A. Standards Of Construction: In all areas of special flood hazard the following standards are required:
1. Anchoring:
a. All new construction and substantial improvements shall be adequately anchored to prevent flotation, collapse or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy.
b. All manufactured homes shall meet the anchoring standards of subsection E, "Standards For Manufactured Homes", of this section.
2. Construction Materials And Methods: All new construction and substantial improvements shall be constructed:
a. With materials and utility equipment resistant to flood damage;
b. Using methods and practices that minimize flood damage;
c. Ensure electrical, heating, ventilation, plumbing, air conditioning equipment and other service facilities are designed or located so as to prevent water from entering or accumulating within the components during conditions of flooding;
d. Within zones AH or AO, so that there are adequate drainage paths around structures on slopes to guide floodwaters around and away from proposed structures.
3. Elevation Requirements For Lowest Floor: Residential construction, new or substantial improvements, shall have the lowest floor, including basement:
a. In zone AO, elevated above the highest adjacent grade to a height two feet (2') above the depth number specified in feet on the FIRM, or elevated at least three feet (3') above the highest adjacent grade if no depth number is specified.
b. In zone A, elevated two feet (2') above the base flood elevation, as determined by this community.
c. In all other zones, elevated two feet (2') above the base flood elevation.
4. Lowest Floor Certification Requirements: Upon completion of the structure, the elevation of the lowest floor including basement shall be certified by a registered professional engineer or surveyor and verified by the community building inspector to be properly elevated. The certification shall be provided to the floodplain administrator using the current FEMA elevation certificate.
5. Nonresidential Floodproofing Requirements: Nonresidential construction shall either be elevated to conform with subsection A3, "Elevation Requirements For Lowest Floor", of this section or together with attendant utility and sanitary facilities:
a. Will be floodproofed below the elevation recommended under subsection A3, "Elevation Requirements For Lowest Floor", of this section so that the structure is watertight with walls substantially impermeable to the passage of water;
b. Will have the structural components capable of resisting hydrostatic and hydrodynamic loads and effects of buoyancy;
c. Will be certified by a registered professional engineer or architect that the standards of subsection A3, "Elevation Requirements For Lowest Floor", of this section are satisfied. The certification shall be provided to the floodplain administrator.
6. Requirements For Areas Below The Lowest Floor: All new construction and substantial improvements with fully enclosed areas below the lowest floor (excluding basements) that are usable solely for parking of vehicles, building access or storage, and which 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 shall follow the guidelines in FEMA technical bulletins TB-1 (openings in foundation walls and walls of enclosures, 2008) and TB-7 (wet floodproofing requirements, 1993) and must either be certified by a licensed professional engineer or architect to meet or exceed the following minimum criteria:
a. Must have a minimum of two (2) openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding;
b. The bottom of all such openings will be no higher than one foot (1') above the lowest adjacent finished grade.
Openings may be equipped with louvers, valves, screens or other coverings or devices provided they permit the automatic entry and exit of floodwaters.
7. Crawl Space Construction: This subsection applies to buildings with crawl spaces up to two feet (2') below grade. Below grade crawl space construction in accordance with the requirements listed below will not be considered basements.
a. The building must be designed and adequately anchored to resist flotation, collapse, and lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy. Crawl space construction is not allowed in areas with flood velocities greater than five feet (5') per second unless the design is reviewed by a qualified design professional, such as a registered architect or professional engineer;
b. The crawl space is an enclosed area below the BFE and, as such, must have openings that equalize hydrostatic pressures by allowing for the automatic entry and exit of floodwaters. For guidance on flood openings, see FEMA technical bulletin TB-1 (openings in foundation walls and walls of enclosures, 2008);
c. Crawl space construction is not permitted in V zones. Open pile or column foundations that withstand storm surge and wave forces are required in V zones;
d. Portions of the building below the BFE must be constructed with materials resistant to flood damage. This includes not only the foundation walls of the crawl space used to elevate the building, but also any joists, insulation, or other materials that extend below the BFE; and
e. Any building utility systems within the crawl space must be elevated above BFE or designed so that floodwaters cannot enter or accumulate within the system components during flood conditions.
