Geology topics

B.A. Bryan

Publications and source records attributed to B.A. Bryan.

3 recordsLinked to original sources

USGS1995

Methods for assessing channel conditions related to scour-critical conditions at bridges in Tennessee

The ability to assess quickly the potential for scour at a bridge site, to evaluate those bridges with the greatest potential for significant amounts of scour, and to then identify scour-critical structures is important for public protection and bridge maintenance planning. A bridge-scour assessment information form was developed for collecting data describing the bridge site; the hydraulic geomorphic, and vegetation characteristics of the channel. Information from site assessments of 3,964 bridges in Tennessee was used to develop indexes of potential scour characteristics over broad geographic areas, such as counties, regions, or drainage basins. Channel instability charac- teristics differ from region to region. In west Tennessee counties, channel instability has progressed from valley bottoms into the uplands through headward degradation. In middle and east counties of Tennessee, channel widening is a dominant process, but widespread degradation has been prevented by stream beds being lines with erosion-resistant bedrock, boulder, cobble, and gravel, and by the absence of channelization. Neither quantifiable headcutting nor degradation in bedrock channels was noted at any site in the State. However, potential for lateral scour is prevalent in Middle and East Tennessee.

Water-Resources Investigations Report↗

USGS1989

Channel evolution of the Hatchie River near the U.S. Highway 51 crossing in Lauderdale and Tipton counties, West Tennessee

An investigation was conducted at the Hatchie River near the U.S. Highway 51 crossing in West Tennessee to (1) describe the channel cross-section evolution near the bridge crossing, (2) describe the evolution of velocity and discharge distributions near the bridge crossing, and (3) define streamflow duration and flood frequencies at the bridge site and compare these statistics with flows prior to the bridge collapse. The project was designed to document the collapse on April 1, 1989, of three spans of the bridge. Discharge measurements at the site available from the U.S. Army Corps of Engineers indicate that the channel was widening at a rate of 0.8 foot per year from 1931 through about 1975. The channel bed was stable at an average elevation of about 235 feet above sea level by 1975. Construction of a southbound bridge in 1974 and 1975 reduced the effective flow width of the channel from about 4,000 to about 1,000 feet. A flood during March 1975 scoured the channel bed lowering its elevation about 6 feet. Data collected by the U.S. Army Corps of Engineers from 1975 to 1981 indicate that the channel bed degraded to an elevation of about 230 feet and the widening rate increased to about 4.5 feet per year. The channel bed returned to approximately the pre-construction level of 235 feet as channel width increased. The widening rate decreased to about 1.8 feet per year based on U.S. Army Corps of Engineers data collected from 1981 through 1989. Channel geometry data indicates that recent channel morphology changes have occurred at the toe of the right bank, and have resulted in continued bank undercutting and ban failure. Cross-section geometry and flow-velocity distributions determined from U.S. Geological Survey discharge measurements made between April 6 and 10, 1989, indicate that there is a high-flow meander pattern through this river reach. The bridges are located at or near the apparent meander inflection.

Tennessee↗

USGS1984

Movement of tractive sediment from disturbed lands

The Smoky Creek basin of the coal area of northeastern Tennessee shows extensive evidence of tractive movement of coarse sediment from mined tributary basins into the main channel. Coal-rich gravel bars and flood-plain debris are common below tributaries. Using a combination of techniques including channel-geometry and bar measurements, sediment sampling for rock-debris and coal size distributions, and botanical dating of flood events and geomorphic features, an average annual yield of 65 metric tons per square kilometer (187 tons per square mile) for tractively moved sediment has been calculated for the period 1977 to 1982. This value, 8 percent of the total sediment load, is probably an underestimate owing to the method of calculation. Slightly more than half of the traction load is coal, which moves through the basin within a few years. Rock debris, however, appears to require years to decades to move similar distances.

Tennessee↗