KDOT Drainage & Storm Water Systems 5 — Questions and Answers
Question 1: Under KDOT's NPDES permit requirements, what must be in place before earth-disturbing activities begin on a highway construction project?
- A completed stormwater pollution prevention plan (SWPPP) (Correct answer)
- A final as-built drainage report
- A signed 404 permit from the Army Corps of Engineers
- An approved construction noise ordinance waiver
Correct answer: A completed stormwater pollution prevention plan (SWPPP)
KDOT projects must have an approved SWPPP in place before any earth disturbance to comply with NPDES stormwater permit requirements.
Question 2: What is the purpose of a check dam installed in a roadside swale?
- To permanently impound water for wildlife habitat
- To slow flow velocity and reduce erosion in steep swales (Correct answer)
- To filter oil and grease from pavement runoff
- To redirect flow away from the roadway surface
Correct answer: To slow flow velocity and reduce erosion in steep swales
Check dams are low barriers placed across swales to reduce flow velocity on steeper grades, thereby limiting erosion and allowing sediment to settle.
Question 3: A KDOT inspector notes that a storm sewer manhole lid is sunken 3 inches below the pavement surface. What hazard does this primarily present?
- Increased hydraulic head reducing inlet capacity
- Vehicle damage and potential loss of vehicle control (Correct answer)
- Groundwater contamination from pavement runoff
- Structural failure of the downstream pipe barrel
Correct answer: Vehicle damage and potential loss of vehicle control
A sunken manhole lid creates a roadway hazard that can cause vehicle damage, tire impact, and possible loss of vehicle control.
Question 4: What is the Manning's roughness coefficient (n) used to calculate in open channel and culvert hydraulics?
- The hydraulic gradient of the channel bed
- The frictional resistance affecting flow velocity in a channel or pipe (Correct answer)
- The sediment transport capacity of the flow
- The storm recurrence interval for the drainage area
Correct answer: The frictional resistance affecting flow velocity in a channel or pipe
Manning's n quantifies the frictional resistance of the channel boundary, directly affecting the calculated flow velocity and discharge.
Question 5: During a post-storm inspection, a KDOT inspector finds that a silt fence has been breached and sediment has entered an adjacent waterway. What must be done first?
- Remove the damaged silt fence and install permanent grass
- Stop additional discharge, contain the spill, and notify the appropriate environmental contacts (Correct answer)
- Document the breach in the inspection log and defer action to next week
- Install additional riprap downstream to capture the sediment
Correct answer: Stop additional discharge, contain the spill, and notify the appropriate environmental contacts
A sediment discharge to a waterway is a potential NPDES permit violation requiring immediate containment of further discharge and notification of environmental contacts.
Question 6: What is the primary difference between a retention basin and a detention basin in highway storm water management?
- Retention basins are lined with concrete; detention basins are earthen
- Retention basins maintain a permanent pool of water; detention basins drain completely between storms (Correct answer)
- Detention basins are designed for 100-year storms; retention basins for 10-year storms
- Retention basins have no outlet; detention basins have multiple outlets
Correct answer: Retention basins maintain a permanent pool of water; detention basins drain completely between storms
Retention basins hold a permanent water pool and provide water quality benefits, while detention basins temporarily store runoff and drain completely after each storm.
Question 7: Which measurement is used to determine whether a culvert has adequate hydraulic opening for the design storm without exceeding allowable headwater?
- Culvert length divided by pipe diameter
- Discharge capacity at the design headwater elevation (Correct answer)
- Manning's n value of the barrel material
- Outlet channel width at the floodplain boundary
Correct answer: Discharge capacity at the design headwater elevation
The culvert's discharge capacity at the allowable headwater elevation is compared to the design storm discharge to verify adequate hydraulic opening.
KDOT Drainage & Storm Water Systems 5
Under KDOT's NPDES permit requirements, what must be in place before earth-disturbing activities begin on a highway construction project?