Cross regulator is provided on the main canal at the downstream of the off-take canal: 

Explanation:

Cross regulator:

• A cross regulator is provided to control the supplies passing down the parent channel.
• Constructed across the parent channel at the d/s of the offtake point of the off-taking canal.
• It raises the water level in the parent channel when its discharge is less than the full supply discharge.
• A cross regulator is necessary on all irrigation systems because the distributaries and field channels are required to be supplied with water according to a set roster even when the parent canal is carrying low supply.

Functions of cross regulators:

• To raise the water level in the parent channel to feed the off-taking channel.
• Enable effective regulation of the entire canal system.
• To shut the supply in the parent channel on its d/s for repairs.
• Usually, a bridge is combined with a cross regulator for communication.
• Helps in absorbing fluctuations in the canal system and in preventing the possibility of breaches in the tail reaches.
• Useful for the effective regulation of the entire canal system.

​Hence option (2) is the correct answer.