                                                           File: ABSTRACT.TXT


                       HSCTM2D Model System Abstract


               Center for Exposure Assessment Modeling (CEAM)
     National Exposure Research Laboratory - Ecosystems Research Division
                  Office of Research and Development (ORD)
               U.S. Environmental Protection Agency (U.S. EPA)
                          960 College Station Road
                         Athens, Georgia 30605-2700

                                706/355-8400



-----------------------------------------------------------------------------

                                  Summary

HSCTM2D (Hydrodynamic, Sediment and Contaminant Transport Model) is a finite
element modeling system for simulating two-dimensional, vertically-
integrated, surface water flow (typically riverine or estuarine
hydrodynamics), sediment transport, and contaminant transport.  The modeling
system consists of two modules, one for hydrodynamic modeling (HYDRO2D) and
the other for sediment and contaminant transport modeling (CS2D).  One
example problem is included.  The HSCTM2D modeling system may be used to
simulate both short term (less than 1 year) and long term scour and/or
sedimentation rates and contaminant transport and fate in vertically well
mixed bodies of water.

HYDRO2D solves the equations of motion and continuity for nodal depth-
averaged horizontal velocity components and flow depths.  The effects of
bottom, internal and surface shear stresses, horizontal salinity gradients,
and the Coriolis force are represented in the equations of motion.

CS2D solves the advection-dispersion equation for nodal vertically-integrated
concentrations of suspended sediment, dissolved and sorbed contaminants, and
bed surface elevations.  The processes of dispersion, aggregation, erosion,
deposition, adsorption and desorption are simulated.  A layered bed model is
used in simulating bed formation and subsequent erosion.  Sediment bed
structure (density and shear strength profiles, thickness and elevation), net
change in bed elevation and net vertical mass flux of sediment over an
interval of time (e.g., over a certain number of tidal cycles), average
amount of time sediment particles are in suspension, and the downward flux of
sediment onto the bed are calculated for each element.

HSCTM2D can be run in an uncoupled or semi-coupled mode.  In the uncoupled
mode, HYDRO2D is run separately from CS2D.  In the semi-coupled mode, HYDRO2D
and CS2D are run in the following fashion.  First, HYDRO2D calculates the
flow field for the current time step.  Second, the predicted flow field is
used in CS2D to calculate the transport of sediments and contaminants during
the same time step.  HYDRO2D is run at every time step to update the flow
field to account for predicted changes in nodal flow depths due to erosion
and deposition.  In addition, HSCTM2D has a default option that will allow
the user to make relative comparisons between sites or designs with limited
data.  To obtain a quantitative analysis, the user must run the non-default
option with a complete set of data.

                                Documentation

The HSCTM2D User's Manual is available as an Adobe(*) Acrobat(*) Portable
Document Format (PDF) file (USERMANU.PDF) within the DOCUMENT sub-directory
if the user chose to install the user's manual from the INSTALHC.EXE program
install menu.  To view, print, and/or navigate a PDF document, a reader
program must be installed on the users computer system.  A free Adobe reader
allows the user to view, navigate, and/or print PDF files across all major
computing platforms.  Acrobat Reader is a free viewing companion to Adobe
Acrobat 3.0 and is available free from the Adobe world wide web (WWW) site at
Uniform Resource Locator (URL) address: http://www.adobe.com.

To ensure that the user can view and/or print a PDF file in its entirety, the
user must down load and install the most recent version/edition of the free
Acrobat Reader.  PDF files can be viewed across multiple platforms (Mac,
Microcomputer, UNIX) using the appropriate reader for that platform.

* Adobe, Acrobat, and Adobe Type Manager are trademarks of Adobe Systems
Incorporated and may be registered in certain jurisdictions.  (C) Copyright
1994 Adobe Systems Incorporated.  All rights reserved.

Refer to file READ.ME in the README sub-directory for further information on
the storage format and hardware and/or software print/view requirement(s) of
the user's manual file.

-----------------------------------------------------------------------------
