A. Artificial Obstructions: Artificial obstructions including alterations and substantial improvements specifically listed in this section may be permitted by the floodplain administrator within the floodway through an approved floodplain development permit, provided the general requirements and specific standards within this section and subsection 14-4-5G of this title are met.
B. General Requirements: An application for a floodplain development 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 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.
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 section 14-3-14 of this title and an approved FEMA conditional letter of map revision occurs before permit issuance.
C. Excavation Of Material: Excavation of material from pits, pools, or stormwater ponds provided that:
1. A buffer strip of undisturbed land of sufficient width as determined by an engineer, but in no case less than twenty feet (20'), to prevent flood flows from channeling into the excavation is left between the edge of the channel and the edge of the excavation;
2. The excavation meets all applicable laws and regulations of other local and state agencies; and
3. Excavated material is stockpiled outside the designated floodway.
D. Transportation Related Crossings: Railroad, highway, street, stream, and other transportation related crossings provided that:
1. The crossings are designed to offer minimal obstructions to the flood flow;
2. Where failure or interruption of public transportation facilities would result in danger to public health or safety and where practicable and in consideration of FHWA federal aid policy guide 23 CFR 650A:
a. Bridge lower chords shall have a freeboard of at least two feet (2') above the BFE to pass ice flows, the base flood discharge and any debris associated with the discharge;
b. Culverts shall be designed to pass the base flood discharge and maintain at least two feet (2') freeboard on the crossing surface;
3. If possible, normal overflow channels are preserved to allow passage of sediments to prevent aggradations; and
4. Midstream supports for bridges, if necessary, must have footings buried below the maximum scour depth.
E. Limited Filling For Road And Railroad Embankments: Limited filling for road and railroad embankments, including other transportation related embankments not associated with stream crossings and bridges provided that:
1. The fill is suitable fill material;
2. Reasonable alternate transportation routes outside the designated floodway are not available;
3. The encroachment is located as far from the stream channel as possible; and
4. Measures are provided to mitigate the impact to property owners and the natural stream function.
F. Buried Or Suspended Utility Transmission Lines: Buried or suspended utility transmission lines, provided that:
1. Suspended utility transmission lines are designed such that the lowest point of the suspended line is at least six feet (6') higher than the base flood elevation;
2. Towers and other appurtenant structures are designed and placed to withstand and offer minimal obstruction to flood flows;
3. When technically feasible, the crossing will not disturb the bed and banks of the stream, alternatives such as alternative routes, directional drilling, and aerial crossings are considered; and
4. Utility transmission lines carrying toxic or flammable materials are buried to a depth of at least twice the calculated maximum depth of scour determined by an engineer for the base flood. The maximum depth of scour may be determined from any of the accepted hydraulic engineering methods, but the final calculated figures shall be subject to approval by the floodplain administrator.
G. Storage Of Materials And Equipment: Storage of materials and equipment provided that:
1. The material or equipment is not subject to major damage by flooding and is properly anchored to prevent flotation or downstream movement; and
2. 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.
H. Domestic Water Supply Wells: Domestic water supply wells, provided that:
1. They are driven or drilled wells located on ground higher than surrounding ground to assure positive drainage from the well;
2. They require no other structures (e.g., a well house);
3. Well casings are watertight to a distance of at least twenty five feet (25') below the ground surface and the well casing height is a minimum of two feet (2') above the base flood elevation or capped with a watertight seal and vented two feet (2') above the base flood elevation;
4. Water supply and electrical lines have a watertight seal where the lines enter the casing;
5. All pumps and electrical lines and equipment are either of the submersible type or are adequately floodproofed; and
6. Check valves are installed on main water lines at wells and at all building entry locations.
I. Sewage Disposal In Campgrounds And Recreation Areas: Buried and sealed vaults for sewage disposal in campgrounds and recreation areas provided, in addition to the requirements of subsection B of this section, demonstrate approval by the Montana department of environmental quality and local health and sanitation permits or approvals.
J. Disposal Systems Meeting Local Regulations: Only those solid and hazardous waste disposal and individual and multiple-family sewage disposal systems that meet the local health and sanitation regulations and when permitted pursuant to these regulations and are designed to minimize or eliminate infiltration of floodwaters and avoid impairment or contamination.
