A canal syphon is a hydraulic structure where the canal is positioned below the drains, the water flows under syphonic action, and the canal is devoid of atmospheric pressure. The flow in the phenomena is a pressurized flow. To create syphonic action, the flooring of canal is lowered like a cistern.
Parts:
In the figure above, the canal is shown moving from left to right, whereas the drain carries water from top to bottom. As the water level in canal is above the bed of the drain, piers are erected to keep the bed intact. The bottom of the canal bed is bent downward to increase the flow area and maintain an equivalent discharge.
Usage:
It is utilized when full supply level of canal is above the bed of the drainage stream crossing the canal.
Disadvantages:
- If velocity is not greater than the silting velocity is not maintained, it becomes difficult to remove silted particles.
- Silting is a bigger issue due to the presence of piers.
- Command area of the canal is reduced.
Design Considerations
- Drain flow is an open channel flow, hence Manning’s equation remain applicable.
- Canal flow is treated as pipe flow.
Animation of Inside of Canal Syphon:
Here is an animation I made to demonstrate the Canal Syphon in action.
