Impact of partially filled pipes on hydraulic performance of canal-pipe water delivery systems

【Objective】 Changes in water pressure in pipe networks can cause partial filling of pipes, leading to non-full flow. The objective of this paper is to investigate the impact of non-full flow on the hydraulic performance of canal-pipe water delivery systems. 【Method】 The study was based on experimental and theoretical analysis. We examined the distribution of water velocity in channels, changes in the water surface profile, flow rates in pipes, and the diversion ratio under different pipe-filling levels. 【Result】 The water velocity distribution along the main channel remained consistent at different filling levels in the pipes, with notable changes occurring within regions approximately twice the longitudinal and 1.5 times the transverse diameter of the pipe. Water velocity fluctuations were most pronounced near the channel walls at the water surface, following a pattern of initial decrease, subsequent increase, and final decrease along the flow path. Through dimensional analysis, a formula was derived for calculating the water velocity coefficient, with a maximum relative error of 8.81% compared to experimental data. For a constant water flow rate in the main channel, the velocity coefficient for the partially filled pipes increased with the Froude number of the main channel but decreased as the water depth ratio and the filling level increased. Additionally, the diversion ratio was found to increase with filling levels. At a constant filling level, increasing the flow rate in the main channel increased the velocity coefficient in the pipes and reduced the diversion ratio. 【Conclusion】 The impact of partially filled pipes on water flow in the main channel is minor. Installing gate valves and water measuring equipment should avoid areas that are likely to be impacted. The formula we derived for calculating velocity coefficient only needs the Froude number and water depth in the main channel, and it can quickly calculate water velocity in partially filled pipes. Under certain conditions, increasing water depth in the main channel can increase flow rate in the pipes.