Abstract: In this study, air accumulation at the top of a long-term-high-lift motionless siphon hose due to air dissolution and diffusion is studied. Many factors can induce air accumulation in siphon hoses during dry seasons. In this study, effects of the unavoidable factors, such as air diffusion and dissolved-air release, are investigated. Based on experimental observations and theoretical analysis, the following results are obtained: (1) pressure decrease in high-lift siphon hoses will cause release of supersaturated air and induce a maximum 1.5 m long air column at the top of the siphon hose; (2) temperature increase will cause a maximum 0.55 m long air column; (3) air diffusion from water will lead to a less than 0.01 mm increment of the air column per day, which is considered to be negligible compared with that induced by air release due to pressure and temperature variations. Results indicate that high-lift siphon drainage can also be effectively used in arid districts. During siphon drainage design, at least 2.05 m long space to the safety level should be left for underground water rise, or the outlet should be kept 4.1 m lower than the inlet to guarantee that the released air will be gathered in the descending hoses.

Key words: Slope, Siphon drainage, Motionless flow during dry season, Air accumulation, Air diffusion, Temperature

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