City of Dardenne Prairie, MO Article III Provisions for Flood Hazard Reduction

Section 415.110 General Standards.

[Ord. No. 1782 §1, 11-18-2015]

A. No floodplain development permit shall be granted for new development or substantial improvements, including the placement of manufactured homes, within any numbered or unnumbered A Zones and AE Zones, unless the conditions of this Section are satisfied.

B. All areas identified as unnumbered A Zones on the FIRM are subject to inundation of the one-percent flood; however, the base flood elevation is not provided. Development within unnumbered A Zones is subject to all provisions of this Chapter. If FIS data is not available, the City shall obtain, review and reasonably utilize any base flood elevation or floodway data currently available from Federal, State or other sources.

C. Agricultural structures may be constructed at grade and floodproofed, provided there is no human habitation or occupancy of the agricultural structure; the agricultural structure is of single-wall design; there is no permanent retail, wholesale, or manufacturing use included in the agricultural structure; a variance has been granted from the floodplain management requirements of this Chapter, if necessary; and a floodplain development permit has been issued.

D. Until a floodway is designated, no new construction, substantial improvements or other development, including fill, shall be permitted within any numbered A Zone or AE Zone on the FIRM, unless it is demonstrated that the cumulative effect of the proposed development, when combined with all other existing and anticipated development, will not increase the water surface elevation of the base flood more than one (1) foot at any point within the City.

E. All new construction, subdivision proposals, substantial improvements, prefabricated structures, placement of manufactured homes and other developments shall require:

1. Design or adequate anchorage to prevent flotation, collapse or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy;

2. Construction with materials resistant to flood damage;

3. Utilization of methods and practices that minimize flood damages;

4. All electrical, heating, ventilation, plumbing, air-conditioning equipment and other service facilities be designed and/or located so as to prevent water from entering or accumulating within the components during conditions of flooding;

5. New or replacement water supply systems and/or sanitary sewage systems be designed to minimize or eliminate infiltration of floodwaters into the systems and discharges from the systems into floodwaters and on-site waste disposal systems be located so as to avoid impairment or contamination; and

6. Subdivision proposals and other proposed new development, including manufactured home parks or subdivisions, located within special flood hazard areas are required to assure that:

a. All such proposals are consistent with the need to minimize flood damage;

b. All public utilities and facilities, such as sewer, gas, electrical and water systems, are located and constructed to minimize or eliminate flood damage;

c. Adequate drainage is provided so as to reduce exposure to flood hazards; and

d. All proposals for development, including proposals for manufactured home parks and subdivisions, of five (5) acres or fifty (50) lots, whichever is lesser, include within such proposals base flood elevation data.

F. Storage, Material and Equipment.

1. The storage or processing of materials within the special flood hazard area that are, in time of flooding, buoyant, flammable, explosive or could be injurious to human, animal or plant life is prohibited.

2. Storage of other material or equipment may be allowed if not subject to major damage by floods, if firmly anchored to prevent flotation or if readily removable from the area within the time available after a flood warning.

G. Accessory Structures. Structures used solely for parking and limited storage purposes, not attached to any other structure on the property, of limited investment value and not larger than four hundred (400) square feet may be constructed at grade and floodproofed, provided there is no human habitation or occupancy of the structure; the structure is of single-wall design; a variance has been granted from the standard floodplain management requirements of this Chapter, if necessary; and a floodplain development permit has been issued.

H. Cumulative Improvement. A structure may be improved (remodeled or enlarged) without conforming to current requirements for elevation so long as the cumulative value of all work done within the last five (5) calendar years does not exceed fifty percent (50%) of the structure's current market value. If the cumulative value of the improvement exceeds fifty percent (50%) of the structure's current market value, the structure must be brought into compliance with Section 415.120.

I. Critical Facilities.

1. All new or substantially improved critical non-residential facilities, including, but not limited to, governmental buildings, police stations, fire stations, hospitals, orphanages, penal institutions, communication centers, water and sewer pumping stations, water and sewer treatment facilities, transportation maintenance facilities, places of public assembly, emergency aviation facilities, and schools shall be elevated above the two-tenths-of-one-percent flood level or together with attendant utility and sanitary facilities, be floodproofed so that below the two-tenths-of-one-percent flood level the structure is watertight with walls substantially impermeable to the passage of water and with structural components having the capability of resisting hydrostatic and hydrodynamic loads and the effects of buoyancy. A registered professional engineer or architect shall certify that the standards of this Subsection are satisfied. Such certification shall be provided to the Floodplain Administrator as set forth in the NFIP regulations.

2. All critical facilities shall have access routes that are above the elevation of the two-tenths of one-percent flood.

J. Hazardous Materials. No hazardous material storage and handling sites shall be located in the floodplain.

K. Nonconforming Use. A structure, or the use of a structure or property, that was lawful before the passage or amendment of this Chapter, but which is not in conformity with the provisions of this Chapter, may be continued subject to the following conditions:

1. If the use of such structure or property is discontinued for a period of more than three hundred sixty-five (365) consecutive days, the structure and any future use of the structure or property shall conform to this Chapter.

