1. Statement of Intent. The GF General Floodplain District reflects those areas that would be inundated during a one percent annual chance or greater flood, but for which specific flood elevations and Floodway and Floodway Fringe limits have not been established. It is the intent of the GF General Floodplain District to impose the development standards of the Floodway and Floodway Fringe after a determination is made to identify the Floodway and Floodway Fringe areas on an individual project basis.
2. Applicant’s Burden to Define Floodway and Floodway Fringe Boundary. Where one percent annual chance or greater flood data has not been provided in the Flood Insurance Study, the burden to demonstrate the boundary of the Floodway and Floodway Fringe rests on the applicant.
3. Permitted Development. The following development shall be permitted within the GF General Floodplain District to the extent they are not prohibited by any other ordinance or underlying zoning district as defined in the Story County Land Development Regulations and provided they do not include placement of structures, factory-built homes, fill or other obstructions, the storage of materials or equipment, excavation or alteration of a watercourse.
A. Agricultural uses such as general farming, pasture, grazing, outdoor plant nurseries, horticulture, viticulture, truck farming, forestry, sod farming and wild crop harvesting.
B. Industrial-commercial uses such as loading areas, parking areas, airport landing strips.
C. Private and public recreational uses such as golf courses, tennis courts, driving ranges, archery ranges, picnic grounds, boat launching ramps, swimming areas, parks, wildlife and nature preserves, game farms, fish hatcheries, shooting preserves, target ranges, trap and skeet ranges, hunting and fishing areas, hiking and horseback riding trails.
D. Residential uses such as lawns, gardens, parking areas and play areas.
E. Replacement or Newly Constructed Bridges and/or Culverts. The requirement to define the floodway and floodway fringe boundary does not apply to proposed replacement or newly constructed bridges and/or culverts wherein the bridge and/or culvert is:
(1) Located in a rural (unincorporated) area where the stream drains less than 100 square miles or in an urban (incorporated) area where the stream drains less than two square miles; and
(2) Not associated with a channel modification that constitutes a channel change as specified in 567-71.2(1)b, Iowa Administrative Code.
In cases of bridges and/or culverts not in compliance with the aforementioned criteria, as well as projects not associated with bridges and/or culverts located within the GF General Floodplain, the following development standards shall apply and review by the Iowa Department of Natural Resources is required.
F. Streambank Stabilizations and Drainage Ditch Maintenance. The requirement to define the floodway and floodway fringe boundary does not apply to proposed drainage ditch maintenance completed by the drainage district in accordance with Chapter 468 of the Code of Iowa and stream bank stabilizations wherein:
(1) Spoils are disposed of outside of the Special Flood Hazard Area or spread less than six inches thick in an even layer away from the top of the bank; and
(2) No fill is proposed; and
(3) Revetment material, if proposed, is placed so that it does not extend past the existing bank or, in the case of severe erosion so that the resulting channel cross-section is not more restrictive than the adjacent natural upstream and downstream channel cross-sections and the revetment material does not extend above the adjacent top of the bank. Revetment material shall also comply with the following best practices, as illustrated in Figure 1:
a. The stream bank is prepared by sloping or terracing prior to the placement of gravel bedding and/or fabric under the revetment material.
b. The revetment material consists of a mixture of sizes so as to form a dense, interlocking blanket.
c. The revetment material is placed on the existing or prepared stream bank with a finished slope of no steeper than two (2) feet horizontal to one (1) foot vertical rise.
d. Revetment material is restricted to field stone, quarry rock and broken concrete. All exposed reinforcing steel shall be removed or cut flush with the surface of the concrete prior to placement. Any concrete slabs larger than three feet across shall be broken into smaller pieces prior to placement. The use of asphalt or other solid waste is prohibited.
e. The thickness of a revetment blanket shall not exceed three (3) feet.
f. A toe of revetment material to protect against scour and erosion is also proposed.
(4) For mowed banks, a finished slope of no steeper than three (3) feet horizontal to one (1) foot vertical rise is recommended.
(5) Other professionally accepted best practices for stream bank stabilization may be utilized at the discretion of the Floodplain Manager or their designee, such as those included in Iowa’s River Restoration Toolbox, as amended by the Iowa Department of Natural Resources.
G. The Floodplain Manager may require the floodway and floodway fringe boundary to be defined in the case development proposed under 80.14(3)(E) or 80.14(3)(F) may increase flood levels, impede flood flows, or otherwise creates a risk for downstream life or property.
(Ord. 312 – Oct. 23 Supp.)