CHAPTER 7: ZONE DISTRICT
Section 8: Floodplain Overlay
A. Purpose: To identify flood-prone areas of Boundary County in order to protect human life and property and to minimize public and private losses due to flood conditions, and to maintain Boundary County's eligibility to participate in the National Flood Insurance Program.
B. Relation to Other Zone Districts: The floodplain overlay district does not modify the boundaries of any underlying zone district. Where identified, the floodplain overlay district shall impose certain requirements on construction and land use in addition to those contained in the underlying zone district.
C. Official Floodplain Overlay District Maps: To establish the areas of special flood hazard, Boundary County hereby adopts the special flood hazard areas identified by the Federal Insurance Administration in a scientific and engineering report titled "The Flood Insurance Study of Boundary County," dated August 2, 1982, with the accompanying Flood Insurance Rate Maps and Flood Boundary and Floodway Maps adopted by reference and declared to be part of this ordinance.
D. Uncertainty of Floodplain Overlay District: Where uncertainties exist as to the actual boundaries of the floodplain overlay district with respect to any parcel of land, the boundary of the district shall be established by actual survey of the parcel. For purposes of administration of this chapter, where actual survey establishes a land surface at an elevation above that which is shown on the flood profile of the flood boundary and floodway map for the base one hundred (100) year flood, such lands shall be considered as existing outside the boundaries of the floodplain overlay district.
E. Permitted, Conditional and Special Uses: All uses permitted in the underlying zone district shall be deemed permitted in the floodplain overlay district, so long as the uses and structures also conform to the requirements of the floodplain overlay district.
F. Prohibited Uses: Encroachments, including fill, new construction, substantial improvements and other development within the portion of the floodplain overlay district designated as "floodway" on the Flood Boundary and Floodway maps, unless certification by a professional surveyor or engineer is provided in compliance with standards for floodway development established by the Federal Emergency Management Agency.
G. Standards for Use Within Flood Plain Overlay:
1. No zoning certificates, conditional use permits, special use permits or site plans will be issued or approved until the requirements of this section are met.
2. All new construction and substantial improvements located within the flood plain shall be anchored to prevent flotation, collapse or lateral movement of the structure.
3. All new construction and substantial improvements will be built with materials and utilities resistant to flood damage.
4. All new construction and substantial improvements will be built using methods and practices to minimize flood damage.
5. Electrical, heating, ventilation, plumbing, air conditioning equipment or other such systems shall be designed, elevated or located to prevent water from entering or accumulating within the components during a base flood occurrence.
6. All new and replacement water supply systems shall be designed to minimize or eliminate infiltration of flood waters during a base flood occurrence.
7. New and replacement sanitary sewage systems shall be designed to minimize or eliminate infiltration into the system and discharge from the system into flood waters.
8. On-site waste disposal systems shall be located to avoid impairment to them or contamination from them during flooding.
9. Located within areas of special flood hazard areas established at Section A, C, are areas designated as floodways. Since the floodway is an extremely hazardous area due to the velocity of floodwaters which carry debris, potential projectiles and erosion potential, no encroachment, including fill, new construction, substantial improvements or other development shall be permitted unless certification from a professional engineer or architect registered in the State of Idaho is provided demonstrating that encroachments shall not result in any increase in flood levels during the occurrence of the base flood discharge.
H. Standards for Residential Construction Within Overlay District:
1. New construction and substantial improvement of any residential structure shall have the lowest floor, including the basement, elevated to or above the base flood elevation.
2. Fully enclosed areas below the lowest floor that are subject to flooding shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of flood waters. Designs for meeting this requirement shall be certified by a registered professional engineer to meet the following minimum requirements:
a. A minimum of two openings having a total net area of not less than one square inch for each square foot of enclosed area below the base flood elevation shall be provided.
b. The bottom of such openings shall be not more than one (1) foot above grade.
c. Openings may be equipped with screens, vents, louvers or other coverings or devices provided they allow automatic entry and exit of floodwaters.
I. Standards for Manufactured and Mobile Homes within Flood Overlay District: All manufactured homes, mobile homes and trailers used as residences and placed within the floodplain overlay district shall be elevated on a permanent foundation to raise the lowest floor of the home to or above the base flood elevation and shall be anchored to prevent flotation, collapse or lateral movement, using methods designed to minimize flood damage.
J. Standards for Non-Residential Construction Within Overlay District: New construction or substantial improvement to any commercial, industrial or other non-residential structure for which a zoning certificate is required will either have the lowest floor, including the basement, elevated to the base flood level or shall meet the remaining requirements of this section:
1. New construction or substantial improvements, along with attendant utility and sanitary system, built below the base flood elevation will be constructed to be water tight, with walls substantially impermeable to the passage of water, and with structural components capable of resisting hydrostatic and hydrodynamic loads and the effects of buoyancy.
2. New construction and substantial improvements that must be built below the base flood elevation must be constructed according to plans certified by a registered professional engineer or architect to assure that design and construction methods are in accordance with accepted standards of practice for meeting provisions of this section.
K. Standards for Subdivision Proposals and Planned Unit Developments in Overlay District: Proposals for new subdivision and planned unit developments located wholly or partially within the floodplain overlay shall comply with the following standards:
1. All proposals shall be consistent with the need to minimize flood damage.
2. All proposals shall have public utilities and facilities, to include sewer, natural gas, electrical and water systems located and constructed to minimize flood damage.
3. All proposals shall provide for adequate drainage to reduce exposure to flood damage.
4. Base flood elevation shall be provided for as part of any subdivision or planned unit development proposal which contains a minimum of either fifty (50) lots or five (5) acres.
5. The cumulative affect of any proposed subdivision or planned unit development, when combined with all other existing and anticipated development, shall not increase the water surface elevation of the base flood by more than one (1) foot at any point.
L. Standards for Proposed Uses Which Include an Alteration of Watercourse:
1. As part of any application submitted to Boundary County as required by this ordinance, the applicant shall provide proof of notification and application for a permit from the Idaho Department of Water Resources for any proposed stream channel alteration or relocation. If the relocation or alteration lies within the area of impact of any city, proof of notification to the city shall also accompany the application. Copies of any required notification shall be sent to the Federal Emergency Management Agency.
2. Provisions for permanent maintenance shall be made so that the altered or relocated portion of the watercourse does not diminish the flood carrying capacity of the waterway.