CFM CFM Hydrology & Hydraulics 1 — Questions and Answers
Question 1: The '100-year flood' is best described as a flood that has a:
- 1% chance of being equaled or exceeded in any given year (Correct answer)
- Recurrence interval of exactly 100 years
- 1% chance of occurring once per century
- 100-year return period with no annual variation
Correct 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.
Question 2: Which hydrologic method is most commonly used in FEMA flood studies to estimate peak discharge for small urban watersheds?
- Manning's Equation
- Rational Method
- TR-55 (SCS Curve Number Method) (Correct answer)
- Muskingum Routing
Correct 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.
Question 3: In hydraulic analysis, Manning's Equation is used to calculate:
- Rainfall runoff volume
- Open-channel flow velocity and discharge (Correct answer)
- Sediment transport rates
- Time of concentration
Correct 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.
Question 4: The HEC-RAS software model is primarily used in flood studies to perform:
- Rainfall-runoff simulation
- One-dimensional steady and unsteady open-channel hydraulic analysis (Correct answer)
- Two-dimensional groundwater modeling
- Coastal wave height prediction
Correct 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.
Question 5: What does the 'regulatory floodway' represent in a hydraulic study?
- The entire 100-year floodplain
- The channel and adjacent floodplain reserved to carry base flood flows without increasing BFE by more than 1 foot (Correct answer)
- The area between the 10-year and 100-year flood boundaries
- The area subject to wave action
Correct 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.
Question 6: Which parameter in the SCS Curve Number method most directly reflects soil type and land use?
- Time of concentration (Tc)
- Curve Number (CN) (Correct answer)
- Lag time
- Hydraulic radius
Correct 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.
CFM CFM Hydrology & Hydraulics 1
The '100-year flood' is best described as a flood that has a: