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Techniques and Methods 4-C1

Userís Manual for the Graphical Constituent Loading Analysis System (GCLAS) 

By G.F. Koltun, Michael Eberle, J.R. Gray, and G.D. Glysson

This report is also available as a pdf.


This manual describes the Graphical Constituent Loading Analysis System (GCLAS), an interactive cross-platform program for computing the mass (load) and average concentration of a constituent that is transported in stream water over a period of time. GCLAS computes loads as a function of an equal-interval streamflow time series and an equal- or unequal-interval time series of constituent concentrations. The constituent-concentration time series may be composed of measured concentrations or a combination of measured and estimated concentrations. GCLAS is not intended for use in situations where concentration data (or an appropriate surrogate) are collected infrequently or where an appreciable amount of the concentration values are censored.

It is assumed that the constituent-concentration time series used by GCLAS adequately represents the true time-varying concentration. Commonly, measured constituent concentrations are collected at a frequency that is less than ideal (from a load-computation standpoint), so estimated concentrations must be inserted in the time series to better approximate the expected chemograph. GCLAS provides tools to facilitate estimation and entry of instantaneous concentrations for that purpose.

Water-quality samples collected for load computation frequently are collected in a single vertical or at single point in a stream cross section. Several factors, some of which may vary as a function of time and (or) streamflow, can affect whether the sample concentrations are representative of the mean concentration in the cross section. GCLAS provides tools to aid the analyst in assessing whether concentrations in samples collected in a single vertical or at single point in a stream cross section exhibit systematic bias with respect to the mean concentrations. In cases where bias is evident, the analyst can construct coefficient relations in GCLAS to reduce or eliminate the observed bias.

GCLAS can export load and concentration data in formats suitable for entry into the U.S. Geological Surveyís National Water Information System. GCLAS can also import and export data in formats that are compatible with various commonly used spreadsheet and statistics programs.






Installing GCLAS

Getting Started with GCLAS 

Starting the Program on a Computer Running the Windows Operating System

Starting the Program on a Computer Running the UNIX Operating System

Importing Data for Analysis — A Short Example

Importing/Opening Data Files

Import Command

Streamflow Data

Water-Quality Data

Open Command

Overview of GCLAS Window and Panel Interface

Organization of the GCLAS Display

Transport-Relation Window

Working with GCLAS Panels, Tabs, and Buttons

Adding and Editing Water-Quality Data

Using the Overview Graph and Working Graph to Display Curves and Data Points

Adding/Editing Estimated Values in the Working-Graph Panel

Setting the Default Representation Type of Estimated Values

Editing Data in the Tabular-Data Panel

Using the Curve-Label Panel

Using Reference Curves

Using the Transport-Relation Window to Aid Estimation

Analyzing and Applying Cross-Section Coefficients

Selecting Samples and Calculating Sample-Based Coefficients

Direct Entry of Coefficients

Applying Coefficients as a Function of Streamflow

Applying Coefficients as a Function of Time

Selecting and Applying a Previously Calculated Coefficient

Creating and Applying a New Ad Hoc Coefficient Relation

Linking Coefficient Relations by Time

Applying Coefficients as a Function of Streamflow and Time

Computing Loads

Saving Your Work

Exporting Data and Tables

Exporting GCLAS gcl Files

Exporting Concentrations and (or) Loads in Card-Image Format

Exporting Streamflow, Concentration and Load Data in Table Format


References Cited

Appendix 1 SEDATA 2- and B-Card-Image Formats

Appendix 2 Keywords, Format Codes, and Value Domains for GCL Files

Appendix 3 Date and Time Editing Functions

Appendix 4 Unit- and Daily-Values Card-Image Formats


This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.

Download the report (PDF, 918KB)

Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. This information provides tools to help make PDF files accessible. These tools convert Adobe PDF documents into HTML or ASCII text, which then can be read by a number of common screen-reading programs that synthesize text as audible speech. In addition, an accessible version of Acrobat Reader 5.0 for Windows (English only), which contains support for screen readers, is available. These tools and the accessible reader may be obtained free from Adobe at Adobe Access.

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