CSLB C-27 Landscaping ContractorSite Preparation and DrainageHard
A landscape contractor is designing a subsurface drainage system for a large, flat lawn area that experiences standing water after rain. To effectively collect and remove excess water, what is the generally recommended maximum spacing between parallel perforated drain pipes in heavy clay soils?
- A10 feet
- B20 feet
- C5 feet
- D30 feet
Show answer & explanationAnswer & explanation
Correct answer: A. 10 feet
In heavy clay soils, water infiltrates very slowly. To effectively capture and remove excess water, perforated drain pipes need to be spaced relatively close together. A maximum spacing of 10 feet is generally recommended for adequate drainage in clay.
Why the other options are wrong
- B. 20 feet is typically suitable for loamy or sandy soils, which have much higher infiltration rates than clay.
- C. 5 feet would provide excellent drainage but is often more than necessary and increases installation cost significantly.
- D. 30 feet is too wide for effective drainage in clay soils, leading to areas of persistent saturation between pipes.
Subsurface Drain Pipe Spacing (Clay)
The maximum distance between parallel perforated drain pipes in heavy clay soils to ensure effective collection and removal of excess subsurface water, typically 10 feet.
- Clay soils have low permeability, requiring closer pipe spacing.
- Purpose is to intercept water before it causes saturation.
- Spacing depends on soil type, depth of pipe, and desired drainage rate.
- Wider spacing for sandy/loamy soils, narrower for clay.
Memory trick: Clay is slow, so 10 feet is the way to go.