Abstract:

The stratification of water temperature in deep-water cascade reservoirs reduces the inflow temperature of downstream reservoir, altering the supersaturation degree of total dissolved gas (TDG) in flow discharges. With the Xiluodu-Xiangjiaba cascade reservoirs as a case study, we investigated the impact of lower-temperature inflow on the longitudinal and vertical transport processes of supersaturated TDG in deep-water reservoir via field observation in association with numerical simulation. Finds reveal that: 1) a 2 ℃ decrease in inflow temperature advances the submersion position of TDG cloud by 36.4 km, shifts the peak TDG saturation down by 55 m, and reduces its vertical influence range by 23%. 2) With a 2 ℃ decrease in inflow temperature, as the TDG cloud with a saturation over 110% transports to front of the Xiangjiaba dam, the decay rate of enveloped area decreases by 16%; in subsequent transport stage, the decay rate reduces by 44%. 3) The average longitudinal transport velocity of supersaturated TDG from the jet flow zone to the interflow zone plunges by 92%. (4) As inflow temperature reduces by 2 ℃, the peak and mean TDG saturation of the outflow from Xiangjiaba’s surface orifices reduce by 3.2 and 4 times that of the outflow from power generating set, respectively. (5) The compensation effect of temperature reduction on the safe water depth threshold for fish can be quantified as 0.20 m/ ℃. The findings provide scientific support for ecological dispatching of deep-water reservoirs during flood seasons.

Key words: TDG transport process, mathematical model, reservoir water temperature stratification, total dissolved gas, cloud position, water temperature compensation, ecological dispatching, cascade deep-water reservoir