The 9-Foot Channel After World War II
The Corps of Engineers constructed the majority of the 9-foot channel structures along the Upper Mississippi River between 1930 and 1940. However, several locks and dams were not constructed until after World War II. While these later structures cannot, technically, be considered part of the original 9-Foot Channel Project, their design and construction reflect the continuing evolution of river engineering and navigation on the Upper Mississippi.
After 1940, only a single impediment prevented the maintenance of a dependable and reliable 9-foot channel extending from New Orleans to St. Paul, and up the Ohio to Pittsburgh. Known as the Chain of Rocks Reach, this obstruction was a 17-mile series of rock ledges that began just north of St. Louis. In two locations, these ledges extended completely across the channel. The ledges acted as submerged dams, causing a sharp increase in the slope of the river. This, in turn, increased the velocity of the current, making the Chain of Rocks extremely difficult and dangerous to navigate. At extreme low water, the navigable depth of this stretch of the Upper Mississippi River was often reduced to as little as 5.5 feet, preventing full use of the 9-foot channel that was available above and below the Chain of Rocks Reach. 
Proposals to construct a canal to bypass the Chain of Rocks Reach originated as early as 1904, all without result. It was not until October 1938 that Congress requested the Chief of Engineers to recommend a plan for the improvement of the Chain of Rocks Reach. In its final report, submitted in December 1938 and printed as House Document No. 231, the Corps of Engineers recommended construction of a bypass canal at the Chain of Rocks. Congress authorized the project in 1939 but, because of the imminence of war, President Franklin D. Roosevelt vetoed the bill. Congress reapproved the project in March 1945, and the President signed the bill into law. The Upper Mississippi Valley Division, regaining some of the authority it had lost during the rush to turn the 9-Foot Channel Project into a public works program, designed the canal and the twin locks located near its lower end. St. Louis District Engineer Colonel Rudolph E. Smyser, Jr., oversaw the construction. 
Lock No. 27 and the Chain of Rocks Canal constituted the first major addition to the original 9-Foot Channel Project, and the final element required to secure a navigable 9-foot channel between St. Paul and New Orleans. As designed by the Corps of Engineers, the canal measures 550 feet wide at the top, 300 feet wide at the bottom, and has an average depth of 32 feet. The twins locks are located at the southern end of the 8.4-mile Chain of Rocks Canal.
The Corps of Engineers constructed the lock installation between 1947 and 1953. The main lock measures 110 by 1,200 feet, and the auxiliary lock is 110 by 600 feet. The lock walls are as much as 92 feet tall, and are of monolithic reinforced concrete construction founded on bedrock. To flood and empty the lock chambers, Corps engineers located longitudinal culverts in the base of the lock walls. However, unlike the earlier installations, where the culvert intakes were located in the lock walls, the intake ports of the new locks are located in the floor immediately above the upper gates. The Corps also redesigned the arrangement of the discharge ports. Instead of placing large ports in the lock walls below the lower gates, the engineers designed the new locks to include a complex discharge manifold that releases water through the floor of the lock structure below the lower gates. The manifold greatly reduces the turbulence associated with the water emptying from the lock chamber. 
The Corps equipped the locks with electrically-operated miter gates, balanced on steel pintles, similar to those on the locks constructed in the 1930s. The gates are extremely large, each leaf of the main lock gate measuring 61 feet across, 72 feet tall, and weighing 170 tons. The auxiliary lock gates are 43 feet tall and weigh 140 tons per leaf.
The upper gates depart from previous practice on the Upper Mississippi. The Corps located the locks at the end of the Chain of Rock Canal, requiring ice to pass through the lock chamber during the winter. Miter gates cannot operate against an appreciable head of water, as required under these circumstances, so Corps engineers designed double-leaf, vertical-lift upper gates. When the lock is empty and the lower miter gates are fully opened, the downstream leaf of the lift gate may be lowered, much like a double-hung window, until it nests behind the upstream leaf. Ice can then pass freely through the lock chamber. 
