Stormwater Management Flashcards

Which federal regulation requires municipalities in urbanized areas to obtain NPDES permits for their stormwater discharges?

Answer: MS4 Phase I and Phase II rules under 40 CFR Part 122

The MS4 (Municipal Separate Storm Sewer System) Phase I and II rules require NPDES permits for stormwater discharges from urbanized area storm sewer systems.

What is the purpose of a vegetated filter strip in stormwater management?

Answer: Remove pollutants and slow runoff velocity through sheet flow over dense vegetation

Vegetated filter strips treat sheet flow runoff by slowing velocity and allowing infiltration and filtering of sediment and associated pollutants through dense grass.

In the context of watershed hydrology, what does 'time of concentration' (Tc) represent?

Answer: Time required for runoff to travel from the hydraulically most remote point to the watershed outlet

Time of concentration is the travel time of runoff from the most remote point in the watershed to the outlet, used to determine the critical duration storm for peak flow design.

Which condition would INCREASE the runoff curve number (CN) for a site?

Answer: Paving a gravel parking lot with asphalt

Paving a gravel lot with asphalt increases imperviousness significantly, raising the CN value and increasing runoff volume and peak rates.

A constructed wetland used for stormwater treatment primarily removes pollutants through which mechanisms?

Answer: Settling, biological uptake, microbial decomposition, and filtration through vegetation

Constructed stormwater wetlands remove pollutants through a combination of settling, plant uptake, microbial activity, and physical filtration through emergent vegetation.

What is the significance of the 'bankfull discharge' concept in stormwater and stream management?

Answer: The flow that just fills the stream channel to its banks and is most effective at shaping channel morphology

Bankfull discharge, which statistically approximates the 1.5- to 2-year recurrence interval flow, is the dominant channel-forming flow that controls stream morphology.

Which stormwater management approach focuses on managing runoff at the source rather than collecting and conveying it to a centralized facility?

Answer: Distributed or decentralized source control

Distributed or decentralized source control manages stormwater where it falls—through rain gardens, green roofs, and permeable pavement—rather than routing all runoff to large centralized systems.