An application for a floodplain permit must demonstrate or meet the following applicable requirements.
(A) Base flood elevation. Where necessary to meet the appropriate elevation requirement in these regulations, the base flood elevation(s) must be determined by an engineer and utilized in the design and layout of the project demonstrating the design and construction criteria herein are met. For regulated flood hazard areas that do not have computed and published base flood elevations in the adopted flood hazard study referenced in §§ 11.06.040.010 through 11.06.040.030, a base flood elevation must be determined or obtained from a reliable source, utilizing appropriate engineering methods and analyses.
(B) Flood damage. Structures must be constructed by methods and practices that minimize flood damage and structures must be reasonably safe from flooding (44 C.F.R. § 60.3(a), (a)(3)(iii)).
(C) Surface drainage. Adequate surface drainage must be provided around structures.
(D) Materials. Structures must be constructed with materials resistant to flood damage (44 C.F.R. § 60.3(a), (a)(3)(ii)).
(E) Artificial obstructions. Structures, excavation or fill must not be prohibited by any other statute, regulation, ordinance or resolution; and must be compatible with subdivision, zoning and any other land use regulations, if any (ARM § 36.15.701(3)(a), (3)(b)).
(F) Anchoring. All construction and substantial improvements must be designed and adequately anchored to prevent flotation, collapse or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy (44 C.F.R. § 60.3(a)(3)).
(G) Certification. Certification by an engineer, architect, land surveyor or other qualified person must accompany the application where required, including for an encroachment analysis, adequacy of structural elevations, base flood elevation determinations, flood proofing, enclosure flood openings, and design and construction to withstand the hydrodynamic forces and hydrostatic pressures of flood depths, velocities, impact, buoyancy, uplift forces associated with the base flood, and surface drainage. A certification is not intended to constitute a warranty or guarantee of performance, expressed or implied (ARM §§ 36.15.606(1), 36.15.702(2)(c) and 36.15.801(3)(b); 44 C.F.R. § 60.3(c)(3), (c)(4), (d)(3)).
(H) Access. Structures must have safe access during times of flooding up to the base flood for ordinary and emergency services; provided there are no reasonable alternate locations for structures; (higher standard).
(I) Encroachment analysis.
(1) All applications in the regulated flood hazard area without a floodway must be supported by an encroachment analysis of the proposed use, a thorough hydrologic and hydraulic analysis, except as provided in division (I)(4) below, prepared by an engineer to demonstrate the effect of the structure on flood flows, velocities and the base flood elevation (ARM § 36.15.604; 44 C.F.R. § 60.3(a)(3));
(2) The maximum allowable encroachment is certified to be at or less than one-half foot increase to the base flood elevation, unless approval of an alteration of the regulated flood hazard area pursuant to §§ 11.06.040.010 through 11.06.040.030 and an approved FEMA conditional letter of map revision occurs before permit issuance (ARM §§ 36.15.505 and 36.15.604; 44 C.F.R. § 60.3(c)(13));
(3) An encroachment analysis is not required for any development in the flood fringe where an accompanying floodway has been designated within the regulated flood hazard area; and
(4) Although all other development standards herein apply, a minimal or qualitative encroachment analysis may be accepted when the project or development does not require a structure, alteration of the floodplain, involve fill, grading, excavation or storage of materials or equipment, and also is certified by an engineer to not exceed the allowable encroachment.
(J) Electrical systems flood proofing. All electrical service materials, equipment and installation for uses in a regulated flood hazard area must be certified to meet the following requirements:
(1) All incoming power service equipment, including all metering equipment, control centers, transformers, distribution and lighting panels, and all other stationary equipment must be located at least two feet above the base flood elevation (ARM § 36.15.901(1)(a));
(2) Portable and movable electrical equipment may be placed below the base flood elevation; provided that the equipment can be disconnected by a single plug and socket assembly of the submersible type (ARM § 36.15.901(1)(b));
(3) The main power service lines must have automatically operated electrical disconnect equipment or manually operated electrical disconnect equipment located at an accessible remote location outside the regulated flood hazard area or two feet above the base flood elevation and (ARM § 36.15.901(1)(c)); and
(4) All electrical wiring systems installed below the base flood elevation must be suitable for continuous submergence and may not contain fibrous components (ARM § 36.15.901(1)(d)).
(K) Heating and cooling systems flood proofing. Heating and cooling systems for uses in a regulated flood hazard area must be certified to meet the following requirements:
(1) Float operated automatic control valves must be installed so that fuel supply is automatically shut off when flood waters reach the floor level where the heating and cooling systems are located (ARM § 36.15.902(1)(a));
(2) Manually operated gate valves must be installed in gas supply lines. The gate valves must be operable from a location above the base flood elevation (ARM § 36.15.902(1)(b));
(3) Electrical systems flood proofing must be met (ARM § 36.15.902(1)(c)); and
(4) Furnaces and cooling units must be installed at least two feet above the base flood elevation and the ductwork installed above the base flood elevation.
