12 Miss. Code. R. 10-300.2 - Specific Standards

In all areas of Special Flood Hazards where base flood elevation data has been provided, the following provisions are required:

(1) Residential Construction - New construction or substantial improvement of any residential structure shall have the lowest floor, including basement, elevated to one foot (1'), above the base flood elevation. A registered (in Mississippi) land surveyor shall certify that the standards of the subsection are satisfied. Should solid foundation perimeter walls be used to elevate a structure, openings sufficient to facilitate the impeded movements of flood waters shall be provided in accordance with standards Elevated Buildings, Section 300, Paragraph 300.2(3).

(2) Non-Residential Construction - New construction or substantial improvement of any commercial, industrial, or non-residential structure shall have the lowest floor, including basement, elevated no lower than one foot (1') above the level of the base flood elevation. Structures located in all A zones may be flood-proofed in lieu of being elevated provided that all areas of the structure below the required elevation are water tight with walls substantially impermeable to the passage of water, and use structural components having the capability of resisting hydrostatic and hydrodynamic loads and the effect of buoyancy. A registered (in Mississippi) professional engineer or architect shall develop and /or review structural design, specifications, and plans for the construction and shall certify that design and method of construction are in accordance with accepted standards of practice.

(3) Elevated Building.

New construction or substantial improvements of elevated buildings that include fully enclosed areas formed by foundation and other exterior walls below the base flood elevation shall be designed to preclude finished living space and designed to allow for the entry and exit of flood waters to the automatically equalize hydrostatic flood forces on exterior walls.

(a) Designs for complying with this requirement must either be certified by a professional engineer or architect, registered in Mississippi, or meet the following minimum criteria:

(i) Provide a minimum of two openings on separate walls having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding;

(ii) The bottom of all openings shall be no higher than one foot above grade; and,

(iii) Openings may be equipped with screens, louvers, valves or other coverings or devices provided they permit the automatic flow of floodwaters in both directions.

(b) Electrical, heating, ventilation, plumbing, air conditioning equipment, and other service facilities shall be designed and/or located so as to prevent water from entering or accumulating within the components during conditions of flooding.

(c) Access to the enclosed area shall be the minimum necessary to allow for parking of vehicles (garage door) or limited storage of maintenance equipment used in connection with the premises (standard exterior door) or entry to the living area (stairway or elevator); and the interior portion of such enclosed area shall not be partitioned or finished into separate rooms.

(4) Floodways - Located within areas of special flood hazard are areas designated as floodways. Since the floodway is an extremely hazardous area due to the velocity of flood waters which carry debris, potential projectiles and has erosion potential, all development with a floodway is permitted (except manufactured homes which are specifically prohibited) provided the development does not result in any increase in the water surface elevation of the base flood, the development is designed to withstand the velocity waters associated waters associated with the base flood waters, and the development would present no significant obstruction to the flow of the base flood waters, and would not create hazards to public health and safety. For purposes of meeting the requirements of "no increase in the water surface elevation of the base flood", the following methods shall be acceptable in order of preference:

(a) Development shall be designed to cause no encroachment within the floodway, and certification by a professional engineer (registered in Mississippi) must be provided demonstrating that the encroachment shall not result in any increase in the water surface elevation of the base flood, based on the present conditions of the floodways;

(b) Based on an engineering analysis and certification, the effect of the encroachment shall be fully offset by the creation of equal floodway hydraulic capacity at that location;

(c) In those areas where base flood elevations have been determined but a floodway has not been designated, an engineering analysis and certification shall be conducted to establish an appropriate floodway, or it must be demonstrated by an engineering analysis and certification that the proposed development will not increase the water surface elevation of the base flood more than one (1) foot at any point within the total floodplain;

(d) In those areas where the proposed construction increases the base flood elevation by more than one (1) foot the adversely affected property owners in the floodplain shall be compensated by securing the affected land by flood easement or fee simple purchase;

(e) In special flood hazard areas where base flood elevations have not been determined, proposed development should be designed so as to minimize any adverse effects to other properties;

(f) Where an engineering analysis and certification are utilized, engineering methodology used in conducting an engineering analysis shall be approved by the Natural and Technological Hazards Division of the Federal Emergency Management Agency (FEMA). Any changes in floodways or base flood water surface elevations (previously established by the Federal Emergency Management Agency) , along with supporting engineering analysis, shall have been submitted to the Natural and Technological Hazards Divisions of FEMA for review and approval prior to any construction taking place.

