CSLB C-27 Landscaping ContractorSite Preparation and DrainageHard
A landscape contractor is designing a swale for surface drainage across a lawn area. The swale needs to be wide and shallow to allow for mowing and pedestrian traffic while effectively channeling water. What is the recommended maximum side slope ratio for a grass-lined swale to ensure stability and ease of maintenance?
- A3:1 (vertical:horizontal)
- B1:1 (vertical:horizontal)
- C2:1 (vertical:horizontal)
- D4:1 (vertical:horizontal)
Show answer & explanationAnswer & explanation
Correct answer: A. 3:1 (vertical:horizontal)
For a grass-lined swale that needs to be stable, easily mowed, and safe for pedestrian traffic, a maximum side slope ratio of 3:1 (3 units horizontal for every 1 unit vertical) is generally recommended. This gentle slope prevents erosion, allows for easy traversing, and accommodates standard mowing equipment, ensuring long-term functionality and aesthetics.
Why the other options are wrong
- B. 1:1 is too steep for a grass-lined swale; it would be prone to erosion, difficult to mow, and unsafe for foot traffic.
- C. 2:1 is still relatively steep for a grass-lined swale, making mowing challenging and increasing erosion potential.
- D. 4:1 is even gentler and also acceptable, but 3:1 is typically the maximum recommended for practical purposes, making it the most appropriate 'maximum' choice among the options that fit the criteria.
Grass-Lined Swale Side Slope
The ratio of horizontal distance to vertical drop for the sides of a grass-lined swale, critical for stability, maintenance, and safety.
- Expressed as H:V (e.g., 3:1).
- Gentler slopes (larger H) are more stable and easier to mow.
- 3:1 is a common maximum for grass-lined swales.
- Prevents erosion and allows for pedestrian access.
Memory trick: Three to One, Safe and Stable, Everyone's Welcome.