Characterizing Streamflow Intermittency and Subsurface Heterogeneity in the Middle Arkansas River Basin

Abstract

Non-perennial streams are widespread but understudied relative to their perennial counterparts. In this study, we investigated the flow and intermittency regimes for the Arkansas River near Larned using historical streamflow, groundwater level, and climate data. We found that the river shifted between a dry regime (characterized by no flow apart from rapid responses to precipitation events) and wet regime (with near-continuous flow) several times over the past two decades. Wet and dry regimes were associated with wetter and drier than average climate conditions at the annual time scale but were not as responsive to seasonal (three-month) climate conditions. The alluvial aquifer exhibits a rapid, flashy response to precipitation, but longer-term (annual) climate appears to sustain groundwater levels in the alluvial aquifer, with wet regimes occurring when alluvial aquifer water levels rise above the streambed elevation. We sought to explore the relationship between aquifer dynamics and surface water intermittency by investigating subsurface heterogeneity. To investigate the subsurface, we conducted electrical resistivity tomography (ERT) surveys and compared ERT results to forward modeling of different subsurface hydrostratigraphic configurations. We found the best agreement between ERT and forward models for a conceptual model that included interbedded silt lenses in the alluvial aquifer, which agrees with past work, though there was substantial uncertainty in the ERT surveys due to the coarse and dry streambank sediment. Furthermore, the ERT profiles did not reach sufficient depth to characterize the confining layer separating the alluvial aquifer from the underlying High Plains aquifer, so potential exchange between these two units remains uncertain.