OXBOW LAKES AS GEOLOGICAL ARCHIVES OF HISTORICAL CHANGES IN CHANNEL SUBSTRATE, SWAN CREEK, TOLEDO, OHIO (U.S.A.)

Urbanization significantly impacts hydrologic systems, including changes in flood magnitude and frequency, sediment input and channel storage, and channel morphology. As attempts are made to restore urban rivers, a complication is understanding human-caused changes in channel substrates. This study looks at the sedimentary record in oxbow lakes as an archive of historical changes in channel substrates. The study area is a focused on approximately 3.5 km reach of Swan Creek (a tributary of the Maumee River in NW Ohio) that contains 4 oxbow lakes of various ages and in-fill histories. The study area has changed over historical times from swamp forest to agricultural fields to suburban housing tracts and light industry. Photographs from 1963 and 2005 and topographic maps from 1935, 1951, 1964, and 1994 were collected from the USGS. These were georeferenced using ground control points, input into ArcGIS, and the RMS error was calculated to be 5.7 meters when comparing each historical image to the 1994 image acquired from the USGS and used as a base map. It was determined that one of the oxbows formed during a channel avulsion event in 1963, based on both the historical aerial photos and historical flood records. Trenches in this oxbow show the pre-1963 channel consisted of coarse-grained sand and fine pebbles. The sediment fill also contained anthropogenic materials, which may be used to date stratigraphic layers. The other 3 oxbows represent channel switching events older than the available historical aerial photos and topographic maps (pre-1930s), which indicate they formed before this period, possibly from the historic 500-year flood of 1913. The channel substrates in these oxbows are appreciable finer-grained (fine- to medium-grained sand). In contrast, the modern channel contains coarse gravel, some of it anthropogenic materials (bricks, etc.), shell debris, and significant submerged wood loads. Trenches were dug near the pre-1963 oxbow and a large pre-1930 oxbow. Depth extended to the water table, which ranged from 2-3m. On-going work will include calculating changes in channel path length and sinuosity resulting from avulsions and cut-offs, match each avulsion to historical flood data, characterize the sedimentary record of each in-filled oxbow sequence, and relate these changes to historical changes in land-use.