Duluth UDC § 1016.03

1. Culverts or pipe systems designed to convey water from one side of a public right-of-way to the other shall be designed to pass the fully developed peak flow associated with a 100-year storm with at least 1.5 feet of freeboard between the 100-year ponding elevation and the centerline of the road, without raising the 100-year flood elevation on upstream properties, and in accordance with Flood-plain Management Ordinance. Fully developed flows shall be based on the Land Use Plan adopted by the City Council. 2. The 100-year ponding limits at and upstream of the culvert shall be shown on the Development Plans and on the Final Plat (if applicable). 3. The minimum allowable culvert diameter under a road shall be 18 inches. 4. Single barrel or single cell culvert structures should be used whenever feasible, as they are less prone to clogging and require less maintenance than multi-barrel or multi-cell structures. 5. The maximum velocity in a corrugated metal culvert for the 100-year flow shall be 15 fps (feet per second). Velocities over 10 fps in a pipe of any material shall be considered a special design, with particular attention required to pipe or structure invert protection and to fill slope, stream bed, and stream bank stability being required. 6. Culvert design is to be in accordance with the methods contained in the Georgia Stormwater Management Manual and shall include a thorough analysis of both inlet and outlet control conditions.