James wrote:
Can anyone calculate the number of gallons that a 30 inch wide
culvert, 48
inches long, will hold ??

Thanks for any info !!!
--James--

Are you doing your homework?

"Can anyone calculate the number of gallons that a 30 inch wide
culvert, 48
inches long, will hold ?? "

Pie are square

Area of a circle equals Pi times the radius squared.

3.14 * 15" * 15"

33912 cuin
33912 cubic inch = 146.8051948 gallon [US, liquid]

This assumes the culvert is round, is capped on one end, and stood up,
then filled to the rim.

A culvert, laid horizontally, in the ground, would be filled to about
85% to 95%, considering air would be at the top. Well, that would be
during a flood, but in dry times, there might be a few inches, flowing.

Is the culvert oval shaped? I'll assume round.

Is the water stagnant or flowing?

Since you are too lazy to do your homework here's a bonus question.

What if you have a drainage canal, 15 feet wide and 10 feet deep. Water
is flowing, and the depth is 2 feet on the wall markings. You look
upstream to the mountains and it is raining steady. You have 3-30 inch
diameter x 20 foot culverts, side by side, in the culvert and they are
covered in concrete, with a road over them. Height from stream bottom
to road is 5 feet. You have someone 100 feet upstream, drop a floating
object in the water, and it takes 10 seconds to reach you.

How many gallons per minute are flowing through the culverts?

At what flow rate will the flow of water, exceed the capacity of the
culverts, and flow over the top of the road:
by 1 inch?
by 12 inches?
by 48 inches?