(5) Manufactured Homes - All manufactured homes (mobile homes shall be installed using methods and practices which minimize flood damage. The placement of manufactured homes (mobile homes) in V Zones is prohibited. For the purpose of this requirement, the following provisions shall apply:

(a) All manufactured homes to be placed or substantially improved within Zones A, AE, AH, and A99 shall be elevated on a permanent foundation such that the lowest floor of the manufactured home is one (1) foot above the base flood elevation and be securely anchored to an adequately anchored foundation;

(b) All manufactured homes shall be anchored to resist flotation, collapse, or lateral movement by providing over-the-top and frame ties to ground anchors as specified under the Mississippi Insurance Department's "Rules and Regulations for the Mobile Home Division of State Fire Marshall's Office For Factory Manufactured Movable Homes." (See Article 6). Specific minimum requirements shall be that:

i. Over-the-top ties be provided at each of the four corners of the manufactured home with one additional tie per side at an intermediate location of the manufactured home of less than 50 feet or more;

ii. Frame ties be provided at each corner of the manufactured home with four additional ties per side at intermediate points for the manufactured home less than 50 feet long and one additional tie for the manufactured home of 50 feet or longer;

iii. Each tie down shall be designed to resist an allowable working load equal to or exceeding 3,150 pounds and shall be capable of withstanding a 50 percent overload without failure;

iv. All components of the anchoring system be capable of carrying a force of 4,800 pounds;

v. Any additions to the manufactured home be similarly anchored;

vi. Where manufactured homes are elevated on compacted fill or on pilings, the lowest floor of the manufactured home will be no lower than one (1) foot above the base flood level;

vii. In the instance of elevation on pilings:

(1) piling foundations are placed in stable soil no more than 10 feet apart, and

(2) reinforcement is provided for pilings more than six feet above ground level.

(6) Access (Ingress-Egress) - New development proposals will be designed, to the maximum extent practicable, so residential building sites, walkways, driveways, and roadways are located on land with a natural grade with elevation not less than the base flood elevation and wit dry land access.

(7) Compensatory Storage Required for Fill - Fill within the special flood hazard area shall result in no net loss of natural floodplain storage, or increase in water surface elevations during the base flood. The volume of the loss of floodwater storage due to filling in the special flood hazard area shall be offset by providing an equal volume of flood storage by excavation or other compensatory measures at or adjacent to the development site.

(8) Critical Development - Critical facilities and developments are prohibited in the 1% flood hazard areas. Where critical developments are located adjacent to 1%-chance flood areas, the flood protection elevation shall be two feet above the 0.2% flood elevation and that elevation shall be used as the basis for the Access (Ingress-Egress) provisions.

(9) Fill - The following standards apply to all fill activities in special flood hazard areas:

a. Fill sites, upon which structures will be constructed or placed, must be compacted to 95 percent of the maximum density obtainable with the Standard Proctor Test method or an acceptable equivalent method;

b. Fill slopes shall not be steeper than one foot vertical to two feet horizontal;

c. Adequate protection against erosion and scour is provided for fill slopes. When expected velocities during the occurrence of the base flood are greater than five feet per second armoring with stone or rock protection shall be provided. When expected velocities during the base flood are five feet per second or less protection shall be provided by covering them with vegetative cover;

d. Fill shall be composed of clean granular or earthen material.

e. In any area that has been removed from the floodplain via a Letter of Map Revision Based on Fill, any existing or new structure, addition, or substantial improvement must meet the required elevation freeboard requirements of the underlying flood hazard elevation.

