Geology abandoned meander9/19/2023 Previous workers have discussed how the morphology and infill of abandoned channels in the geologic record allow for the reconstruction of flow parameters about ancient streams. Finally, the abandoned channel evolves from an oxbow lake into a riparian wetland, infills with peat, and is capped by organic-rich soils (histosols).Ībandoned channels have long been of interest. Over time, the interbedded flood deposits become less frequent and represent only the higher magnitude flooding events, because the abandoned channel becomes more spatially disconnected from the active channel. Farther away from this junction, the abandoned channel evolves through an initial lacustrine phase (oxbow lake) that is gradually infilled by lacustrine gyttjas interbedded with episodically deposited, flood-generated, suspension-load sediments. Sand accumulates at the junction between the abandoned channel and active channel, effectively plugging the mouth of the abandoned channel. The infill of an abandoned channel varies spatially. The channel substrates are overlain by finer-grained deposits (fine-grained sand, silt, mud, and peat) deposited after the oxbow has been disconnected from the active channel. These former fluvial channel deposits represent the channel substrates that existed at the time of channel cut-off and abandonment. The lowest portion of abandoned channel fills consists of coarse-grained sediment (gravel, coarse-grained sand, and shell fragments), deposited by bedload transport through the active channel prior to the cut-off event. The properties of such abandoned channels are the focus of this paper.Įach oxbow has a sedimentary infill history which can be observed in a vertical stratigraphic section (such as a sediment core or trench). The last three of these channel migration processes can produce oxbows or abandoned channels (this paper will use the terms synonymously). River channels can shift location through lateral channel migration (erosion at the cutbank and deposition on the point bar), through chute cut-offs (re-occupation of a former chute channel crossing the point bar, followed by abandonment of the previous channel), through neck cut-offs (intersection of meander loops, followed by abandonment of the previous channel) and through avulsion (levee breaching and crevasse splay evolution, followed by abandonment of the previous channel). Increasing channel mobility as the stream removes legacy sediment from These results indicate recent urban runoff created fluvial pavements and Historical coarsening-upward trend: the largest clast size interval ( f 5 ) changes from +0.78 f in pre-1935 channels, to - 1.15 f in pre-1940 channels, to - 1.69 f in the 2006 channel. Grain-size analysis of channel substrates shows a Provided by 14C geochronology and labels on food packaging materialsįound in flood layers. Trenches were used to recognize historical channel substrates. Probably formed in 1913, and the third formed in 1940. (DOQQ) image used as the basis for comparison. = 0.47 ± 0.20 m) when compared to the 2006 digital ortho quarter-quadrangle Historical aerial photographs and maps from 1935, 1940, 1950, 1963,ġ974, and 1994 were georeferenced using ground control points, input to ArcGIS,Īnd have root mean square error (RMSE) ranging from 0.19 - 0.77 m (average RMSE Run-off systems from streets, parking lots, housing developments, and shoppingĬenters. Human impacts in the watershed were: 1) land clearance forĪgriculture (peaking in 1900-1920) and for suburban housing tracts (peaking inġ945-1970), followed by 2) the post-1940 creation of more efficient urban Through the City of Toledo, Ohio (USA) to reconstruct historical changes inĬhannel substrate. Uses three naturally-occurring oxbows in a 3.5 km reach of Swan Creek, flowing Understanding of human-influenced changes in channel substrates. Efforts to restore urban rivers require an
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