ANS:D - trough stage of the river.

Location of canal headwork:

It depends upon the stages of the flow of a river:

Rocky stage: In this stage, a river is in the hills. The bed slope and velocities are high. It is generally not suitable for the location of a diversion headworks.

Boulder stage: In this stage, the beds and the banks of the river are composed of boulders and gravel. In this stage, seepage losses are high.

Trough stage: In this stage, the cross-section of the river is made up of alluvial sand and silt. The bed slope and velocity are small. In this stage, seepage losses are less that\'s why the most suitable location for canal headworks is in this stage.

Delta stage: As the river cross-section is very wide, therefore this stage is not suitable for the location of canal headworks.