Landscape Design Grading and Drainage 1 — Questions and Answers
Question 1: What is the minimum recommended slope for lawn areas to ensure proper drainage away from structures?
- 1%
- 2% (Correct answer)
- 5%
- 10%
Correct answer: 2%
A 2% minimum slope (approximately 1/4 inch per foot) is the industry standard for directing surface water away from buildings.
Question 2: What does 'finish grade' refer to in landscape design?
- The initial rough grading of a site
- The final elevation of the soil surface after all grading work is complete (Correct answer)
- The grade of the subsoil before topsoil application
- The slope ratio of a retaining wall
Correct answer: The final elevation of the soil surface after all grading work is complete
Finish grade is the final elevation of the ground surface after all grading, soil amendments, and topsoil placement are complete.
Question 3: Which drainage structure collects surface water through a grated inlet and directs it into underground pipes?
- French drain
- Swale
- Catch basin (Correct answer)
- Bioswale
Correct answer: Catch basin
A catch basin is a below-grade structure with a grated surface inlet that intercepts runoff and channels it into an underground pipe system.
Question 4: What is a swale in landscape design?
- A type of retaining wall used on slopes
- A shallow, vegetated channel designed to convey and filter stormwater runoff (Correct answer)
- A deep trench filled with gravel for subsurface drainage
- A raised planting bed for water-loving plants
Correct answer: A shallow, vegetated channel designed to convey and filter stormwater runoff
A swale is a shallow, broad channel that conveys stormwater runoff while allowing infiltration and filtration through vegetation and soil.
Question 5: What percentage of slope is typically required for a paved patio surface to drain effectively?
- 0.5%
- 1–2% (Correct answer)
- 5%
- 8%
Correct answer: 1–2%
Paved surfaces like patios require a 1–2% slope to drain water effectively while remaining comfortable and safe for users.
Question 6: What does 'positive drainage' mean in landscape grading?
- Using pumps to move water uphill to an outlet
- Grading the land so water flows away from structures toward appropriate collection points (Correct answer)
- Installing pressurized underground pipe systems
- Adding soil berms around the perimeter of a property
Correct answer: Grading the land so water flows away from structures toward appropriate collection points
Positive drainage means the site is graded so all surface water naturally flows away from buildings and toward designated drainage outlets, preventing water intrusion.
Question 7: In a grading plan, what do drainage flow arrows indicate?
- The direction of prevailing winds across the site
- The intended direction of surface water movement across the graded site (Correct answer)
- The location of underground drainage pipes
- The orientation of irrigation heads
Correct answer: The intended direction of surface water movement across the graded site
Drainage flow arrows on a grading plan show the intended direction surface water will travel across the finished grade toward collection points or outlets.
Landscape Design Grading and Drainage 1
What is the minimum recommended slope for lawn areas to ensure proper drainage away from structures?