16.36.145 Shallow flooding areas (AO zones).
Shallow flooding areas appear on FIRMs as AO zones with depth designations. The base flood depths in those zones range from 1 to 3 feet where a clearly defined channel does not exist, or where the path of flooding is unpredictable and where velocity flow may be evident. Such flooding is usually characterized as sheet flow. In these areas, the following provisions apply:
A. Require adequate drainage paths around structures on slopes to guide floodwaters around and away from proposed structures, and to ensure that floodwater in likely flow pathways such as swales is not blocked and cause it to be diverted to adjacent properties.
B. New construction, substantial improvement of any residential structure and manufactured home, and improvement of any post-FIRM residential structure and manufactured home within AO zones shall have the lowest floor (including basement) elevated to or above the flood protection elevation level and highest adjacent grade to the structure, 2 feet or more above the depth number specified in feet on the community’s FIRM (at least 3 feet above the highest adjacent grade to the structure if no depth number is specified):
1. Fully enclosed areas below the lowest floor that are subject to flooding are prohibited, or if used solely for parking, access or storage 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 be certified by a registered professional engineer or must meet or exceed the following minimum criteria:
a. A minimum of 2 openings having a total net free area of not less than 1 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 1 foot above the adjacent exterior grade;
c. Openings may be equipped with screens, louvers, or other coverings or devices; provided, that they permit the automatic entry and exit of floodwaters; and provided, that the screens, louvers, or other devices meet the requirements of the International Building Code.
C. New construction, substantial improvement of any commercial, industrial or other nonresidential structure, and improvement of any post-FIRM commercial, industrial or other nonresidential structure within AO zones shall either:
1. Have the lowest floor (including basement) elevated at or above the flood protection elevation level and highest adjacent grade of the building site, 2 feet or more above the depth number specified on the FIRM (at least 3 feet if no depth number is specified); or
2. Together with attendant utility and sanitary facilities, be completely floodproofed to or above that level so that any space below that level 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. If this method is used, compliance shall be certified by a registered professional engineer as set forth in IMC 16.36.100(B).
3. Applicants floodproofing nonresidential buildings shall be notified that flood insurance premiums will be based on rates that are 1 foot below the floodproofed level (e.g., a building constructed to the base flood level will be rated as 1 foot below that level).
D. Recreational Vehicles. Recreational vehicles placed on sites are required to either:
1. Be on the site for fewer than 180 consecutive days;
2. Be fully licensed and ready for highway use, on their wheels or jacking system, be attached to the site only by quick disconnect type utilities and security devices, and have no permanently attached additions; or
3. Meet the requirements for manufactured homes. (Ord. 2989 § 3 (Exh. A3), 2022; Ord. 2915 § 1 (Exh. A), 2020; Ord. 2775 § 1 (Exh. A), 2016; Ord. 2420 § 1, 2005).