LARE Drainage System Design Flashcards

A landscape architect is designing a rain garden on a residential lot with silty clay soils. Which modification is most appropriate to improve performance?

Answer: Amend native soil with compost and sand to improve infiltration

Amending heavy clay soils with compost and sand increases infiltration rates, which is essential for rain garden function.

In the Rational Method (Q = CiA), what does the runoff coefficient 'C' represent?

Answer: The fraction of rainfall that becomes surface runoff

The runoff coefficient C represents the proportion of rainfall that becomes surface runoff, ranging from 0 (no runoff) to 1 (all rainfall runs off).

Which stormwater BMP is best suited to treat highway runoff containing petroleum hydrocarbons and heavy metals?

Answer: Underground hydrodynamic separator

Hydrodynamic separators are effective at removing sediment-bound metals and hydrocarbons from concentrated highway runoff in space-constrained sites.

What is the primary purpose of a flared end section (FES) at a culvert outlet?

Answer: To reduce outlet velocity and minimize erosion at the discharge point

A flared end section spreads and slows the discharge, reducing scour and erosion at the culvert outlet.

During a grading review, a plan shows a drainage divide running through the center of a proposed parking lot. What does this mean for stormwater design?

Answer: Runoff flows in two directions toward separate drainage systems or outfalls

A drainage divide is the high point from which runoff flows in opposite directions, requiring separate stormwater management for each drainage area.

Which factor most significantly increases the time of concentration (Tc) for a watershed?

Answer: Increasing the length of the drainage path

A longer drainage path increases travel time, which directly increases the time of concentration.

A retention pond differs from a detention pond primarily because it:

Answer: Maintains a permanent pool of water between storm events

A retention pond maintains a permanent pool that provides water quality treatment through settling and biological uptake, while detention ponds drain completely.