f. Requirements for all below grade crawl space construction, in addition to the above requirements, to include the following:
(1) The interior grade of a crawl space below the BFE must not be more than two feet (2') below the lowest adjacent exterior grade (LAG), shown as D in figure 3 of FEMA technical bulletin 11-01 (crawlspace construction for buildings located in special flood hazard areas, 2001);
(2) The height of the below grade crawl space, measured from the interior grade of the crawl space to the top of the crawl space foundation wall must not exceed four feet (4') (shown as L in figure 3 of technical bulletin 11-01, crawlspace construction for buildings located in special flood hazard areas, 2001) at any point;
(3) There must be an adequate drainage system that removes floodwaters from the interior area of the crawl space within a reasonable period of time after a flood event, not to exceed seventy two (72) hours; and
(4) The velocity of floodwaters at the site should not exceed five feet (5') per second for any crawl space. For velocities in excess of five feet (5') per second, other foundation types should be used.
8. Garages And Low Cost Accessory Structures:
a. Attached Garages:
(1) A garage attached to a residential structure, constructed with the garage floor slab below the BFE, must be designed to allow for the automatic entry of floodwater in accordance with subsection A6, "Requirements For Areas Below The Lowest Floor", of this section. Areas of the garage below the BFE must be constructed with flood resistant material in accordance with subsection A2a of this section.
(2) A garage attached to a nonresidential structure must meet the above requirements or be floodproofed. For guidance on below grade parking areas, see FEMA technical bulletin TB-6 (below- grade parking requirements, 1993).
b. Detached Garages And Accessory Structures:
(1) "Accessory structures" used solely for parking (2 car detached garages or smaller) or limited storage (small, low cost sheds), as defined in section 3-8-2, "Definitions", of this chapter, may be constructed such that its floor is below the base flood elevation (BFE), provided the structure is designed and constructed in accordance with the following requirements:
(A) Use of the accessory structure must be limited to parking or limited storage;
(B) The portions of the accessory structure located below the BFE must be built using flood resistant materials;
(C) The accessory structure must be adequately anchored to prevent flotation, collapse and lateral movement;
(D) Any mechanical and utility equipment in the accessory structure must be elevated or floodproofed to or above the BFE;
(E) The accessory structure must comply with floodplain encroachment provisions in subsection G, "Floodways", of this section; and
(F) The accessory structure must be designed to allow for the automatic entry of floodwaters in accordance with subsection A6, "Requirements For Areas Below The Lowest Floor", of this section.
(2) Detached garages and accessory structures not meeting the above standards must be constructed in accordance with all applicable standards in subsection A6, "Requirements For Areas Below The Lowest Floor", of this section.
B. Standards For Utilities:
1. All new and replacement water supply systems shall be designed to minimize or eliminate infiltration of floodwaters into the system.
2. All new and replacement sanitary sewage systems shall be designed to minimize or eliminate infiltration of floodwaters or discharge from the systems into floodwaters. Sanitary sewer and storm drainage systems for buildings that have openings below the base flood elevation shall be provided with automatic backflow valves or other automatic backflow devices that are installed in each discharge line passing through a building's exterior wall.
3. On site waste disposal systems shall be located to avoid impairment to them or contamination from them during flooding.
C. Standards For Subdivisions:
1. All preliminary subdivision proposals shall identify the flood hazard area and the elevation of the base flood.
2. All subdivision plans will provide the elevation of proposed structures and pads. If the site is filled above the base flood, the final lowest floor and pad elevation shall be certified by a registered professional engineer or surveyor and provided to the floodplain administrator.
3. All subdivision proposals shall be consistent with the need to minimize flood damage.
4. All subdivision proposals shall have public utilities and facilities such as sewer, gas, electrical and water systems located and constructed to minimize flood damage.
5. All subdivisions shall provide adequate drainage to reduce exposure to flood hazards.
6. Additionally all subdivision proposals will demonstrate, by providing a detailed hydrologic and hydraulic analyses that 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 foot (1') at any point within the community.
