The following details pertain to the crossing of a canal and a drain. Bed level of Canal = + 211 m; Full Supply depth of Canal = 1.8 m; Bed level of Drain = + 209.4 m; depth of flow at High Flood Level = + 2.2 m. The suitable type of cross drainage work is:

Concept:

For the given data, the most suitable cross drainage work is syphon aqueduct. 

There are mainly two conditions for syphon aqueduct-

• The canal passes over drainage system
• HFL of the drain is much higher than above the canal bed (on canal bottom).

Full Supply Level (FSL): It is the elevation of water surface when then the channel is carrying the discharge at its peak capacity.

High flood level (HFL): It is the maximum elevation of the water surface in the river when it is carrying maximum discharge during high flood time.

Calculation:

Bed level of Canal = + 211 m,

Bed level of Drain = + 209.4 m

High flood level(HFL) = Depth of flow at High Flood Level + Bed level of Drain

High flood level(HFL) = 2.2 m + 209.4 m = 211.6 m

Hence, 

(i) Bed level of Canal > Bed level of Drain

(ii) High flood level > Bed level of Canal

Important Points

The drainage water intercepting the canal can be classified in the following ways:

i) By passing the canal over the drainage

a) Aqueduct

b) Syphon aqueduct

ii) By passing the canal below the drainage

a) Super passage

b) Syphon