LARE LARE Stormwater Management 2 — Questions and Answers
Question 1: Which stormwater BMP is specifically designed to treat road runoff containing high concentrations of heavy metals and petroleum hydrocarbons?
- Constructed wetland
- Vegetated filter strip
- Dry extended detention basin
- Bioretention cell with amended soil media (Correct answer)
Correct answer: Bioretention cell with amended soil media
Bioretention cells with engineered soil media are particularly effective at removing heavy metals and hydrocarbons through adsorption and biological uptake.
Question 2: What is the primary purpose of a forebay in a stormwater retention pond?
- To aerate the water before it enters the main pool
- To capture coarse sediment before it enters the main pond (Correct answer)
- To regulate overflow during large storm events
- To provide habitat for aquatic vegetation
Correct answer: To capture coarse sediment before it enters the main pond
A forebay is a smaller settling chamber at the inlet of a stormwater pond that captures coarse sediment, reducing maintenance needs for the main pool.
Question 3: Under the Rational Method (Q = CiA), if the drainage area doubles but the runoff coefficient and rainfall intensity remain constant, what happens to peak runoff?
- It remains the same
- It doubles (Correct answer)
- It quadruples
- It increases by the square root of 2
Correct answer: It doubles
In the Rational Method, peak runoff Q is directly proportional to area A, so doubling A doubles Q when C and i are constant.
Question 4: Which approach does Low Impact Development (LID) primarily emphasize for managing stormwater?
- Centralizing large detention basins at the downstream end of the watershed
- Treating stormwater at the source through distributed, small-scale practices (Correct answer)
- Increasing pipe sizing to convey runoff faster
- Applying chemical treatments to neutralize pollutants
Correct answer: Treating stormwater at the source through distributed, small-scale practices
LID emphasizes distributed, small-scale practices that manage runoff close to its source, mimicking pre-development hydrology.
Question 5: A site has a pre-development CN of 58 and a post-development CN of 80. What is the primary concern this change reflects?
- Decreased evapotranspiration rates
- Significantly increased runoff volume and peak flow (Correct answer)
- Reduced groundwater contamination risk
- Improved water quality through increased contact time
Correct answer: Significantly increased runoff volume and peak flow
A higher Curve Number (CN) indicates greater imperviousness, resulting in significantly more runoff volume and higher peak flows after development.
Question 6: Which factor is most critical when sizing a stormwater infiltration trench?
- Depth to seasonal high groundwater table (Correct answer)
- Proximity to impervious surfaces
- Slope of the contributing drainage area
- Vegetation type surrounding the trench
Correct answer: Depth to seasonal high groundwater table
Infiltration trenches must maintain adequate separation (typically 2-4 feet) from the seasonal high groundwater table to prevent groundwater contamination and ensure adequate storage.
Question 7: What is 'channel protection volume' (Cpv) in stormwater management design?
- The storage needed to prevent overtopping of channel banks during the 100-year storm
- Storage designed to control frequent runoff events that cause stream channel erosion (Correct answer)
- The volume of sediment deposited annually in a stream channel
- The minimum channel cross-section required for fish passage
Correct answer: Storage designed to control frequent runoff events that cause stream channel erosion
Channel protection volume (Cpv) is designed to control the frequent 1-year storm event runoff, which is the primary driver of bank erosion and channel instability.
LARE LARE Stormwater Management 2
Which stormwater BMP is specifically designed to treat road runoff containing high concentrations of heavy metals and petroleum hydrocarbons?