Bonner County, ID Environmental Rules: Stormwater Management (2026)

The standards in Bonner County Revised Code § 12-726 apply to all design, construction, implementation and maintenance of stormwater management systems required by Subchapter 7.2 of Title 12. Collection and conveyance: no stormwater can be collected or concentrated except within a channel or artificial watercourse protected against erosion with energy dissipation measures. Existing watercourses must be protected from disturbance, installed system components preserved, and all disturbed soils protected during construction. Disposal: the system must collect, convey and detain a twenty five (25) year design storm without damage to the system or adjacent land.

Treatment: stormwater from impervious areas goes to a system drawn from the Panhandle health district best management practices handbook (Kennedy Engineers, April 1992), sized to hold and treat the first one-half inch of runoff from impervious surfaces. For new subdivisions, planned unit developments, commercial and industrial development and public projects, there can be no increase in the peak rate of runoff compared with pre-construction conditions for the first one-half inch, and project retention capacity must hold that volume. Section 12-723.2(B) bars accelerating or concentrating runoff beyond predevelopment levels past the property lines, unless the Planning Director accepts a joint agreement with adjoining owners.

Anyone building a grass covered retention area must set up a maintenance system. Under § 12-722.5, a grading/stormwater plan is required for over 500 cubic yards of fill, grading or excavation, and for 100 cubic yards or more within 300 feet of water or a 15 percent slope. Section 12-724.1 requires the plan to carry a design professional's stamp, with drainage drawings, calculations, a construction schedule and a maintenance system. Developments other than subdivisions must also enter a surety agreement under § 12-727.2 backed by a guarantee equal to one hundred percent (100%) of the design professional's estimated cost of the improvements.