D. Standards For Critical Structures: Critical structures are not authorized in a special flood hazard area, unless:
1. All alternative locations in flood zone X have been considered and rejected.
2. All alternative locations in flood zone shaded X have been considered and rejected.
If the floodplain manager determines the only practical alternative location for the development of a new or substantially improved critical structure is in a special flood hazard area he must:
1. Give public notice of the decision and reasons for the elimination of all alternative locations.
E. Standards For Manufactured Homes:
1. All manufactured homes that are placed or substantially improved, within zones A, AH, AE, and on the community's flood insurance rate map, on sites located:
a. Outside of a manufactured home park or subdivision;
b. In a new manufactured home park or subdivision;
c. In an expansion to an existing manufactured home park or subdivision; or
d. In an existing manufactured home park or subdivision on a site upon which a manufactured home has incurred "substantial damage" as a result of a flood:
(1) Shall be elevated on a permanent foundation so that the lowest floor will be elevated at least two feet (2') above the base flood elevation and be securely anchored to an adequately anchored foundation system to resist flotation, collapse and lateral movement. Methods of anchoring may include, but are not to be limited to, use of over the top or frame ties to ground anchors. This requirement is in addition to applicable state and local anchoring requirements for resisting wind forces.
2. All manufactured homes to be placed or substantially improved on sites in an existing manufactured home park or subdivision within zones A, AH, and AE on the community's flood insurance rate map that are not subject to the provisions of subsection D, "Standards For Critical Structures", of this section will be elevated so that either:
a. The bottom of structural frame or the lowest point of the manufactured home is at least two feet (2') above the base flood elevation; or
b. 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 inches (36") in height above grade and securely anchored to an adequately anchored foundation system to resist flotation, collapse, and lateral movement.
3. Within zone A, when no base flood elevation data is available, new and substantially improved manufactured homes shall have the floor elevated at least three feet (3') above the highest adjacent grade.
4. Within zone AO, the floor of all new and substantially improved manufactured homes will be elevated above the highest adjacent grade at least two feet (2') above the depth number specified on the FIRM, or at least three feet (3') above the highest adjacent grade if no depth number is specified.
F. Standards For Recreational Vehicles: All recreational vehicles placed on sites within the floodplain on the community's flood insurance rate map will either:
1. Be on the site for fewer than one hundred eighty (180) consecutive days;
2. 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, is attached to the site only by quick disconnect type utilities and security devices, and has no permanently attached additions; or
3. Will meet the permit requirements of subsection 3-8-4C, "Permit Application", of this chapter and the elevation and anchoring requirements for manufactured homes in subsection E, "Standards For Manufactured Homes", of this section.
G. Floodways: Since the floodway is an extremely hazardous area due to the velocity of floodwaters, which carry debris, potential projectiles, and erosion potential, the following provisions apply:
1. If a floodway has not been designated within the special flood hazard areas established in subsection 3-8-3B, "Basis For Establishing Areas Of Special Flood Hazard", of this chapter, no new construction, substantial improvement, or other development (including fill) shall be permitted within zones A1-30 and AE, unless it has been 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 foot (1') at any point within the community.
2. In designated floodways located within the special flood hazard areas established in subsection 3-8-3B, "Basis For Establishing Areas Of Special Flood Hazard", of this chapter encroachment shall be prohibited, including fill, new construction, substantial improvements, storage of equipment or supplies, and any 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 community during the occurrence of the base flood discharge, and the federal emergency management agency has issued a conditional letter of map revision (CLOMR).
3. If subsections G1 and G2 of this section have been satisfied; all proposed new development and substantial improvements will comply with all other applicable flood hazard reduction provisions of this section.
H. Mudslide (i.e., Mudflow) Prone Areas:
1. All permit applications will be reviewed by the floodplain administrator to determine if the proposed development will be located within a mudslide area.
2. The reviewing process will determine if the proposed site and improvements will be reasonably safe from mudslide hazards. Factors to be considered in making this determination include, but are not limited to, the following:
a. Type and quality of soils.
b. Evidence of groundwater or surface water problems.
c. Depth and quality of any fill.
d. The overall slope of the site.
e. The weight that any proposed structure will impose on the slope.
3. When a proposed development is located in an area that may have mudslide hazards, the following will be the minimum requirements:
a. A site investigation and further review be made by persons qualified in geology and soils engineering.
b. The proposed grading, excavations, new construction, and substantial improvements are adequately designed and protected against mudslide damages.
c. The proposed grading, excavations, new construction and substantial improvements do not aggravate the existing hazard by creating either on site or off site disturbances.
d. Drainage, planting, watering, and maintenance be such as not to endanger slope stability.