(L) Plumbing systems flood proofing. Plumbing systems for uses in the regulated flood hazard area must be certified to meet the following requirements:
(1) Sewer lines, except those to a buried and sealed vault, must have check valves installed to prevent sewage backup into permitted structures and (ARM § 36.15.903(1)(a)); and
(2) All toilets, stools, sinks, urinals, vaults and drains must be located so the lowest point of possible flood water entry is at least two feet above the base flood elevation (ARM § 36.15.903(1)(b)).
(M) Structural fill flood proofing. Fill used to elevate structures, including, but not limited to, residential and non-residential buildings must be certified to meet the following requirements:
(1) The filled area must be at or above the base flood elevation and extend at least 15 feet beyond the structure in all directions;
(2) Fill material must be suitable fill, that is stable, compacted, well graded and pervious, not adversely affected by water and frost, devoid of trash or similar foreign matter, tree stumps or other organic material; and is fitting for the purpose of supporting the intended use and/or permanent structure (ARM § 36.15.101(22));
(3) The fill must be compacted to minimize settlement and compacted to 95% of the maximum density. Compaction of earthen fill must be certified by an engineer;
(4) No portion of the fill is allowed within the floodway;
(5) The fill slope must not be steeper than one and one-half horizontal to one vertical, unless substantiating data justifying a steeper slope is provided and adequate erosion protection is provided for fill slopes exposed to floodwaters; and
(6) The fill must be a minimum of one-half feet above the base flood elevation and extend at least 15 feet beyond the structure in all directions.
(N) Wet flood proofing. Building designs with an enclosure below the lowest floor must be certified to meet the following:
(1) Materials used for walls and floors are resistant to flooding to an elevation two feet or more above the base flood elevation (ARM § 36.15.702(2)(a)); and
(2) The enclosure must be designed to equalize hydrostatic forces on walls by allowing for entry and exit of floodwaters. Opening designs must either be certified by an engineer or architect or meet or exceed the following:
(a) Automatically allow entry and exit of floodwaters through screens, louvers, valves and other coverings or devices;
(b) Have two or more openings with a total net area of not less than one square inch for every one square foot of enclosed area below the lowest floor, except if the enclosure is partially subgrade, a minimum of two openings may be provided on a single wall; and
(c) Have the bottom of all openings no higher than one foot above the higher of the exterior or interior adjacent grade or floor immediately below the openings (44 C.F.R. § 60.3(c)(5); NFIP Insurance Manual, Rev. October 2021).
(O) Dry flood proofing. Building designs that do not allow internal flooding must be certified according to these regulations to meet the following:
(1) Building use must be for non-residential use only and does not include mixed residential and non-residential use;
(2) Be flood proofed to an elevation no lower than two feet above the base flood elevation;
(3) Be constructed of impermeable membranes or materials for floors and walls and have water tight enclosures for all windows, doors and other openings; and
(4) Be designed to withstand the hydrostatic pressures and hydrodynamic forces resulting from the base flood and the effects of buoyancy (ARM § 36.15.702(2)(b); 44 C.F.R. § 60.3(c)(3)).
(P) Elevation of the lowest floor. Elevating the lowest floor may be by either suitable fill, foundation wall enclosure, stem walls, pilings, posts, piers, columns or other acceptable means (MCA § 76-5-402(2)(b); 44 CFR 60.3(b)(8), (c)(6)).
(Q) Crawlspaces. Crawlspace foundation enclosures, including subgrade crawlspace enclosures below the lowest floor must meet the wet flood proofing requirements and be designed so that the crawlspace floor is at or above the base flood elevation. Crawlspace foundations must have an inside dimension of not more than five feet from the ground to the top of the living floor level, and a subgrade crawlspace must also have the interior ground surface no more than two feet below the exterior lowest adjacent ground surface on all sides. A subgrade foundation exceeding either dimension is a basement.
(R) Manufactured home anchors. For new placement, substantial improvement or replacement of manufactured homes for residential or non-residential use, including additions, the chassis must be secure and must resist flotation, collapse or lateral movement by anchoring with anchoring components capable of carrying a force of 4,800 pounds and as follows:
(1) For manufactured homes less than 50 feet long, over-the-top ties to ground anchors are required at each of the four corners of the home, with two additional ties per side at intermediate locations; or
(2) For manufactured homes more than 50 feet long, frame ties to ground anchors are required at each corner of the home with five additional ties per side at intermediate points (44 C.F.R. § 60.3(b)(8), (c)(6)).
(S) Access. Access for emergency vehicles is provided. For manufactured homes, access for a manufactured home hauler is also provided (higher standard).
(Prior Code, § 11.06.100.020) (Ord. 6, passed 3-16-1981; Ord. 2021-15, passed 12-20-2021)
Statutory reference:
Elevation of the lowest floor, see MCA § 76-5-402(2)(b)