Thermal variations of water in the Nam Song stream/Mekong River: II. Experimental data and theoretical predictions

Abstract

The goals of this study were to use the Nam Song River as a case study for parameters determination and a comparison between the measured data and the mathematical model developed in the first paper of this study. The kinematic wave equation [especially Eq. 16a in Ben-Asher et al. (Sustain Water Resour Manag, 2016. doi: 10.1007/s40899-016-0044-9 )] was expanded to a Taylor series that was used to determine several system parameters including the thermal time constant, the steady state solution, and the daily thermal cycle. Water temperature measured and calculated by the model varied from minimum of 23–24 °C at night to maximum of 27–29 °C at midday. From March 16 to March 25 2004, stream and air temperature were monitored at a point located 4 km downstream from the Nam Song Dam. The average hourly water temperature and its standard deviation were extracted from a family of daily sinusoidal curves. Monitoring downstream data were similar to results assumed by the theoretical model. The effect of water discharge rate on its temperature and on the changing energy input during daytime hours was considered. The analysis indicated that the only controllable system variable is the water flow velocity (V). It can be optimized through a controlled release of water from the dam. The mathematical analysis also identified and quantified the parameters which govern the water environment. The theory as well as the experimental data indicated that for the conditions studied, an increase in water discharge at the dam prevents an increase in water temperature downstream and thus helps to keep the fisheries and domestic water quality of the river in a healthier condition.