JR Engineering prepared a drainage analysis and construction plans for the Bryant Drive Storm Drain Improvement Project, which involved the removal and replacement of an existing private storm sewer system with a public system having adequate capacity.

Bryant Drive is located within a private mobile home park in Federal Heights.  An existing system installed with the development in the 1960s was undersized and at various times the owner has added parallel storm sewer systems to increase its carrying capacity, which in places was comprised of reinforced concrete pipe, PVC pipe, and clay pipe.

JR Engineering evaluated the hydrology of the 41-acre basin and determined inflows at the many storm inlets in the system as well as offsite flows from the Cascade mobile home park and 96th Avenue.  An alternatives analysis was prepared which evaluated full or partial replacement of the existing storm sewer system to capture and convey either the 5-year or the 100-year storm event.  JR Engineering recommended complete replacement of the old system with the replacement storm sewer designed to capture and convey the 100-year storm event.  The proposed replacement system was comprised of a single 42” HDPE pipe down the center of the private roadway, located inside a drainage easement dedicated to the City.

A critical aspect of the design was the decrease in time of concentration and a corresponding increase in piped peak flows resulting from the replacement of the old undersized system with an appropriately-sized replacement, as well as the effects of these larger flows on receiving infrastructure.  The selected alternative of a replacement system that conveyed the 100-year event was based on mitigating existing local flooding concerns.

The project is intended to be constructed in 2018 and will include roughly 1,180 linear feet of 42” HDPE storm sewer, 13 manholes, and 415 tons of asphalt.