BACKWATER AT BRIDGES AND DENSELY WOODED FLOOD PLAINS, FLAGON BAYOU NEAR LIBUSE, LOUISIANA
by George J. Arcement, B.E. Colson, and C.O. MingNOTICE! Due to large file sizes, it is recommended that you right-click on the link for each sheet and select "Save Target As..." when trying to view atlases in order to save the MrSID file directly to your hard disk rather than trying to view it in your browser.
ATLAS HA-604
Prepared in cooperation with the Department of Transportation Federal Highway Administration and the Louisiana Department of Transportation and Development 1978
Atlas HA-604, Sheet 1
TABLE OF CONTENTS
Introduction
Hydrologic Investigations Atlas Number
Description of Data
Type of Data
High-water Marks
Bridge Geometry
Manning's Roughness Coefficient
Presentation of Data
Datum
Flood Frequency
International System of Units (SI)
Data for Flagon Bayou near Libuse, Louisiana
Flood of December 7, 1971
Summary
Additional Information
Selected References
FIGURES
1. Index map of study sites in the bridge backwater investigation project, Alabama, Louisiana, and Mississippi
2. Index map showing study reach, Flagon Bayou near Libuse, Louisiana
3. Aerial view looking upstream at bridge on State Highway 116 near Libuse, Louisiana
4. Frequency of Floods, Flagon Bayou near Libuse, Louisiana
TABLES
1. Valley cross-section data for Flagon Bayou near Libuse, Louisiana. Zero station is at the left edge of the valley (facing downstream)
2. Discharge measurement of December 6, 1971, Flagon Bayou near Libuse, Louisiana Louisiana. Zero station is at the edge of the left abutment (facing downstream).
Locations of representative ground elevations are shown. These are points of significant changes in cross- section elevations and alignment of the axis. Plots of cross sections are graphic presentations of the tabular data. Bridge geometry and road embankments are also shown as they existed at the time of the floods. Manning's roughness coefficient values and December 7, 1971, flood boundaries are shown.
Atlas HA-604, Sheet 2A
Atlas HA-604, Sheet 2B
Peak water-surface elevations and locations are shown for the flood of December 6, 1971. Velocity distributions and sounded cross sections obtained at the downstream side of the bridge during discharge measurement on December 7, 1971, are shown. Manning's roughness coefficient values and December 7, 1971, flood boundaries are shown.
Atlas HA-604, Sheet 3A
Atlas HA-604, Sheet 3B
ABSTRACT
New techniques for predicting water-surface profiles, needed in the design of economical, structurally sound, and environmentally compatible stream crossings, are under investigation. The investigation has accelerated with the advent of digital computers capable of analyzing large quantities of data. Among the techniques is the development of two-dimensional (2-D) digital models. Field data are essential for development and evaluation of these techniques for predicting water-surface profiles. This atlas is one of a series that provides a wide range of field data.
Since 1969, the U.S. Geological Survey has been collecting backwater data where wide, densely vege- tated flood plains are crossed by highway embankments and single-opening bridges. This work was done in cooperation with the Federal Highway Administration Department of Transportation, the Alabama State Highway Department, the Louisiana Department of Transportation and Development, and the Mississippi State Highway Department. The objective of this cooperative project is to present the data in a format conducive to the development of improved models for predicting hydraulic responses of flow at highway crossings of streams in complex hydrologic and geographic settings.
Backwater data were obtained at 22 sites for 35 floods; that is, 11 sites had 1 flood each; 9 sites, 2 floods each; and 2 sites, 3 floods each. Analysis of data showed that backwater and discharge at these sites com- puted by methods presently in use, would be inaccurate. The floodflow data are unique in the range and detail in which information was collected, and provide a base for evaluating digital models relating to open- channel flow. This atlas shows data obtained for the flood December 7, 1971, on Flagon Bayou near Libuse, Louisiana, one of the 22 sites. Data for this site are presented on three sheets covering a 2-kilometer reach crossed midway by State Highway 116.
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