A. The following general regulations are applicable to all development within any special flood hazard area:
1. Minimize Flood Damage Potential: Methods and practices shall be used that minimize flood damage potential to all new development and that do not increase the flood damage potential to other properties.
2. Flood Resistant Materials: All new development shall use materials and utility equipment resistant to flood damage.
3. Anchoring: All new construction and substantial improvements of structures shall be anchored to prevent flotation, collapse, or lateral movement of the structure.
4. Drainage: Drainage practices that minimize exposure to flood hazards and that maintain the original or historic drainage patterns to the greatest extent possible shall be used.
5. Grading: Grading is considered development and may not take place on property within a special flood hazard area unless a floodplain permit is issued. All grading shall be done so as to minimize impacts within all special flood hazard areas. Floodwater carrying capacity shall not be diminished and adjacent properties shall not be adversely impacted by the proposed improvements. Minor landscape features (cumulative fill or excavation less than then (10) cubic yards) and at grade driveways, at grade private roads, and at grade parking lots shall be exempt from the LOMA process. Depending on the extent and nature of the grading and landscape features, a FES may be required.
6. Electrical, Mechanical And Plumbing Equipment/Facilities: Electrical, heating, ventilation, plumbing, and air conditioning equipment and other service facilities shall be elevated to at least one and a half feet (1.5') above the BFE.
7. Utility Work:
a. All utility work shall use designs, materials, and construction methods that preclude failure due to flooding and assure continued service during flood events.
b. All new and replacement water supply systems shall be designed to eliminate infiltration of floodwaters into the system.
c. New and replacement sewage treatment infrastructure and sewage collection and disposal systems shall be designed to eliminate infiltration of floodwaters into the systems and discharge from the systems into floodwaters.
8. Subdivisions:
a. All subdivisions shall be consistent in design and construction with the need to minimize flood damage and shall be reasonably safe from flooding.
b. Public utilities and facilities including, but not limited to: sewer, gas, electrical, telephone, and water systems shall be located and constructed to minimize flood damage and certified by a professional engineer licensed in the state of Idaho.
c. Adequate drainage shall be provided to reduce exposure to flood damaged. The following must be placed up on the Final Plat:
(1) All the SFHA boundary lines must be drawn on the plat.
(2) Plat notes designating:
a. FEMA FIRM panel(s): #160xxxxxxC, and 160xxxxxxE, etc.;
b. FIRM effective date(s): mm/dd/year;
c. Flood Zone(s): Zone X, Zone A, Zone AE, A Zone AO, Zone, AH, Zone D, etc.;
d. Base Flood Elevation(s): AE .0 ft., etc.; and
e. The following statement: "Flood Zones are subject to change by FEMA and all land within a floodway or floodplain is regulated by section 8-3F of Ada County Code."
d. A FES shall be done to determine the BFE for the subdivision if it is located in an A Zone. The applicant shall then submit a LOMR to update the map with the information from the FES.
e. If a Conditional Letter of Map Revision (CLOMR) is required, the approval of the CLOMR must be obtained prior to any site improvements and approval of the LOMR must be obtained prior to approval of the Final Plat.
9. Watercourse Alteration/Relocation: If a watercourse is to be altered or relocated, the following shall all be submitted by the permit applicant prior to issuance of a floodplain development permit:
a. A description of the extent of watercourse alteration or relocation;
b. A professional engineer's certified report on the effects of the proposed project on the flood-carrying capacity of the watercourse and the effects to properties located both upstream and downstream. This would include engineering showing:
(1) Prior conditions (FIRM Model conditions);
(2) Existing conditions; and
(3) Post-construction conditions.
c. A map showing the location of the proposed watercourse alteration or relocation;
d. An Idaho Stream Channel Alteration Permit approval shall be provided by the applicant to the floodplain administrator.
No alteration or relocation of a watercourse shall be permitted if it diminishes the floodway and floodplain carrying capacity of the watercourse. This includes floodplain and bank restoration projects.
10. Substantial Damage: A structure, regardless of whether it was covered by flood insurance, shall be considered to have sustained substantial damage if it meets either of the substantial damage definitions in section 8-3F-5 of this article. Work on structures that have been substantially damaged is considered to be a substantial improvement regardless of the actual repair work performed, and must comply with the applicable general regulations and standards in this section and section 8-3F-8 of this article.
11. Accessory And Agricultural Structures: An accessory or agricultural structure as defined in this title may be granted relief from elevation or dry floodproofing requirements if the following standards are met:
a. The structure shall be one thousand (1,000) square feet or less in size.
b. The structure shall represent a minimal investment, meaning the proposed structure's estimated square foot construction cost as determined by the floodplain administrator shall not be greater than ten percent (10%) of the total market value of the property on which the structure is located;
c. The structure is not used for human habitation;
d. The structure is constructed of flood resistant materials;
e. The structure is constructed and placed on the property to offer the minimum resistance to the flow of floodwaters;
f. The structure is firmly anchored to prevent flotation;
g. The structure's mechanical and utility equipment, if any, are elevated or floodproofed one and a half feet (1.5') above BFE or two feet (2') above the highest adjacent grade where BFE has not been established; and
12. Roads and Driveways: Driveways, roads, bridges, low-water crossings, and similar means for vehicles or pedestrians to travel, which encroach into the SFHA shall be designed to:
a. Be elevated at least one and a half feet (1.5') above the established base flood elevation;
b. Allow flood water to pass under so that it does not act as a check dam.
13. Riparian Areas: Since riparian areas provide critical flood management and fish and wildlife habitat, the following provisions apply for any development in the SFHA and riparian areas as defined:
a. Preservation or restoration of the inherent natural characteristics of the river and creeks within the floodplain;
b. Preservation of riparian vegetation and wildlife habitat, if any, along the stream bank and within the required minimum twenty-five foot (25') setback of the floodway boundary or riparian zone;
c. No development other than development by a public entity, for public use or required for emergency access shall occur within the twenty-five foot (25') setback of the floodway boundary with the exception of approved stream stabilization work;
d. Plan and time frame shall be provided for restoration of riparian vegetation damaged as a result of the work done; and
e. New or replacement planting and vegetation shall include plantings that are low growing and have dense root systems for the purpose of stabilizing stream banks and repairing damage previously done to riparian vegetation. Examples of such plantings include: red osier dogwood, common chokecherry, serviceberry, elderberry, river birch, skunk bush sumac, Bebb's willow, Drummond's willow, little wild rose, gooseberry, and honeysuckle.
14. Compensatory Storage: New development shall not reduce the effective flood storage volume of the Regulatory Floodplain and SFHA. A development proposal shall provide compensatory storage if grading or other activity eliminates any effective flood storage volume. Compensatory storage shall:
a. Provide equivalent volume at equivalent elevations to that being displaced. For this purpose, "equivalent elevation" means having similar relationship to ordinary high water and the best available one hundred (100) year water surface profiles;
b. Be hydraulically connected to the source of flooding; and
c. Provide compensatory storage in the same construction season as when the displacement of flood storage volume occurs and before the flood season begins.
d. The newly created storage area shall be graded and vegetated to allow fish access during flood events without creating fish stranding sites.
15. Fences and Walls: Table 8-3F-1 lists the fences and walls allowed or prohibited under this article in the Regulatory Floodplain and SFHA. Allowed fences and walls must also meet the standards found in section 8-5-3-44 of this title.
Fence Or Wall Type | Floodplain (A, AE) | Floodway | Shallow Sheet Flow Area (AO) |
Fence Or Wall Type | Floodplain (A, AE) | Floodway | Shallow Sheet Flow Area (AO) |
A | Yes | Yes, unless the purpose is to contain livestock within a corral | Yes |
B | Yes | Yes, with limited cross fencing | Yes |
C | Case by case review of design required. | ||
D | Yes, if elevated to or above the flood height.1 | Case by case review of design required. | Yes, if elevated to or above the flood height.1 |
E | Yes, if elevated to or above the flood height.1 | No | Yes, if elevated to or above the floodheight.1 |
F | Case by case review of design required. | No | Yes, if elevated to or above the flood height1, or adequate openings provided |
A. "Open" barbed or barbless wire. For floodplain management purposes, barbed and/or barbless wire will be considered "open" if there is no more than one horizontal strand per foot of height1 and no more than one vertical wire or post every six feet (6'). | |||
B. "Open" pipe or rail fencing (e.g. corrals). For floodplain management purposes, pipe/rail fencing will be considered open if the horizontal pipes/rails occupy less than ten percent (10%) of the area fenced and posts are spaced no closer than eight feet (8'). | |||
C. Collapsible fencing. | |||
D. Other wire, pipe, or rail type fencing (e.g. field fence, chicken wire, etc.) which does not meet the "open" requirements described above. | |||
E. Chain link fencing. | |||
F. Continuous wood or vinyl fencing or masonry walls. | |||
Note:
1. Individual horizontal wire strands can be placed below the flood height provided 1they are spaced no closer than six inches (6") apart. Individual vertical wire strands can be placed below the flood height provided they are spaced no closer than six feet (6') apart. For wire, pipe, or rail fencing that does not meet the "open" requirements, and for wood or masonry walls/fences, the bottom of the wall/fence must be elevated to or above the elevation of the water during the one hundred (100) year flood event. Wood and masonry fencing/walls do not need to be elevated if they provide enough openings at their bases to allow the free flow of floodwaters without increasing the depth of water at all.
