(A) Flood control and bank protection measures must be designed by an engineer and constructed to withstand the flood depths, hydrodynamic and hydrostatic pressures, velocities, impact, buoyancy and uplift forces associated with the base flood and include an encroachment analysis.
(B) The design shall also show compliance with the following additional criteria.
(1) Levee and floodwall construction or alteration.
(a) The proposed construction or alteration of a levee or floodwall must be designed and constructed with suitable fill and to safely convey a base flood;
(b) Except to protect agricultural land only, are constructed at least three feet higher than the elevation of the base flood;
(c) Unless to protect only agricultural land, protection of structures of more than one land owner requires engineering and construction to meet state and federal levee standards and be publically owned for the purpose of construction, operation and maintenance; and
(d) For any increase in the elevation of the base flood the following information must be provided:
1. The estimated cumulative effect of other reasonably anticipated future permissible uses;
2. The type and amount of existing flood prone development in the affected area; and
3. Impacts to existing or foreseeable development.
(2) Bank stabilization projects, pier and abutment protection. Bank stabilization projects, pier and abutment protection projects shall be permitted if:
(a) The materials for the project should be the least environmentally damaging and practicable designed to withstand a base flood within five years or other time as required by the Floodplain Administrator and does not require substantial yearly maintenance after that period;
(b) Materials for the project may be designed to erode over time but not fail catastrophically and impact others. Erosions and raveling of the materials may be designed to be a least similar in amount and rate to existing natural stream banks during the base flood;
(c) The project must not increase erosion upstream, downstream or adjacent to the site;
(d) Materials for the project may include but not limited to rip rap, root wads, brush mattresses, willow watting, woody debris or combinations of analogous materials;
(e) The stream’s biological capacity and habitat potential shall be incorporated in the project design; and
(f) Projects including compensating efforts by replacing and providing substitute resources or environments through creation, restoration, enhancement or preservation of similar or appropriate resource areas are subject to a higher regulatory standard.
(3) Channelization projects. Channelization projects where the excavation and/or construction of an artificial channel is for the purpose of diverting the entire flow of a stream from its established course and provided the projects do not increase velocity to a level that will cause erosion.
(4) Dams.
(a) The design and construction is in accordance with the Montana Dam Safety Act and applicable safety standards; and
(b) The project will not increase flood hazards downstream either through operational procedures or improper hydrologic/hydraulic design.
(Ord. 2013-01, passed 1-30-2013)
Federal law reference:
Encroachments; substantial improvements, see 44 C.F.R. § 60.3(a)(3), (d)(3)
Statutory reference:
Alteration of floodplains, see ARM 36.15.505(1)(c)(ii)and (iii)
Definitions, see ARM 36.15.101(7)
Permits, see ARM 36.15.606