When an irrigation canal is taken over a drainage channel the crossing is called
an aqueduct
Understanding Irrigation Canal and Drainage Channel Crossings
When an irrigation canal and a drainage channel need to cross paths, special structures are built to manage the flow of water in both. These structures are collectively known as cross drainage works. The type of structure built depends primarily on the relative bed levels of the canal and the drainage channel.
Let's look at the main types of crossings:
- Aqueduct: This is a structure where the irrigation canal is carried over the drainage channel. The bed level of the canal is higher than the highest flood level (HFL) of the drainage. The canal water flows in a trough supported by piers, allowing the drainage water to pass below it.
- Super Passage: This is the opposite of an aqueduct. In a super passage, the drainage channel is carried over the irrigation canal. The bed level of the drainage is higher than the full supply level (FSL) of the canal. The drainage water flows in a structure supported over the canal.
- Level Crossing: In this case, the irrigation canal and the drainage channel cross each other approximately at the same level. This is generally avoided as it involves mixing of canal and drainage water, which can cause silting in the canal and waterlogging issues. Regulatory structures like regulators are needed on both channels to control flow.
The question specifically asks about the crossing where an irrigation canal is taken over a drainage channel. Based on the definitions above, this description perfectly matches an aqueduct.
Here is a summary of the main types of cross drainage works:
| Type of Crossing | Relative Position | Description |
|---|---|---|
| Aqueduct | Canal over Drainage | Canal bed level > Drainage HFL |
| Super Passage | Drainage over Canal | Drainage bed level > Canal FSL |
| Level Crossing | Canal and Drainage at Same Level | Requires regulators on both channels |
Therefore, when an irrigation canal crosses over a drainage channel, the structure is called an aqueduct.
Revision Table: Key Concepts in Canal Crossings
| Term | Brief Definition | Key Feature |
|---|---|---|
| Aqueduct | Canal over drainage | Canal bed is above drainage HFL |
| Super Passage | Drainage over canal | Drainage bed is above canal FSL |
| Level Crossing | Channels at same level | Requires careful regulation |
| Cross Drainage Work | Structure managing crossings | Handles canal & drainage interaction |
Additional Information on Aqueduct and Canal Crossings
Aqueducts are common structures in irrigation systems. They are designed based on hydraulic principles to ensure smooth flow in both the canal and the drainage channel. There are different types of aqueducts based on the type of support and material used.
Sometimes, if the difference in levels is small or flow is under pressure, siphons are used instead of aqueducts or super passages. A siphon aqueduct is used when the drainage bed level is slightly below the canal bed level, causing the drainage water to flow under the canal under siphonic action. A siphon super passage is used when the canal bed level is slightly below the drainage bed level, causing the canal water to flow under the drainage under siphonic action.
Understanding the difference between an aqueduct and a super passage is crucial for designing efficient irrigation and drainage networks.
Important Questions from Cross Drainage Works - Teaching
The uplift pressure on the roof of a siphon aqueduct is maximum when
A hydraulic structure is constructed when a Full Supply Level (FSL) of a canal is much higher than the High Flood Level (HFL) of the stream which in turn, is lower than the bottom of the canal trough. Such a structure is called as:
