Rick wrote:We have a 22" ID pipe under a driveway. Can its maximum water runoff volume be contained with a 32" wide and 10" deep gutter? How do we calculate the two? The gutter is a crescent ( shape or semicircle with the 10" depth at the deepest.
I would start by comparing areas. The 22" pipe has a radius of 11" and an are of pi*11*11 = 121*pi.
The gutter (hopefully) is approximateky an ellipse with semidiameters of 10" and 16" and an area of pi*10*16 = 160*pi, a little bigger.
In flow, surface roughness also matters. is the "gutter" a manufactured material about as smooth as the pipe, or is it a ditch with grass? In the first case, the gutter probably has a little more capacity, in the second case, the pipe.
The other question is whether there is enough downward slope to the system to move enough water. However, the pipe and the gutter are probably in reasonable balance.
