CSLB C-27 Landscaping ContractorSite Preparation and DrainageMedium
A landscape contractor is designing a subsurface drainage system for a large, flat lawn area that experiences frequent waterlogging. To effectively collect and remove excess water, what is the typical recommended spacing between parallel perforated drain pipes in heavy clay soil?
- A20 to 30 feet
- B5 to 10 feet
- C30 to 50 feet
- D10 to 20 feet
Show answer & explanationAnswer & explanation
Correct answer: D. 10 to 20 feet
In heavy clay soils, which have low permeability, drain pipes need to be spaced closer together to effectively intercept and remove excess water. A typical recommendation for heavy clay is 10 to 20 feet between parallel perforated drain pipes.
Why the other options are wrong
- A. 20 to 30 feet is more appropriate for loamy soils or soils with moderate permeability, not heavy clay.
- B. 5 to 10 feet might be used in extremely impermeable or critical areas, but is generally closer than typical for heavy clay.
- C. 30 to 50 feet would be suitable for highly permeable sandy soils, which allow water to move more freely to the drains.
Drain Pipe Spacing (Clay Soil)
In heavy clay soils, perforated drain pipes should be spaced 10 to 20 feet apart to effectively manage waterlogging due to low permeability.
- Closer spacing for lower soil permeability.
- Wider spacing for higher soil permeability (e.g., sand).
- Ensures adequate dewatering of the root zone.
Memory trick: Clay means 'close' pipes, sand means 'spread' pipes.