Streambed temperature dynamics and corresponding heat fluxes in small streams experiencing seasonal ice cover

- Research describing the streambed heat flux for two small streams.
- Streambed temperatures were used to calibrate model.
- Streambed heat fluxes were from advection (groundwater) and conduction.

SummaryStreambed temperature and heat fluxes are important for aquatic habitats as well as in the development and improvement of water temperature models. In the present study, measured streambed temperatures at different depths were used as a tracer to predict the magnitude and direction of groundwater flow using an advection-conduction heat transport model. This analysis was carried out under different conditions, namely under natural surface water temperature conditions (i.e., as measured in the field), under steady-state conditions (e.g. under stream ice cover) and for conditions where the surface water temperatures followed a sinusoidal function. In Catamaran Brook, results from the advection-conduction numerical model showed good agreement between predicted and observed streambed temperatures with root-mean-square errors (RMSEs) ranging between 0.07 °C to 0.6 °C. A comparison of streambed fluxes showed that the heat flux by conduction was more important during the summer period for upwelling conditions (mean value 96 W m−2 at 25 °C), but was also present in winter (−20 W m−2). Variability in heat flux by conduction was also greater when the diel surface water temperature variability was high (e.g. range of 6 °C). The heat flux by advection varied between −120 and 145 W m−2 (for typical water temperatures and vertical flow conditions within Catamaran Brook, 0-25 °C and ±0.005 m h−1). Short-term heat exchange (diel) occurred within the thermally active depth, typically <0.7 m. The long-term annual streambed heat flux by conduction was also calculated and daily mean was generally less than ±11 W m−2. Winter conditions provided a unique opportunity to analyse streambed heat fluxes under steady-state conditions when both conduction and advection fluxes were present.