Flood Study Facts
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A flood study must be performed if the proposed construction activity involves a roadway, driveway and other encroachments crossing through Wake County Flood hazard soils or FEMA floodplain.
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A flood study may be conducted in order to define the flood boundaries for a stream that is not in a designated FEMA flood hazard area.
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A flood study or flood soils re-delineation may be conducted to show that a building site is not in a flood hazard area.
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A flood study is an engineering analysis of the impact of the proposed encroachment during the 100-year storm.
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A flood study must be performed by a Professional Engineer or Professional Land Surveyor and reviewed by Wake County Floodplain Management Staff.
What is included in a flood study submittal?
A Flood Study submittal includes an application, submittal checklist, site plans and calculations.
- Flood Study Plan Checklist
- Application
Fees will be invoiced through the Permit Portal.
The fee for each minor flood study (drainage area less than 100 acres) is $500. The fee for each major flood study (drainage areas of 100 acres or more), including No Rise Certifications and CLOMRs, is $1,000
Minor Flood Study
A minor flood study is required for development proposed in flood hazard soil locations involving 25 acres or more of drainage area but less than 100 acres of drainage area. The permit review fee is $500 per crossing or encroachment area. The analysis may be conducted using NCDOT Hydraulics Guidance.
The study shall delineate HW/D backwater area plus 1 (one) foot rise and label as Q100 backwater easement and label FFE on all affected lots with Special Flood Hazard Areas.
Major Flood Study
A major flood study is required for development in flood hazard soil locations involving 100 acres or more of drainage area or a FEMA mapped area. The analysis shall be submitted using HEC-RAS modeling.
The study shall delineate HW/D backwater area plus 1 (one) foot rise and label as Q100 backwater easement and label FFE on all affected lots with Special Flood Hazard Areas.
The State Model Plan recommends a 4 foot freeboard above BFE.
CLOMRs and No Rise Certifications
A Letter of Map Revision is required for new development shown to modify FEMA mapped elevations. A No Rise Certification may be requested when the development is shown to result in no change to flood elevations. Review by Local, State and Federal floodplain officials may be required. These are considered a major flood study and shall be uploaded through the Permit Portal.