4. When a proposed development is determined to be within a mudslide hazard area, the following requirements will include, but not be limited to:
a. Adopting and enforcing a grading ordinance in accordance with data supplied by the federal emergency management agency.
b. Regulate the location of foundation systems and utility systems of new construction and substantial improvements.
c. Regulate the location, drainage and maintenance of all excavations, cuts and fills and planted slopes.
d. Provide special requirements for protective measures including, but not necessarily limited to, retaining walls, buttress fills, subdrains, diverted terraces, and benching.
e. Require engineering drawings and specifications to be submitted for all corrective measures, accompanied by supporting soils engineering and geology reports.
I. Flood Related Erosion Prone Areas:
1. All permit applications will be reviewed by the floodplain administrator to determine if the proposed development will be located within a special flood related erosion hazard area.
2. The reviewing process will determine if the proposed site alterations and improvements will be reasonably safe from flood related erosion and will not cause flood related erosion hazards or otherwise aggravate the existing flood related erosion hazard.
3. When the proposed development is found to be in the path of flood related erosion or to increase the erosion hazard, require the improvement to be relocated or adequate protective measures to be taken which will not aggravate the existing erosion hazard.
4. When it has been determined the proposed development is in a special flood related erosion hazard, as delineated zone E on the community FIRM, require:
a. A setback for all new development from the lake, bay, riverfront or other body of water, to create a safety buffer consisting of a natural vegetative or contour strip. This buffer will be designated according to the flood related erosion hazard and erosion rate, in conjunction with the anticipated "useful life" of structures, and depending upon the geologic, hydrologic, topographic and climatic characteristics of the community's land. The buffer may be used for suitable open spaces purposes, such as for agricultural, forestry, outdoor recreation and wildlife habitat areas, and for other activities using temporary and portable structures only.
J. Alluvial Fan Advisory:
1. Alluvial fans present a unique flood hazard environment where the combination of sediment, slope, and topography create an ultra hazardous condition for which elevation on fill will not provide reliable protection. Active alluvial fan flooding is characterized by flow path uncertainty combined with abrupt deposition and erosion. As a result, any area of an alluvial fan may be subject to intense flood hazards.
The technology of mathematically modeling the hydrodynamics of water and debris flows for alluvial fans is still in the early development stage. The federal emergency management agency (FEMA) has formulated a mapping procedure for the purpose of defining the likelihood of flood hazards on inundated alluvial fan zones to be used for flood insurance purposes and general floodplain regulation, referred to as the FEMA alluvial fan methodology.
An active alluvial fan flooding hazard is indicated by three (3) related criteria:
a. Flow path uncertainty below the hydrographic apex;
b. Abrupt deposition and ensuing erosion of sediment as a stream or debris flow loses its competence to carry material eroded from a steeper, upstream source area; and
c. An environment where the combination of sediment availability, slope, and topography creates an ultra hazardous condition for which elevation on fill will not reliably mitigate the risk.
Inactive alluvial fan flooding is similar to traditional riverine flood hazards, but occurs only on alluvial fans. It is characterized by flow paths with a higher degree of certainty in realistic assessments of flood risk or in the reliable mitigation of the hazard. Counter to active alluvial fan flooding hazards, an inactive alluvial fan flooding hazard is characterized by relatively stable flow paths. However, areas of inactive alluvial fan flooding, as with active alluvial fan flooding, may be subject to sediment deposition and erosion, but to a degree that does not cause flow path instability and uncertainty.
An alluvial fan may exhibit both active alluvial fan flooding and inactive alluvial fan flooding hazards. The hazards may vary spatially or vary at the same location, contingent on the level of flow discharge. Spatially, for example, upstream inactive portions of the alluvial fan may distribute flood flow to active areas at the distal part of the alluvial fan. Hazards may vary at the same location, for example, with a flow path that may be stable for lower flows, but become unstable at higher flows.
More detailed information can be found at FEMA's website: "Guidelines For Determining Flood Hazards On Alluvial Fans" at http://www.fema.gov/.
2. The NFIP does not allow for the removal of land from the floodplain based on the placement of fill (LOMR-F) in alluvial fan flood hazard areas. The NFIP will credit a major structural flood control project, through the LOMR process, that will effectively eliminate alluvial fan flood hazards from the protected area. Details about map revisions for alluvial fan areas can be found in the code of federal regulations at title 44, part 65.13. (Ord. 736, 6-14-2011)