LARE Drainage System Design Flashcards

A stormwater system must pass a 100-year storm event. Which design element is specifically sized to convey this extreme flow?

Answer: The major conveyance system including overland flow paths and open channels

The major conveyance system — streets, channels, and overland flow paths — is designed to safely convey extreme storm events like the 100-year storm.

Which soil characteristic is most important to measure before designing an infiltration-based BMP such as a permeable pavement system?

Answer: In-situ saturated hydraulic conductivity (Ksat)

In-situ saturated hydraulic conductivity (Ksat) determines how quickly water moves through the native soil, which directly controls infiltration BMP performance.

What is the key hydrologic advantage of green infrastructure over conventional gray infrastructure in urban areas?

Answer: Green infrastructure restores predevelopment hydrology by promoting infiltration and evapotranspiration

Green infrastructure mimics natural hydrology by returning water to the ground and atmosphere, reducing runoff volume and restoring watershed water balance.

A site's pre-development CN (curve number) is 65 and post-development CN is 85. What is the primary design implication?

Answer: Post-development runoff volume will be significantly higher, requiring stormwater management

A higher CN indicates more runoff generation, meaning development has increased impervious cover and requires stormwater management to reduce post-development runoff.

In open channel hydraulics, critical flow occurs when:

Answer: The Froude number equals 1.0

Critical flow occurs when the Froude number (Fr) equals 1.0, representing the transition between subcritical and supercritical flow.

A drainage easement on a plat restricts the placement of structures within 20 feet of a drainage channel. A client wants to build a deck within this easement. What is the landscape architect's best response?

Answer: Advise the client that the easement prohibits the deck and coordinate with the governing jurisdiction for any variance

Drainage easements are legal encumbrances that restrict construction; the designer must advise the client and work through proper legal and regulatory channels.

Which outlet structure configuration best provides both water quality treatment and channel protection for a multi-stage stormwater pond?

Answer: Riser structure with multiple outlets at different elevations controlling different design storms

A multi-stage riser with outlets at different elevations independently controls the water quality volume, channel protection volume, and peak flood control storage.