Abstract
Abstract. Seven Landsat thermal infrared (TIR) images taken over the period 2000–2010 were used to establish longitudinal temperature profiles of the middle Loire River where it flows above the Beauce aquifer. The groundwater discharge along the river course was quantified for each identified groundwater catchment area using a heat budget based on temperature variations of the Loire River estimated from the TIR images. The results showed that 75 % of the temperature differences, between in situ observations and TIR image-based estimations, remained within the ±1 °C interval. The main discharge area of the Beauce aquifer into the Loire River was located between river kilometers 630 and 650, where there was a temperature drop of 1–1.5 °C in the summer and a rise of 0.5 °C in winter. According to the heat budgets, groundwater discharge was higher during the winter period (13.5 m3 s−1) than during the summer period (5.3 m3 s−1). These findings are in line with the results of both a groundwater budget and a process-based distributed hydrogeological model. Groundwater input was also found to be higher during the Loire's flow recession periods.
Highlights
Water temperature is a key factor for aquatic fauna (Ward, 1992; Caissie, 2006)
Temperature accuracy is the average difference between the temperature estimated from the thermal infrared (TIR) images and the temperature measured in situ (Handcock et al, 2012)
No atmospheric correction was implemented and non-pure water pixels were taken into account, temperature differences from in situ observations and TIR-image based estimations remain within the interval defined in previous studies (i.e., 75 % of these differences being in the ±1 ◦C interval)
Summary
Water temperature is a key factor for aquatic fauna (Ward, 1992; Caissie, 2006). For instance, it controls oxygen dissolution, essential for aquatic organisms. Since the late 1990s, thermal infrared (TIR) images have been used to determine river water temperature along sections ranging from tens to hundreds of kilometers (Torgersen et al, 2001; Handcock et al, 2006, 2012). Until now, these images of watercourses have mainly been used (i) to identify cold refuges for fish in the summer (Belknap and Naiman, 1998; Torgersen et al, 1999; Tonolla et al, 2010; Monk et al, 2013); (ii) to study the thermal variability of rivers or alluvial floodplains and locate areas of similar thermal characteristics (Smikrud et al, 2008; Tonolla et al, 2010; Wawrzyniak et al, 2012, 2013, Fullerton et al, 2015); and (iii) to validate river temperature models (Boyd and Kasper, 2003; Cristea and Burges, 2009)
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