In its design of the locks, the Corps made several other departures from earlier practice. Instead of the single, central, control station used at earlier 9-foot channel sites, Corps engineers designed No. 27 with six separate control stations. The Corps located these stations at both ends of the east and intermediate lock walls, the upper end of the west wall, and the mid-point of the intermediate wall. Emergency bulkheads, placed by stiffleg derricks, are provided to close off the upper gate bays of the locks for repairs. Dewatering pumps, located within the lock walls, are then used to completely empty the lock chambers. 
The Corps constructed Dam No. 27, also known as the Chain of Rocks Dam, to provide additional water in the pool below Lock and Dam No. 26. Congress authorized the construction of Dam No. 27 in 1958. In 1964, the Corps completed the dam, which assures a minimum depth of 10.5 feet of water over the lower gate sills at Lock No. 26. Designed and constructed by the St. Louis District, the fixed-crest rock dam is 3,240 feet long, and constitutes the first, complete, non-navigable barrier across the Mississippi. 
Congress authorized Lock No. 19 as part of the original 9-Foot Channel Project legislation. However, because of design changes, the project required new congressional approval in 1952 and was not completed until 1957. Lock No. 19 is located at the site of the Keokuk and Hamilton Water Power Plant near Keokuk, Iowa. The Keokuk and Hamilton Water Power Company, now the Union Electric Power Company, constructed the power plant between 1910 and 1914, and the installation included a lock and dam. Although the Corps incorporated the existing lock and dam into the 9-foot channel system, it was also authorized to build a new lock at the site.
Corps engineers began planning for the new lock in 1930, but encountered serious problems concerning where to locate it without interfering with the operation of either the powerplant or the dry dock. The Corps finalized the lock's location in 1937, by which time all the structures in the Rock Island District were already either completed or under construction. At this point, however, Corps engineers began to tinker with the design of Lock No. 19. Because of the 40-foot lift at Keokuk, the engineers considered deviating from the standard 110 by 600 foot design.
In 1945, however, even before specifications and model studies had been completed for the proposed lock, the Rock Island District recommended that Lock No. 19 be expanded to a length of 1,200 feet. The larger size would allow the new, longer tows to pass through the lock in one piece, rather than being broken up into lockable pieces, as was becoming routine at the other locks in the 9-foot channel system. In 1952, Congress authorized the Corps to build the lock at this enlarged size.
In the design of Lock No. 19, the Corps of Engineers utilized much of the technology developed in the 9-Foot Channel Project of 1930-1940. However, the Corps also incorporated newer technologies that had developed in the 10 years since the completion of the original system. Other than the larger size, the most important difference is found in the gate design. The upper gates of Lock No. 19 are single leaf, hydraulically-operated gates, and in no way resemble the lock gates built as part of the original project. There are two gates and either one functions to hold back the upper pool, although the innermost gate is considered to be the main gate. Corps engineers designed the lower gates in a more standard fashion, but used a modern form of steel framing based on solid "L" irons. Another unique feature of Lock No. 19 is its system of underground tunnels that run under the walls and chamber of the lock. These tunnels provide ready access to the electric cables that they house, as well as being a means to get to the other side of the lock chamber. 
The most recent alteration to the Upper Mississippi River 9-foot channel system occurred in 1990, when the Corps of Engineers replaced the original Lock and Dam No. 26 with Lock and Dam No. 26R, also known as the Melvin Price Lock and Dam. The administrative and political history of Lock and Dam No. 26R, located just downstream from the original installation, is reminiscent of the controversy that surrounded the 9-Foot Channel Project of the 1930s. The Government authorized Lock and Dam No. 26R in 1969, and the St. Louis District began planning the new installation in 1970. In September 1974, however, the Sierra Club, the Izaak Walton League, and the Western Railroad Association filed lawsuits to halt work on the project. The lawsuits charged that the environmental analysis of the project was inadequate and that the Congressional authorization, under the Rivers and Harbors Act of 1909, applied only to maintenance work. 
