Numerical modelling of hydrodynamic condition and the CO2 flux distribution under the effect of waterway regulation

Abstract

With the intensification of human activities, large-scale water conservancy project is regarded as one of the important factors affecting the transportation, transformation and degassing of carbon dioxide (CO2) in the river network. However, little is known about the CO2 emissions from channels suffering waterway regulation measures (such as spur dike, dredging, etc.) in the context of the high-quality development of inland shipping. In this study, based on the lattice Boltzmann method, we established a CO2 transport and emission model with double distribution function, evaluated and compared CO2 diffusion and emission before and after waterway regulation. The emissions of the regulated river sections (average = 151.9 mmol/m2/d) are higher than those from the original free-flowing river sections (average = 125.2 mmol/m2/d), but exerts a decreased in the area affected by the spur dike (from 122.55 mmol/m2/d to 65.50 mmol/m2/d). We attribute this discovery to the dependence of gas transport velocity ( ) on flow velocity. Compared with the original river, the waterway regulation measures have caused an increase in turbulence in the mainstream area and a decrease in the shore. Meanwhile, the water flow deviation and higher water retention time formed by the regulation are conducive to the enrichment of dissolved CO2. Overall, our results highlight that waterway regulation, with the changes of hydrodynamic conditions of rivers, will alter the spatial distribution of CO2 concentration and emissions in river. This study presented a method for predicting CO2 in rivers, which would be a useful tool for exploring the carbon emission assessment of waterway regulation in rivers.