PALEOFLOOD RECONSTRUCTION EFFORTS ALONG THE MIDDLE TENNESSEE RIVER VALLEY, USA

Paleohydrological investigation along the middle Tennessee River, near Huntsville, AL shows that soil and sediment stored in alluvial terraces reflect flood frequency and magnitude in the past ca. 1500 years. A combined stratigraphic, sedimentologic and geochronologic assessment of three alluvial profiles and optically stimulated luminescence dating (OSL) of quartz grains and micromorphology focused on sequences inferred to be flood deposits. Buried soils at three locations are > 630 CE and suggest a multi-century period of landscape stability. Multiple flood deposits occur subsequently separated by weakly developed soils, indicating an increased flood frequency until ca. 1910 CE. The OSL dating of flood deposits yielded ages of 580+/-110, 835+/-80, 1665+/-35, 1660+/- 30, 1875+/-10 and 1910+/-10 CE. Age-depth modeling shows increased sediment accumulation rates following ca. 1800 CE. Particle size analysis of historic floods demonstrates a relative increase in fine sand (RFS) content and poorer grain sorting with increasing flood magnitude, which is consistent with a priori analysis upstream. The highest RFS with poorest sorting coincides with a flood ca. 1660 CE flood. The second highest RFS with poor sorting appears at 1875 +/-10 CE, which appears coincident with a historic flood of the Tennessee River, 1867 CE. The high magnitude flood of 1660+/- 30 CE is consistent with USGS paleoflood analysis upstream that documents a paleoflood occurring ~1600 CE that was higher in elevation than the historic flood of record. The earliest observed flood deposits appear to occur during transition into the Medieval Climate Anomaly between 800 and 1300 CE with increased flood magnitude through the Little Ice Age (1400-1800 CE), and with peak magnitude occurring 1660+/-30 CE. This study demonstrates that stratigraphy, sedimentology and geochronology of flood deposits within floodplains and terraces are important archives to estimate paleoflood frequency and relative magnitude.