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GCLAS (Graphical Constituent Loading Analysis System): A tool for computing loads of constituents transported in rivers

August 21, 2019

Overview of GCLAS

Screenshot of GCLAS
Screenshot of GCLAS

GCLAS is a program designed to compute daily and annual loadings of constituents transported in rivers. Use of GCLAS is appropriate when concentration data are collected at relatively high frequency (i.e. approximately daily to more frequent samples depending on the temporal variability of streamflow and concentrations) and concentration data are nearly or completely free of censored (e.g. "less than") values. Concentration data can be at equal or unequal time intervals. Depending on the frequency with which water-quality data are collected, computation of daily constituent loads can be independent of, to highly dependent on, human interpretation of the relation between streamflow and constituent transport.

GCLAS provides a visual environment for evaluating the relation between covariate time series and the constituent chemograph. The GCLAS graphical interface permits easy entry of estimated concentrations and provides tools to aid in making those estimates. Some of the features of GCLAS include:

  • directly handles periods of zero or reverse flow,
  • can apply coefficient adjustments to concentrations as a function of time, streamflow, or both,
  • Computes loadings of a wide variety of constituents,
  • Provides views of data related to the chemograph at varying levels of temporal detail, and
  • Easily displays covariate time-series data to provide enhanced visual cues for drawing the constituent chemograph.


Download GCLAS

Current version

GCLAS installer packaged for Windows and Unix/Linux (current version that creates tab-delimited [rdb] outputs): gclas_install_2_4_1.jar (6.6 MB)


Legacy version

GCLAS installer packaged for Unix and Windows (legacy version that creates card-image outputs): gclas_install_1_06c.jar (4.5 MB)


Version History and Installation Instructions

  • Version history (note: As of version 2.20, GCLAS is being compiled with the OpenJDK)
  • UNIX or Windows installation instructions for version 2.4.1
  • UNIX or Windows installation instructions for version 1.06c


Documentation for GCLAS

Koltun, G.F., Eberle, M., Gray, J.R., Glysson, G.D., 2006, User's manual for the Graphical Constituent Loading Analysis System (GCLAS), U.S. Geological Survey Techniques and Methods, 4-C1, 51 p.,


Publication Year 2019
Title GCLAS (Graphical Constituent Loading Analysis System): A tool for computing loads of constituents transported in rivers
Product Type Software Release
Record Source USGS Digital Object Identifier Catalog