CTQP Drainage Systems Inspection 5 — Questions and Answers
Question 1: Which type of drainage structure is specifically designed to remove sediment and debris from stormwater before it enters the pipe system?
- Junction box
- Nutrient-separating baffle box (NSBB) (Correct answer)
- Drop inlet
- Manhole with flat top
Correct answer: Nutrient-separating baffle box (NSBB)
An NSBB uses internal baffles to trap sediment, floatables, and debris before stormwater enters the conveyance system.
Question 2: During inspection of a corrugated metal pipe (CMP), an inspector finds that the pipe invert has lost more than 40% of its wall thickness due to corrosion. What should the inspector recommend?
- Apply a bituminous coating to slow future corrosion
- Schedule a follow-up inspection in 12 months
- Recommend immediate pipe replacement or structural lining (Correct answer)
- Increase the maintenance cleaning frequency
Correct answer: Recommend immediate pipe replacement or structural lining
Loss of more than 25–40% of CMP wall thickness is generally the threshold requiring replacement or structural rehabilitation to prevent collapse.
Question 3: What is the purpose of a flared end section (FES) on a culvert?
- To increase hydraulic roughness at the culvert entrance
- To transition flow smoothly and improve hydraulic efficiency while reducing embankment erosion (Correct answer)
- To prevent wildlife from entering the culvert barrel
- To serve solely as an energy dissipator at the culvert outlet
Correct answer: To transition flow smoothly and improve hydraulic efficiency while reducing embankment erosion
A flared end section reduces entrance losses, improves the hydraulic coefficient of discharge, and protects the embankment slope from erosion at inlet and outlet.
Question 4: When inspecting roadside swales after a storm event, an inspector observes rills and small channels eroded into the swale bottom. What does this indicate?
- The swale is functioning correctly with adequate velocities
- Flow velocities are exceeding the erosive velocity of the soil, requiring erosion protection (Correct answer)
- Sediment deposition is blocking the swale and must be removed
- The swale cross-section is oversized for the contributing drainage area
Correct answer: Flow velocities are exceeding the erosive velocity of the soil, requiring erosion protection
Rilling in a swale bottom indicates flow velocities exceed the permissible velocity for the soil type, and erosion protection measures are needed.
Question 5: Which document serves as the primary reference for drainage inspection procedures and condition rating in Florida CTQP Drainage training?
- AASHTO Drainage Manual, 4th Edition
- FDOT Drainage Manual and FDOT Structures Inspection Manual (Correct answer)
- FHWA Hydraulic Design Series No. 5 (HDS-5)
- ASTM C76 Standard Specification for Reinforced Concrete Culvert Pipe
Correct answer: FDOT Drainage Manual and FDOT Structures Inspection Manual
FDOT's Drainage Manual and Structures Inspection Manual are the primary state-specific references for Florida CTQP drainage inspection procedures.
Question 6: An inspector observes that a stormwater pond's control structure weir board is missing one of three boards. What is the most likely consequence?
- The pond will drain faster than designed, reducing water quality treatment time (Correct answer)
- The pond will overflow its embankment more frequently
- Sediment will accumulate faster at the pond outlet
- The pond water surface will rise above the design normal pool elevation
Correct answer: The pond will drain faster than designed, reducing water quality treatment time
A missing weir board lowers the effective weir crest, causing the pond to drain sooner and reducing hydraulic retention time needed for pollutant settling.
Question 7: What condition exists when a culvert operates with the outlet submerged but the pipe is not flowing full under pressure throughout its length?
- Inlet control with free-surface flow
- Outlet control with full-pipe pressure flow
- Outlet control with partly full (open-channel) pipe flow (Correct answer)
- Inlet control with pressure flow at the inlet
Correct answer: Outlet control with partly full (open-channel) pipe flow
When tailwater submerges the outlet but the pipe does not run under full pressure, the culvert operates under outlet control with open-channel (partly full) flow.
CTQP Drainage Systems Inspection 5
Which type of drainage structure is specifically designed to remove sediment and debris from stormwater before it enters the pipe system?