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|Title:||Hydrographic and hydraulic investigation of Mississippi River revetments : field investigations|
|Authors:||United States. Mississippi River Commission.|
U.S. Army Engineer Waterways Experiment Station.
Reid Bedford Bend
|Publisher:||U.S. Army Engineer Waterways Experiment Station.|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Potamology investigations report ; no. 17-1.|
Summary: As part of the Potarnology Investigations program) hydrographic and hydraulic field investigations were undertaken in July 1946 for the purpose of obtaining and analyzing factual data obtained therefrom concerning various types of reaches with a view to isolating factors affecting revetment and bank stability. Three types of revetments were chosen for study : (a) a relatively new unstable revetment (Reid Bedford Bend, mile 425 AHP) where active caving had been observed and where failures were considered possible; (b) a relatively new stable revetment (False Point, mile 437 AHP) where no major changes in river regimen were expected; and (c) an old stable revetment (Bauxippi-Wyanoke, mile 725 AHP) where a major change in basic river conditions was anticipated. During the period July 1946 to June 1948 observations were made only at Reid Bedford Bend; observations were made at all three sites during the period July 1948 to May 1951. This report presents results of observations made at the three sites during the nearly three years of observations under the potamology program and also includes results of the 1953 annual low-water survey at Reid Bedford Bend. Results of observations made at Reid Bedford Bend through June 1948 are contained in Potamology Investigations Report No . 5-2, "Field Investigation of Reid Bedford Bend Revetment, Mississippi River," dated June 1948. No major revetment failures occurred at any of the three sites under observation during the period covered by these investigations, although major failures had occurred at Reid Bedford prior to that period. Therefore, no definite conclusion can be drawn from data obtained during this period as to the probable nature and causes of failures. However, results of the investigations did indicate certain trends and developments that may account for the absence of major failures. These results are summarized below: (A.) Reid Bedford Bend: Maximum velocities of about 10 ft per sec were measured at Reid Bedford Bend revetment during the period of observation. In general, falling stages produced considerable deposition of material along the revetment toe, while rising stages resulted in considerable scour along the toe. Although the banks at this site are considered to be susceptible to large flow slides, there were no major failures in the revetted area. Caving of the right bank along Racetrack Towhead upstream from the revetment caused increased attack on the upper end of the revetment, and failure of the upper-bank paving as well as flanking of the revetment occurred during a period of falling stages. Flanking also occurred at the downstream end of the revetted area, and the revetment was extended about 200 ft upstream and 600 ft downstream in September 1948. Minor failures also developed in the upper-bank asphalt paving at ranges 15+50, 52, and 65 during highwater periods. (B.) False Point: Maximum velocities of some 10 to 11 ft per sec were observed at the False Point revetment, but there was no evidence of any considerable scour or fill along the revetment toe except during and after the high water of early 1950. Soil conditions at False Point revetment are not believed to be conducive to large-scale flow failures of the type that occurred at Reid Bedford Bend. Minor failures and cracks in the upper-bank asphalt paving were observed on field inspection trips, but there were no major failures in the revetted area. Extensive damage did occur to the asphalt spurs at the upstream end of the revetment soon after their construction, and major repairs were made in December 1949. The continued migration eastward of the channel up stream along Browns Point and the resultant progressive shifting upstream of the point of flow impingement on the revetment probably prevented a prolonged attack along any portion of the revetted area. (C.) Bauxippi-Wyanoke. Velocities observed at Bauxippi-Wyanoke revetment on a 37-ft stage prior to closure of Tennessee Chute did not exceed about 9 ft per sec; velocities measured on a 37-ft stage after the chute was closed were as high as 13 ft per sec. For the over-all period of observation, fill deposited along each end of the revetment and scour occurred through the middle portion of the revetted area. Scour occurred along most of the revetment toe during the seven-month interval (extending through one high-water period) subsequent to closure of Tennessee Chute. In general, thalweg depths downstream from about the middle of the revetment tended to increase with increase in stage and to decrease as stages fell; this trend was reversed near the upstream end of the revetted area where depths increased with decrease in stage. Minor failures occurred after closure of Tennessee Chute in a local area of the old revetment which had not been reinforced, but there were no failures of a major nature. The possibility of a liquefaction failure in the banks at Bauxippi-Wyanoke was considered remote, principally because of the comparative thinness of the upper sand series and the stability of the bank slopes from the standpoint of shear failure. Also, the widening of the channel along the revetment by dredging along the opposite point bar may have been an important factor in the stability of the revetment. NOTE: This file is very large. Allow your browser several minutes to download the file.
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