U.S. Department of the Interior

U.S. Geological Survey

Techniques and Methods 4-C1

User’s Manual for the Graphical Constituent Loading 

Analysis System (GCLAS)
User’s Manual for the Graphical Constituent 

Loading Analysis System (GCLAS)

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

U.S. Department of the Interior

U.S. Geological Survey

Techniques and Methods 4-C1
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2006

For product and ordering information:

World Wide Web: http://www.usgs.gov/

Telephone: 1-888-ASK-USGS

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Suggested citation:

Koltun, G.F., Eberle, Michael, Gray, J.R., and Glysson, G.D, 2006, User's manual for the Graphical Constituent Loading 

Analysis System (GCLAS): U.S. Geological Survey Techniques and Methods, book 4, chap. C1, 51 p.

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report.
 iii

Contents

Preface...................................................................................................................................................................................... vi

Abstract ................................................................................................................................................................................... 1

Introduction ............................................................................................................................................................................. 1

Installing GCLAS ..................................................................................................................................................................... 2

Getting Started with GCLAS ................................................................................................................................................. 7

Starting the Program on a Computer Running the Windows Operating System .............................................. 7

Starting the Program on a Computer Running the UNIX Operating System....................................................... 8

Importing Data for Analysis — A Short Example..................................................................................................... 8

Importing/Opening Data Files .............................................................................................................................................. 12

Import Command .......................................................................................................................................................... 12

Streamflow Data ................................................................................................................................................ 12

Water-Quality Data ............................................................................................................................................ 13

Open Command ............................................................................................................................................................ 15

Overview of GCLAS Window and Panel Interface ............................................................................................................ 16

Organization of the GCLAS Display ........................................................................................................................... 17

Transport-Relation Window ....................................................................................................................................... 18

Working with GCLAS Panels, Tabs, and Buttons .................................................................................................... 18

Adding and Editing Water-Quality Data .............................................................................................................................. 19

Using the Overview Graph and Working Graph to Display Curves and Data Points ........................................ 19

Adding/Editing Estimated Values in the Working-Graph Panel ........................................................................... 21

Setting the Default Representation Type of Estimated Values.............................................................................. 21

Editing Data in the Tabular-Data Panel ..................................................................................................................... 22

Using the Curve-Label Panel ...................................................................................................................................... 24

Using Reference Curves .............................................................................................................................................. 26

Using the Transport-Relation Window to Aid Estimation ................................................................................................. 26

Analyzing and Applying Cross-Section Coefficients......................................................................................................... 28

Selecting Samples and Calculating Sample-Based Coefficients......................................................................... 28

Direct Entry of Coefficients ......................................................................................................................................... 31

Applying Coefficients as a Function of Streamflow................................................................................................ 31

Applying Coefficients as a Function of Time ............................................................................................................ 34

Selecting and Applying a Previously Calculated Coefficient...................................................................... 35

Creating and Applying a New Ad Hoc Coefficient Relation ........................................................................ 35

Linking Coefficient Relations by Time.............................................................................................................. 36

Applying Coefficients as a Function of Streamflow and Time............................................................................... 37

Computing Loads..................................................................................................................................................................... 37

Saving Your Work.................................................................................................................................................................... 39

Exporting Data and Tables..................................................................................................................................................... 40

Exporting GCLAS gcl Files .......................................................................................................................................... 40

Exporting Concentrations and (or) Loads in Card-Image Format ........................................................................ 41

Exporting Streamflow, Concentration and Load Data in Table Format ............................................................... 42

Acknowledgments .................................................................................................................................................................. 42

References Cited..................................................................................................................................................................... 43

Appendix 1 SEDATA 2- and B-Card-Image Formats ........................................................................................................ 44

Appendix 2 Keywords, Format Codes, and Value Domains for GCL Files .................................................................... 45
iv 

Appendix 3 Date and Time Editing Functions.................................................................................................................... 48

