CPESC Stormwater Management 2 — Questions and Answers
Question 1: What is the primary purpose of a stormwater detention basin?
- Permanently store runoff to reduce total volume
- Temporarily store runoff to reduce peak discharge rates (Correct answer)
- Filter pollutants through biological uptake
- Infiltrate all runoff into the groundwater table
Correct answer: Temporarily store runoff to reduce peak discharge rates
Detention basins temporarily hold stormwater to attenuate peak flow rates before releasing water at a controlled rate.
Question 2: Which hydrologic method is most commonly used to estimate peak runoff rates for small watersheds in the US?
- SWMM continuous simulation
- Rational Method (Q = CiA) (Correct answer)
- TR-55 Tabular Hydrograph
- USGS StreamStats regression
Correct answer: Rational Method (Q = CiA)
The Rational Method (Q = CiA) is the most widely used approach for small urban watersheds to estimate peak runoff rates.
Question 3: A Curve Number (CN) of 98 indicates what type of land surface?
- Highly permeable forest with good cover
- Moderately permeable grassland
- Nearly impervious surface such as pavement or rooftops (Correct answer)
- Poorly drained agricultural land
Correct answer: Nearly impervious surface such as pavement or rooftops
A CN of 98 represents nearly impervious surfaces where almost all rainfall becomes runoff with minimal infiltration.
Question 4: What is the function of an outlet control structure's emergency spillway?
- Regulate normal pool elevation during design storms
- Handle flows exceeding the principal spillway capacity to prevent dam failure (Correct answer)
- Filter sediment before discharge
- Provide low-flow channel maintenance releases
Correct answer: Handle flows exceeding the principal spillway capacity to prevent dam failure
The emergency spillway safely passes extreme storm flows that exceed the principal spillway's capacity, preventing overtopping and dam failure.
Question 5: Under the EPA's NPDES Construction General Permit, what rainfall threshold typically triggers a site inspection requirement?
- 0.10 inch
- 0.25 inch (Correct answer)
- 0.50 inch
- 1.00 inch
Correct answer: 0.25 inch
The EPA CGP typically requires site inspections after any storm event of 0.25 inch or greater within a 24-hour period.
Question 6: Which soil group has the LOWEST runoff potential according to the NRCS hydrologic soil group classification?
- Group A (Correct answer)
- Group B
- Group C
- Group D
Correct answer: Group A
Hydrologic Soil Group A has the highest infiltration rates and lowest runoff potential, consisting of well-drained sands and gravels.
Question 7: What stormwater management practice involves routing runoff through a shallow, vegetated channel to promote infiltration and filtering?
- Dry swale (Correct answer)
- Wet pond
- Cistern
- Underground vault
Correct answer: Dry swale
A dry swale is a vegetated, linear depression that conveys and treats stormwater through filtering and infiltration before it reaches receiving waters.
CPESC Stormwater Management 2
What is the primary purpose of a stormwater detention basin?