1. Statement of Intent. The intent of the FF Floodway Fringe District is to require special site planning and construction standards to minimize the threats to personal safety and damage to property caused by flooding.
2. Permitted Development. All development within the FF Floodway Fringe District shall meet all applicable performance standards of the FF Floodway Fringe District and any other ordinance or underlying zoning district as defined in the Story County Land Development Regulations.
3. Development Standards. All development must be consistent with the need to minimize flood damage and meet the following applicable development standards. Until a regulatory floodway is designated no development may increase the Base Flood Elevation more than one (1) foot. The applicant will be responsible for providing the Department of Natural Resources with sufficient technical information to make such a determination.
A. Fill. Any fill allowed shall be subject to the following standards:
(1) No more than twenty percent (20%) of the area of the lot located in the Floodway Fringe District shall be filled above the grade as demonstrated on the 2-foot elevation contours as developed using elevation data from the State of Iowa’s by the 2008 LiDAR program.
(2) The fill material must be compacted to at least ninety five percent (95%) of Standard Laboratory Maximum Dry Density (Standard Proctor), according to ASTB Standard D-698. Fill soils must be fine grained soils of low permeability such as those classified as CH, CL, SC or ML according to ASTM Standard D-2487, "Classification of Soils for Engineering Purposes". The fill material must be homogenous and isotropic.
(3) The fill cannot alter existing drainage patterns on the lot.
(4) A certification from an accredited soil testing professional, certifying that the requirements of this subsection are met, shall be submitted prior to issuance of any permits for further construction on the site.
B. New and Substantially Improved Structures. All new and substantially improved structures shall:
(1) Be adequately anchored to prevent flotation, collapse, or lateral movement of the structure.
(2) Use construction methods and practices that will minimize flood damage.
(3) Use construction materials and utility equipment that are resistant to flood damage.
(4) Fully enclosed areas below the lowest floor (not including basements) which are subject to flooding shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. Designs for meeting this requirement must either be certified by a registered professional engineer or meet or exceed the following minimum criteria:
a. A minimum of two openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding shall be provided.
b. The bottom of all openings shall be no higher than one foot above grade.
c. Openings may be equipped with screens, louvers, valves, or other coverings or devices provided they permit the automatic entry and exit of floodwaters.
d. Such areas shall be used solely for parking of vehicles, structure access and low damage potential storage.
(5) New and substantially improved structures must be designed (or modified) and adequately anchored to prevent flotation, collapse, or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy.
(6) New and substantially improved structures shall be constructed with electric meter, electrical service panel box, hot water heater, heating, air conditioning, ventilation equipment (including ductwork), and other similar machinery and equipment elevated (or in the case on non-residential structures, optionally floodproofed to) a minimum of three (3) foot above the base flood elevation.
(Ord. 293 - Sep. 22 Supp.)
(7) New and substantially improved structures shall be constructed with plumbing, gas lines, water/gas meters and other similar service utilities elevated (or in the case of non-residential structures, optionally floodproofed to) a minimum of three (3) feet above the base flood elevation or designed to be watertight and withstand inundation to such a level.
(Ord. 293 - Sep. 22 Supp.)
C. Residential Structures. All new or substantially improved residential structures shall have the lowest floor (including basements) elevated a minimum of three (3) feet above the one percent annual chance or greater flood level. Construction shall be upon compacted fill meeting the requirements in Subsection 80.13.3.A which shall, at all points, be no lower than three (3) feet above the one percent annual chance or greater flood level and extend at such elevation at least 18 feet beyond the limits of any structure erected thereon.
(1) Alternate methods of elevating (such as piers) may be allowed, subject to favorable consideration by the Board of Adjustment and concurrence of Iowa Department of Natural Resources, as a variance to requirements of Section 80.13(3)(C), where existing topography, street grades, or other factors preclude elevating by fill. In such cases, the methods used must be adequate to support the structure as well as withstand the various forces and hazards associated with flooding.
