Are temperature time series measured at hydrometric stations representative of the river’s thermal regime?

Abstract

River temperature is a key variable for water quality assessment. It can alter different chemical water properties. Indeed, it is considered as determining criterion in the adequacy of cold water fish habitat, and the overall health of the river ecosystem and aquatic biota. Consequently, monitoring this variable and understanding the river thermal variation are highly important. Temperature monitoring along the rivers is often done by deploying autonomous temperature loggers. However, recently, temperature sensors were installed at hydrometric stations in conjunction with water level gauges for monitoring the river temperature, thereby providing an opportunity to expand the temperature network across the region and eventually, the country. In this study, a comparative analysis was conducted to find if the temperatures at the hydrometric station are representative of the river thermal variation upstream and downstream of that location. This comparative analysis was completed using a number of different statistical tools: entropy analysis, Gaussian function fit, and thermal sensitivity analysis. These statistical analyses confirm that temperature loggers that are collocated with the level gauges at hydrometric stations are generally representative of the thermal variation of the river main stem over a distance of a few tens of kilometres. However, the thermal variation observed in temperature loggers located at distances of the order of 100 km or in a different river reach than the hydrometric station, is different from that of the temperature logger located at the hydrometric station.