Investigations on the internal dissipation coefficient of supersaturated total dissolved gas: focus on vegetation-influenced flow

The total dissolved gas (TDG) supersaturation caused by high dam discharges pose significant ecological risks to aquatic organisms inhabiting downstream river systems, thereby representing a critical concern in hydropower development. Aquatic vegetation zones, distinguished by their characteristic low-flow regimes and intricate vegetative structures, function as essential habitats for aquatic biota. Consequently, it is imperative to examine the dissipation dynamics of supersaturated TDG within these aquatic vegetation zones. Previous studies have conceptualized the dissipation of supersaturated TDG as a process involving liquid-gas interfacial transfer, solid wall adsorption, and the internal dissipation. While, the factors influencing the internal dissipation coefficient and its quantitative characterization remain inadequately elucidated, resulting in an incomplete understanding of the overall supersaturate TDG dissipation process. To address this gap, flume experiments and numerical simulations were conducted in the present study. The determinants affecting the internal dissipation coefficient were identified. Findings indicate that the internal dissipation coefficient exhibits a positive correlation with water depth. Under equivalent vegetation densities, scenarios characterized by elevated flow velocities and increased turbulence intensities correspond to higher internal dissipation coefficients. Moreover, for consistent flow conditions, an increase in vegetation density is associated with an augmented internal dissipation coefficient. Through multiple regression analysis, a predictive formula for the internal dissipation coefficient was derived. This research advances the quantitative understanding of supersaturated TDG dissipation in vegetated flow environments and provides a theoretical foundation for subsequent investigations in this research field.