M3 was part of the team for a project to replace three existing box culverts in St. Louis County: Villa Dorado Drive Culvert No. C-2-416 (11’h x 15’ w), Lackland Road Culvert No. C-2-116 (6’h x 12’w) and Lockwood Avenue Culvert No. C-4-224 (12’w x 8’h). M3 performed floodplain studies on the streams to ensure that the proposed structures do not cause an increase in the 100 year floodplain. While not all the structures were located within FEMA defined floodplains, the hydraulic analyses and No-Rise verifications were required due to an MSD Special Requirement for any watercourse, not identified by FEMA, for which the 15-year, 20-minute design storm exceeds the capacity of a (60) inch diameter sewer.

In addition to hydraulic design, M3 also helped coordinate water and sewer piping relocation, secured a USACE 404 Permit, and performed a rapid geomorphic assessment (RGA) on each stream to gage the bank stability. The results of the RGA were used to design bank armoring upstream and downstream from the new structures.