Chapter 25.86 FLOOD PLAIN MANAGEMENT AND OVERLAY ZONES


Section 25.86.120 Floodway Fringe Overlay District (FF).

    1. Permitted Uses. All uses within the Floodway Fringe District shall be permitted to the extent that they are not prohibited by any other ordinance or by the underlying zoning district and provided they meet applicable performance standards of the Floodway Fringe District.
    2. Performance Standards. All uses must be consistent with the need to minimize flood damage and shall meet the following applicable performance standards:
        a. All structures shall be
            (1) Adequately anchored to prevent flotation, collapse or lateral movement of the structure,
            (2) Constructed with materials and utility equipment resistant to flood damage, and
            (3) Constructed by methods and practices that minimize flood damage.
        b. Residential Buildings. All new or substantially improved residential structures shall have the lowest floor, including basements, elevated a minimum of one foot above the 100-year flood level.  Construction shall be upon compacted fill which shall, at all points, be no lower than one foot above the 100-year flood level and extend at such elevation at least 18 feet beyond the limits of any structure erected thereon. Alternate methods of elevating (such as piers) may be allowed, subject to favorable consideration by the Board of Adjustment and issuance of a Conditional Use Permit, 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 withstanding the various forces and hazards associated with flooding.
        c. Non-Residential Buildings. All new and substantially improved nonresidential buildings shall have the lowest floor (including basement) elevated a minimum of one foot above the 100-year flood level, or together with attendant utility and sanitary systems, be floodproofed to such a level. When floodproofing is utilized, a professional engineer or architect 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 100-year flood; and that the structure, below the 100-year 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 National Geodetic Vertical Datum) to which any structures are floodproofed shall be maintained by the Zoning Administrator.
        d. All new and substantially improved structures:
            (1) Fully enclosed areas below the "lowest floor" (not including basements) that 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 architect 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 that they permit the automatic entry and exit of floodwaters.
            (2) 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.
            (3) New and substantially improved structures must be constructed with electrical, heating, ventilation, plumbing, and air conditioning equipment and other service facilities that are designed and/or located so as to prevent water from entering or accumulating within the components during conditions of flooding.
        e. Factory-built structures:
            (1) Factory-built structures including those placed in existing mobile home parks or subdivisions shall be anchored to resist flotation, collapse, or lateral movement.  Methods of anchoring may include, but are not limited to, use of over-the-top or frame ties to ground anchors.
            (2) Factory-built structures including those placed in existing mobile home parks or subdivisions shall be elevated on a permanent foundation such that the lowest floor of the structure is a minimum of one foot above the 100-year flood level.
        f. Utility and Sanitary Systems:
            (1) All new and replacement sanitary sewage systems shall be designed to minimize and eliminate infiltration of flood waters into the system as well as the discharge of effluent into flood waters. Wastewater treatment facilities shall be provided with a level of flood protection equal to or greater than one foot above the 100-year flood elevation.
            (2) On-site waste disposal systems shall be located or designed to avoid impairment to the systems or contamination from the systems during flooding.
            (3) New or replacement water supply systems shall be designed to minimize or eliminate infiltration of flood waters into the systems. Water supply treatment facilities shall be provided with a level of protection equal to or greater than one foot above the 100-year flood elevation.
            (4) Utilities such as gas or electrical systems shall be located and constructed to minimize or eliminate flood damage to the systems and the risk associated with such flood damaged or impaired systems.
        g. Storage of materials and equipment that are flammable, explosive or injurious to human, animal or plant life is prohibited unless elevated a minimum of one foot above the 100-year flood level. Other material and equipment must either be similarly elevated or
            (1) not be subject to major flood damage and be anchored to prevent movement due to flood waters or
            (2) be readily removable from the area within the time available after flood warning.
        h. Flood control structural works such as levees, flood walls, etc. shall provide, at a minimum, protection from a 100-year flood with a minimum of three feet of design freeboard and shall provide for adequate interior drainage. In addition, structural flood control works shall be approved by the Iowa Department of Natural Resources.
        i. No use 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.
        j. Subdivisions (including mobile 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 shall meet the applicable performance standards of this ordinance.  Subdivision proposals intended for residential use shall provide all lots with a means of access which will be passable by wheeled vehicles during the 100-year flood.  Proposals for subdivisions greater than 5 acres or 50 lots (whichever is less) shall include 100-year flood elevation data for those areas located within the Flood Plain (Overlay) District.
        k. The exemption of detached garages, sheds, and similar structures from the 100-year elevation requirements may result in increased premium rates for insurance coverage of the structure and contents, however, said detached garages, sheds, and similar accessory type structures are exempt from the 100-year flood elevation requirements when:
            (1) The structure shall not be used for human habitation.
            (2) The structure shall be designed to have low flood damage potential.
            (3) The structure shall be constructed and placed on the building site so as to offer minimum resistance to the flow of floodwaters.
            (4) Structures shall be firmly anchored to prevent flotation which may result in damage to other structures.
            (5) The structure's service facilities such as electrical and heating equipment shall be elevated or floodproofed to at least one foot above the 100-year flood level.
        l. Recreational vehicles.
            (1) Recreational vehicles are exempt from the requirements of subsection (e) above 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. 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 permanent attached additions.
            (2) Recreational vehicles that are located on the site for more than 180 consecutive days or are not ready for highway use must satisfy the requirements of subsection (e) above regarding anchoring and elevation of factory-built homes.
        m. Pipeline river and stream crossings shall be buried in the streambed and banks, or otherwise sufficiently protected to prevent rupture due to channel degradation and meandering.
(Ord. 2001-0415; 89/T-7348)