Information For Obtaining A Permit In A Floodway
When property is located in or close to a flood hazard area, or in multiple flood zones, the following will be required:
- Original Construction Drawing Elevation Certificate
- Original Survey from a Mississippi registered engineer or land surveyor
(This survey needs to show the property layout with all zones delineated as they will fall on the property, placement of structure on the property, show elevation shots on the four (4) corners of the proposed structure if it is within the flood zone boundaries)
If the structure is within the floodway boundary, a Mississippi registered engineer must design, stamp, and sign the footing and foundation plan. A Floodway Calculations Data Report and a No-Rise Certification must be submitted with the plans. This must be stamped and signed by a Mississippi registered engineer.
Note: as of October 2000, the zoning ordinance adopted by Harrison County requires that the lowest floor be an additional two (2) feet higher than FEMA's required base flood elevation.
If the structure is a new construction being built, a certification of the lowest floor must be provided within ten (10) days after the lowest floor is established.
(Under construction elevation certificate)
When the structure is completed, a finished construction elevation certificate will need to be furnished before a final inspection can be made.
Procedures for "No Rise' Certification for Proposed Developments in Regulatory Floodways
Section 60.3 (d) (3) of the National Flood Insurance Program (NFIP) regulations states that a community shall "prohibit encroachments, including fill, new construction, substantial improvements, and other development within the adopted regulatory floodway unless it has been demonstrated through hydrologic and hydraulic analyses performed in accordance with standard engineering practice that the proposed encroachment would not result in any increase in flood levels within the community during the occurrence of the base (100 year) flood discharge."
Prior to issuing any building grading or development permits involving activities in a regulatory floodway, the community must obtain a certification stating the proposed development will not impact the pre-project base flood elevations, floodway elevations, or floodway data widths. The certification should be obtained from the permittee and be signed and sealed by a professional engineer.
The engineering or "no-rise" certification must be supported by technical data. The supporting technical data should be based upon the standard step-backwater computer model utilized to develop the 100-year floodway shown on the community's effective Flood Insurance Rate Map or Flood Boundary and Floodway Map (FBFM) and the results tabulated in the community's Flood Insurance Study (FIS).
Although communities are required to review and approve the "no-rise" submittals, they may request technical assistance and review from the FEMA regional office. However, if this alternative is chosen, the community must review the technical submittal package and verify that all supporting data, listed in the following paragraphs,a re included in the package before forwarding to FEMA.
To support a "no-rise" certification for proposed developments encroaching into the the regulatory floodway, a community will require that the following procedures be followed:
- Currently Effective Model
Furnish a written request for the step-backwater computer model for the specified stream and community, identifying the limits of the requested data. A fee will be assessed for providing the data.
Send data requests to:
Federal Emergency Management Agency
1371 Peachtree Street N.E., Suite 735
Atlanta, Ga 30309
FIS Information Specialist
Dewberry & Davis
8401 Arlington Boulevard
Fairfax, Va 22031-4666
- Duplicate Effective Model
Upon receipt of the step-backwater computer model, the engineer should run the original step-backwater model to duplicate the data in the effective FIS.
- Existing Conditions Model
Revise the original step-backwater model to reflect site specific existing conditions by adding new cross-sections (two (2) or more) in the vicinity of the proposed development in place. Floodway limits should be manually set at the new cross-section locations by measuring from the effective FIRM or FBFM. The cumulative reach lengths of the stream should also remain unchanged. The results of the analyses will indicate the 100-year floodway elevations for revised existing conditions at the proposed project site.
- Proposed Conditions Model
Modify the revised existing conditions model to reflect the proposed development at the new cross-sections, while retaining the currently adopted floodway widths. The overbank roughness coefficients should remain the same unless a reasonable explanation of how the proposed development will impact Manning's "n" values should be included with the supporting data. The results of this floodway run will indicate the 100-year floodway elevations for proposed conditions at the project site. These results must indicate NO impact on the 100-year flood elevations, floodway elevations, or floodway widths shown in the Duplicate Effective Model or in the Existing Conditions Model.
The original FIS model, the duplicate effective FIS model, the revised existing conditions model, and the proposed conditions model should all produce the same exact results.
The "no-rise" supporting data and a copy of the engineering certification must be submitted to and reviewed by the appropriate community official prior to issuing a permit.The "no-rise" supporting data should include, but may not be limited to:
- Duplicate of the original FIS step-backwater model printout or floppy disk
- Revised existing conditions step-backwater model
- Proposed conditions step-backwater model
- FIRM and topographic map, showing floodplain and floodway, the additional cross-sections, the site location with the proposed topographic modification superimposed onto the maps, and a photocopy of the effective FIRM or FBFM showing the current regulatory floodway
- Documentation clearly stating analysis procedures. All modifications made to the original FIS model to represent revised existing conditions, as well as those made to the revised existing conditions model to represent proposed conditions, should be well documented and submitted with all supporting data
- Copy off effective Floodway Data Table copied from the FIS report
- Statement defining source of additional cross-section topographic data and proposed conditions
- Certified planemetric (boundary survey) information indicating the location of structures on the property
- Copy of the microfiche, or applicable source, from which input for original FIS HEC-2 model was taken
- Floppy disk with all input files
- Printout of output files from EDIT runs for all three (3) floodway models
The engineering "no-rise" certification and supporting technical data must stipulate NO impact on the 100-year flood elevations, floodway elevations, or floodway widths at the new cross-sections and at all existing cross-sections anywhere in the model. Therefore, the revised computer model should be run for a sufficient distance (usually one (1) mile, depending on hydraulic slope of the stream) upstream and downstream of the development site to insure proper "no-rise" certification.
Attached is a sample "no-rise" certification form that can be completed by a registered professional engineer and supplied to the community along with the supporting technical data when applying for a development permit.