Environmental Rules in Twin Falls County, ID (2026)
4 rules for unincorporated Twin Falls County, Idaho.
Verified from official government sources
Stormwater Management
Any land divided into a subdivision in unincorporated Twin Falls County must be graded to handle its own storm water. County Code section 10-2-9 puts that burden on the subdivider, requiring grading and drainage structures the county considers essential to provide adequate storm water drainage before the county will approve the plat.
Stormwater Drainage Rules in Twin Falls County
Some RestrictionsTwin Falls County Code § 10-2-9
Such grading shall be done and such structures shall be provided by the subdivider as are deemed essential by the County to provide adequate storm water drainage.
Erosion Control
Twin Falls County's only sediment-control mandate sits in its energy production chapter: anyone building a solar or wind project must hold an NPDES permit and submit an erosion and sediment control plan before roadwork or other site development begins, per County Code section 8-21-7(C). The county has no separate general grading ordinance for other construction.
Erosion Control for Energy Projects in Twin Falls County
Some RestrictionsTwin Falls County Code § 8-21-7(C)
C. Erosion And Sediment Control: The applicant must conduct all roadwork and other site development work in compliance with a National Pollutant Discharge Elimination System (NPDES) permit as required by U.S. Environmental Protection Agency regulations. Applicants must submit copies of their NPDES permit and erosion and sediment control plan as part of the application submittal. The plan must...
Flood Zones
Twin Falls County requires a development permit before any construction, fill, or land disturbance begins within an area of special flood hazard in unincorporated Twin Falls County outside the cities' areas of impact. The Planning and Zoning Administrator issues and reviews the permit, and builders must submit an as-built elevation certificate once the lowest floor is complete.
Flood Zone Development Permits in Twin Falls County
Some RestrictionsTwin Falls County Code § 8-19-6(A)
A. Development Permit Required: A development permit shall be obtained from Twin Falls County planning and zoning administrator before construction or development begins within any area of special flood hazard. The permit shall be for all structures including manufactured homes, as set forth in the definitions section of this chapter, and for all development including fill and other activitie...
Flood Elevation Requirements
New homes and additions in Twin Falls County's flood hazard areas must sit at least one foot above the base flood elevation, the county's built-in freeboard margin above FEMA's 100-year flood line. County Code section 8-19-8 also requires elevated utility systems and flood-resistant materials below that line.
One-Foot Freeboard Rule in Twin Falls County
Some RestrictionsTwin Falls County Code § 8-19-8(G)(1)
1. Residential Construction: a. New construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated one foot (1') or more above the base flood elevation (BFE). ... ... d. Any building utility systems shall be elevated one foot (1') above the BFE.
All Twin Falls County ordinances
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