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Scaling up point-in-space heat tracing of seepage flux using bed temperatures as a quantitative proxy

Research paper by Laura K. Lautz, Rachel E. Ribaudo

Indexed on: 26 May '12Published on: 26 May '12Published in: Hydrogeology Journal



Abstract

It is challenging to quantify reach-scale surface-water–groundwater interactions, while maintaining the fine-scale spatial resolution required in hyporheic studies. One-dimensional heat-transport modeling was used to simulate streambed fluxes at discrete points using time-series temperature records. A predictive relationship was then developed between point-in-time streambed temperature and modeled flux rates. Flux was mapped at high spatial resolution by applying the predictive relationship to mapped streambed temperatures, which allowed for high-resolution quantification of flux by proxy. Inferred patterns of flux are consistent with morphology and yielded a net flux to a 30-m stream reach of 1.0 L s–1. Discharge of saline groundwater (5.7 g L–1 Cl–) allowed for comparison between the temperature proxy method and geochemical variability. Maximum upwelling locations (>35 cm day–1) were spatially coincident with areas of high conductance at the bed interface (5–25 mS cm–1). Differences between gross flux estimates from heat and geochemical methods are attributed to differences in the spatial extent over which estimates were derived and limited sensitivity of the temperature-as-proxy method. When bed temperatures are near their inherent limits (groundwater and stream-water temperatures) the flux magnitude can be underestimated. Caution must be used when determining gross, reach-scale fluxes from temperature-as-proxy methods when flux rates are outside the sensitivity limits.