Barry A. Vittor & Associates, Inc. analyzed potential ecological impacts to upper Mobile Bay and the lower Mobile-Tensaw Delta due to bridge construction at Choccolatta Bay, Justins Bay, and Shellbank River, along the Highway 90 Causeway. This project investigated potential effects on natural communities due to habitat alteration and restoration of hydrology north and south of the Causeway. The analysis was based primarily on bridge construction scenarios and hydrologic modeling.

A historical data review assessed previous studies to determine potential areas of concern and data gaps. Wetland and SAV distributions were delineated and mapped, with a focus on those areas in proximity to the alternative study locations. Field surveys were performed with emphasis on validating the estimated boundaries of wetlands and SAV in the study area, including along the Causeway right-of-way. A list of plant species was generated for each potential restoration location.

Re-establishment of hydrology through bridge construction at Choccolatta Bay, Justins Bay, and Shellbank River is expected to result in a variety of ecological impacts, including both beneficial and detrimental effects on the natural communities of upper Mobile Bay and the lower delta. Based on the project mapping, estimates of habitat alteration were made for each alternative study location. Potential effects analyzed included changes to wetlands, SAV, habitat for endangered species, nekton and benthic communities, sedimentation and sediment quality, tidal flux, circulation, and water quality.