CSLB C-36 Plumbing ContractorRough-in PlumbingHard
A plumbing contractor is installing a new storm drainage system for a commercial building. The design calls for a 6-inch storm drain pipe laid with a 1/8 inch per foot slope. Based on typical code requirements, what is the approximate maximum design flow capacity for this pipe, in gallons per minute (GPM)?
- A200 GPM
- B700 GPM
- C350 GPM
- D500 GPM
Show answer & explanationAnswer & explanation
Correct answer: C. 350 GPM
For a 6-inch storm drain pipe laid at a 1/8 inch per foot slope, the California Plumbing Code (CPC) storm drainage tables indicate an approximate maximum design flow capacity of around 350 GPM. This is derived from hydraulic calculations considering pipe diameter, slope, and roughness.
Why the other options are wrong
- A. This capacity is typically too low for a 6-inch pipe with this slope.
- B. This capacity is significantly too high for a 6-inch pipe at this slope.
- D. This capacity is typically too high for a 6-inch pipe with this slope, more typical of a steeper slope or larger pipe.
Storm Drain Flow Capacity
The maximum volume of rainwater a storm drainage pipe can effectively carry, determined by its diameter and slope.
- Expressed in GPM (gallons per minute) or CFS (cubic feet per second).
- Crucial for preventing flooding.
- Calculated using hydraulic tables and formulas.
Memory trick: Big pipe, good slope, means lots of rain can cope.