(A) Uses requiring permits. Artificial obstructions, including alterations and substantial improvements specifically listed in division (C) below, may be allowed by permit within the floodway, provided the general requirements in division (B) below and the applicable requirements in division (C) below are met.
(Prior Code, § 15.52.350)
(B) General requirements. An application for a permit shall meet the following requirements:
(1) All projects shall be designed and constructed to ensure that they do not adversely affect the flood hazard on other properties and are reasonably safe from flooding;
(2) All projects shall assure that the carrying capacity of the floodway is not reduced. All projects in the floodway shall meet the following:
(a) Demonstrate that the project does not increase the base flood elevation by conducting an encroachment analysis certified by an engineer. A minimal or qualitative encroachment analysis may be accepted when the project or development does not require a structure, alteration of the floodway, involve fill, grading, excavation or storage of materials or equipment but is also certified by an engineer to not exceed the allowable encroachment to the base flood elevation; and
(b) The allowable encroachment to the base flood elevation is 0.00 feet, and no significant increase to the velocity or flow of the stream or watercourse unless approval of an alteration of the regulated flood hazard area pursuant to § 154.037 of this chapter and an approved FEMA Conditional Letter of Map Revision occurs before permit issuance.
(A.R.M. §§ 36.15.505, 36.15.604, 36.15.605(1)(b)) (44 C.F.R. §§ 60.3(a)(3) and (4), 65.12(a))
(3) An application for a floodplain permit must also demonstrate the following factors are considered and incorporated into the design of the use or artificial obstruction in the floodway:
(a) The danger to life and property due to backwater or diverted flow caused by the obstruction or use;
(A.R.M. § 36.15.216(2)(a)) (M.C.A. § 76-5-406(1))
(b) The danger that the obstruction or use may be swept downstream to the injury of others;
(A.R.M. § 36.15.216(2)(b)) (M.C.A. § 76-5-406(2)
(c) The availability of alternative locations;
(A.R.M. § 36.15.216(2)(c)) (M.C.A. § 76-5-406(3))
(d) Construct or alter the obstruction or use in such manner as to lessen the flooding danger;
(A.R.M. § 36.15.216(2)(d)) (M.C.A. § 76-5-406(4))
(e) The permanence of the obstruction or use and is reasonably safe from flooding;
(A.R.M. § 36.15.216(2)(e)) (M.C.A. § 76-5-406(5))
(f) The anticipated development in the foreseeable future of the area which may be affected by the obstruction or use;
(A.R.M. § 36.15.216(2)(f)) (M.C.A. § 76-5-406(6))
(g) Relevant and related permits for the project have been obtained;
(44 C.F.R. § 60.3(a)(2))
(h) Such other factors as are in harmony with the purposes of these regulations, the Floodplain and Floodway Management provisions found in Chapter 5 of Title 76, M.C.A. §§ 76-5-101 through 76-5-406, and the accompanying Administrative Rules of Montana; and
(A.R.M. § 36.15.216(2)(g)) (M.C.A. § 76-5-406(7))
(i) The safety of access to property in times of flooding for ordinary and emergency services.
(44 C.F.R. § 60.22(c)(7))
(Prior Code, § 15.52.360)
(C) Artificial obstructions. The following may be allowed as indicated:
(1) Mining of material requiring excavation from pits or pools provided, in addition to the requirements of division (B) above, that:
(a) A buffer strip of undisturbed land of sufficient width as determined by an engineer to prevent flood flows from channeling into the excavation is left between the edge of the channel and the edge of the excavation;
(A.R.M. § 36.15.602(1)(a))
(b) The excavation meets all applicable laws and regulations of other local and state agencies; and
(A.R.M. § 36.15.602(1)(b))
(c) Excavated material may be processed on site but is stockpiled outside the floodway.
(A.R.M. § 36.15.602(1)(c))
(2) Railroad, highway and street stream crossings, including other transportation related crossings provided, in addition to the requirements of division (B) above, that:
(a) Crossings are designed to offer minimal obstructions to the flood flow;
(A.R.M. § 36.15.602(2))
(b) Where failure or interruption of public transportation facilities would result in danger to public health or safety and where practicable and in consideration of Additional Guidance on 23 C.F.R. 650A, (formerly Federal-Aid Policy Guide Non-Regulatory Supplement NS 23 C.F.R., part
650A, September 30, 1992, Transmittal 5).
1. Bridge lower chords shall have freeboard to at least two feet above the base flood elevation to help pass ice flows, the base flood discharge and any debris associated with the discharge; and
2. Culverts shall be designed to pass the base flood discharge and maintain at least two feet freeboard on the crossing surface.
(c) Normal overflow channels, if possible are preserved to allow passage of sediments to prevent aggradations; and
(d) Mid stream supports for bridges, if necessary, have footings buried below the maximum scour depth.
