1. General Floodplain Standards. All development must be consistent with the need to minimize flood damage and meet the following applicable performance standards. Where base flood elevations have not been provided in the Flood Insurance Study, the Iowa Department of Natural Resources shall be contacted to determine (i) whether the land involved is either wholly or partly within the floodway or floodway fringe and (ii) the base flood elevation. Until a regulatory floodway is designated, no development may increase the Base Flood Elevation more than one foot. The applicant will be responsible for providing the Department of Natural Resources with sufficient technical information to make such determination. Review by the Iowa Department of Natural Resources is not required for the proposed construction of new or replacement bridges or culverts where (i) the bridge or culvert is located on a stream that drains less than two square miles, and (ii) the bridge or culvert is not associated with a channel modification that constitutes a channel change as specified in 567-71.2(2) of the Iowa Administrative Code.
A. All development within the special flood hazard areas shall:
(1) Be designed and adequately anchored to prevent flotation, collapse, or lateral movement.
(2) Use construction methods and practices that will minimize flood damage.
(3) Use construction materials and utility equipment that are resistant to flood damage.
B. Residential Structures. All new or substantially improved residential structures shall have the lowest floor, including basement, elevated a minimum of one foot above the base flood elevation. Construction shall be upon compacted fill which shall, at all points, be no lower than one foot above the base flood elevation and extend at such elevation at least 18 feet beyond the limits of any structure erected thereon. Alternate methods of elevating (such as piers or extended foundations) may be allowed subject to favorable consideration by the City Council, 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. All new residential structures located in areas that would become isolated due to flooding of surrounding ground shall be provided with a means of access that will be passable by wheeled vehicles during the base flood. However, this criterion shall not apply where the Administrator determines there is sufficient flood warning time for the protection of life and property. When estimating flood warning time, consideration shall be given to the criteria listed in 567-75.2(3) of the Iowa Administrative Code.
C. Non-residential Structures. All new or substantially improved non-residential structures shall have the lowest floor (including basement) elevated a minimum of one foot above the base flood elevation, 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 base flood; and that the structure, below the base 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 North American Vertical Datum 1988) to which any structures are floodproofed shall be maintained by the 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 meet or exceed the following minimum criteria:
a. A minimum of two openings, with positioning on at least two walls, 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.
Such areas shall be used solely for parking of vehicles, building access and low damage potential storage.
(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 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 one foot above the base flood elevation.
(4) New and substantially improved structures shall be constructed with plumbing, gas lines, water and gas meters, and other similar service utilities either elevated (or in the case of non-residential structures, optionally floodproofed to) a minimum of one foot above the base flood elevation or designed to be watertight and withstand inundation to such a level.
E. Factory-built homes.
(1) 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 one foot above the base flood elevation.
(2) 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. Methods of anchoring may include, but are not limited to, use of over-the-top or frame ties to ground anchors. Anchorage systems may include, but are not limited to, use of over-the-top or frame ties to ground anchors as required by the State Building Code.
F. Utility and Sanitary Systems.
(1) On-site waste disposal and water supply systems 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 flood waters into the system as well as the discharge of effluent into flood waters. Wastewater treatment facilities (other than on-site systems) shall be provided with a level of flood protection equal to or greater than one foot above the base flood elevation.
(3) New or replacement water supply systems shall be designed to minimize or eliminate infiltration of flood waters 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 one foot above the base flood elevation.
(4) 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 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 base flood elevation. Other material and equipment must either be similarly elevated or (i) not be subject to major flood damage and be anchored to prevent movement due to flood waters or (ii) 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 the base 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 Department of Natural Resources.
I. Watercourse alterations or relocations must be designed to maintain the flood carrying capacity within the altered or relocated portion. In addition, such alterations or relocations must be approved by the Department of Natural Resources.
J. 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 performance standards of this chapter. Subdivision proposals intended for residential use shall provide all lots with a means of access which will be passable by wheeled vehicles during the base flood. Proposals for subdivisions greater than five acres or 50 lots (whichever is less) shall include base flood elevation data for those areas located within the Special Flood Hazard Area.
K. 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. Its size shall not exceed 600 sq. ft. in size. Those portions of the structure located less than one foot above the base flood elevation must be constructed of flood-resistant materials.
b. 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.
c. The structure shall be constructed and placed on the building site so as to offer minimum resistance to the flow of floodwaters.
d. The structure shall be firmly anchored to resist flotation, collapse, and lateral movement.
e. The structure’s service facilities such as electrical and heating equipment shall be elevated or floodproofed to at least one foot above the base flood elevation.
f. The structure’s walls shall include openings that satisfy the provisions of Subparagraph 9-9-05(1)(D)(1) of this chapter.
(2) Exemption from the base flood elevation requirements for such a structure may result in increased premium rates for flood insurance coverage of the structure and its contents.
L. Recreational Vehicles.
(1) Recreational vehicles are exempt from the requirements of Paragraph 9-9-05(1)(E) of this chapter 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 or are not ready for highway use must satisfy requirements of Paragraph 9-9-05(1)(E) of this chapter 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.
N. Maximum Damage Potential Development. All new or substantially improved maximum damage potential development shall have the lowest floor (including basement) elevated a minimum of one foot 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 two tenths percent annual chance flood; and that the structure, below the two tenths percent 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 North American Vertical Datum 1988) to which any structures are floodproofed shall be maintained by the Administrator. Where two tenths percent 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.
2. Special Floodway Provisions. In addition to the General Floodplain Standards, development within the floodway must meet the following applicable standards. The floodway is that portion of the floodplain which must be protected from developmental encroachment to allow the free flow of flood waters. Where floodway data has been provided in the Flood Insurance Study, such data shall be used to define the floodway. Where no floodway data has been provided, the Department of Natural Resources shall be contacted to provide a floodway delineation. The applicant will be responsible for providing the Department of Natural Resources with sufficient technical information to make such determination.
A. No development shall be permitted in the floodway that would result in any increase in the base flood elevation. Consideration of the effects of any development on flood levels shall be based upon the assumption that an equal degree of development would be allowed for similarly situated lands.
B. All development within the floodway shall:
(1) Be consistent with the need to minimize flood damage.
(2) Use construction methods and practices that will minimize flood damage.
(3) Use construction materials and utility equipment that are resistant to flood damage.
C. No development shall affect the capacity or conveyance of the channel or floodway of any tributary to the main stream, drainage ditch, or any other drainage facility or system.
D. Structures, buildings, recreational vehicles, and sanitary and utility systems, if permitted, shall meet the applicable General Floodplain standards and shall be constructed or aligned to present the minimum possible resistance to flood flows.
E. Structures, if permitted, shall have a low flood damage potential and shall not be for human habitation.
F. Storage of materials or equipment that are buoyant, flammable, explosive or injurious to human, animal or plant life is prohibited. Storage of other material may be allowed if readily removable from the floodway within the time available after flood warning.
G. Watercourse alterations or relocations (channel changes and modifications) must be designed to maintain the flood carrying capacity within the altered or relocated portion. In addition, such alterations or relocations must be approved by the Department of Natural Resources.
H. Any fill allowed in the floodway must be shown to have some beneficial purpose and shall be limited to the minimum amount necessary.
I. Pipeline river or stream crossings shall be buried in the streambed and banks or otherwise sufficiently protected to prevent rupture due to channel degradation and meandering or due to the action of flood flows.
I. Pipeline river or stream crossings shall be buried in the streambed and banks or otherwise sufficiently protected to prevent rupture due to channel degradation and meandering or due to the action of flood flows.