Storm driven seasonal variation in the thermal response of the streambed water of a low-gradient stream

Abstract

Storm events strongly influence water temperatures in the saturated substrate underlying stream channels, or the hyporheic zone (HZ). The goal of this study was to evaluate the impacts of storm events on thermal transport in the HZ. A year of temperature data were collected from six (6) multi-level samplers at multiple depths (30 cm, 60 cm, 90 cm and 150 cm) and were categorized into seasonal storm events. Analysis of the HZ temperature profiles revealed a seasonal reversal in the post-storm temperature change (DT) in the substrate. Increases in the DT were observed in the warm period (summer), whereas decreases occurred during the cold period (winter); both were associated with the direction of the pre-storm thermal gradient between the stream and substrate temperatures. The amplitude of DT became muted with increasing depth. Two-sample t-test analyses showed statistically significant differences between the pre- and post-storm temperatures at all depths during the warm period and at all depths except 150 cm in the cold period. Upwelling groundwater moderates the thermal response. There were no statistically significant differences in the pre- and post-storm stream temperatures during both the cold and warm periods.