Mapping Sediment Thickness Using Airborne Electromagnetics

An airborne electromagnetic (AEM) survey was conducted to support a feasibility study for the placement of a riverbank filtration system. The goal of the survey was to map sediment thickness along a narrow corridor centered on the Missouri River in North Dakota. This case history presents the results of that survey. A total of 1,184 line km of data were acquired along a 116 km stretch of the Missouri River using the SkyTEM 301 time domain electromagnetic system. This system, using a combination of early time (approximately 5 microseconds for the first time gate) and spatially dense data, successfully mapped the alluvial sediment - bedrock contact. Using a spatially constrained inversion in conjunction with borehole data, the AEM data reveal a paleochannel where sediment thicknesses exceed 75 meters. Six locations were identified for future investigation based on interpreted alluvial sediment thickness, sediment resistivities, and location.