2. If any nonconforming use or structure is destroyed by any means, including flood, the structure shall not be reconstructed if the cost is more than fifty percent (50%) of the predamaged market value of the structure. This limitation does not include the cost of any alteration to comply with existing State or local health, sanitary, building, safety codes, regulations or the cost of any alteration of a structure listed on the National Register of Historic Places, the State Inventory of Historic Places, or local inventory of historic places upon determination.

Section 415.120 Specific Standards.

[Ord. No. 1782 §1, 11-18-2015]

A. In all areas identified as numbered and unnumbered A Zones and AE Zones, where base flood elevation data have been provided as set forth in Article III, Section 415.110(B), the following provisions apply:

1. Residential construction. New construction or substantial improvement of any residential structures, including manufactured homes, shall have the lowest floor, including basement, elevated to at least one (1) foot above base flood elevation.

2. Non-residential construction. New construction or substantial improvement of any commercial, industrial or other non-residential structures shall have the lowest floor, including basement, elevated to at least one (1) foot above the base flood elevation or, together with attendant utility and sanitary facilities, be floodproofed so that below the base flood elevation the structure is watertight with walls substantially impermeable to the passage of water and with structural components having the capability of resisting hydrostatic and hydrodynamic loads and effects of buoyancy. A registered professional engineer or architect shall certify that the standards of this Subsection are satisfied. Such certification shall be provided to the Floodplain Administrator as set forth in Article II, Section 415.090(A)(9).

3. For all new construction and substantial improvements, fully enclosed areas below the lowest floor used solely for parking of vehicles, building access or storage in an area other than a basement and 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 (2) openings having a total net area of not less than one (1) square inch for every square foot of enclosed area subject to flooding; and

b. The bottom of all openings shall be no higher than one (1) foot above grade. Openings may be equipped with screens, louvers, valves or other coverings or devices, provided that they permit the automatic entry and exit of floodwaters.

Section 415.130 Manufactured Homes.

[Ord. No. 1782 §1, 11-18-2015]

A. All manufactured homes to be placed within all unnumbered and numbered A Zones and AE Zones on the City's FIRM shall be required to be installed using methods and practices that minimize flood damage. For the purposes of this requirement, manufactured homes must be elevated and 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.

B. Manufactured homes that are placed or substantially improved within unnumbered or numbered A Zones and AE Zones on the City's FIRM on sites that are outside of a manufactured home park or subdivision; in a new manufactured home park or subdivision; in an expansion to an existing manufactured home park or subdivision; or in an existing manufactured home park or subdivision on which a manufactured home has incurred substantial damage as the result of a flood shall be elevated on a permanent foundation such that the lowest floor of the manufactured home is elevated to at least one (1) foot above the base flood elevation and be securely attached to an adequately anchored foundation system to resist flotation, collapse and lateral movement.

C. Manufactured homes that are placed or substantially improved on sites in an existing manufactured home park or subdivision within all unnumbered and numbered A Zones and AE Zones on the City's FIRM, that are not subject to the provisions of Article III, Section 415.130(B) of this Chapter, shall be elevated so that either:

1. The lowest floor of the manufactured home is at least one (1) foot above the base flood level; or

2. The manufactured home chassis is supported by reinforced piers or other foundation elements of at least equivalent strength that are no less than thirty-six (36) inches in height above grade and are securely attached to an adequately anchored foundation system to resist flotation, collapse and lateral movement.

Section 415.140 Floodway.

[Ord. No. 1782 §1, 11-18-2015]

A. Located within areas of special flood hazard established in Article I, Section 415.010, are areas designated as floodways. Since the floodway is an extremely hazardous area due to the velocity of floodwaters that carry debris and potential projectiles, the following provisions shall apply:

1. The City shall select and adopt a regulatory floodway based on the principle that the area chosen for the regulatory floodway must be designed to carry the waters of the base flood without increasing the water surface elevation of that flood more than one (1) foot at any point.

2. The City shall prohibit any encroachments, including fill, new construction, substantial improvements and other development, within the adopted regulatory floodway unless it has been demonstrated through hydrologic and hydraulic analyses performed in accordance with standard engineering practice that the proposed encroachment would not result in any increase in flood levels within the City during the occurrence of the base flood discharge.

3. If Article III, Section 415.140(A)(2) is satisfied, all new construction and substantial improvements shall comply with all applicable flood hazard reduction provisions of Article III.

4. In unnumbered A Zones, the City shall obtain, review and reasonably utilize any base flood elevation or floodway data currently available from Federal, State or other sources as set forth in Article III, Section 415.110(B).

Section 415.150 Recreational Vehicles.

[Ord. No. 1782 §1, 11-18-2015]

A. Recreational vehicles placed on sites within all unnumbered and numbered A Zones and AE Zones on the City's FIRM shall either:

1. Be on the site for fewer than one hundred eighty (180) consecutive days;

2. Be fully licensed and ready for highway use*; or

3. Meet the permitting, elevation and the anchoring requirements for manufactured homes of this Chapter.

* A recreational vehicle is ready for highway use if it is on its wheels or jacking system, is attached to the site only by quick-disconnect-type utilities and security devices and has no permanently attached additions.