Beyond Control by James F. Barnett Jr

Author:James F. Barnett Jr.
Language: eng
Format: epub
Publisher: University Press of Mississippi
Published: 2017-06-15T00:00:00+00:00

CHAPTER 8

Preparing for Uncertainty

Good luck plus General Noble’s bold activation of the Morganza Floodway prevented the Kazmann, Johnson, and Harris scenario from becoming a reality. Coming more than forty years after the 1927 flood, the flood of 1973 showed a new generation of Americans what the Mississippi River is capable of doing. As the high water receded, Noble called for the construction of a new control structure at Old River, but he noted that the 1973 flood revealed changes in the Mississippi’s channel from the time the low sill came into operation. This meant that hydraulic testing at the site and with models at the Corps’ Waterways Experiment Station at Vicksburg would have to precede any new installation. In the meantime, the low sill needed extensive repairs.1

With no other options available, the low sill had to continue operating at full capacity while the engineers did their best to patch the wounded edifice. Corps engineers knew that scouring had occurred in both the fore bay and tail bay but were unsure about the extent of the damage underneath the structure. To find out, they drilled a hole down through the low sill and lowered a television camera into the depths. The camera showed that the floodwaters had washed away the earth beneath the structure, exposing the pilings. When General Noble looked at the television monitor, he saw fish swimming around instead of solid ground and concrete.2

While the new wing wall was taking shape, flotillas of barges loaded with riprap arrived to fill the fore- and tail bay holes. This approach might offset the damages on either side of the low sill, but there was no practical way to place the riprap boulders into the cavity the river had hollowed out underneath the structure. The best solution for repair beneath the low sill was to inject grout, a mortar compound treated to solidify in water, into the void around the pilings. According to Perry Gustin, the Corps experimented with grout mixed with shavings of fiberglass and metal and decided to use the mixture containing metal.3

While the underwater work progressed, crews assessed the wear and tear on the overbank structure and the low sill’s upper works. During periods of seasonal low water, the Corps modified the low sill’s gates to allow better control of flow through the structure. The addition of a second hundred-ton gantry crane added versatility that was lacking in the 1973 emergency and facilitated the work on the gates. The low sill’s original design included piezometers placed at critical points to measure water pressure on the structure. The engineers replaced the old sensors with new instruments during the post-1973 overhaul.4

Despite a decade’s worth of repairs, the low sill’s foundation remained permanently damaged. The Corps cautiously raised the head differential that the structure could safely handle from eighteen feet right after the flood to a modest twenty-two feet, well below the low sill’s original design head differential of thirty-seven feet. The engineers agreed that the reduced capability would suffice for operations

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