Generalized Environmental Modeling System for Surfacewaters
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GEMSS (Generalized Environmental Modeling System for Surfacewaters) is an integrated system of 3-D hydrodynamic and transport modules embedded in a geographic information and environmental data system. GEMSS is in the public domain and has been used for similar studies throughout the USA and worldwide. ERM’s Surfacewater Modeling Group has special expertise with the model in that ERM staff contributes to the source code and has completed many applications with the model.
GEMSS includes a grid generator and editor, control file generator, 2-D and 3-D post processing viewers, and an animation tool. It uses a database approach to store and access model results. The database approach is also used for field data; as a result, the GEMSS viewers can be used to display model results, field data or both, a capability useful for understanding the behavior of the prototype as well as for calibrating the model. The field data analysis features can be used independently using GEMSS modeling capability.
GEMSS was developed in the mid-1980s as a hydrodynamic platform for transport and fate modeling. The hydrodynamic platform (“kernel”) provides 3-D flow fields from which the distribution of various constituents can be computed. The constituent transport and fate computations are grouped into modules. GEMSS modules include thermal analysis, water quality, sediment transport, particle tracking, oil and chemical spills, entrainment, and toxics. Additional modules are being tested, developed or planned.
The theoretical basis of the hydrodynamic kernel of GEMSS is the three-dimensional Generalized, Longitudinal-Lateral-Vertical Hydrodynamic and Transport (GLLVHT) model which was first presented in Edinger and Buchak (1980) and subsequently in Edinger and Buchak (1985). The GLLVHT computation has been peer reviewed and published (Edinger and Buchak, 1995; Edinger, et al., 1994). The kernel is an extension of the well known longitudinal-vertical transport model that forms the hydrodynamic and transport basis of the Corps of Engineers' water quality model CE-QUAL-W2 (U. S. Army Engineer Waterways Experiment Station, 1986). Improvements to the transport scheme, construction of the constituent modules, incorporation of supporting software tools, GIS interoperability, visualization tools, graphical user interface (GUI), and post-processors have been developed by Kolluru et al. (1998; 1999; 2003a; 2003b).
Applications of GEMSS and its individual component modules have been accepted by regulatory agencies in the U.S. and Canada. GEMSS-based studies have been accepted by the U.S. Environmental Protection Agency (EPA), and state agencies including those of California, Massachusetts, Pennsylvania, Louisiana, Texas, New York, and Delaware. Washington State’s Department of Ecology has adopted GEMSS as its standard tool for estuarine and water quality modeling. Most recently GEMSS has been published as a recommended three-dimensional hydrodynamic and water quality model in studies funded by EPA (HGL and Aqua Terra, 1999) and by the Water Environment Research Foundation (WERF). It is the sole hydrodynamic model listed in the model selection tool database for hydrodynamic and chemical fate models that can perform 1-D, 2-D, and 3-D time-variable modeling for most waterbody types, consider all state variables, include the near- and far-fields; can provide GUI’s, grid generation, and GIS linkage tools; and has strong documentation (Water Environment Federation, 2001).
GEMSS has been used for ultimate heat sink analyses at Comanche Peak, Farley, and Arkansas Nuclear One. In Pennsylvania, it has been applied at PPL’s Brunner Island Steam Electric Station on the lower Susquehanna River, Exelon’s Cromby and Limerick Generating Stations on the Schuylkill River, and at several other electric power facilities. River applications for electric power facilities have been made on the Susquehanna (Brunner Island), the Missouri (Labadie), the Delaware (Mercer and Gilbert), the Connecticut (Connecticut Yankee), and others.
A GEMSS application requires two types of data: (1) spatial data, primarily the waterbody shoreline and bathymetry, but also the locations, elevations, and configurations of man-made structures and (2) temporal data, that is, time-varying boundary condition data defining tidal elevation, inflow rate and temperature, inflow constituent concentration, outflow rate, and meteorological data. All deterministic models, including GEMSS, require uninterrupted time-varying boundary condition data. There can be no long gaps in the datasets and all required datasets must be available during the span of the proposed simulation period.
For input to the model, the spatial data is encoded primarily in two input files: the control and bathymetry files. These files are geo-referenced. The temporal data is encoded in many files, each file representing a set of time-varying boundary conditions, for example, meteorological data for surface heat exchange and wind shear, or inflow rates for a tributary stream. Each record in the boundary condition files is stamped with a year-month-day-hour-minute address. The data can be subjected to quality assurance procedures by using GEMSS to plot, then to visually inspect individual data points, trends and outliers. The set of input files and the GEMSS executable constitute the model application.
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