The environmentalists feared that the new facility represented an effort to promote a 12-foot channel on the Upper Mississippi River. In fact, the design of Lock and Dam No. 26R met the construction requirements for a 12-foot channel as outlined in a 1972 Upper Mississippi River Comprehensive Basin Study. But that same study had also declared a 12-foot channel economically infeasible above the mouth of the Illinois River. Echoing the concerns of the 1930s, railroad officials opposed Lock and Dam No. 26R because they believed a government-owned, river improvement was unfair competition. 
The draft supplemental environmental impact statement for Lock and Dam No. 26R was issued in June 1975. In February 1976, the Board of Engineers for Rivers and Harbors, at the request of the Chief of Engineers, recommended construction of the new lock and dam. This recommendation was forwarded to Congress in July 1976, and signed into law by President James Carter in October 1978. The Corps began constructing Lock and Dam No. 26R in 1980; work on the project was estimated to cost approximately $900 million. 
The Corps of Engineers designed Lock and Dam No. 26R to include all the basic elements of the first 9-foot channel installations. The biggest difference is the enormous scale of the project. The Tainter gates, vertical lift gates, and other components at the new installation dwarf those of the earlier complexes. Still, despite the size difference, the movable dam, navigation lock, and submersible dikes connecting the structure to shore are all readily identifiable, The construction process also closely resembled the construction of the 9-Foot Channel Project of the 1930s.
The main lock measures 1,200 by 110 feet, and is a U-shaped "megastructure" supported on steel H-piles up to 81 feet long. The piles are not driven vertically into the riverbed, but are battered at angles to form a web-like foundation. This design is a significant departure from the traditional lock design of independent, isolated, gravity side walls with a base slab between them. It provides a more fully integrated structure that is less susceptible to movement over time and, ultimately, more cost efficient. The base slab of Lock No. 26R is 20 feet thick at each end, tapering to 15 feet in the middle. The side walls, 40 feet thick at their bases, rise more than 60 feet above the base slab. As with Lock No. 27, Corps engineers fitted the new structure with downstream miter gates and upstream vertical lift gates, although the latter have three leaves rather than the two at Lock No. 27. 
The Corps of Engineers conducted an extensive program of measurement, observation, and computer testing at Lock No. 26R. A host of monitors, sensors, lasers, and computers measured and analyzed virtually every aspect of the project's design and construction. This work resulted in the refinement of a host of details, including the design and construction of cofferdams, the mixing and distribution of concrete, and the placement of guidewalls. Engineers analyzed each section of the structure in terms of as many as 30 different combinations of loads. Staff members at the Corps' waterway experiment station at Vicksburg, Mississippi, conducted research on concrete creep and shrinkage, projected over the life of the structure, and determined that these conditions may impose greater force and stress upon the structure than other loads. Perhaps the most widely applicable benefit to emerge from the testing program was the discovery that the steel sheet piling used to construct cofferdams did not have to be driven into the riverbed as deeply as previously thought. Driving the piling to a shallower depth significantly reduced costs, and increased the amount of piling that could be reused upon the removal of the cofferdam. 
The Corps also constructed the lock guidewalls at Lock No. 26R in a non-traditional manner. Construction crews built the 1,500-foot upstream and 855-foot downstream guidewalls "in the wet," rather than following the usual method of erecting a cofferdam and working "in the dry." For the downstream wall, Corps workers drove a series of sheet pile cells into the river bottom. H-beam piles were driven through the center of each cell to increase its stability. Workers then placed tremied concrete, a form of concrete capable of being placed underwater, into each cell, providing a foundation for a series of precast concrete beams, each weighing 225 tons, that were stacked atop the cells by a massive heavy-lift cantilever crane riding on a runway girder. 
