From where are irrigation canals typically built?

• A. From sea
• B. From groundwater wells
• C. From rainfall ponds
• D. From rivers

Answer: (D)

Irrigation canals are designed to move large, dependable supplies of water to fields, and the most practical source for that is a river. Rivers provide a steady flow of water that can be controlled with dams, headworks, and reservoirs, allowing canals to be fed and distributed across long distances to reach farmland. Building canals from rivers makes it possible to create broad irrigation networks that serve large areas.

Sea water isn’t used for most irrigation because it’s salty and can harm crops, and desalination is expensive. Groundwater wells pump water up from below the surface, but that tends to supply individual farms or smaller systems rather than a wide canal network. Rainfall ponds store water, but they don’t offer the continuous, large-scale supply that a river can provide, so canals built from ponds aren’t the typical method for extensive irrigation systems.