NETTCP Drainage & Stormwater Management 1 — Questions and Answers
Question 1: Which type of culvert pipe material is most resistant to corrosion in acidic soil environments common in New England?
- Corrugated metal pipe (CMP)
- Reinforced concrete pipe (RCP)
- High-density polyethylene (HDPE) pipe (Correct answer)
- Cast iron pipe
Correct answer: High-density polyethylene (HDPE) pipe
HDPE pipe is highly resistant to corrosion from acidic soils and is commonly specified in New England where acidic glacial soils are prevalent.
Question 2: What is the primary purpose of a catch basin in a highway drainage system?
- To retain stormwater for groundwater recharge
- To collect surface runoff and trap sediment before it enters the storm sewer (Correct answer)
- To measure peak flow rates during storm events
- To distribute flow evenly across multiple outlet pipes
Correct answer: To collect surface runoff and trap sediment before it enters the storm sewer
Catch basins are designed to intercept surface runoff and allow sediment and debris to settle before water enters the storm sewer system.
Question 3: Manning's equation is used in drainage design primarily to calculate:
- Soil permeability coefficients
- Flow velocity and discharge in open channels and pipes (Correct answer)
- Groundwater table elevation
- Sediment load in stormwater runoff
Correct answer: Flow velocity and discharge in open channels and pipes
Manning's equation relates channel geometry, roughness coefficient, slope, and hydraulic radius to determine flow velocity and discharge.
Question 4: During a culvert inspection, you observe headwater depth approaching the crown of the inlet. This condition indicates:
- The culvert is operating under inlet control at full capacity
- The culvert barrel is undersized or partially blocked and flow is restricted (Correct answer)
- Normal operating conditions for a properly designed culvert
- The outlet is submerged causing backwater effects
Correct answer: The culvert barrel is undersized or partially blocked and flow is restricted
When headwater approaches the crown, it signals the culvert is near or at hydraulic capacity, indicating potential undersizing or blockage that requires attention.
Question 5: What minimum pipe bedding material gradation is typically required beneath drainage pipe to provide uniform support and prevent settlement?
- Bank-run gravel with up to 50% fines
- Clean crushed stone or gravel free of fines, typically 3/4" to 1-1/2" (Correct answer)
- Native soil compacted to 95% density
- Cement-stabilized sand
Correct answer: Clean crushed stone or gravel free of fines, typically 3/4" to 1-1/2"
Clean, well-graded crushed stone or gravel free of fines provides uniform bearing, promotes drainage around the pipe, and prevents point loading that causes cracking.
Question 6: The rational method formula Q = CiA is used to estimate peak stormwater runoff. What does the variable 'C' represent?
- Channel conveyance factor
- Runoff coefficient reflecting land use and soil type (Correct answer)
- Time of concentration in minutes
- Catchment area in acres
Correct answer: Runoff coefficient reflecting land use and soil type
The runoff coefficient C accounts for the fraction of rainfall that becomes surface runoff, varying by land use, soil type, and surface cover.
Question 7: Under federal NPDES Phase II regulations, which of the following highway construction activities requires a stormwater pollution prevention plan (SWPPP)?
- Any project disturbing more than 1 acre of land (Correct answer)
- Only projects within 200 feet of a waterbody
- Projects with an estimated cost exceeding $500,000
- Only projects on federal-aid highways
Correct answer: Any project disturbing more than 1 acre of land
NPDES Phase II requires a SWPPP and permit coverage for construction sites that disturb one or more acres of land, regardless of proximity to water or project cost.
NETTCP Drainage & Stormwater Management 1
Which type of culvert pipe material is most resistant to corrosion in acidic soil environments common in New England?