Modelling the promotion effect of vegetation on the dissipation of supersaturated total dissolved gas

Flood plays a vital role in aquatic organisms' subsistence and reproduction. It can bring spawning signals to fishes and excessive foods fattening fishes up in the flood plain. Nowadays, with an increasing number of high dams being put into operation, huge changes have happened in the process of natural flood. In order to maintain the ecological function of flood, sometimes hydropower stations have to make artificial flood peak by the power station's spillway discharging. Water discharge from high dams leads to the supersaturation of total dissolved gas (TDG), thus causing fish to suffer from gas bubble disease (GBD) and even death. The downstream water level rises during the period of discharge, inundating part of the vegetation on the bottomland. The existence of vegetation can affect the hydrodynamic characteristics of flood water flows and then change the transportation and dissipation of the supersaturated TDG. The stems and leaves of the submerged vegetation provide a large amount of solid-liquid interfaces, which adsorb gas dissolved in water, consequently influencing the dissipation process of supersaturated TDG. In this paper, research about the effect of vegetation on supersaturated TDG is conducted underpinned by laboratory mechanism experiments. The supersaturated TDG dissipation process with vegetation existing in the water was obtained. The results indicate that planting vegetation in water can effectively bolster the releasing of TDG, and as the density of vegetation increases, the promotion effect is commensurately enhanced. Based on the experimental data, this paper proposes a supersaturated TDG dissipation model describing the function of the vegetation's wall adsorption of the TDG, and the formula for the adsorption flux Fa of supersaturated TDG in a unit area over a unit time is achieved. This paper obtains a significant parameter representing how fast the vegetation's surfaces adsorb the supersaturated TDG, namely, the adsorption rate ka. It is determined that ka is solely related to the vegetation's material and surface characteristics.