re: Morganza Spillway may or may not open for a 3rd time -- lack of clear info from ACoE

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Maybe I'm misusing flow for velocity, but I believe the Corps calls it flow. Perhaps flow rate.

If X volume of water moves thru river cross section A in 1 second, does the same volume move through a downstream river cross section that is 10% larger than A in 1 second? It seems like the flow (flow rate? Velocity?) would decrease to me. I always thought the increasing channel depth and river width slowed the river as it got closer to the mouth.

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So volume and mass always have to be conserved (because water is not compressed)- what goes in must come out, unless otherwise detained like I mentioned previously.

With that in mind Q=V*A
Where Q=flow, V=velocity, and A=Cross sectional area

So for example, say a hypothetical river has a cross sectional area of 30 feet wide by 10 feet deep rectangle, and has a uniform velocity of 10 ft/second.

That flow is going to be equal to Q=V*A=(10 ft/s)*(10 ft x 30 feet)=3000 ft3/second.

Now say that river comes to a point where it gets really narrow-say 5 feet wide. Assuming it keeps the same energy head, it's going to have the same flow with a much higher velocity.

3000 ft3/s=V2*(5 ft wide x 10 ft high)
=>V2=(3000 ft3/s)/(50 ft2)=60 ft/s

This is obviously simplified and has many assumptions but you get the basic idea.

Eta:

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. I always thought the increasing channel depth and river width slowed the river as it got closer to the mouth.

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Thats true, but the total volume of water moving down stream is basically constant past Bonne Carre to bird foot delta.