CFS Floodplain Mapping & Elevation Determination 2 — Questions and Answers
Question 1: On a FIRM, what does a Zone AE designation indicate?
- Area outside the 500-year floodplain
- Special Flood Hazard Area with Base Flood Elevations determined (Correct answer)
- Area of minimal flood hazard
- Coastal high-hazard area with wave action
Correct answer: Special Flood Hazard Area with Base Flood Elevations determined
Zone AE is a Special Flood Hazard Area where BFEs have been determined through detailed hydraulic analysis.
Question 2: What vertical datum is currently used for most FEMA FIRMs produced after 1991?
- NGVD 29
- NAVD 88 (Correct answer)
- IGLD 85
- WGS 84
Correct answer: NAVD 88
NAVD 88 (North American Vertical Datum of 1988) replaced NGVD 29 as the standard datum for modern FIRMs.
Question 3: A Letter of Map Amendment (LOMA) is appropriate when a structure is removed from a SFHA based on what condition?
- The structure has been elevated on fill
- Natural ground elevation is at or above the BFE (Correct answer)
- A levee has been constructed nearby
- A new hydrologic study was performed
Correct answer: Natural ground elevation is at or above the BFE
A LOMA is used when the natural ground (not fill) at or around a structure is at or above the BFE, indicating the FIRM incorrectly included that property.
Question 4: Which cross-section data element is most critical for determining the BFE at a specific river reach using the HEC-RAS model?
- Manning's roughness coefficient (Correct answer)
- Watershed area
- Soil infiltration rate
- Land use classification
Correct answer: Manning's roughness coefficient
Manning's n values define channel and floodplain roughness, directly controlling computed water-surface elevations in HEC-RAS.
Question 5: What is the purpose of a 'Starting Water Surface Elevation' (starting WSEL) in a step-backwater analysis?
- Sets the upstream boundary condition for flow routing
- Provides the downstream boundary condition from which computations proceed upstream (Correct answer)
- Defines the 100-year flood frequency
- Establishes the NAVD 88 benchmark elevation
Correct answer: Provides the downstream boundary condition from which computations proceed upstream
In subcritical flow, HEC-RAS computes upstream from a known downstream starting WSEL, which serves as the boundary condition.
Question 6: A floodway is defined as the channel plus the portion of the floodplain needed to convey the 1% annual chance flood while not increasing the BFE by more than how many feet?
- 0.5 feet
- 1.0 foot (Correct answer)
- 2.0 feet
- 3.0 feet
Correct answer: 1.0 foot
FEMA's standard allows a maximum 1.0-foot surcharge (encroachment increase) when establishing the regulatory floodway.
Question 7: Which FEMA product provides the official flood zone determination for a specific parcel when the FIRM panel boundary falls through the property?
- FIS Report
- FIRM Index
- FEMA Map Service Center print
- Flood Zone Determination from a certified flood zone researcher (Correct answer)
Correct answer: Flood Zone Determination from a certified flood zone researcher
When a FIRM panel boundary bisects a property, a certified flood zone determination is used to identify the applicable flood zone(s) for that parcel.
CFS Floodplain Mapping & Elevation Determination 2
On a FIRM, what does a Zone AE designation indicate?