CTQP Drainage Systems Inspection 2 — Questions and Answers
Question 1: What is an 'inlet' in a storm drainage system?
- The downstream connection of a pipe to a retention pond
- A structure that collects surface runoff and directs it into the underground pipe system (Correct answer)
- The opening in a retention pond berm for overflow
- A valve that controls flow into a detention system
Correct answer: A structure that collects surface runoff and directs it into the underground pipe system
A drainage inlet is a structure (curb inlet, grate inlet, junction box) that collects surface water and channels it into the underground storm sewer system.
Question 2: What is the minimum longitudinal slope required for storm drain pipes to maintain self-cleaning velocity?
- 0.10%
- 0.20%
- 0.50% (Correct answer)
- 1.00%
Correct answer: 0.50%
A minimum pipe slope of approximately 0.5% is generally required to maintain a self-cleaning velocity of about 2.5 feet per second in storm drain pipes.
Question 3: What is a 'French drain' or 'underdrains'?
- A drainage system imported from European construction standards
- A subsurface perforated pipe system that collects and removes groundwater or infiltrated water (Correct answer)
- A surface swale with a French curve alignment
- A deep drainage well connected to an aquifer
Correct answer: A subsurface perforated pipe system that collects and removes groundwater or infiltrated water
Underdrains (French drains) are subsurface systems using perforated pipe surrounded by filter aggregate to intercept and remove groundwater that would otherwise weaken the pavement subgrade.
Question 4: What does 'hydraulic gradient' refer to in storm drainage design?
- The slope of the pipe invert
- The slope of the energy line in a pipe system under pressure or gravity flow (Correct answer)
- The rate at which water enters the drainage system
- The difference in elevation between two manholes
Correct answer: The slope of the energy line in a pipe system under pressure or gravity flow
The hydraulic gradient is the slope of the pressure or energy line through a drainage system, and must remain below the rim of manholes and inlets to prevent surcharging.
Question 5: When inspecting a reinforced concrete pipe (RCP) joint, what is the inspector checking for?
- The type of reinforcing steel used in the pipe wall
- Proper gasket installation, joint gap, and alignment between pipe sections (Correct answer)
- The concrete mix design used in pipe fabrication
- The thickness of the pipe wall at the joint
Correct answer: Proper gasket installation, joint gap, and alignment between pipe sections
At RCP joints, the inspector verifies that the rubber gasket is properly seated, the joint gap is within tolerance, and the pipe sections are properly aligned without offsets.
Question 6: What is 'endwall scour' and how is it prevented?
- Corrosion of metal pipe ends; prevented by galvanizing
- Erosion at the outlet of a culvert caused by high-velocity flow; prevented by riprap or energy dissipators (Correct answer)
- Cracking of concrete headwalls; prevented by using air-entrained concrete
- Settlement at the headwall foundation; prevented by deep footings
Correct answer: Erosion at the outlet of a culvert caused by high-velocity flow; prevented by riprap or energy dissipators
Outlet scour is erosion at the downstream end of a culvert caused by high-velocity discharge; it is controlled by placing riprap, concrete aprons, or other energy dissipators at the outlet.
CTQP Drainage Systems Inspection 2
What is an 'inlet' in a storm drainage system?