Appendix 4 Unit- and Daily-Values Card-Image Formats................................................................................................ 50

Figures

1. Sample Excel-based input template for creating GCLAS gcl input files............................................................. 13

2. Schematic of GCLAS main window showing panel arrangement. ...................................................................... 17

3-20. Computer-screen images showing—

3. Transport-relation window. ............................................................................................................................... 18

4. Time-series overview panel. ............................................................................................................................. 19

5. Working-graph panel.......................................................................................................................................... 20

6. Tabular-data panel. ............................................................................................................................................. 22

7. Tabular-data panel showing expanded spanner heading............................................................................ 23

8. Curve-label panel. ............................................................................................................................................... 24

9. Curve label pop-up menu................................................................................................................................... 25

10. Get Coeffs. tab of the Calculate Coefficients panel....................................................................................... 29

11. Coefficient holding area (top) and coefficient relation area (bottom) of the Calculate Coefficients 

panel...................................................................................................................................................................... 29

12. Graphs tab of the Calculate Coefficients panel. ............................................................................................ 30

13. Panel showing cross-section coefficient as a function of streamflow. .................................................... 33

14. Working-graph panel showing streamflow (red), concentration (dark blue), and cross-section 

coefficient (light blue) time series.................................................................................................................... 33

15. Application of coefficient relations panel showing a coefficient relation that varies as a function of 

streamflow............................................................................................................................................................ 34

16. Options tab on the load-computation panel. .................................................................................................. 38

17. Summary tab on the load-computation panel. ............................................................................................... 39

18. Tab views of the rdb report options window. ................................................................................................. 40

19. Load table showing card-image export options. ........................................................................................... 41

20. Load table showing daily-load report option.................................................................................................. 42

21. Sample of daily-load report output............................................................................................................................ 42

Tables

1. Generic parameter codes that can be used within GCLAS. ................................................................................. 14

2-1. Time keywords and permissible format codes........................................................................................................ 45

2-2. Sample metadata keywords, format codes, and value domains. ........................................................................ 45

2-3. Parameter keywords, format codes, and value domains...................................................................................... 47

3-1. Date-editing functions................................................................................................................................................. 48

3-2. Time-editing functions................................................................................................................................................. 49
 v

Conversion Factors

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 x °C) + 32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F - 32) / 1.8

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or micrograms per liter (μg/L).

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

Volume

gallon (gal) 0.003785 cubic meter (m3)

million gallons (Mgal) 3,785 cubic meter (m3)

cubic inch (in3) 16.39 cubic centimeter (cm3)

cubic foot (ft3

) 0.02832 cubic meter (m3)

acre-foot (acre-ft) 1,233 cubic meter (m3)

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg)

ton, short (2,000 lb) 0.9072 megagram (Mg)

ton, long (2,240 lb) 1.016 megagram (Mg)

ton per day (ton/d) 0.9072 metric ton per day (ton/d)

ton per day (ton/d) 0.9072 megagram per day (Mg/d)

ton per year (ton/yr) 0.9072 megagram per year (Mg/yr)

ton per year (ton/yr) 0.9072 metric ton per year (ton/yr)
vi 

Preface

This report describes the Graphical Constituent Loading Analysis System (GCLAS), a program developed by the U. S. Geological Survey (USGS) to facilitate computation of loads and average concentrations of physical and chemical constituents 

transported in streams. The documentation and program, including sample datasets, are available for download over the Internet from a USGS software Web page at http://water.usgs.gov/software/surface_water.html. Any future revisions or 

updates to GCLAS will be made available at the same location. 

Although we have attempted to make GCLAS accurate and error free, complex programs such as GCLAS almost certainly 

will contain some errors. Users are encouraged to report any errors in this user’s guide or in GCLAS itself to the contact listed 

on software distribution Web page.
User’s Manual for the Graphical Constituent Loading 

Analysis System (GCLAS)

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

Abstract

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 timevarying 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. 

