CPESC Stormwater Management 4 — Questions and Answers
Question 1: What does the term 'impervious cover' refer to in stormwater management?
- Vegetation that slows runoff velocity
- Surfaces that prevent or severely limit infiltration of water into soil (Correct answer)
- Geosynthetic liner material used in detention basins
- Compacted soil with reduced permeability
Correct answer: Surfaces that prevent or severely limit infiltration of water into soil
Impervious cover includes surfaces like pavement, rooftops, and compacted areas that prevent rainfall infiltration, increasing runoff volume and peak flows.
Question 2: A stormwater retention pond differs from a detention pond in that a retention pond:
- Releases all water within 24 hours of a storm
- Maintains a permanent pool of water between storm events (Correct answer)
- Uses only dry extended detention
- Treats water through infiltration only
Correct answer: Maintains a permanent pool of water between storm events
Retention ponds maintain a permanent water pool that provides treatment through settling and biological uptake, while detention ponds drain completely between storms.
Question 3: Under post-construction stormwater regulations, what is the typical maximum drawdown time for extended detention facilities treating the water quality volume?
- 12 hours
- 24 hours
- 48 hours (Correct answer)
- 72 hours
Correct answer: 48 hours
Extended detention facilities are typically designed to release the water quality volume over 24-48 hours to promote settling of fine particles.
Question 4: Which best management practice (BMP) is specifically designed to remove sediment from stormwater through gravity settling in a confined area before discharge?
- Vegetated filter strip
- Sediment forebay (Correct answer)
- Riprap channel lining
- Perforated riser pipe
Correct answer: Sediment forebay
A sediment forebay is a pretreatment cell at the inlet of a stormwater BMP designed to capture coarse sediment through gravity settling.
Question 5: The term 'water quality volume' (WQv) typically represents runoff from which storm size?
- The 100-year, 24-hour storm
- The 10-year, 1-hour storm
- A small, frequently occurring storm (e.g., 1-inch or 90th percentile) (Correct answer)
- The 2-year, 24-hour storm
Correct answer: A small, frequently occurring storm (e.g., 1-inch or 90th percentile)
Water quality volume is sized to capture the runoff from small, frequent storms (often 1-inch or the 90th percentile event) that carry the majority of annual pollutant loads.
Question 6: Which component of a wet detention pond is critical for preventing short-circuiting of stormwater flows?
- Emergency spillway elevation
- Inlet-to-outlet separation distance and length-to-width ratio (Correct answer)
- Riprap apron at the inlet
- Anti-seep collar on the barrel pipe
Correct answer: Inlet-to-outlet separation distance and length-to-width ratio
Adequate separation between the inlet and outlet (typically a length-to-width ratio of at least 3:1) prevents stormwater from flowing directly through without adequate treatment time.
Question 7: What is the primary mechanism by which a permeable pavement system manages stormwater?
- Evapotranspiration from pavement surface heating
- Allowing runoff to infiltrate through the pavement into a stone reservoir base (Correct answer)
- Directing runoff to underground cisterns via drains
- Treating runoff with chemical amendments in the base course
Correct answer: Allowing runoff to infiltrate through the pavement into a stone reservoir base
Permeable pavement allows water to pass through the surface and into an aggregate base reservoir, where it infiltrates into the subsoil or is released through an underdrain.
CPESC Stormwater Management 4
What does the term 'impervious cover' refer to in stormwater management?