Reports
Bottom sediment characterization of Baltimore Harbor
1997, Halka, J.P., and Ortt, R.A., Jr.
File Reports, Coastal and Estuarine Geology, File Report 1997-01
Introduction
The University of Maryland Center for Environmental and Estuarine Studies, Hom Point Environmental Laboratory was contracted by the Maryland Department of the Environment to investigate the processes governing suspended sediment transport in Baltimore Harbor. The results of this study could be used to help account for the observed distributions of sediment pollutants in the harbor area, assist in modelling the transport of fine grained suspended sediments, and address concerns about the movement and impacts of toxic compounds of concern. There were three broadly defined components to the study. First, characterization of the Harbor bottom sediments, bottom roughness characteristics, and suspended sediment regimes. Second, a series of intensive observations and analysis at selected sites to parameterize sediment resuspension and settling as a function of physical forcing. Finally, incorporating the derived parameterizations into a numerical model of Baltimore Harbor circulation.
The Maryland Geological Survey - Coastal and Estuarine Geology Program provided direct support to the first two components of this study. The characterization of the harbor bottom roughness and surficial sediment characteristics were undertaken to assist in determining the distribution of bottom types and to select areas for more detailed surveys. Initially a side scan sonar survey of the Harbor was conducted. Information from this survey was used to examine boundaries between different sediment types and variations in benthic microtopography. Bottom roughness can have a strong influence on sediment erodability and provide input to other, more detailed, components of the study. In addition, the images could be useful in identifying areas that were physically disrupted by shipping activities in the harbor. Sediment disturbance from activities such as anchoring, dredging, and ship groundings have important implications for the erosion of sediments and associated contaminants of concern.
The characteristics of surficial sediment including grain size, porosity, and organic carbon were determined. Many pollutants, including both trace metals and organic compounds, have been shown to preferentially adsorb to fine grained, organic carbon rich sediments. Thus compounds of concern are likely to be located in areas where the bottom sediments have these characteristics. This study component provided the first detailed, harbor wide, survey of bottom sediment characteristics in the Patapsco River estuary. The bottom sediment grain size, porosity, and carbon content all have a strong influence on the sediment erodability and particle settling behavior. Thus efforts to determine the potential for erosion of sediment and associated ' contaminants, transport pathways, and the likely areas of deposition are dependent on the these factors. Data from the surficial sediment sampling grid combined with the results of the side scan survey were used to assist in determining the appropriate locations for detailed tidal cycle anchor station and sediment flume observations carried out by other participants in the project.
The database of large vessel movement in the harbor area, maintained by the Baltimore Maritime Exchange, was analyzed to determine recent shipping channel usage and provide a qualitative assessment of the potential effects of shipping on sediment resuspension processes. This database covered only larger vessels using the dredged shipping channels and berth areas. The movement of smaller vessels, primarily consisting of tug and barge traffic, operating both within and outside of the dredged channels, is not routinely tracked or maintained by harbor interests.
The Coastal and Estuarine Geology Program also assisted in the second portion of the study, by assisting in site selection for the suspended sediment parameterization studies, determine the settling velocities of resuspended sediments, and assist in the data collection, reduction, and analysis for development of sediment resuspension parameters. The support functions are not reported herein.
