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properties. In coastal areas, because of the irregular coast line and topography and the 

 complex forcing of the flow, it is difficult to obtain measurements in sufficient detail and 

 frequency to resolve the spatial and temporal scales of the circulation. 



In recent years significant progress has been made in the development of numerical 

 circulation models which are able to simulate and predict the transport processes which 

 operate in coastal areas. Such models, when properly configured and validated with 

 observational data, often provide the best information on water transport processes in these 

 geographic areas. Due to the complexity of the driving forces and topography in Boston 

 Harbor and Massachusetts Bay, the circulation model provides one of the best mechanisms 

 for understanding how material released from the new outfall pipe will be subsequently 

 transported and diluted. 



DESCRIPTION OF HYDRODYNAMIC MODELING STUDIES 



Over the past two years, the USGS has conducted extensive modeling studies of 

 transport processes in Massachusetts Bay using the Estuarine and Coastal Ocean Model 

 (ECOM) circulation model developed by Blumberg and Mellor (1980). The version used by 

 the USGS is an improved version that allows for larger time steps called ECOM-si (si stands 

 for semi-implicit). This model is used in conjunction with available observational data to 

 determine the fate and transport of contaminants, nutrients, and other water-borne materials 

 in Massachusetts Bay, including effluent from the proposed outfall site. The modeling work 

 has been reviewed by the Massachusetts Bay Model Evaluation Group, consisting of a group 

 of distinguished scientists having expertise in hydrodynamic processes and computer 

 modeling. The MWRA, under separate contract to Hydroqual, Inc., is using the 

 hydrodynamic model to develop a water quality model of Massachusetts Bay. 



ECOM-si is a coastal ocean model highly respected among oceanographic scientists. 

 Developed over the past 10 years, the basic ECOM model has been used on over 30 major 

 studies including studies of ocean dynamics; semi-enclosed seas; estuarine systems; flows in 

 open channels; and it is actively being applied in forecasting for Great Lakes and Norwegian 

 coastal waters. It is recognized among oceanographers as a useful tool for simulating ocean 

 transport processes. 



The ECOM-si model is a time-dependent, three-dimensional model that is capable of 

 simulating currents and water properties driven by the full suite of coastal ocean forcing 

 mechanisms. Wind-stress, river runoff, offshore discharges of fresh water, heat flux, 

 precipitation and evaporation, tides, and remote forcing by the open ocean all are 

 incorporated in the model framework. It can account for evolving water masses, fresh water 

 plumes, fronts, and eddies. Free surface elevation is also calculated so that tides and storm 

 surge events can be simulated. Vertical variations in the currents, such as coastal upwelling, 

 are simulated. Vertical mixing processes are accounted for through the use of a submodel 

 developed by Mellor and Yamada (1982). A complete description of the governing equations 



