What does it mean by those FIRE WATER DRAINAGE?

[kkelvin]

Hi, there

I just touch some documents realated to the fire water drainage. I got some questions about them. Could you give me some idea? Thanks.

"500 gpm per catch basin (2 most upstream catch basin)" and "250 gpm per catch basin (3rd and each subsequent catch basins).

My questions are:
1. How to decide the volume for the catch basin? Here are 500 pgm and 250 pgm.
2. Why choose 2 most upstream catch basin as 500 pgm? Why not 3?

 

[civilperson]

Volume is not needed for drainage design. Flow rate, (gpm or cfs), is used to size pipes. The number of simultaneous basin flows is arbitrary and set by code or local jurisdiction with the rationale that a maximum flow will be less than the maximum from all basins.