ELECTROMAGNETIC INDUCTION FOR POINT BAR ANALYSIS ALONG THE GREAT MIAMI RIVER AT HERITAGE PARK, COLERAIN TOWNSHIP, HAMILTON COUNTY, OHIO

The Great Miami River runs alongside Heritage Park in Colerain Township, Hamilton County, Ohio. According to FEMA, this area is classified as a high-risk flood zone, with historically significant floods in 1913 and 1959. Major floods can change the river’s flow path, altering point bars and compound bars. For this project, we sought to analyze the stratigraphy of a point bar along the river using electromagnetic induction (EMI). This technique allows for the imaging of the EMI properties of the point bar sediments, enabling a better understanding of point bar development and sediment distribution. Spatial variability of sediment types within a point bar is crucial to understand, as it can be used to evaluate the interactions between groundwater and surface water and, ultimately, how river systems transport contaminants.

Data were collected along 18 transects using a DUALEM-412, which has three pairs of dual-geometry sensors located at 1, 2, and 4 meters along its length. This allows for the electromagnetic imaging of six depths of investigation whose thickness is dependent on the sediment matrix being surveyed. The survey was done by walking E-W transects along the bar's long axis, spaced 5m apart. N-S crosslines were done with 20m spacing. Three Wenner array resistivity surveys with 1, 3, and 5 m a spacing were collected to help with data inversion. Raw data were trimmed to remove outliers, processed and inverted in Resipy. Modeling results were contoured using kriging in Surfer.

We interpret that the current point bar overlays sediment from an older channel of the Great Miami River. At the survey site, larger, well-established cobbles were cut by a swath of fine-grained sediment, most prominently along the northern part of the point bar. Lower conductivity readings at the larger cobbles, coupled with higher conductivities within the finer sediments, point to a recent filling of a former smaller channel. Looking forward, a survey with closer passes could be conducted to create a more accurate inversion of the dataset. Also, other programs, such as EMagPy, could be used to process both surveys to verify the results obtained.