Correct Answer!

The amount of water that passes through an imaginary cross section slice of a river depends on the area of the cross sectional slice and the velocity of the water passing through the slice. The garden hose analogy is often used to illustrate this principle. When the faucet is only partially turned on, the entire cross section of the hose end is full of flowing water but the flow is not very high. When the faucet is turned fully on, the cross sectional area of the hose end has not changed, but the velocity has gone up significantly and the flow goes up accordingly. Similarly, in a river, both the area of the flow (depth and width) and the velocity, or current, must be measured.