CEPSCI Stormwater Management and Hydrology 1 — Questions and Answers
Question 1: The rational method formula Q = CiA is used to calculate:
- Soil erodibility
- Peak stormwater runoff rate (Correct answer)
- Sediment pond volume
- BMP maintenance frequency
Correct answer: Peak stormwater runoff rate
The rational method calculates peak runoff rate (Q) using the runoff coefficient (C), rainfall intensity (i), and drainage area (A).
Question 2: A peak discharge from a construction site is most critical because:
- It determines the daily work schedule
- It represents the highest flow rate BMPs must handle without failure (Correct answer)
- It sets the final cost of the project
- It determines the number of workers needed
Correct answer: It represents the highest flow rate BMPs must handle without failure
Peak discharge is the maximum flow rate during a storm event, and BMPs must be designed to handle this flow without being overwhelmed or failing.
Question 3: Which factor in the rational method accounts for the type of ground surface?
- Q (peak runoff rate)
- C (runoff coefficient) (Correct answer)
- i (rainfall intensity)
- A (drainage area)
Correct answer: C (runoff coefficient)
The runoff coefficient (C) represents the fraction of rainfall that becomes runoff, which varies based on ground cover type, soil type, and slope.
Question 4: What is the design storm typically used for sizing temporary sediment basins?
- 1-year, 24-hour storm
- 2-year or 10-year storm depending on jurisdiction (Correct answer)
- 50-year storm
- 100-year storm
Correct answer: 2-year or 10-year storm depending on jurisdiction
Many jurisdictions require temporary sediment basins to be sized for the 2-year or 10-year design storm, though specific requirements vary by state and local regulations.
Question 5: Time of concentration in hydrology refers to:
- The time required to install a BMP
- The time for runoff to travel from the most remote point in a watershed to the outlet (Correct answer)
- The duration of a rainfall event
- The time needed for sediment to settle in a basin
Correct answer: The time for runoff to travel from the most remote point in a watershed to the outlet
Time of concentration is the time it takes for runoff from the hydraulically most distant point in a drainage area to reach the outlet, which affects peak discharge calculations.
Question 6: Concentrated flow on a construction site is more erosive than sheet flow because:
- It contains more chemicals
- It moves faster and exerts greater shear stress on the soil surface (Correct answer)
- It occurs less frequently
- It is easier to control with BMPs
Correct answer: It moves faster and exerts greater shear stress on the soil surface
Concentrated flow channels all runoff into a narrow path, creating higher velocities and greater shear stress on the soil, which significantly increases erosive potential compared to distributed sheet flow.
CEPSCI Stormwater Management and Hydrology 1
The rational method formula Q = CiA is used to calculate: