(A) Purpose. The purpose of this subchapter is to reduce risks to public health, safety and property damage from flood events that may impact or be impacted by new development associated with subdivisions.
(B) Applicability.
(1) This subchapter applies to subdivisions that are intended for placement of new buildings or other development in the vicinity of a 100-year floodplain. The 100-year floodplains are depicted on the adopted flood insurance rate maps (FIRMs) published by the Federal Emergency Management Agency (FEMA). As of the date of these regulations, the 100-year floodplains include both Approximate Zone A 100-year floodplains and other zones designated as 100- year floodplains by detailed study. The Approximate Zone A base flood elevations (BFEs) have not been determined, while other 100-year floodplain zones designated by detailed study have BFEs that have been determined.
(2) It is the intent of this subchapter that any subdivision containing areas within a 100-year floodplain include sufficient information to demonstrate the location of all development in relation to the actual delineated BFE.
(C) General provision. Land located in the floodway of a 100-year flood event as defined by MCA Title 76, § 5, or other land determined by the City Council to be subject to flooding may not be subdivided for building or residential purposes or other uses that may increase or aggravate flood hazards to life, health or welfare, or that may be prohibited by state or local floodplain regulations.
(D) Determining base flood elevations (BFE).
(1) For areas where BFE is determined. For areas where the BFE has been identified as part of flood studies and maps adopted by the City Council that are within the jurisdiction of the local floodplain regulations:
(a) The areas at and below the BFE shall be identified on the preliminary plat as a flood hazard area. The flood hazard area shall be identified on the final plat as a no build zone;
(b) Any improvements within a flood hazard area, 100-year floodplain or the floodway within the jurisdiction of the local floodplain regulations shall meet the requirements of the local floodplain regulations prior to final plat approval; and
(c) Interpretation of floodplain boundary, if the property owner believes the subject property has been inadvertently included in the 100-year floodplain, the property owner may provide information and request a determination from the Floodplain Administrator, adhering to applicable provisions for such determinations in the floodplain regulations.
(2) For areas where BFE is not determined. If any portion of a proposed subdivision is within 1,000 horizontal feet and ten vertical feet of the ordinary high water mark of a watercourse draining an area of 25 square miles or more, and no official floodway delineation or floodway studies of the watercourse have been made, or within 2,000 horizontal feet and 20 vertical feet of the ordinary high water mark of the Clark Fork River where no official floodway delineation or floodway studies have been made, the subdivider shall do one of the following:
(a) Identify the area less than 1,000 horizontal feet and less than ten vertical feet of the ordinary high water mark of a watercourse draining an area of 25 square miles or more as a flood hazard area on the preliminary plat. This area shall be shown on the final plat as a no build zone (Figure 5);
(b) If on the Clark Fork River, identify the area less than 2,000 horizontal feet and less than 20 vertical feet of the ordinary high water mark of the river as a flood hazard area on the preliminary plat. This area shall be shown on final plat as a no build zone; or
(c) Complete an engineering study that identifies the BFE. This detailed evaluation must be performed by a professional engineer registered in the state experienced in this field of work.
1. A copy of the study identifying the BFE shall be submitted with the preliminary plat application to the local Administrator.
a. The Administrator shall forward the study to the Floodplain Administrator and the Water Resources Division of the Montana Department of Natural Resources and Conservation (DNRC) for comment.
b. The City Council shall not delay the preliminary plat review process to wait for comments. Any comments received by the city shall be forwarded to the subdivider.
2. a. The areas at and below the BFE shall be identified as flood hazard areas.
b. The flood hazard area shall be identified on the final plat as a no build zone.
(E) Standards.
(1) General criteria.
(a) When applicable, BFEs and the boundary of the 100-year floodplain must be considered during lot layout and building location design (44 C.F.R. § 60.3(b)(3));
(b) Locations for future structures and development must be reasonably safe from flooding (44 C.F.R. § 60.3(a)(4));
(c) Streets, utilities and similar facilities, such as sewer, gas, electrical and water systems must be located and constructed to minimize or eliminate flood damage (44 C.F.R. § 60.3(a)(4)(ii));
(d) Adequate surface water drainage must be provided to reduce exposure to flood hazards (44 C.F.R. § 60.3(a)(4)(iii));
(e) All subdivisions and development activities within the 100-year floodplain are subject to the city’s floodplain regulations; and
(f) Floodplain development permits must be obtained according to the city’s floodplain regulations before development occurs within the 100-year floodplain (44 C.F.R. § 60.3(b)).
(2) Design standards.
(a) Lots.
1. The desired design standard of lots for residential or building purposes shall include no portion of nor be immediately adjacent to the 100-year floodplain.
2. If that is not achievable due to site constraints, lots may contain areas in the 100-year floodplain, but each lot must have an area outside of the floodplain suitable for the lot’s intended purposes.
(b) Access. The subdivider shall demonstrate that safe access to the designated building site(s) is possible during a 100-year flood.
(c) Infrastructure.
1. Subdivisions should be designed to avoid placing subdivision-related infrastructure (streets, bridges, utilities and the like) within the boundaries of the 100-year floodplain.
2. Where there is no alternative to placement within the floodplain, streets and utilities, such as sewer, gas, electrical and water systems that must be located in the 100-year floodplain shall be designed and installed so as to minimize or eliminate flood damage and not adversely affect public health and safety.
(d) Bridges. Bridges within the 100-year floodplain shall be designed so the lowest horizontal chord of the bridge is at least two feet above the BFE.
(F) Final plat and noticing requirements. The City Council may require final plats of subdivisions with areas located within a 100-year floodplain to provide notice of any or all of the following:
(1) Locations of boundaries of the 100-year floodplain and floodway based on where the BFEs intersect surveyed ground elevations;
(2) Elevation of the existing ground;
(3) Flood water depths;
(4) The required lowest floor elevation for each building site;
(5) Lot owners’ responsibility for obtaining a floodplain development permit according to the city’s floodplain regulations before development occurs within a 100-year floodplain;
(6) Lot owners’ responsibility for complying with any specific provisions of the city’s floodplain regulations; and
(7) Applicable information regarding flood insurance.
(Prior Code, § 11.02.060.070) (Ord. 151, passed 6-20-2016)