Stormwater Management Flashcards

Which parameter is NOT part of the Rational Method formula for peak runoff calculation?

Answer: Time of concentration (Tc)

The Rational Method formula Q = CiA uses the runoff coefficient, rainfall intensity, and drainage area; time of concentration is used to determine rainfall intensity but is not directly in the formula.

Green infrastructure practices that mimic natural hydrology are often grouped under what broad term?

Answer: Low Impact Development (LID)

Low Impact Development (LID) encompasses practices that manage stormwater close to the source by mimicking natural hydrologic processes.

A bioretention cell differs from a rain garden primarily in that it:

Answer: Is designed for larger drainage areas and includes engineered soil media and underdrain

Bioretention cells are engineered systems with specified soil media, gravel layers, and underdrains designed for larger areas, while rain gardens are simpler residential-scale features.

What is 'first flush' in stormwater management?

Answer: The phenomenon where the highest pollutant concentrations occur in the early portion of a runoff event

The first flush effect describes the disproportionately high pollutant loads carried by the initial runoff that washes accumulated pollutants off impervious surfaces.

Which of the following is an example of a volume-based stormwater management requirement?

Answer: Retaining the 1-inch water quality volume on-site

Retaining a water quality volume (typically 1 inch) on-site is a volume-based requirement focused on treating runoff from frequent, smaller storms.

An infiltration trench is most suitable for soils with a minimum saturated hydraulic conductivity (Ksat) of approximately:

Answer: 0.27 inch/hour

Infiltration practices typically require a minimum Ksat of about 0.27 inch/hour (0.5 cm/hr) to ensure adequate drainage within 72 hours.

Which pollutant is of greatest concern in stormwater runoff from parking lots and roadways?

Answer: Polycyclic aromatic hydrocarbons (PAHs) and heavy metals

Parking lots and roadways generate PAHs from vehicle exhaust and tire wear, along with heavy metals like zinc, copper, and lead from vehicle components.