The Metropolitan St. Louis Sewer District seeks authorization to discharge fill material below the ordinary high water mark of Black Jack Creek by reconfiguring approximately 1,280 linear feet of the existing channel into a U-shaped concrete lined channel for a project known as Hallstead Storm Channel Phase IV. The proposed creek channel reconfiguration would match an existing 45 foot wide concrete lined channel located immediately upstream of the project. The proposed vertical walled channel would gradually increase from 45 feet wide to 59 feet wide at the downstream limits of the project. At the upstream end of the project limits, the channel walls are proposed to be 12 feet high and would gradually increase to 18 feet high in a downstream direction. The vertical concrete walls at the downstream terminus of the project would flare into the existing banks into a new 120-foot long rip rap or gabion lined plunge pool. The plunge pool is designed to dissipate water velocities before the proposed concrete channel transitions back into a natural creek channel downstream of the project limits. All work would occur within an existing 80-foot wide drainage right-of-way and include improvements to existing storm sewer outfalls. The purpose of the project is to eliminate erosion within the project limits and improve conveyance to reduce potential for overbank flooding. As a result of the flood reduction, approximately 50 homes would no longer be located in the 15 or 100- year floodplain.
Authorization for this project was granted February 7, 2006 (P-2481) and compensatory mitigation associated with unavoidable impacts to 1400 feet of Black Jack Creek was completed downstream through the creation of riparian buffer habitat in 2007. The project authorization was extended until December 30, 2015, however, construction was never initiated by the applicant. In accordance with the 2008 Compensatory Mitigation Rulemaking Regulations, compensatory mitigation for the proposed project is currently being re-evaluated. The applicant is exploring mitigation options within an approved wetland mitigation bank.
The site is located immediately upstream of Vorhof Drive at the downstream end of a 45 foot wide vertical wall concrete channel that was completed in 2003 as part of the Hallstead Storm Channel Phase III project. Black Jack Creek channel improvements are proposed to continue in a downstream direction and cease approximately 120 linear feet downstream of Hudson Drive. More specifically, the site is located Section 5, Township 46 North, Range 7 East, near Dellwood, St. Louis County, Missouri. The Public Notice comment period opens on March 29, 2019, and closes April 19, 2019.