I have been puzzled with two questions recently:
How to calculate the number of downspouts on a house and how to size them, but by somehow using the flow rate of the gutters?
I found that there are a number of sources which offer the sizing of downspouts by the usage of tables.
I also found that some USA manufacturers recommend defining the number of downspouts by putting one downspout on ever 20 to 40 feet length of gutter.
But is it possible not to use the tables approach nor 20-40 feet rules of thumb?
Is it possible to to somehow calculate the number of downspouts by knowing the flow rate of the gutters?
Let's say that my roof produces 0.2 cfs (cubic feet per second) of runoff.
I can use Manning's formula to size my gutter. If I pick 6 inch rectangular gutter, it can take 0.21 cfs.
Can I now size the downsprouts and their number, based on this 0.21 cfs gutters's flow rate ?
I apologies for not asking the question directly related to SWMM.
Thank you in advance.