CFS Surveying Techniques & Data Documentation 2 — Questions and Answers
Question 1: When performing a cross-section survey for a flood study, at what minimum interval are cross-sections typically required in meandering stream reaches?
- Every 100 feet regardless of channel geometry
- At every bend apex and inflection point, plus additional sections to capture geometry changes (Correct answer)
- Only at bridges and culverts
- At uniform 500-foot intervals throughout the study reach
Correct answer: At every bend apex and inflection point, plus additional sections to capture geometry changes
In meandering reaches, cross-sections must capture the channel geometry at bend apexes and inflection points, with additional sections added wherever significant changes in shape or roughness occur.
Question 2: A surveyor uses a total station to measure a horizontal distance of 1,250 feet. The instrument displays a slope distance of 1,252.3 feet and a vertical angle of +2°10'. What is the correct horizontal distance?
- 1,249.3 feet (Correct answer)
- 1,250.5 feet
- 1,252.3 feet
- 1,248.1 feet
Correct answer: 1,249.3 feet
Horizontal distance = slope distance × cos(vertical angle); 1252.3 × cos(2°10') ≈ 1249.3 feet.
Question 3: Which datum is required for all FEMA Flood Insurance Rate Map (FIRM) elevations submitted after 2015?
- NGVD 29
- NAVD 88 (Correct answer)
- MLLW
- WGS 84 ellipsoid height
Correct answer: NAVD 88
FEMA requires all FIRM elevations to be referenced to NAVD 88 for submissions after 2015.
Question 4: During a Level 2 structure survey for FEMA, what does the term 'LAG' refer to?
- Lowest Adjacent Grade to the structure (Correct answer)
- Lowest Available Ground elevation
- Lateral Adjustment Grade
- Levee Alignment Grade
Correct answer: Lowest Adjacent Grade to the structure
LAG stands for Lowest Adjacent Grade, the lowest natural ground surface elevation adjacent to a structure, used in flood insurance rating.
Question 5: A surveyor establishes a benchmark network for a flood study using differential leveling. The allowable closure error for Third-Order leveling is:
- ±3 mm √K
- ±8 mm √K
- ±12 mm √K (Correct answer)
- ±24 mm √K
Correct answer: ±12 mm √K
FGDC standards specify Third-Order leveling closure tolerance of ±12 mm √K, where K is the distance in kilometers.
Question 6: When documenting field survey data for a LOMR, which information is NOT required on a survey field sketch?
- North arrow and scale
- Datum and benchmark used
- Surveyor's license number
- Property owner's Social Security Number (Correct answer)
Correct answer: Property owner's Social Security Number
Personal identification such as Social Security Numbers is never required on field survey documentation; only professional and technical information is needed.
Question 7: What is the purpose of collecting 'overbank' cross-section data in a floodplain survey?
- To calculate channel bank full discharge only
- To define the floodplain geometry that conveys flow during flood events beyond the main channel (Correct answer)
- To establish property boundary lines
- To measure sediment transport rates
Correct answer: To define the floodplain geometry that conveys flow during flood events beyond the main channel
Overbank data defines the floodplain geometry on both sides of the main channel that carries floodwater during events exceeding bankfull discharge.
CFS Surveying Techniques & Data Documentation 2
When performing a cross-section survey for a flood study, at what minimum interval are cross-sections typically required in meandering stream reaches?