(10) ASCE 24 Flood Resistant Design and Construction - The American Society of Civil Engineers (ASCE) 24-14 is a referenced standard in the 2015 International Building Code® (IBC) and the 2015 International Residential Code® (IRC). Building and structures within the scope of the IBC proposed to be constructed in flood hazard areas must be designed in accordance with ASCE 24-14. The IRC requires dwellings in floodways to be designed in accordance with ASCE 24-14 and includes an alternative that allows communities to require homes in any flood zone to be designed in accordance with ASCE 24-15. Highlights of ASCE 24-14 that complement the NFIP minimum requirements include: Building Performance; Flood-Damage Resistant Materials; Utilities and Service Equipment and Siting Considerations.

(11) Future Conditions Flood Hazard Area - Require that all map revisions and watershed studies include analyses based on future conditions associated with anticipated watershed growth and land-use and land-cover changes. These future condition analyses shall be included on community floodplain maps and will serve as the basis for this regulation.

(12) Storage of Materials - Storage of material or equipment not otherwise prohibited shall be firmly anchored to prevent flotation.

(13) Setbacks - Setbacks in riverine floodplains:

a. Proposed development adjacent to riverine floodplains shall be set back fifty feet (50') from the floodway boundary or from the centerline of the stream if the floodway has not been delineated.

Setbacks adjacent to blue-line tributaries:

b. Proposed development adjacent to blue-line tributaries as shown on the United States Department of the Interior Geological Survey (hereafter referred to as "USGS") quadrants shall be set back thirty feet (30') from the center line of the stream. The setback shall be increased in areas with flood prone soils which are contiguous to blue line streams.

Setbacks in coastal floodplains

c. Proposed development adjacent to coastal floodplains, mapped as Coastal High Hazard Areas -Zones V, V1-30 and VE, shall be set back one hundred feet (100') from the mean low tide boundary. Proposed development in areas designated as coastal A Zones (areas between the 3' breaking wave and the 1.5', 1.0' breaking wave), shall have the same development requirements as development in Coastal High Hazard Area, Zones V, V1-30 and VE. Setbacks in erosion areas

d. Development in areas with annual erosion (advance) rates of (5, 10-) feet or more per year, based on a study by a Federal, State or local agency and adopted by the community, shall be set back one hundred feet (100') from the mean low tide boundary in coastal areas and setback one hundred feet (100') from the floodway boundary or stream centerline if the floodway has not been defined.

(14) Stormwater Regulations - All development proposals which (involve disturbing more than 10,000 square feet of land - removed) disturb one acre of land or more shall include a storm water management plan which is designed to limit peak runoff from the site to predevelopment levels for the 1, 10, and 100 year rainfall event. These plans shall be designed to limit adverse impacts to downstream channels and floodplains.

(15) Elevation of All Additions - All new horizontal additions must have the lowest floor and all HVAC elevated to one foot above the base flood elevation. Non-residential additions may be dry flood proofed to one foot above the base flood elevation.

(16) Sinkholes - A sinkhole, the immediate sinkhole drainage area, a sinkhole cluster area, or portions of such items shall be shown on any development or preliminary subdivision plan for land where they exist. Sinkhole-related nonbuildable areas and restricted fill areas shall be shown on final subdivision plans and development plans. No buildings, parking areas, or other structures shall be permitted within the sinkhole related, non-buildable area. Development may occur in the immediate sinkhole drainage area if the developer provides alternative surface drainage away from the sinkhole, while keeping the water in the same surface drainage basin, and provided further that the water shall not go into another sinkhole drainage area off the petitioner's property, nor into another stream of known flooding problems. The immediate sinkhole drainage system area (or portion thereof) which cannot be provided with an alternative drainage system can be deleted from the development area and can be used to meet the normal open space requirements.

Notes

12 Miss. Code. R. 10-300.2

Adopted 8/16/2019 Amended 2/3/2020