KDOT Drainage & Storm Water Systems 2 — Questions and Answers
Question 1: What is the primary purpose of a riprap apron placed at a culvert outlet?
- To increase flow velocity
- To prevent erosion by dissipating energy (Correct answer)
- To filter sediment from runoff
- To redirect flow into a detention basin
Correct answer: To prevent erosion by dissipating energy
Riprap aprons dissipate the kinetic energy of water exiting a culvert, preventing scour and erosion at the outlet.
Question 2: During a KDOT inspection, you find a pipe culvert with 25% of its cross-section filled with sediment. What action is required?
- No action needed; up to 30% blockage is acceptable
- Document and schedule cleaning before the next rain event (Correct answer)
- Immediately close the road and replace the culvert
- Install a headwall to increase capacity
Correct answer: Document and schedule cleaning before the next rain event
A culvert with 25% sediment blockage requires documentation and cleaning to restore hydraulic capacity before it worsens.
Question 3: Which type of inlet is most efficient for capturing gutter flow along a roadway curb?
- Drop inlet
- Curb opening inlet (Correct answer)
- Grate inlet set in pavement
- Slotted drain inlet
Correct answer: Curb opening inlet
Curb opening inlets are specifically designed to intercept flow traveling along the gutter line adjacent to a curb.
Question 4: What does the term 'headwater depth' refer to in culvert hydraulics?
- The depth of water in the outlet channel
- The depth of water ponded at the culvert entrance (Correct answer)
- The total length of the culvert barrel
- The velocity of flow at the crown of the pipe
Correct answer: The depth of water ponded at the culvert entrance
Headwater depth is the depth of water above the culvert invert at the inlet, indicating the degree of ponding upstream.
Question 5: A KDOT inspector observes longitudinal cracking along the top of a concrete box culvert. What is the most likely cause?
- Excessive hydraulic pressure from inside the barrel
- Differential settlement or overburden loading (Correct answer)
- Improper joint sealant application
- Freeze-thaw cycling inside the barrel
Correct answer: Differential settlement or overburden loading
Longitudinal cracks at the crown of a box culvert typically indicate differential settlement or excessive fill loading above the structure.
Question 6: Which KDOT-standard material is typically used for slope protection on fill embankments adjacent to drainage channels?
- Asphalt pavement overlay
- Grouted riprap or dry-laid riprap (Correct answer)
- Concrete curbing
- Geotextile fabric alone
Correct answer: Grouted riprap or dry-laid riprap
Grouted or dry-laid riprap is the KDOT standard for protecting embankment slopes from erosion by channel or storm flows.
Question 7: What minimum cover is generally required over a corrugated metal pipe (CMP) culvert under a KDOT roadway to prevent structural failure from traffic loads?
- 6 inches
- 12 inches (Correct answer)
- 18 inches
- 24 inches
Correct answer: 12 inches
KDOT standards generally require a minimum of 12 inches of cover over CMP culverts to adequately distribute traffic loads and prevent collapse.
KDOT Drainage & Storm Water Systems 2
What is the primary purpose of a riprap apron placed at a culvert outlet?