CFM Hydrology & Hydraulics Flashcards

The '100-year flood' is best described as a flood that has a:

Answer: 1% chance of being equaled or exceeded in any given year

The 100-year flood (Base Flood) has a 1% annual chance of being equaled or exceeded, meaning it can occur multiple times in any 100-year period.

Which hydrologic method is most commonly used in FEMA flood studies to estimate peak discharge for small urban watersheds?

Answer: TR-55 (SCS Curve Number Method)

TR-55, developed by the USDA Soil Conservation Service, uses the Curve Number method to estimate runoff and peak discharge and is widely used in FEMA studies for small watersheds.

In hydraulic analysis, Manning's Equation is used to calculate:

Answer: Open-channel flow velocity and discharge

Manning's Equation relates channel geometry, roughness coefficient (n), hydraulic radius, and slope to compute average flow velocity and discharge in open channels.

The HEC-RAS software model is primarily used in flood studies to perform:

Answer: One-dimensional steady and unsteady open-channel hydraulic analysis

HEC-RAS (Hydrologic Engineering Center – River Analysis System) performs 1D and 2D steady and unsteady flow hydraulic analysis to compute water surface profiles.

What does the 'regulatory floodway' represent in a hydraulic study?

Answer: The channel and adjacent floodplain reserved to carry base flood flows without increasing BFE by more than 1 foot

The regulatory floodway is the channel plus the portion of floodplain that must remain open to convey the base flood discharge without increasing BFE by more than 1 foot.

Which parameter in the SCS Curve Number method most directly reflects soil type and land use?

Answer: Curve Number (CN)

The Curve Number (CN) encapsulates the combined effect of soil hydrologic group and land cover/use to estimate direct runoff from rainfall.