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 CO MS4 permit requirements and Colorado environmental regulations.
All work under this section shall comply with CDOT current standards and applicable AASHTO, ASTM, and federal requirements. The Engineer has authority to accept or reject materials and workmanship that do not conform to the specifications.
Source: CDOT Highway Design Manual, 2024 Edition. Pages 23–24 of 37.