Which one of the following equation is applicable to unsteady flow in open channels :

• A. <img src="/_files/images/civil-engineering/hydraulics/163-7.286-1.png">
• B. <img src="/_files/images/civil-engineering/hydraulics/163-7.286-2.png">
• C. <img src="/_files/images/civil-engineering/hydraulics/163-7.286-3.png">
• D. <img src="/_files/images/civil-engineering/hydraulics/163-7.286-4.png">