G103.3 Determination of flood elevations.

Flood elevations shall be determined in accordance with Sections G103.3.1 through G103.3.2.

G103.3.1 Determination of base flood elevations.

Where the proposed development is within a special flood hazard area but the base flood elevations are not specified in the FEMA FIRMs 360497, the commissioner shall require the applicant to request base flood elevation data from the New York State Department of Environmental Conservation (DEC); and

   1.   Submit to the commissioner either:

      1.1.   A letter from DEC making such a determination of base flood elevation; or

      1.2.   A letter from the DEC indicating that the data are not available. When such a letter from DEC indicates that the data are not available, the base flood elevation shall be equal to 3 feet (914 mm) above the highest adjacent pre-FIRM grade.

   Exception: Large lots. Where the base flood elevation is not specified, the applicant shall submit a detailed engineering study establishing the base flood elevation, performed by an engineer in accordance with accepted hydrologic and hydraulic engineering techniques, in sufficient detail to allow review by the commissioner for any of the following conditions:

      1.   For a development which is located on a tax lot greater than 5 acres (2.02 hectares), or is located on property that was part of a tax lot that was greater than 5 acres (2.02 hectares) at the time of the adoption of the FIRM (October 1, 1984), or at any subsequent applicable map change thereto; or

      2.   For subdivisions resulting in 50 or more tax lots, including all tax lots previously subdivided from the same tax lot since the adoption of the FIRM (October 1, 1984), or since any subsequent applicable map changes thereto.

G103.3.2 Determination of 500-year flood elevations.

Where 500-year flood elevations are not specified in the FEMA FIRMs 360497 or FEMA FIS 360497, such elevations shall be determined by a registered design professional using modeling based on generally accepted engineering methods or a review of available data from city, state and federal agencies.

G103.4 Reserved.

G103.5 Floodway encroachment.

Prior to issuing a permit for any floodway encroachment, including fill, new construction, substantial improvements and other development or land-disturbing activity, the commissioner shall require submission of a certification, prepared by a registered design professional, along with supporting technical data, demonstrating that such development will not cause any increase of the level of the base flood.

G103.5.1 Floodway revisions.

A floodway encroachment that increases the level of the base flood is authorized if the applicant has applied for a conditional Flood Insurance Rate Map (FIRM) revision and has received the approval of the Federal Emergency Management Agency (FEMA).

G103.6 Watercourse alteration.

Prior to issuing a permit for any alteration or relocation of any watercourse within a special flood hazard area, the commissioner shall require the applicant to:

   1.   Notify any affected adjacent municipalities or government jurisdictions;

   2.   Notify the DEC;

   3.   Submit evidence of such notifications to the commissioner and the Regional Director, Region II, the Federal Emergency Management Agency (FEMA);

   4.   Submit to the commissioner evidence of all such notifications;

   5.   Submit an engineering analysis demonstrating that the flood-carrying capacity of the altered or relocated portion of the watercourse will not be decreased; and

   6.   Submit evidence that such watercourses will be maintained in a manner which preserves the channel's flood-carrying capacity.

G103.7 Alterations in coastal areas .

Prior to issuing a permit for any alteration of sand dunes in coastal high-hazard areas and coastal A- zones, the commissioner shall require submission of an engineering analysis, prepared by a registered design professional, demonstrating that the proposed alteration will not increase the potential for flood damage.

G103.8 Records.

The commissioner shall maintain records of the following:

   1.   Applications and supporting documents for development in flood hazard areas;

   2.   Permits issued in flood hazard areas;

   3.   Inspection reports;

   4.   Certifications required in this appendix; and

   5.   Certificate of occupancy where applicable.