16. Functionally Dependent Use: Functionally dependent uses shall follow the standards of this article, provided that the use does not cause a rise in the one hundred (100) year flood level (BFE) within a regulatory floodway, and the structure and other development must be protected by methods that minimize flood damages.
17. General Irrigation Floodplain Development (GIFD) Permit: There are three (3) categories of GIFD permits as outlined by Idaho Department of Water Resources (IDWR). The floodplain administrator will determine which category the proposed work falls under based on the following criteria:
a. Non-development activities requiring no permit: Consistent with Idaho Code sections 46-1021 and 46-1022, operation, cleaning, maintenance or repair of any ditch, canal, lateral, drain, diversion structure or other irrigation or drainage works, do not constitute development under Idaho law and therefore do not require either a GIFD permit or an floodplain permit. Examples of activities and projects that do not require floodplain permitting.
(1) General farming, pasture, horticultural and forestry activities that do not involve earthwork that permanently alter the topography or any clearing/grubbing of an area.
(2) Grading of existing roads or easements along or near channels and within the SFHA, when the grading does not add fill within the regulatory floodway or SFHA.
(3) Maintenance of underground utilities (work must not permanently alter topography).
(4) In-kind replacement of existing piers or posts supporting a conforming deck.
(5) Activities associated with land-surface construction stormwater Best Management Practices ("BMP"), when the measures are temporary in nature (i.e. not in place for longer than one hundred and eighty (180) days) or do not increase the BFE. Examples of stormwater BMP activities that do not require a permit include the following: dust control; materials and equipment covers; mulching; geotextile fabrics; matting; bio-filter bags; fiber rolls; silt fences; vegetative buffer strips; temporary swales; and temporary berms.
b. GIFD permit eligible activities: Low-to-no impact irrigation and drainage development activities or uses in the floodplain which inherently do not increase the BFE. GIFD permits apply to all qualifying activities within the spatial extents of an irrigation delivery or drainage system and within the regulatory floodway or SFHA, over a predetermined period of time, not to exceed five years.
(1) Process for GFID approval:
a. Initial consultation, in-person meeting between the floodplain administrator and the irrigation entity.
b. Submittal by the irrigation entity of the following materials prior to consultation visit:
i. Service area map with delineated activities;
ii. A timeline identifying the sequence and timing that proposed activities will occur (not to exceed five years); and
iii. Supporting documentation, as needed.
c. The floodplain administrator shall timely review submitted material and ask for additional documentation as needed.
d. The floodplain administrator shall timely review submitted material and identify any activities that require an individual permit.
e. The floodplain administrator shall issue a GIFD permit.
f. The irrigation entity shall notify the floodplain administrator when changes to activities permitted under a GIFD are anticipated.
(2) Examples of activities that require a GFID:
a. Dredging and grading of irrigation and drainage channels, when the fill from dredging or grading is not deposited on the banks of channels or anywhere within the regulatory floodway or SFHA for longer than ten (10) days.
b. Seasonal grading within natural stream channels to check or direct water into irrigation facilities (i.e. earthen "push- up dams" and "wing dams").
c. Deposition of fill within the SFHA for less than ten (10) days. After then (10) days, deposited fill must be removed from the SFHA, or graded and compacted to existing grade within ± 0.2 feet. Deposition of fill includes deposition of material resulting from grading or excavating irrigation or drainage channels. Deposition of fill within the mapped floodway requires an individual permit.
d. Construction of new underground utilities that do not permanently alter the existing grade elevations by ± 0.5 feet. Excess soil from new pipes larger than two feet (2') in diameter must be disposed of outside the regulatory floodway and SFHA.
e. In-kind replacement of irrigation and drainage works or components including but not limited to control gates or head gates, measuring devices and their housing structures/stilling wells, culverts, pumps, pipes, flumes, siphons and similar works. GIFD permits cannot authorize the In-kind replacement of dams or bridge structures.
f. New driveways, trails, sidewalks, roads and streets constructed completely at-or-below existing grade.
g. Armoring, stabilizing, securing, or in-kind replacement of existing infrastructure within the channel banks (such as bridge piers, sewer/utility supports and storm water/sewer drainage outfalls/headwalls) when the dimensions (bank slopes, channel location, channel elevation) of the channel are not altered. This should not involve replacement with larger or additional above ground infrastructure.
B. Development activities requiring an floodplain development permit: A floodplain development permit is required for all other permitted activities and projects within the regulatory floodway and SFHA that do not meet the requirements of a GIFD permit. (Ord. 835, 12-3-2014; amd. Ord. 848, 12-9-2015; amd. Ord. 914, 6-10-2020)