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| Techniques and Methods 4-C1 |
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 Survey’s National Water Information System. GCLAS can also import and export data in formats that are compatible with various commonly used spreadsheet and statistics programs.
Preface
Abstract
Introduction
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
Acknowledgments
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
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