(2) All new residential structures shall be provided with a means of access which will be passable by wheeled vehicles during the one percent annual chance or greater flood.
D. Nonresidential Structures. All new or substantially improved nonresidential structures shall have the lowest floor (including basement) elevated a minimum of three (3) feet above the one percent annual chance or greater flood level, or together with attendant utility and sanitary systems, be flood proofed to such a level. When flood proofing is utilized, a professional engineer registered in the State of Iowa shall certify that the flood proofing methods used are adequate to withstand the flood depths, pressures, velocities, impact and uplift forces and other factors associated with the one percent annual chance or greater flood; and that the structure, below the one percent annual chance or greater flood level, is watertight with walls substantially impermeable to the passage of water. A record of the certification indicating the specific elevation (in relation to North American Vertical Datum 1988) to which any structures are flood proofed shall be maintained by the Floodplain Manager.
E. Factory-Built Homes. All new and substantially improved factory-built homes, including those placed in existing factory-built home parks or subdivisions, shall be elevated on a permanent foundation such that the lowest floor of the structure is a minimum of three (3) feet above the one percent annual chance or greater flood level. All new and substantially improved factory-built homes, including those placed in existing factory-built home parks or subdivisions, shall be anchored to resist flotation, collapse, or lateral movement. The following specific requirements (or their equivalent) shall be met:
(1) Over-the-top ties shall be provided at each of the four corners of the factory-built home, with two additional ties per side at intermediate locations and factory-built homes less than 50 feet long requiring one additional tie per side.
(2) Frame ties shall be provided at each corner of the home with five additional ties per side at intermediate points and factory-built homes less than 50 feet long requiring four additional per side.
(3) All components of the anchoring system shall be capable of carrying a force of 4,800 pounds.
(4) Any additions to factory-built homes shall be similarly anchored.
F. Utility and Sanitary Systems.
(1) On-site wastewater disposal and water supply systems, including geothermal wells, shall be located or designed to avoid impairment to the system or contamination from the system during flooding.
(2) All new and replacement sanitary sewage systems shall be designed to minimize or eliminate infiltration of floodwaters into the system as well as the discharge of effluent into floodwaters.
(3) Wastewater treatment facilities (other than on-site systems) shall be provided with a level of flood protection equal to or greater than three (3) feet above the one percent annual chance or greater flood elevation.
(4) All new or replacement water supply systems shall be designed to minimize or eliminate infiltration of floodwaters into the system. Water supply treatment facilities (other than on-site systems) shall be provided with a level of protection equal to or greater than three (3) feet above the one percent annual chance or greater flood elevation.
(5) Utilities such as gas or electrical systems shall be located and constructed to minimize or eliminate flood damage to the system and the risk associated with such flood damaged or impaired systems.
G. Storage of Equipment and Materials. Storage of equipment and materials that are flammable, explosive, or injurious to human, animal, or plant life is prohibited unless elevated a minimum of three (3) feet above the one percent annual chance or greater flood level. Other material and equipment must either be similarly elevated or: (i) not subject to major flood damage and anchored to prevent movement due to floodwaters; or (ii) readily removable from the area within the time available after flood warning, subject to submission and approval by the Floodplain Manager of an evacuation plan.
H. Flood Control Structures. Flood control structural works such as levees, flood walls, etc. shall provide, at a minimum, protection from a one percent annual chance or greater flood with a minimum of three feet of design freeboard and shall provide for adequate interior drainage. Structural flood control works shall be approved by the Iowa Department of Natural Resources.
I. Watercourse Alterations or Relocations. Watercourse alterations or relocations must be designed to maintain the flood carrying capacity within the altered or relocated portion. Such alterations or relocations must be approved by the Iowa Department of Natural Resources prior to approval of a permit by Story County.
J. No development shall affect the capacity or conveyance of the channel or floodway of any tributary to the main stream, drainage ditch, or other drainage facility or system.
