Vermilion Parish, LA Environmental Rules: Stormwater Management (2026)

The stormwater rules sit in Appendix A, the parish Subdivision Regulations adopted by the Police Jury. Section 4 requires a comprehensive Drainage Impact Analysis after preliminary plat approval, and the construction plans and final plat are not approved until the Police Jury certifies it favorably. A developer can ask in writing for a waiver, and a granted waiver must be issued as a written approval. The report needs an area drainage map showing each drainage area, its acreage and its slope, plus the cubic feet per second entering and leaving the site. It also has to test downstream ditches, culverts and structures to the first outfall, coulee, canal or river, though no developer must evaluate an outfall beyond 1,000 feet downstream.

Design storms are set by use: a 5-year minimum for residential drainage design and a 10-year minimum for commercial. Outfall channels and collector street crossings use a 10-year storm, arterial crossings a 25-year storm, and open channels serving more than one development need 1 foot of freeboard above the 10-year water surface. Section 8(D) then requires any development whose post-development runoff exceeds its pre-development rate to mitigate the increase.

Non-residential sites detain runoff in ponds, parking lots with ponding no deeper than 6 inches, underground storage, perimeter swales or green areas. Residential subdivisions use roadside ditches, ponds, perimeter ditches or curb-to-curb detention. Outlets are designed for a 10-year storm (commercial) or 5-year storm (residential) and analyzed for a 100-year event. The Police Jury can allow a discharge increase of 5 percent, not to exceed 5 cubic feet per second, and no detention is required for developments of three-quarters of an acre or less, though a drainage site and grading plan is still submitted.

Owners must keep each stormwater facility at its approved design section. After written notice from the Police Jury they have 30 days to fix deficiencies, or the Police Jury does the work and bills the owner at its operating cost. Each facility needs a clear 30-foot-wide access way for de-siltation, and designs should include a fore-bay to capture incoming sediment. Section 8(G) also requires a drainage right-of-way of a minimum of 25 feet beyond the ditch width, and natural drainage channels cannot be blocked or altered without the Police Jury's written consent. Stormwater plan review carries its own fee under Section 9(B).