Collection and application of outcrop measurements in glacial materials for geo-engineering and hydrogeology along the Vermilion River, east-central Illinois

Outcrop mapping by close-range photogrammetry was undertaken at three remote sites as part of a study of water resources to improve characterization of glacial sedimentary assemblages and to evaluate the utility of terrestrial remote sensing to supplement routine geologic mapping. Two features were measured from georeferenced stereomodels, clast pavements, and buried channel deposits over a 2-year period along a segment of the Middle Fork of the Vermilion River. Cobble-size clasts, spaced less than 3.28 ft (1 m) apart, form clusters approximately 6.56 to 9.84 ft (2 to 3 m) in length. These clasts compose a semi-continuous pavement between two tills deposited during the Wisconsin Episode. Five of the 26 clusters measured occur within the Tiskilwa Formation. Deposits of coarse- and finegrained sediments, informally assigned to the Glasford Formation lithostratigraphic unit, fill buried channels that provide an important source of groundwater in east-central Illinois for areas that do not receive water from the Mahomet aquifer. Measurements of buried channels included width, maximum sediment thickness, area, and perimeter. Widths equated to more than half of the outcrop length. Aspect ratios (width:thickness) of the channels are consistent with deltaic distributary systems formed in front of retreating ice margins, and systems having varying interconnectivity. Differences in area:perimeter of the buried channels provide a measure of shape that may partially account for the variation in yields from water wells in this area. Consequently, we postulate that yield could be improved through lateral drilling within the channel or by connecting adjacent channels.