Understanding Watershed Canal Alignment

A watershed canal, also known as a ridge canal, is a type of irrigation canal that follows the natural watershed line or ridge line of the area. The ridge line is the highest ground, separating drainage basins where water flows down on either side.

Why Align Canals Along the Ridge Line?

Aligning an irrigation canal along the ridge line has several advantages:

• It allows the canal to command areas on both sides for irrigation.
• Water can flow by gravity from the canal to the fields on either side, minimizing the need for pumping.
• Since the canal is on the highest ground, it minimizes the number of natural drainages it needs to cross. Natural drainages flow down the slopes away from the ridge.
• Minimizing the crossing of natural drainages significantly reduces the number and cost of cross-drainage structures (like aqueducts, super passages, or syphon aqueducts) required during construction.

Analyzing the Given Options

Let's evaluate each statement based on the principles of watershed canal alignment:

• Option 1: In alignment of canals along the watershed, there is no use of gravity.

  This statement is incorrect. Aligning along the watershed (ridge line) is ideal precisely because it *maximizes* the use of gravity. Water flows by gravity from the high-level canal to the lower-lying fields on either side.

• Option 2: Alignment of canal along watershed increases the cost of construction of cross-drainage works.

  This statement is incorrect. Aligning a canal along the watershed *decreases* the cost of cross-drainage works. Because the canal is on the highest ground, it intercepts very few natural drainage paths, which run perpendicular to the ridge line, flowing downwards. Crossing fewer drainages means fewer expensive structures are needed.

• Option 3: Canal should be aligned along the ridge line.

  This statement is correct. As explained above, aligning an irrigation canal along the ridge line (watershed line) is the most efficient and economical method for command area and gravity flow irrigation.

• Option 4: In canal alignment along the watershed, drainage flows towards the ridge.

  This statement is incorrect. Natural drainage always flows *away* from the ridge line, down the slopes into the valleys. The ridge line is the dividing line for drainage flow.

Based on the analysis, the statement that is TRUE for the alignment of watershed canals is that the canal should be aligned along the ridge line.