CPD CPD Storm Drainage & Site Utilities 1 — Questions and Answers
Question 1: What is the primary purpose of a storm drainage system in a building site design?
- To convey rainwater and surface runoff away from structures to prevent flooding (Correct answer)
- To supply potable water to fire suppression systems
- To manage sanitary sewage from restrooms and kitchens
- To circulate chilled water through HVAC coils
Correct answer: To convey rainwater and surface runoff away from structures to prevent flooding
Storm drainage systems collect and convey rainwater and surface runoff away from buildings and paved areas to prevent flooding and structural damage.
Question 2: Which hydraulic method is most commonly used to size storm drainage piping in the US?
- Manning's equation for open-channel flow (Correct answer)
- Bernoulli's principle for pressurized flow
- Hazen-Williams formula for velocity head
- Darcy-Weisbach equation for laminar flow
Correct answer: Manning's equation for open-channel flow
Manning's equation is the standard hydraulic method for sizing storm drainage and other gravity-flow piping systems in the US.
Question 3: What is the 'rational method' used for in storm drainage design?
- Estimating peak stormwater runoff from a drainage area (Correct answer)
- Calculating pipe friction losses under pressure flow
- Determining the pH balance of stormwater discharge
- Sizing sump pump horsepower requirements
Correct answer: Estimating peak stormwater runoff from a drainage area
The rational method (Q = CiA) estimates peak stormwater runoff by combining runoff coefficient, rainfall intensity, and drainage area.
Question 4: Which coefficient in the rational method accounts for the type of surface (e.g., pavement vs. lawn)?
- Runoff coefficient (C) (Correct answer)
- Rainfall intensity (i)
- Drainage area (A)
- Manning's roughness (n)
Correct answer: Runoff coefficient (C)
The runoff coefficient C represents the fraction of rainfall that becomes runoff, varying by surface type such as impervious pavement or pervious lawn.
Question 5: What is the function of a catch basin in a site storm drainage system?
- To collect surface runoff and remove debris before it enters underground piping (Correct answer)
- To store potable water for emergency irrigation use
- To equalize pressure between storm and sanitary sewer lines
- To filter sediment from domestic hot water systems
Correct answer: To collect surface runoff and remove debris before it enters underground piping
Catch basins collect surface runoff at low points and remove sediment and debris through a sump before directing flow into the underground storm piping.
Question 6: Per IPC and most US plumbing codes, what minimum slope is typically required for horizontal storm drainage piping 3 inches in diameter?
- 1/8 inch per foot
- 1/4 inch per foot (Correct answer)
- 1/2 inch per foot
- 1 inch per foot
Correct answer: 1/4 inch per foot
Most US plumbing codes require a minimum slope of 1/4 inch per foot for horizontal storm drainage piping 3 inches in diameter to maintain self-cleansing velocity.
CPD CPD Storm Drainage & Site Utilities 1
What is the primary purpose of a storm drainage system in a building site design?