Drainage design covers storm drain systems, culverts, ditches, and stormwater management. Design storm frequency: Interstate 50-year, arterial 25-year, collector 10-year. Culvert design per FHWA HDS-5 using HY-8 software. Storm drain systems designed using the rational method for areas <200 acres and NRCS methods for larger watersheds. Stormwater quality per TN MS4 permit requirements and Tennessee environmental regulations.
References: AASHTO current edition, TN Standard Specifications, FHWA Technical Advisories, and applicable federal regulations (23 CFR). Contractors shall maintain current copies of all referenced standards on the project site.
Source: TDOT Highway Design Manual, 2024 Edition. Pages 23–24 of 37.