The correct answer is:
(b) Contour Canal
Explanation:
In flatlands, the contour canal is typically used for canal alignment. A contour canal is designed to follow the natural contour of the land, minimizing the need for major embankments and ensuring a gentle gradient. This type of canal alignment helps in preventing waterlogging and erosion, making it ideal for areas with relatively flat terrain.
Other types of canals, such as side slope canals or watershed canals, are more suited to regions with varying elevations or hilly areas, where the natural topography requires different approaches to manage water flow. Field channels are smaller canals used to distribute water from main canals to fields, but they are not typically aligned based on the terrain.
Thus, for flatlands, contour canals are preferred as they are efficient in maintaining consistent flow and minimizing soil erosion.