K. Fences Crossing Channels: Fences crossing channels that have the potential to stop or impede flow or debris such as a chainlink or privacy fence require a floodplain development permit and meet the requirements of subsection M of this section.
L. Campgrounds: Public or private campgrounds provided that:
1. Access roads require only limited fill and do not obstruct or divert floodwaters;
2. Any proposed structures shall meet the requirements of subsection M of this section;
3. No dwellings or permanent mobile homes are allowed;
4. Off property impacts have been considered and found to be nonexistent, neutral or can be mitigated;
5. There is no large scale clearing of riparian vegetation within fifty feet (50') of the mean annual high water mark; and
6. Recreational vehicles and travel trailers are licensed and ready for highway use with wheels intact, with only quick disconnect type utilities and securing devices, and have no permanently attached additions.
M. Structures Accessory Or Appurtenant To Permitted Uses: Structures accessory or appurtenant to the uses permitted in this section, such as permanent nonfloating boat docks, floating docks which exceed the standards outlined in subsection 14-5-4B11 of this chapter, loading and parking areas, marinas, sheds, emergency airstrips, permanent fences crossing channels, picnic shelters and tables and lavatories, that are incidental to a principal structure or use, provided that:
1. The structures are not intended for human habitation or supportive of human habitation;
2. The structures will have low flood damage potential;
3. The structures will, insofar as possible, be located on ground higher than the surrounding ground and as far from the channel as possible;
4. Only those wastewater disposal systems that are approved under health and sanitation regulations are allowed;
5. Service facilities within these structures such as electrical, heating and plumbing are floodproofed in accordance with chapter 7 of this title;
6. The structures will be constructed and placed so as to offer a minimal obstruction to flood flows and are firmly anchored to prevent flotation;
7. The structures do not require fill and/or substantial excavation;
8. The structures or use cannot be changed or altered without permit approval; and
9. The use does not require the large scale clearing of riparian vegetation within fifty feet (50') of the mean annual high water mark.
N. New Surface Water Diversions And Changes: New surface water diversions and changes in place of diversion, provided that, in addition to the requirements of subsection B of this section, the design is reviewed and approved by a registered engineer and includes:
1. The proper permits or documentation has been obtained from DNRC water rights bureau for new surface water diversions and changes in place of diversion;
2. The proposed diversion is designed and constructed to minimize potential erosion from a base flood; and
3. The structure is designed and constructed to withstand up to a 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.
O. Flood Control And Stream Bank Stabilization Measures: The following flood control and stream bank stabilization measures provided that the design is reviewed and certified by a registered professional 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 conditions set forth:
1. Levee and floodwall construction or alteration that meet the following:
a. The proposed levee or floodwall must be designed and constructed with suitable fill to safely convey a base flood;
b. The proposed levee or floodwall, except those to protect agricultural land, must be constructed at least three feet (3') higher than the base flood elevation;
c. 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
d. For an increase in the elevation of the base flood, an alteration of the regulated flood hazard area requires approvals pursuant to section 14-3-14 of this title.
2. Stream bank stabilization, pier and abutment protection projects that meet the following:
a. 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 (5) 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;
b. 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;
c. 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
d. 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.
3. 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, that meet the following:
a. Do not increase the magnitude, velocity, or base flood elevation; and
b. Meets the requirements for stream bank stabilization listed above.
4. Dams provided that:
a. They are designed and constructed in accordance with the Montana dam safety act and applicable safety standards; and
b. They will not increase flood hazards downstream either through operational procedures or improper hydrologic/hydraulic design.
P. Stream And Bank Restoration Projects: 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 that:
1. The project will not increase velocity or erosion upstream, downstream, across from or adjacent to the site;
2. Materials may include, but are not limited to, boulders, rock cobble, gravel, native streambed 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;
3. 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
4. The project may be designed to allow vegetative materials to mature within a period of five (5) 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.
Q. Alteration Or Substantial Improvement To An Existing Building: Any alteration or substantial improvement to an existing building in the floodway that meets the general requirements of this section and applicable requirements for residential and nonresidential buildings in section 14-5-6 of this chapter. (Ord. 15-16, 10-5-2015)