[rmh47]

At the confluence of the Ohio and Mississippi rivers, the Ohio contributes to the lower Mississippi about three and a half times as much water as the upper Mississippi.

Because of this, The lower Mississippi will never flood solely because of flooding on the upper Mississippi/Missouri, no matter how bad.

The "mighty Mississippi" is mighty only because of the Ohio River.

[blam]

To put river sizes into perspective, consider:

The water flow of the Amazon is greater than the next ten largest rivers in the world combined. It it the second longest because the Nile just barely beats it in length.