Landscape Design Grading and Drainage 2 — Questions and Answers
Question 1: What is a French drain?
- A decorative drainage channel lined with cobblestones
- A gravel-filled trench containing a perforated pipe that redirects groundwater away from an area (Correct answer)
- A surface channel based on French formal garden design principles
- A type of catch basin with a decorative ornamental grate
Correct answer: A gravel-filled trench containing a perforated pipe that redirects groundwater away from an area
A French drain is a subsurface drainage solution consisting of a gravel-filled trench with a perforated pipe that collects and redirects groundwater away from problem areas.
Question 2: What is the primary purpose of a retaining wall in landscape grading?
- To provide a decorative border between lawn and garden areas
- To hold back soil and resist lateral earth pressure on graded or terraced slopes (Correct answer)
- To channel stormwater into specific drainage collection areas
- To support the root systems of large trees on hillsides
Correct answer: To hold back soil and resist lateral earth pressure on graded or terraced slopes
Retaining walls are structural elements engineered to hold back soil and resist lateral earth pressure when significant changes in grade must be maintained.
Question 3: What term describes water that flows across the soil surface rather than infiltrating into the ground?
- Percolation
- Transpiration
- Runoff (Correct answer)
- Leaching
Correct answer: Runoff
Runoff is water that flows over the ground surface when precipitation exceeds the soil's infiltration capacity or when the surface is impervious.
Question 4: What does 'daylighting' a drain mean in landscape design?
- Installing transparent covers to allow visual inspection of drain pipes
- Extending a drainage pipe until it opens to the surface at a lower elevation (Correct answer)
- Using solar-powered pumps to move water through underground drainage lines
- Orienting drainage channels to receive sunlight and prevent biological growth
Correct answer: Extending a drainage pipe until it opens to the surface at a lower elevation
Daylighting refers to extending an underground drainage pipe to the surface at a lower point so water can exit the system by gravity into a vegetated area or waterway.
Question 5: What is the primary function of a dry well in a landscape drainage system?
- To store harvested rainwater for landscape irrigation use
- To provide a subsurface reservoir that allows collected water to slowly percolate into surrounding soil (Correct answer)
- To filter sediment from surface runoff before it enters underground pipes
- To pump excess groundwater to a municipal stormwater system
Correct answer: To provide a subsurface reservoir that allows collected water to slowly percolate into surrounding soil
A dry well is an underground structure designed to temporarily hold stormwater and allow it to gradually infiltrate into the surrounding native soil.
Question 6: Which instrument is most commonly used to establish and verify grades on a landscape site?
- Theodolite
- Magnetic compass
- Transit level or laser level (Correct answer)
- Soil penetration probe
Correct answer: Transit level or laser level
A transit level or laser level projects a horizontal reference plane across a site, allowing accurate measurement and verification of grade elevations.
Question 7: What does 'cut and fill' mean in landscape grading operations?
- Removing existing vegetation and replanting with erosion-resistant species
- Excavating soil from high areas and relocating it to fill low areas to achieve the desired grade (Correct answer)
- Installing drainage trenches and backfilling them with gravel and pipe
- Removing contaminated topsoil and replacing it with imported clean fill
Correct answer: Excavating soil from high areas and relocating it to fill low areas to achieve the desired grade
Cut and fill is a grading technique where soil excavated from elevated areas (cut) is moved and compacted into lower areas (fill) to achieve the target finished elevation.
Landscape Design Grading and Drainage 2
What is a French drain?