In 1937, Congress authorized a 4.6 mile extension of the 9-foot channel at its upstream end and 2 additional complexes were built in Minneapolis: the Lower St. Anthony Falls Lock and Dam, and the Upper St. Anthony Falls Lock and Dam. The Corps built these two structures, respectively, in 1956 and 1963. The construction of these complexes, also known as the Upper Minneapolis Harbor Development, extended the 9-foot channel over the St. Anthony Falls. Below the St. Anthony Falls, the narrow gorge of the Upper Mississippi River only allowed for a relatively small river terminal. By extending the 9-foot channel, the Upper Minneapolis Harbor Development project permitted the construction of larger and more suitable river terminal sites above the falls.
St. Anthony Falls has a fall of 74 feet, and had historically been used to furnish waterpower for sawmills and flour mills in the area. In order to ascend the falls, the Corps of Engineers needed a 25-foot lift at the lower lock, and a 49.2-foot lift at the upper lock. The Lower St. Anthony Falls Lock and Dam project also replaced the original Northern States Power Company Dam, which had been built in 1897. Corps engineers equipped the new dam with Tainter gates, 19 feet high and 56 feet long. The lock measures 56 by 400 feet, and has a lift of 25 feet.
The Upper St. Anthony Falls Lock and Dam complex includes a fixed concrete dam. The dam was built in 1951, when an existing timber dam was destroyed by flood. The timber dam had been constructed in the 1870s in an effort to protect the St. Anthony Falls from upstream progression. Since the concrete dam was in place, the Corps of Engineers only needed to construct a navigation lock. But, with a rise of 49.2 feet, the lock was the highest lift on the river and an engineering challenge that cost over $18 million to build. Like the lower lock, the Upper St. Anthony Falls lock measures 56 by 400 feet. 
3. Smyser, "Chain of Rocks Project," 16; and Mississippi River Lock & Dam No. 27, LocksGeneral PlanElevations and Sections, Drawing No. M-L 27 20/2 (April 1947), Intake and Upper SillMain Lock, Drawing No. M-L 27 20/51 (April 1947), and Discharge ManifoldBoth Locks, Drawing No. M-L 27 20/54 (April 1947).
4. Smyser, "Chain of Rocks Project," 17; "Biggest Lock on the Mississippi," Engineering News-Record, 145 (October 5, 1950): 30; and Mississippi River Lock & Dam No. 27, LocksLift Gate MachineryGeneral Arrangement, Drawing No. M-L 27 22/51 (April 1947).
5. Mississippi River Lock & Dam No. 27, LocksBuildingsKey Plan, Drawing No. M-L 27 70/0 (April 1947); Unwatering & Drainage EquipmentGeneral Arrangement, Drawing No. M-L 27 36/1 (April 1947); and Lock Bulkhead Handling EquipmentGeneral Arrangement, Stiffleg Derrick, Hoist & Pickup, Drawing No. M-L 27 35/1 (April 1947).
8. Ibid., 150-152; Colonel Thorwald R. Peterson, "Replacement for Locks and Dam No. 26," The Military Engineer, 66 (1974): 287; and Carol Koch, "Old 26An Economic Bottleneck," Soybean Digest, 37 (December 1976): 6.
12. Soast, "Navigation Lock," 38-40; "Barge Bottleneck Uncorked," Civil Engineering (January 1987); and "Girder-Mounted Crane Cuts Guidewall Costs," Highway and Heavy Construction, 130 (January 1988): 52-55.
14. Martin Nelson, "The St. Anthony Falls Upper Harbor Project," copy in the files of the St. Paul District Office, U.S. Army Corps of Engineers; Francis E. Mullen, "St. Anthony Falls Navigation Project," Journal of the Construction Division, Proceedings of the American Society of Civil Engineers, March 1963; and Jon Gjerde, "St. Paul Locks and Dams."
Last Updated: 01-Feb-2008