Stormwater Management & Drainage Engineering Flashcards

The Rational Method formula Q = CiA is used to estimate which quantity in stormwater design?

Answer: Peak runoff discharge

The Rational Method calculates peak runoff discharge (Q) in cubic feet per second using runoff coefficient (C), rainfall intensity (i), and drainage area (A).

What does NPDES stand for in the context of stormwater regulation?

Answer: National Pollution Discharge Elimination System

NPDES (National Pollution Discharge Elimination System) is the EPA permit program that controls water pollution by regulating point sources that discharge pollutants into waters of the United States, including stormwater.

In stormwater design, 'time of concentration' (Tc) is defined as:

Answer: The time for runoff to travel from the hydraulically most remote point in a watershed to the design point

Time of concentration is the travel time for runoff from the hydraulically most remote point in the watershed to reach the outlet, which determines the critical storm duration for peak flow calculations.

What is the primary functional difference between a retention pond and a detention pond?

Answer: Retention ponds hold a permanent pool of water; detention ponds drain completely between storms

Retention ponds maintain a permanent pool of water (wet ponds) and provide additional storage above the permanent pool, while detention ponds (dry ponds) temporarily store runoff and drain completely between storm events.

Manning's equation is primarily used in stormwater engineering to calculate:

Answer: Flow velocity and discharge in open channels and pipes

Manning's equation (V = (1/n) R^(2/3) S^(1/2)) calculates flow velocity in open channels and pipes based on hydraulic radius, slope, and Manning's roughness coefficient, which allows discharge to be computed.

A '100-year storm event' in municipal drainage design refers to:

Answer: A storm with a 1% annual probability of exceedance

A 100-year storm has a 1% probability of being equaled or exceeded in any given year, meaning it is a statistical return period rather than a guarantee of a 100-year recurrence interval.

Which of the following best describes green infrastructure in the context of stormwater management?

Answer: Practices that mimic natural hydrology by infiltrating, evapotranspiring, or harvesting stormwater near its source

Green infrastructure uses natural processes — such as bioretention, rain gardens, green roofs, and permeable pavements — to manage stormwater at or near its source, reducing runoff volume and improving water quality.