Water Movement in Till of East‐Central South Dakota

Abstract

ABSTRACT Results from the first phase of a study on water movement within the till of east‐central South Dakota indicate that little to no water passes from the weathered till through the underlying unweathered till into underlying outwash deposits. Based on hydrographic analyses, field hydraulic conductivity measurements, and major‐ion sampling at 22 study sites, discharge from the weathered till is hypothesized to be primarily from evapotranspirative losses during periods of high water table. Hydraulic conductivity of the unweathered till is typically 10 to 200 times lower than the weathered till. Water sampled from the unweathered till is up to three times higher in major‐ion concentrations than water in underlying outwash deposits. Carbon‐age dates of water from the buried outwash deposits suggest an age in excess of 9,000 years before the present, corresponding to the Late Wisconsinan glacial epoch.