LARE LARE Stormwater Management 4 — Questions and Answers
Question 1: Which soil hydrologic group has the highest infiltration rate and lowest runoff potential?
- Group A (Correct answer)
- Group B
- Group C
- Group D
Correct answer: Group A
Hydrologic Soil Group A soils (typically sandy or gravelly) have the highest infiltration rates and lowest runoff potential due to their large pore sizes.
Question 2: A landscape architect is designing a rain garden with a ponding depth of 6 inches. The measured soil infiltration rate is 0.5 inches/hour. Approximately how many hours will it take to drain after a storm?
- 3 hours
- 6 hours
- 12 hours (Correct answer)
- 24 hours
Correct answer: 12 hours
Dividing the ponding depth (6 inches) by the infiltration rate (0.5 in/hr) gives a drain time of 12 hours.
Question 3: Which of the following is a characteristic of a 'first flush' in urban stormwater runoff?
- The largest volume of runoff occurs at the beginning of a storm
- The highest concentration of pollutants typically occurs early in a storm event (Correct answer)
- The first 1 inch of rainfall is always the cleanest
- Runoff velocity is highest during the initial minutes of rainfall
Correct answer: The highest concentration of pollutants typically occurs early in a storm event
The 'first flush' phenomenon describes the elevated pollutant concentrations found in the initial portion of stormwater runoff as pollutants accumulated between storms are mobilized.
Question 4: What is the function of an anti-seep collar (seepage collar) in a stormwater pond embankment?
- To filter sediment from outlet flow
- To prevent piping failure along the outlet pipe through the embankment (Correct answer)
- To aerate water as it exits the pond
- To anchor the outlet structure against flotation
Correct answer: To prevent piping failure along the outlet pipe through the embankment
Anti-seep collars increase the seepage path length along the pipe-embankment interface, preventing piping failure — a major cause of embankment dam failure.
Question 5: Which stormwater management strategy best addresses the problem of stream temperature increase caused by urban runoff?
- Increasing detention time in a wet pond
- Using underground detention to avoid solar heating
- Directing runoff through shaded riparian buffers or infiltrating it before it reaches streams (Correct answer)
- Installing mechanical aerators in receiving water bodies
Correct answer: Directing runoff through shaded riparian buffers or infiltrating it before it reaches streams
Infiltrating runoff or routing it through shaded riparian buffers reduces thermal loading to streams by preventing sun-heated impervious surface runoff from direct discharge.
Question 6: In a watershed with significant agricultural land use, which stormwater pollutant is typically the primary water quality concern?
- Heavy metals
- Petroleum hydrocarbons
- Nutrients (nitrogen and phosphorus) (Correct answer)
- Trash and debris
Correct answer: Nutrients (nitrogen and phosphorus)
Agricultural areas are the leading source of nutrient (nitrogen and phosphorus) loading to water bodies through fertilizer and manure runoff, causing eutrophication.
Question 7: What does the term 'headwater protection' mean in the context of stormwater and watershed management?
- Protecting the structural integrity of stormwater pond outlet headwalls
- Conserving upstream source areas to maintain downstream water quality and flow regimes (Correct answer)
- Installing check dams at the tops of drainage swales
- Managing runoff from ridgelines and hilltops
Correct answer: Conserving upstream source areas to maintain downstream water quality and flow regimes
Headwater protection focuses on conserving or restoring upper watershed areas — forests, wetlands, and natural cover — that provide filtration, baseflow, and flow attenuation for the entire watershed.
LARE LARE Stormwater Management 4
Which soil hydrologic group has the highest infiltration rate and lowest runoff potential?