Monitoring Suspended Sediment Plumes to Evaluate the Effects of Agitation Dredging in Savannah Harbor

Abstract

Resource agency concerns over the dredging practices in the Savannah Harbor prompted the USACE Savannah District (CESAS) to commission a comprehensive study to evaluate environmental effects. CESAS is currently citing findings and recommendations in the final report in their permitting effort for existing and future maintenance dredging activities that involve agitation dredging and open water disposal. The comprehensive Scope of Work (SOW) developed was a collaborative effort between CESAS, reviewing agencies, and Applied Technology and Management (ATM) technical staff. The data collection study design required three distinct simultaneous efforts: water chemistry sampling, in situ water quality profiling, and monitoring the dredged material discharge plume. This last effort utilized acoustic doppler technology. SEDIVIEW, an acoustic doppler post-processing software package, was employed to quantify total suspended solids (TSS) concentrations from the acoustic backscatter signal. Total recoverable chemistry (TRC) samples were collected both upgradient and downgradient of the dredged material discharge to quantify the concentrations of selected constituents released to the water column as a result of the dredging activity. In situ profiles were also performed upgradient and downgradient to measure changes to water quality (especially, dissolved oxygen) resulting from thedredging activity. All data were analyzed and presented in the final report. Effects to aquatic resources resulting from changes to suspended sediment concentrations, water chemistry, and water quality were also evaluated. The fate of the suspended material was also modeled using SSFATE, a program developed for the USACE by Applied Science Associates, Inc.