BCC’s drainage and water resources group was tasked with the drainage design review for all drainage design submittals.  The stormwater management and drainage systems are designed to meet all required stormwater quality and quantity requirements for the Interstate 395 (I-395) project from the SR 836/I-95/I-395 (Midtown) Interchange to the MacArthur Causeway, which is 1.4 miles long.  The drainage design also includes all the surface street drainage systems.  The stormwater management system includes drainage wells to provide retention of the first inch of runoff from the project area.  Prior to being discharged through the wells, runoff received pretreatment from Advanced Vortex Separators (AVS) and/or detention boxes.  All drainage wells operate via gravity except for three (3) wells, which uses a stormwater pump station to achieve the necessary hydraulic head.  The stormwater pump station includes two, 9,000 gallons per minute pumps.  As required by FDOT D6, all the hydrologic/hydraulic analyses were performed with the ICPR V3 model.

BCC was also tasked by FDOT to perform a resilience analysis of the Biscayne Boulevard drainage system just north and south of I-395.  This portion of Biscayne Boulevard floods frequently during King Tides and during normal rainfall events.  This portion of the drainage system is not included as part of the I-395 proposed project improvements.  After evaluating the proposed I-395 drainage system and drainage constraints of the Biscayne Blvd drainage system, BCC provided the following recommended revisions of the I-395 drainage system without impacting the overall project cost or schedule:

• Separate the Biscayne Boulevard drainage system from the City of Miami Drainage system.
• Drain the portions from Biscayne Boulevard just north and south of I-395 to the proposed stormwater pump station.
• Adjust pump on/off elevations to accommodate the drainage from Biscayne Boulevard without impacting the capacity of the I-395 drainage system.
• Add a backflow preventer to the existing 66-inch outfall to remain, to reduce the King Tide flooding conditions to the surface streets and Biscayne Boulevard.