MEMORANDUM FOR RECORD (MFR) SUBJECT: Mobile Harbor Interagency Working Group Meeting

Authors: U.S. Army Corps of Engineers, Mobile District

Year: 2014

Reference: U.S. Army Corps of Engineers, Mobile District. (2014) “MEMORANDUM FOR RECORD (MFR) SUBJECT: Mobile Harbor Interagency Working Group Meeting”

Summary: A range of options for dredged material placement in Mobile Bay were covered. Open water placement areas have been selected where no more than 12 inches thickness of material will be allowed. An SAV survey showed that there are no SAV beds in the placement areas. A cultural resource survey showed several shipwrecks of cultural importance that will have to be avoided. A comprehensive sediment budget showed that about 4.2 million cubic yards have been dredged from the Mobile Bay shipping channel per year since about 1913. The budget showed that the Bay is a net depositional area, and this natural deposition amounts to 64% of annual dredging. Monitoring showed that after about 3 months, an oxygenated layer at the thin-layer placement sites can be seen, which is from currents and wave action. Modeling showed that 35% of the dredged material will erode from the placement area and find its way back into the navigation channel. The remaining 65% will be dispersed widely though-out the bay. Modeling also showed that the thin-layer placed material is less erodible than naturally deposited sediment. It was suggested that disposal sites could be alternated, so that each site will receive material about every six years. This will provide adequate time for benthic recovery. Even though the long-term impacts of open water thin-layer disposal has not been determined, the technology is being considered “beneficial use”.

What You Will Find Here: Brookley Hole p. 2, Beneficial use p. 2, Open water thin-layer disposal p. 2, sediment budget p. 3, monitoring p. 3, Cultural Resources p. 4