低温来流对深水水库过饱和总溶解气体输移的影响

Influence of Low-temperature Inflow on the Transport of SupersaturatedTotal Dissolved Gas in Deep-Water Reservoir

梯级深水水库产生的水温分层现象可降低下游水库来流水温,导致泄洪水体总溶解气体(TDG)的过饱和程度随库区密度分层流的输移过程产生变化。以溪洛渡—向家坝区间为研究区域,基于原位观测和数值模拟相结合的研究手段,研究低温来流对深水水库过饱和TDG纵向和垂向输移过程的影响规律。研究表明:①来流水温降低2℃,TDG云团潜入位置提前36.4 km,峰值垂向位置下移55 m、垂向影响范围减少23%;②来流水温降低2℃,TDG饱和度110%以上云团输移至向家坝坝前阶段和后续阶段,包络面积衰减速率降幅分别为16%和44%;③从射流区到交换区过饱和TDG平均纵向迁移速度显著降低,降幅达92%;④来流水温降低2℃,向家坝表孔出流TDG饱和度峰值和均值的降低程度分别为机组出流的3.2倍和4倍;⑤水温降低对鱼类安全水深阈值的补偿效应可量化为0.20 m/℃。研究成果可为梯级深水水库汛期生态调度提供科学支撑。

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.