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

doi:10.11988/ckyyb.20230454

Abstract

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

CLC Number:

TV131.34

ZHOU Zhe-cheng, SHI Hao-yang, GUO Hui, WANG Zhi-xin, LI Xi-nan, YANG Wen-jun, JIN Guang-qiu. Influence of Low-temperature Inflow on the Transport of Supersaturated Total Dissolved Gas in Deep-Water Reservoir[J]. Journal of Changjiang River Scientific Research Institute, 2024, 41(9): 35-43.

Figures/Tables 15

Fig.1 Diagram of the study area

Table 1 Information of field observation cross-sections

断面编号	监测断面名称	坝下距离/ km	监测数据范围
断面编号	监测断面名称	坝下距离/ km	测点水深/m	水温/℃	TDG饱和度/ %
1	溪洛渡电站尾水出口	1	—	19.4	134.0
2	永久大桥	3	2.0	19.5	127.1
3	洋丰码头	20	4.8	19.4	138.6
4	桧溪镇	33	[2.0,12.9]	[19.3,19.5]	[131.8,134.3]
5	南岸镇	80	[2.5,22.2]	[19.4,19.7]	[129.8,132.4]
6	向家坝坝前	150	[1.5,26.2]	[19.3,19.4]	[122.6,130.2]

Fig.2 Upstream and downstream boundary conditions

Fig.3 Calibration result of water level at cross-section in front of Xiangjiaba dam

Fig.4 Calibration result of vertical water temperature distribution

Fig.5 Calibration result of longitudinal distribution of TDG saturation at different depths

Fig.6 Validation results of vertical distribution of water temperature and TDG saturation

Fig.7 Zoning of supersaturated TDG in Xiluodu-Xiangjiaba cascade reservoirs

Fig.8 Transport processes of supersaturated TDG clouds with different inflow temperatures under temperature compensation effect

Fig.9 Accumulated curves of the percentage of TDG saturation area

Fig.10 Time-dependent change in mean longitudinal position of saturation front (saturation degree 130%)

Fig.11 Time-dependent change in the anomaly of mean longitudinal position of saturation front (saturation degree 130%)

Fig.12 Time-dependent variations of the saturation degrees of TDG in the outflow from surface orifices and power generating sets

Fig.13 Effect of temperature compensation and depth compensation on TDG saturation

Table 2 Safe water depth thresholds for fish at different TDG saturation levels under compensation effects at local atmospheric pressure of 96.84 kPa

坝下近区 TDG饱和度/%	不同水温下的安全水深阈值/m
坝下近区 TDG饱和度/%	22.2 ℃	21.8 ℃	21.4 ℃	21.0 ℃	20.6 ℃	20.2 ℃
140	2.48	2.42	2.30	2.24	2.13	2.06
130	1.60	1.53	1.43	1.36	1.27	1.20
120	0.71	0.64	0.56	0.49	0.41	0.34

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