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

Release Date:

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_30.jar (6.7 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 2.30
  • 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 pUSGS Techniques and Methods 4-C1, Portable Document Format (PDF) (918 KB).


Software License and Purchase Information

This software is a product of the U.S. Geological Survey, which is part of the U.S. Government.


This software is freely distributed. There is no fee to download and (or) use this software.


Users do not need a license or permission from the USGS to use this software. Users can download and install as many copies of the software as they need.

Public Domain

As a work of the United States Government, this USGS product is in the public domain within the United States. You can copy, modify, distribute, and perform the work, even for commercial purposes, all without asking permission. Additionally, USGS waives copyright and related rights in the work worldwide through CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/ ).