Observations from a 24-hour survey examining exchange between a deep shipping channel and shallow estuary in a microtidal system, Mobile Bay, AL.

Mobile Bay is a broad shallow (3m) microtidal estuary with a deep (12m) man-made shipping channel that runs the length of the system. This deep but narrow (120m) channel accounts for 1% of the estuary width and has been shown to impact the cross-estuary flow and enhance offshore connectivity (Coogan and Dzwonkowski 2018, Coogan et al. 2019). The goal of this study was to examine the channels impact on the along-estuary momentum balance and subtidal salt balance based on observations from a 24-hour survey. The 24-hour survey was comprised of 13 cross-estuary crossings to measure currents with a ship board ADCP, and moored ADV. Salinity and temperature were measured with CTD cast, and nutrients were measured with water samples. Near bottom tidal currents in the shipping channel were unidirectional and flowed continuously into the estuary on both ebb and flood tides during a relatively weak neap tidal period. Ongoing analysis of this data set seeks to highlight the importance of exchange dynamics between the deep shipping channel and shallow regions and quantify the influence of the shipping channel on bay wide estuary dynamics.