HR: 0800h
AN: H31F-1359    [Abstracts]
TI: Investigating the Influence of Clay Mineralogy on Stream Bank Erodibility
AU: * Ambers, R K
EM: rambers@sbc.edu
AF: Sweet Briar College, Dept. of Environmental Studies, Sweet Briar, VA 24595 United States
AU: Stine, M B
EM: stine07@sbc.edu
AF: Sweet Briar College, Dept. of Environmental Studies, Sweet Briar, VA 24595 United States
AB: Soil scientists concerned with erosion of agricultural fields and geotechnical engineers concerned with the mechanical behavior of soils under different conditions have both examined the role of clay mineralogy in controlling soil/sediment properties. Fluvial geomorphologists studying stream channel erosion and stability have focused more on the effects of particle-size distribution, vegetation and rooting. The clay mineralogy of bed and bank sediment has the potential to influence cohesiveness and erodibility, however. The goal of this study is to determine the influence of clay mineralogy on the erodibility of natural stream bank sediment, utilizing techniques drawn from pedology and soil mechanics. Bank samples were collected from eleven sites in small watersheds in central and western Virginia. To obtain sediment containing a range of different clay minerals, watersheds with different types of bedrock were chosen for sampling. Rock types included mafic to felsic metamorphic and igneous rocks, shale, sandstone, and limestone. Where stream bank materials were clearly stratified, different layers were sampled separately. X-ray diffraction of the clay-fraction of the sediment indicates the presence of kaolinite, illite, vermiculite, and mixed-layer clay minerals in various abundances in the different samples. Clay content is 9-46%, as determined by the hydrometer method, and textures range from silty clay and silt loam to clay loam and sandy loam. Organic mater contents range from 1-5% by the loss-on-ignition method. Bulk density of intact sediment samples averages 1.5 g/cc. Liquid limits range from 23-41 with one sample having a value of 65; plasticity indices range from 15-22. While these tests predict that the samples would show a range of mechanical behaviors, the channel morphology at the sampling sites was not strikingly different, all having steep cut banks eroded primarily by scour with no evidence of mass movement and most having a width/depth ratio around 4.5. The ASTM pinhole test for identifying dispersive clay soils is being adapted to measure erodibility of intact and remolded sediment samples in the laboratory to look for more subtle differences in behavior under erosive conditions. Factors such as the extent and method of sample compaction are being taken into account in order to standardize the method.
DE: 1815 Erosion
DE: 1825 Geomorphology: fluvial (1625)
DE: 1856 River channels (0483, 0744)
DE: 1865 Soils (0486)
SC: Hydrology [H]
MN: Fall Meeting 2005