically designed by the Army Corps of Engineers for work on the Mississippi River. The dustpan is very efficient in excavating sand material from the river bottom.

Dredge America is a cutterhead dredge operated by a contractor. This type of dredge is used to excavate hard material and pump it a long distance.

Dredging is coordinated with other agencies so that our operations are done with as little disruption as possible and in an environmentally sensitive manner.

The combined waters of the Missouri and Mississippi Rivers typically assure adequate depths for navigation, except for periods of prolonged drought. Still, much effort is needed to facilitate navigation in the open river, usually in the form of maintenance dredging and regulating works. Maintenance dredging operations involve the repetitive removal of naturally deposited sediment from the navigation channel.

The St. Louis District Applied River Engineering Center uses table-top “micro-models” to develop innovative solutions to various sedimentation problems. More often than not, these solutions are found in what we call “regulating works”. Regulating works are structural designs, such as chevron dikes, bendway weirs, off-bankline revetments, and notched dikes. By necessity, our river engineers seeks to implement structural designs that work in harmony with the natural laws of the river to solve problems involving sedimentation, erosion and biological diversity, all while providing a safe and dependable navigation channel.

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