Abstract: In a long-distance water supply project, generally the pipeline is arranged according to topography. In view of certain special topographic conditions, this paper presents a water hammer protection scheme of combining an air vessel with an outlet overflow tank, and develops a mathematical model of the overflow tank. For the air vessel of fixed shapes and sizes, we derive a theoretical formula for calculating the cross-sectional area of the tank, which can effectively reduce the blindness and labor cost in the initial selection of the tank parameters. In a case study of a real long-distance water supply project, we compare the water hammer protection performance of the combination scheme with that of no overflow tank. The results show that the combination scheme is better for long-distance water supply projects pipelines with a steep slope in front and a mild slope behind, and that it achieves a better protective effect against negative pressure if a higher overflow threshold level in the tank is adopted.

Key words: long-distance water supply, special topography, water hammer, combined protection, air vessel, overflow tank