Quantification of Postsettlement Deposition in a Northwestern Illinois Sediment Basin

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Abstract
The purpose of this study was to quantify the postsettlement deposition in a 24 900‐m2 (2.49‐ha) sediment basin with a single outlet in a 105 400‐m2 (10.54‐ha) watershed and estimate the sediment delivery to a first‐order stream in northwestern Illinois. Methods included direct measurements of the eroded sediment deposited in the sediment basin. Buried A horizons (dated using fly ash as a time marker) identify the presettlement (≈1854) surface, which was overlain by as much as 116 cm of sediment. Volume of the sediment within the basin was calculated at 11 394 m3 with a weight of 16 480 Mg. The modern soils of the sediment basin were characterized, classified, and the spatial variability of the sedimentation process was examined. Based on representative measurements of postsettlement sediment delivery obtained from research of drainage basins having similar size or soil characteristics, it was inferred that 20 975 Mg of sediment was delivered to the stream with a total of 37 455 Mg of soil being removed from the watershed hillslopes as a result of accelerated soil erosion. The measured rate of postsettlement sediment accumulation has been approximately 0.34 cm yr−1. Based on the tightly packed deposits, redeposition probably occurred as overland flow during storm events, rather than as overland flow occurring after a rainfall or as rain‐splash transport. However, machinery traffic and cultivation could have contributed to the high soil bulk density. Intensive cultivation, biotic activity, and freeze‐thaw are probably responsible for destroying any evidence of stratification.
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Funding Information
  • U.S. Department of Agriculture

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