Drainage & Stormwater Management Flashcards
7 cards from real NETTCP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Drainage & Stormwater Management flashcards as text
When installing a corrugated metal pipe (CMP) culvert, the minimum cover depth over the crown of the pipe under a roadway is typically determined by:
Answer: The pipe material strength, diameter, and expected live load (vehicle loading)
Minimum cover is determined by structural analysis accounting for pipe wall strength, pipe diameter, and anticipated live load, as insufficient cover causes pipe deflection and failure under vehicle loads.
A French drain (blind drain) differs from a standard storm drain primarily because it:
Answer: Collects and conveys subsurface groundwater without a defined inlet structure
A French drain consists of perforated pipe surrounded by permeable aggregate that passively collects infiltrating groundwater and subsurface flow without a formal surface inlet.
According to typical MassDOT and NHDOT specifications, what maximum pipe deflection is acceptable for flexible pipe (HDPE/PVC) after installation and backfilling?
Answer: 5% of the pipe inside diameter
Most state DOT specifications limit deflection of flexible pipe to 5% of the pipe diameter to ensure structural integrity and long-term performance.
What is the purpose of a geotextile filter fabric wrapped around underdrain aggregate?
Answer: To prevent migration of fine soil particles into the aggregate while allowing water to pass
Geotextile filter fabric acts as a separator allowing water to enter the drain while preventing fine soil particles from migrating into and clogging the permeable aggregate.
During a post-storm inspection of a highway drainage system, you find a catch basin sump filled to within 6 inches of the outlet pipe invert. The appropriate action is to:
Answer: Clean the catch basin immediately to restore design sediment storage capacity
When sediment approaches the outlet invert, it begins to enter the storm sewer and can cause downstream blockages; immediate cleaning is required to restore capacity and prevent system degradation.
Which hydrologic method is most appropriate for computing peak runoff from large complex watersheds (greater than 2,000 acres) for culvert and bridge design in New England?
Answer: NRCS (SCS) Curve Number Method with unit hydrograph
The NRCS Curve Number Method with unit hydrograph is designed for larger, more complex watersheds and accounts for soil type, land use, and storm distribution, making it appropriate where the Rational Method's assumptions break down.
When a stormwater outfall discharges directly to a classified cold-water fishery stream in New England, additional design requirements typically include:
Answer: Thermal impact analysis and possible temperature mitigation measures to protect aquatic habitat
Cold-water fisheries (trout and salmon habitat) are sensitive to thermal pollution; paved surface runoff can significantly elevate water temperature, requiring analysis and mitigation such as detention, shading, or energy dissipation.