Summer 2023 - Flipbook - Page 24
Eads’ South Pass Navigation Works
Tonja Koob Marking, Ph.D., P.E., D.WRE, F.ASCE
History &
Heritage
Spotlight
About 18 miles below Ft. Jackson, in Plaquemines
Parish, Louisiana, at Head of Passes, the
Mississippi River branches into Southwest Pass,
South Pass and Pass A L’Outre before emptying
into the Gulf of Mexico. As early as 1723, French
colonists found navigation difficult and looked for
ways to deepen the passes. The problem
continued well into Louisiana's statehood.
In the Rivers and Harbors Act of 1875, Congress
authorized James Buchanan Eads of St. Louis,
Missouri “to open a wide and permanent deep
channel between the Mississippi River and the Gulf
of Mexico through South Pass.” He was “not simply
to secure the wide and deep channel … but likewise to provide for the construction of thoroughly
substantial and permanent works, by which the said
channel may be maintained for some time after its
completion.”
Construction began on June 14, 1875, with provisional works for the East Jetty the first to take shape. By June
26, Eads had extended the work 1,000 feet from land’s end and was advancing at the rate of 200 feet per day.
The channel first secured a depth of 20 feet and a width of 200 feet in December 1876. To build up a jetty wall,
Eads used woven willow “mattresses” piled on top of each other and held down with riprap. Sand and mud
gradually filled crevices between the logs and mattresses, forming a semi-permanent dike. For the last step,
Eads placed concrete slabs atop the jetties, completed in December 1878.
By June 1879, it reached a depth of over 26 feet, and less than a month later, it achieved a record depth of 30
feet. Eads maintained that depth with a minimum of failures for twenty years, until the contract with the federal
government naturally terminated.
In creating a deep-draft navigation channel through
shallow and shoaled South Pass (it had an average
depth of 8 feet over the bar before Eads’ jetties), Eads
proved beyond doubt and over concerted opposition
that the construction of parallel jetties and ancillary
structures at the mouth of an alluvial river would serve
to scour a navigable deepwater channel. Although
comparative numbers are not available, it appears that
Eads’ jetties were the longest on record at the time of
their construction: the east jetty was 11,700 feet and
the west jetty was 10,125 feet by 1877.
Eads constructed a system of ancillary structures
designed to improve scour action and create a
navigable channel. At the head of South Pass he built
a T-dam and made use of multiple wing dikes perpendicular to the flow to force the current into a narrower
cross-section, thus inducing more channel scour. He also placed sill dams across Pass A’Loutre and
www.asce.org/ewri • EWRI Currents • Volume 25 Number 1 • Winter 2023