Stormwater Management and Hydrology Flashcards

The rational method formula Q = CiA is used to calculate:

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).

A peak discharge from a construction site is most critical because:

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.

Which factor in the rational method accounts for the type of ground surface?

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.

What is the design storm typically used for sizing temporary sediment basins?

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.

Time of concentration in hydrology refers to:

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.

Concentrated flow on a construction site is more erosive than sheet flow because:

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.