(3) Limited filling for road and railroad embankments, including other transportation related embankments not associated with stream crossings and bridges provided, in addition to the requirements of division (B) above, that:
(a) The fill is suitable fill;
(b) Reasonable alternate transportation routes outside the floodway are not available; and
(A.R.M. § 36.15.602(3))
(c) The encroachment is located as far from the stream channel as possible.
(A.R.M. § 36.15.602(3))
(4) Buried or suspended utility transmission lines provided, in addition to the requirements of division (B) above, that:
(a) Suspended utility transmission lines are designed such that the lowest point of the suspended line is at least six feet higher than the base flood elevation;
(A.R.M. § 36.15.602(4))
(b) Towers and other appurtenant structures are designed and placed to withstand and offer minimal obstruction to flood flows;
(A.R.M. § 36.15.602(4))
(c) Alternatives such as alternative routes, directional drilling and aerial crossings are considered when technically feasible; and
(d) Utility transmission lines carrying toxic or flammable materials are buried to a depth of at least twice the calculated maximum scour depth determined by an engineer for the base flood.
(A.R.M. § 36.15.602(4))
(5) Storage of materials and equipment provided, in addition to the requirements of division (B) above, that:
(a) The material or equipment is not subject to major damage by flooding and is properly anchored to prevent flotation or downstream movement; or
(A.R.M. § 36.15.602(5)(a))
(b) The material or equipment is readily removable within the limited time available after flood warning. Storage of flammable, toxic or explosive materials shall not be permitted.
(A.R.M. § 36.15.602(5)(b))
(6) Domestic water supply wells provided, in addition to the requirements of division (B) above, that:
(a) They are driven or drilled wells located on ground higher than surrounding ground to assure positive drainage from the well;
(A.R.M. § 36.15.602(6))
(b) They require no other structures (e.g., a well house);
(A.R.M. § 36.15.602(6))
(c) Well casings are water tight to a distance of at least 25 feet below the ground surface and the well casing height is a minimum of two feet above the base flood elevation or capped with a water-tight seal and vented two feet above the base flood elevation;
(A.R.M. § 36.15.602(6))
(d) Water supply lines have a watertight seal where the lines enter the casing;
(A.R.M. § 36.15.602(6))
(e) All pumps and electrical lines and equipment are either of the submersible type or are adequately flood-proofed; and
(A.R.M. § 36.15.602(6))
(f) Check valves are installed on main water lines at wells and at all building entry locations.
(A.R.M. § 36.15.602(6)) (44 C.F.R. § 60.3(a)(5))
(7) Buried and sealed vaults for sewage disposal in campgrounds and recreational areas provided, in addition to the requirements of division (B) above, demonstrate approval by the state’s Department of Environmental Quality and local health and sanitation permits or approvals;
(A.R.M. § 36.15.602(7)) (44 C.F.R. § 60.3(a)(6))
(8) Public and private campgrounds provided, in addition to the requirements of division (B) above, that:
(a) Access roads require only limited fill and do not obstruct or divert flood waters;
(A.R.M. § 36.15.602(8))
(b) The project meets the accessory structures requirements in this section;
(c) No dwellings or permanent mobile homes are allowed;
(A.R.M. § 36.15.602(8))
(d) Recreational vehicles and travel trailers are ready for highway use with wheels intact, with only quick disconnect type utilities and securing devices, and have no permanently attached additions; and
(44 C.F.R. § 60.3(c)(14))
(e) There is no large-scale clearing of riparian vegetation within 50 feet of the mean annual high water mark.
(9) Structures accessory or appurtenant to permitted uses such as boat docks, loading and parking areas, marinas, sheds, emergency airstrips, permanent fences crossing channels that may impede or stop flows or debris, picnic shelters and tables and lavatories, that are incidental to a principal structure or use, provided in addition to the requirements of division (B) above, that:
(a) The structures are not intended for human habitation or supportive of human habitation;
(A.R.M. § 36.15.602(9))
(b) The structures will have low flood damage potential;
(A.R.M. § 36.15.602(9))
(c) The structures will, insofar as possible, be located on ground higher than the surrounding ground and as far from the channel as possible;
(A.R.M. § 36.15.602(9))
(d) The structures will be constructed and placed so as to offer a minimal obstruction to flood flows;
(A.R.M. § 36.15.602 (9))
(e) Only those wastewater disposal systems that are approved under health and sanitation regulations are allowed;
(f) Service facilities within these structures such as electrical, heating and plumbing are flood-proofed according to the requirements in § 154.071 of this chapter;
(A.R.M. § 36.15.602(9))
(g) The structures are firmly anchored to prevent flotation;
(A.R.M. § 36.15.602(9))
(h) The structures do not require fill and/or substantial excavation;
(i) The structures or use cannot be changed or altered without permit approval; and
(j) There is no clearing of riparian vegetation within 50 feet of the mean annual high water mark.
