CPII Drainage & Stormwater Management 2 — Questions and Answers
Question 1: What does the Manning's equation primarily calculate in open-channel drainage design?
- The volume of a detention pond required for a 100-year storm
- The flow velocity and discharge in an open channel (Correct answer)
- The groundwater infiltration rate beneath a drainage swale
- The sediment load carried by a stream over time
Correct answer: The flow velocity and discharge in an open channel
Manning's equation is used to calculate flow velocity and volumetric discharge in open channels based on channel geometry, slope, and roughness.
Question 2: An inspector finds that a roadside drainage ditch has experienced severe erosion and channel widening. Which BMP would BEST stabilize the channel long-term?
- Installing a temporary silt fence along the ditch bank
- Lining the channel with riprap or seeding with erosion-resistant vegetation (Correct answer)
- Placing orange construction barrels along the eroded section
- Increasing the ditch depth by excavating to original design elevation
Correct answer: Lining the channel with riprap or seeding with erosion-resistant vegetation
Riprap lining or erosion-resistant vegetation provides durable channel bank protection against hydraulic shear forces that cause erosion.
Question 3: In drainage infrastructure, what is the primary difference between a retention pond and a detention pond?
- Retention ponds are lined with concrete; detention ponds use natural materials
- Retention ponds hold a permanent pool of water; detention ponds drain completely between storms (Correct answer)
- Retention ponds are above ground; detention ponds are underground structures
- Retention ponds are for industrial use; detention ponds are for residential areas
Correct answer: Retention ponds hold a permanent pool of water; detention ponds drain completely between storms
A retention pond maintains a permanent pool of water and provides water quality treatment, while a detention pond is dry between storm events and controls only peak flow.
Question 4: When inspecting a reinforced concrete pipe (RCP) storm drain, which defect classification indicates the pipe requires immediate action?
- Hairline surface cracks with no spalling
- Moderate joint offset with minor leakage
- Full circumferential cracking with active leakage and soil intrusion (Correct answer)
- Slight discoloration from mineral deposits
Correct answer: Full circumferential cracking with active leakage and soil intrusion
Full circumferential cracking with active leakage and soil intrusion indicates imminent structural failure requiring immediate repair or replacement.
Question 5: What is the purpose of a check dam installed in a drainage swale or channel?
- To increase channel velocity and flush accumulated sediment
- To reduce flow velocity and promote sediment deposition upstream (Correct answer)
- To redirect flow to an adjacent retention basin
- To prevent unauthorized vehicle access to drainage easements
Correct answer: To reduce flow velocity and promote sediment deposition upstream
Check dams reduce flow velocity, which allows suspended sediment to settle out and prevents channel erosion downstream.
Question 6: Under the NPDES program, which document must be completed before a stormwater discharge from a construction site can legally begin?
- A soil boring report from a licensed geotechnical engineer
- A Notice of Intent (NOI) filed with the appropriate permitting authority (Correct answer)
- An Environmental Impact Statement (EIS) approved by the EPA
- A dewatering plan signed by a licensed civil engineer
Correct answer: A Notice of Intent (NOI) filed with the appropriate permitting authority
A Notice of Intent (NOI) must be submitted to obtain coverage under the NPDES Construction General Permit before construction activities that disturb soil begin.
Question 7: Which measurement is most important when evaluating whether a storm drain pipe can handle design storm flows without surcharging?
- Pipe material and wall thickness
- Pipe diameter, slope, and Manning's roughness coefficient (Correct answer)
- The pipe installation depth below finished grade
- The number of joints per linear foot of pipe
Correct answer: Pipe diameter, slope, and Manning's roughness coefficient
Pipe diameter, slope, and Manning's roughness coefficient together determine the hydraulic capacity of a storm drain pipe under full-flow conditions.
CPII Drainage & Stormwater Management 2
What does the Manning's equation primarily calculate in open-channel drainage design?