IMPACTS OF LAND USE AND CHANNEL MORPHOLOGY ON HYDROLOGIC REGIME AS INFERRED FROM FIELD/GIS MAPPING AND HYDROLOGIC MODELING

Many streams in the eastern US have been profoundly transformed, both in morphology and hydrologic regime since European settlement. An understanding of the impacts of land use and channel morphology on hydrologic regime is critical to stream and floodplain management, which has become increasingly important because of widespread stream instability. This project establishes the linkage between runoff and channel changes by quantitatively evaluating the effects of changing land use and stream incision on hydrologic regime in Southwest Ohio. Using field-based and GIS/LiDAR data mapping and HEC-HMS and HEC-RAS hydrologic models, we assessed the impact of historic climate and land use change on stream hydrology and channel hydraulics. The ages of the historic fill terrace deposits were determined using dendrochronology of buried logs and stumps, radiocarbon dating of wood pieces, and amino acid racemization of gastropod shells. Mapping results indicate that Bull Run, Darrs Run and Four Mile Creek have incised about 6m during historic times. Valley fills record channel filling in response to deforestation of southwest Ohio ca. 1800-1850, subsequest channel incision, and incision below the pre-agricultural channel bed into glacial deposits after ca. 1960, presumably as a result of declining soil erosion rates resulting from improved land management. This project demonstrates the use of LiDAR elevation data model to map modern channel and historic terraces with great accuracy and coverage as well as the applicability of an inexpensive and widely applied amino acid racemization dating technique to reconstruct stream alluvial histories. These tools can help stream managers incorporate essential historic contextual information more easily in their decision-making.