CSLB C-27 Landscaping ContractorSite Preparation and DrainageMedium
A landscape contractor is designing a swale for surface drainage across a lawn area. To ensure stability and ease of mowing, what is the generally recommended maximum side slope ratio for a grass-lined swale?
- A4:1 (vertical:horizontal)
- B2:1 (vertical:horizontal)
- C3:1 (vertical:horizontal)
- D1:1 (vertical:horizontal)
Show answer & explanationAnswer & explanation
Correct answer: C. 3:1 (vertical:horizontal)
A 3:1 (horizontal:vertical) side slope ratio is generally recommended as the maximum for grass-lined swales. This balance provides sufficient stability for the soil and vegetation, prevents erosion, and allows for safe and easy mowing with standard equipment.
Why the other options are wrong
- A. A 4:1 slope is even gentler and provides excellent stability and ease of maintenance, but 3:1 is typically the maximum recommended for practical purposes.
- B. A 2:1 slope is steep for a grass-lined swale; it can be prone to erosion, difficult to establish turf, and challenging to mow.
- D. A 1:1 slope is too steep for a grass-lined swale; it would be unstable, highly prone to erosion, and impossible to mow safely.
Grass-Lined Swale Side Slope
The maximum recommended side slope ratio for a grass-lined swale, typically 3:1 (horizontal:vertical), to ensure stability, prevent erosion, and allow for safe maintenance.
- Ensures soil stability and prevents sloughing.
- Allows for establishment of dense turf to prevent erosion.
- Facilitates safe operation of mowing equipment.
- Steeper slopes are prone to erosion and difficult to maintain.
Memory trick: Three to one, for a stable, mowable swale that's fun.