What are the standards for the design of a square rain water pipe?

What are the standards for the design of a square rain water pipe?
The application of square rain water pipe in our lives more and more widely, and its design is directly related to the quality of the construction, so what are the standard square rain water pipe in the design? Let's see it!
Storm intensity, is refers to the rainfall process, a continuous period of rainfall
2 drainage area, a square pipe to collect rainwater in rain area.
The 3 bottom surface catchment time, refers to the water to reach the starting point from the time of discharge pipe boundaries.
4 runoff coefficient is the ratio of rain water and total amount of rain water flowing into the pipeline.
5 the return period of the rainstorm is the average time interval of the occurrence of the rainstorm intensity equal to or greater than the prescribed time.
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