K. Subdivisions. Subdivisions (including factory-built home parks and subdivisions) shall be consistent with the need to minimize flood damages and shall have adequate drainage provided to reduce exposure to flood damage. Development associated with subdivision proposals (including the installation of public utilities) shall meet the applicable development standards of this chapter as well as those regulations defined in the Story County Land Development Regulations.
(1) Subdivision proposals intended for residential development shall provide all lots with a means of vehicular access that will remain dry during occurrence of the one percent annual chance or greater flood.
(2) Preliminary and Final Plats for all new subdivisions shall include base flood elevation data for those areas located within the Floodway, Floodway Fringe, or General Floodplain Districts.
L. Accessory Structures to Residential Uses.
(1) Detached garages, sheds, and similar structures that are incidental to a residential use are exempt from the base flood elevation requirements where the following criteria are satisfied.
a. The structure shall be designed to have low flood damage potential. The structure shall be used solely for low flood damage potential purposes such as vehicle parking and limited storage. The structure shall not be used for human habitation.
b. Its size shall not exceed 600 sq. ft. in size.
c. Those portions of the structure located less than one (1) foot above the one percent annual chance or greater flood elevation must be constructed of flood-resistant materials.
d. The structure shall be constructed and placed on the building site so as to offer minimum resistance to the flow of floodwaters.
e. The structure shall be firmly anchored to resist flotation, collapse and lateral movement.
f. The structure’s service facilities such as electrical and heating equipment shall be elevated or floodproofed to at least three (3) feet above the one percent annual chance or greater flood elevation.
g. The structure’s walls shall include openings that satisfy the provisions of Section 80.13(3)(B).
(2) Exemption from the one percent annual chance or greater flood elevation requirements for such a structure may result in increased premium rates for flood insurance coverage of the structure and its contents.
M. Recreational Vehicles.
(1) Recreational vehicles are exempt from the requirements of paragraph E of this subsection regarding anchoring and elevation of factory-built homes when the following criteria are satisfied.
a. The recreational vehicle shall be located on the site for less than 180 consecutive days; and
b. The recreational vehicle must be fully licensed and ready for highway use. A recreational vehicle is ready for highway use if it is on its wheels or jacking system and is attached to the site only by quick disconnect type utilities and security devices and has no permanently attached additions.
(2) Recreational vehicles that are located on the site for more than 180 consecutive days and are not ready for highway use must satisfy requirements of paragraph E of this subsection regarding anchoring and elevation of factory-built homes.
N. Pipeline Crossings. Pipeline river or stream crossings shall be buried in the streambed and banks or otherwise sufficiently protected to prevent rupture due to channel degradation, meandering, and the action of flood flows. Only trenchless construction methods shall be permitted for pipeline installations. An undisturbed stream buffer shall be maintained where trenchless methods are also required. The buffer shall be 50 feet or the channel width, measured as the average width between the top of the opposing banks, whichever is greater. The buffer shall be the required width on either side of the stream, measured from the stream edge The buffer may be reduced to the width of the Special Flood Hazard Area in the case that the required buffer is larger than the Special Flood Hazard Area.
(Ord. 302 - Sep. 22 Supp.)
O. Maximum Damage Potential Development. All new or substantially improved maximum damage potential development shall have the lowest floor (including basement) elevated a minimum of three (3) feet above the elevation of the 500-year flood, or together with attendant utility and sanitary systems, be floodproofed to such a level. When floodproofing is utilized, a professional engineer registered in the State of Iowa shall certify that the floodproofing methods used are adequate to withstand the flood depths, pressures, velocities, impact and uplift forces and other factors associated with the 0.2% annual chance flood; and that the structure below the 0.2% annual chance flood elevation is watertight with walls substantially impermeable to the passage of water. A record of the certification indicating the specific elevation (in relation to NAVD 1988 ) to which any structures are floodproofed shall be maintained by the Floodplain Manager. Where 0.2% chance flood elevation data has not been provided in the Flood Insurance Study, the Iowa Department of Natural Resources shall be contacted to compute such data. The applicant will be responsible for providing the Department of Natural Resources with sufficient technical information to make such determinations.