|Abstract/Description or Keywords
||Groundwater contributions to streams often vary both spatially and temporally. In this study, the relative contributions of groundwater to Fishtrap and Bertrand Creeks in the Lower Fraser Valley are compared during the summer and annually using a combination of methods. The streams drain watersheds that have a similar climate, area and topographic relief. However, the geological substrate differs, with finer grained material underlying Bertrand Creek. A simplified heat budget model is first used to estimate temperature at the air–water interface. Then, the correlation between the air–water and bed–water (interface) temperatures is compared for both annual and summer periods in each stream. The air temperature explains ~30% of the variance in the summer interface temperature in Fishtrap Creek, but more than 75% in Bertrand Creek. This difference suggests that factors at the bed–water interface influence the heat budgets, and that these factors differ between the two sites. The measured groundwater flux during the summer periods was higher in Fishtrap Creek than in Bertrand Creek, due to a higher vertical hydraulic gradient into the stream and higher aquifer sediment permeability. Thus, the larger groundwater contribution to Fishtrap Creek moderates stream temperature and stream discharge during the summer periods, whereas Bertrand Creek has greater potential for elevated stream temperatures and lower flows during the critical summer period The combination of methods used in this study strengthens the interpretations given the wide range of uncertainty in measurements.