(10) Construction of or modifications to surface water diversions provided, in addition to the requirements of division (B) above, that the design is reviewed and approved by an engineer and includes:
(a) Measures to minimize potential erosion from a base flood; and
(A.R.M. § 36.15.603(3)(b))
(b) Designs and plans that demonstrate any permanent structure in the stream is designed to safely withstand up to the base flood considering the forces associated with hydrodynamic and hydrostatic pressures including flood depths, velocities, impact, ice buoyancy and uplift forces associated with the base flood.
(A.R.M. § 36.15.603(3)(c)) (44 C.F.R. § 60.3(a)(3), 60.3(d)(3))
(11) Flood control and stream bank stabilization measures provided, in addition to the requirements of division (B) above, that the design is reviewed and approved by an engineer and constructed to substantially resist or withstand the forces associated with hydrodynamic and hydrostatic pressures, including flood depths, velocities, impact, ice, buoyancy and uplift associated with the base flood. The design must also show compliance with the following applicable criteria:
(A.R.M. § 36.15.606) (44 C.F.R. § 60.3(a)(3), 60.3(d)(3))
(a) Levee and floodwall construction or alteration:
1. Must be designed and constructed with suitable fill and be designed to safely convey a base flood;
(A.R.M. § 36.15.606(1)(a))
2. Must be constructed at least three feet higher than the elevation of the base flood unless the levee or floodwall protects agricultural land only;
(A.R.M. § 36.15.606(2)(a))
3. Must meet state and federal levee engineering and construction standards and be publicly owned and maintained if it protects structures of more than one landowner; and
(A.R.M. § 36.15.505(1)(c)(ii) and (iii))
4. For any increase in the elevation of the base flood, an alteration of the regulated flood hazard area requires approvals pursuant to § 154.037 of this chapter.
(b) Stream bank stabilization, pier and abutment protection projects:
1. Must be designed and constructed using methods and materials that are the least environmentally damaging yet practicable, and should be designed to withstand a base flood once the project’s vegetative components are mature within a period of up to five years or other time as required by the Floodplain Administrator. Once vegetation is mature and established, it should not require substantial yearly maintenance after the initial period;
2. Materials for the project may be designed to erode over time, but not fail catastrophically and impact others. Erosion, sedimentation and transport of the materials may be designed to be at least similar in amount and rate of existing stable natural stream banks during the base flood;
3. Must not increase erosion upstream, downstream, across from or adjacent to the site in excess of the existing stable natural stream bank during the base flood; and
(A.R.M. § 36.15.606(1)(b))
4. Materials for the project may include, but are not limited to, riprap, root wads, brush mattresses, willow wattles, natural woody debris or combinations of analogous materials.
(c) Channelization projects where the excavation and/or construction of a channel is for the purpose of diverting the entire or a portion of the flow of a stream from its established course, the project must:
1. Not increase the magnitude, velocity or elevation of the base flood; and
2. Meet the requirements of this division (C)(11).
(A.R.M. §§ 36.15.101(7), 36.15.606(1)(c))
(d) Dams:
1. The design and construction shall be in accordance with the state’s Dam Safety Act and applicable safety standards; and
2. The project shall not increase flood hazards downstream either through operational procedures or improper hydrologic/hydraulic design.
(A.R.M. § 36.15.606(1)(d))
(12) Stream and bank restoration projects intended to reestablish the terrestrial and aquatic attributes of a natural stream and not for protection of a structure or development provided, in addition to the requirements of division (B) above, that:
(a) The project will not increase velocity or erosion upstream, downstream, across from or adjacent to the site;
(A.R.M. § 36.15.606(1)(b))
(b) Materials may include, but are not limited to, boulders, rock cobble, gravel, native stream bed materials, root wads, brush mattresses, willow wattles, natural woody debris or combinations of analogous materials and that reasonably replicates the bed and bank of the natural stream;
(c) Erosion, sedimentation and transport of the materials are not more than the amount and rate of existing natural stream banks during the base flood; and
(d) The project may be designed to allow vegetative materials to mature within a period up to five years or other time as required by the Floodplain Administrator. Once vegetation is mature and established, it should not require substantial yearly maintenance after the initial period.
(13) Existing residential and non-residential buildings in the floodway. Any alteration or substantial improvement to an existing building must meet the requirements of division (B) above and the applicable requirements in this section for residential or non-residential buildings.
(M.C.A. § 76-5-404(3)(b))
(Prior Code, § 15.52.370)
(Ord. 455, passed 11-23-2021)