§ 38-16. Engineering study requirements for floodplain encroachments.

An engineering study is required, as appropriate to the proposed development activities on the site, whenever a development proposes to disturb any land within the future-conditions floodplain, except for a residential single-lot development on streams without established base flood elevations and floodways. This study shall be prepared by a licensed professional engineer and made a part of the application for a permit. This information shall be submitted to and approved by the City of Riverdale Planning and Zoning Department prior to the approval of any permit which would authorize the disturbance of land located within the future-conditions floodplain. Such study shall include:

(1)

Description of the extent to which any watercourse or floodplain will be altered or relocated as a result of the proposed development;

(2)

Step-backwater analysis, using a FEMA-approved methodology approved by the City of Riverdale. Cross-sections (which may be supplemented by the applicant) and flow information will be obtained whenever available. Computations will be shown duplicating FIS results and will then be rerun with the proposed modifications to determine the new base flood profiles, and future-conditions flood profiles;

(3)

Floodplain storage calculations based on cross-sections (at least one every 100 feet) showing existing and proposed floodplain conditions to show that base flood floodplain and future-conditions floodplain storage capacity would not be diminished by the development;

(4)

The study shall include a preliminary plat, grading plan, or site plan, as appropriate, which shall clearly define all future-conditions floodplain encroachments.

( Ord. No. 13-2016 , § 1, 11-14-16)