CFM CFM Hydrology & Hydraulics 2 — Questions and Answers
Question 1: A watershed with impervious surfaces increased from 10% to 40% will generally experience what change in peak runoff?
- Peak runoff decreases due to increased infiltration
- Peak runoff increases due to reduced infiltration and faster response time (Correct answer)
- Peak runoff remains unchanged if detention is provided
- Peak runoff increases only during 500-year events
Correct answer: Peak runoff increases due to reduced infiltration and faster response time
Increased impervious cover reduces infiltration and shortens time of concentration, resulting in higher and faster peak runoff from the same storm event.
Question 2: What is the primary purpose of a 'No-Rise Certification' in floodway encroachment analysis?
- To certify that a new structure will not sink into saturated soils
- To demonstrate that proposed development will not increase the BFE in the floodway (Correct answer)
- To confirm that a FIRM revision is not needed
- To certify that a property is naturally above the BFE
Correct answer: To demonstrate that proposed development will not increase the BFE in the floodway
A No-Rise Certification, sealed by a licensed engineer, verifies that proposed floodway encroachment will not cause any increase in BFE based on hydraulic modeling.
Question 3: Which of the following best describes 'effective hydraulic connectivity' in floodplain management?
- The structural connection between levee panels
- The ability of floodwaters to move freely across the floodplain without obstruction (Correct answer)
- The efficiency of stormwater inlets in capturing runoff
- The link between FEMA's mapping database and local GIS systems
Correct answer: The ability of floodwaters to move freely across the floodplain without obstruction
Effective hydraulic connectivity refers to the unobstructed movement of floodwaters across the floodplain, which is critical for maintaining conveyance and reducing upstream flood levels.
Question 4: In a Detailed Flood Insurance Study, cross-section data is used in hydraulic modeling to determine:
- Soil permeability
- Water surface elevations at specific locations along a stream (Correct answer)
- Storm sewer capacity
- Groundwater recharge rates
Correct answer: Water surface elevations at specific locations along a stream
Cross-sections represent channel and floodplain geometry at selected locations, enabling HEC-RAS or similar models to compute water surface elevations for the base flood discharge.
Question 5: What does a Flood Insurance Rate Map (FIRM) show that an older Flood Hazard Boundary Map (FHBM) did not?
- The general location of the 100-year floodplain only
- Base Flood Elevations and insurance risk zones (Correct answer)
- Historical flood extents from recorded events
- Levee certification status
Correct answer: Base Flood Elevations and insurance risk zones
FIRMs include Base Flood Elevations and detailed flood insurance risk zones derived from engineering studies, providing quantitative data that FHBMs lacked.
Question 6: The 'regulatory floodway fringe' (flood fringe) is defined as:
- The area within the floodway where development is prohibited
- The portion of the 100-year floodplain outside the floodway that can accommodate limited development (Correct answer)
- The area between the 10-year and 50-year flood boundaries
- The coastal zone subject to wave run-up
Correct answer: The portion of the 100-year floodplain outside the floodway that can accommodate limited development
The flood fringe is the area of the 100-year floodplain outside the designated floodway; it can be developed if structures are elevated to or above BFE.
CFM CFM Hydrology & Hydraulics 2
A watershed with impervious surfaces increased from 10% to 40% will generally experience what change in peak runoff?