Johnson County, IA Environmental Rules: Stormwater Management (2026)

6(A) bars the Board from approving any preliminary, combined, or final plat for a commercial or industrial subdivision, a residential subdivision with two or more buildable lots, or a rezoning to the RE-Renewable Energy district unless the application includes a stormwater management plan adequate to serve the development, and requires all stormwater facilities to be installed under the approved preliminary plat before final plat approval. The Zoning Administrator can accept a performance guarantee in place of pre-final-plat installation where installing every facility first is not practicable, and can defer stormwater planning to the building permit stage for pre-existing subdivision lots or for site-plan and conditional-use properties where an Iowa Stormwater Management Manual runoff analysis shows post-development runoff will not increase.

6(E) is required instead of full planning. No conditional use requiring stormwater compliance may begin operating until its plan is submitted, approved, and implemented, and subsection (A)(5) blocks a permanent certificate of occupancy until final site stabilization is achieved and a Professional Engineer licensed in Iowa certifies as-built stormwater infrastructure plans. The Zoning Administrator can waive some or all requirements if a prior stormwater analysis on the property already covers the proposal, or if the new use will not permanently and significantly increase impervious surface, harm water quality, or increase soil erosion.