Introduction

The Graphical Constituent Loading Analysis System (GCLAS) is a program designed by the U.S. Geological 

Survey (USGS) to compute daily loads of sediment or other stream-water constituents from time series of streamflow 

and concentration data. GCLAS computes loads as a function of an equal-interval streamflow time series and an equalor unequal-interval time series of constituent concentrations. GCLAS was created to replace and improve upon the 

USGS Sedcalc program (Koltun and others, 1994), which was abandoned because software and hardware for which it 

had been developed became obsolete. 

Primary features of GCLAS are the following: 

• A visual approach to data analysis. GCLAS simultaneously displays data in graphical and tabular formats. 

Rather than typing in command lines to do computations and then generating plots to see the results, the analyst can manipulate graphical elements directly with a mouse or by editing data tables. Because the graphs and 

tables are dynamically linked, results of data manipulations can be seen immediately in both graphs and tables. 
2 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

• A comprehensive set of analytical tools. In addition to providing editable graphs and tables already mentioned, GCLAS can 

1. display transport curves showing the relation between streamflow and concentration data being 

worked, a “reality check” for adding or repositioning estimated data points on a concentration curve, 

2. compute and (or) apply cross-section coefficients as a constant, as a function of streamflow, as a function of time, or combinations thereof, and

3. compute loads for an entire year or any part of a year and export the load data to files for subsequent 

entry into the USGS National Water Information System (NWIS) (U.S. Geological Survey, 2003) or 

import into other analytical software. 

• The ability to compute loads for streams where reverse and (or) zero flows occur. Because GCLAS makes 

it easy to resize, rescale, and zoom in within graphs, logarithmic transformations are not needed to constrain 

the y-axis, so working with zero and reverse flows is feasible. 

• Calculation of loads for constituents other than sediment. GCLAS can compute loads for many constituents and can report loads in a variety of units. 

Installing GCLAS

GCLAS was developed using the Java programming language, so it can be installed and run on computers with 

a variety of operating systems1

. Installing GCLAS requires that a Java run-time engine (version 1.4 or higher) also be 

installed on the destination computer. It is recommended that GCLAS be installed on a system with at least 128 megabytes of RAM, a graphics card and monitor capable of displaying 1024 by 768 pixels or higher, and at least a 16-bit 

color display.

With the Java run-time engine installed, the GCLAS installer (which can be obtained from the USGS Water 

Resources Applications Software Web site at http://water.usgs.gov/software/surface_water.html) can be run by typing 

java -jar gclas_install_1.05e.jar2 in a DOS or Unix window from the directory in which the jar file resides. Alternatively, with some operating systems (such as Windows) the GCLAS installer can be run by double left-clicking on the 

installer jar file. Proper installation requires that the person doing the installation have sufficient rights to create and 

write to directories where the GCLAS program and data will be stored.

After the installer has been started, the following windows will appear. (Note: The installation shown is for a 

computer with the Windows operating system. A Unix installation will result in a similar sequence; however, the installation paths will be different, and no option will be given to create a program group.)

1

Although GCLAS should run on a variety of operating systems, testing of GCLAS has been predominately limited to the 

Microsoft Windows and Sun Solaris operating systems.

2

As of this writing (May 2006), the current version of GCLAS is 1.05e. As new versions become available, the GCLAS 

installer’s name will change to reflect the new version.
Installing GCLAS 3

Click the Next button.

Click on the radio button to accept the terms of the license agreement.
4 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

Click the Next button.

Accept or change the default installation path, then click the Next button.
Installing GCLAS 5

If the installation path does not exist, a pop-up message will inform you that the directory will be created. Click the 

OK button to proceed. 

Choose whether you want to install the optional data pack (by checking or unchecking the adjacent box), then click 

the Next button. The data pack contains data input templates and sample input data sets.
6 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

Accept the default menu program group for the shortcut (recommended) or supply a different program group, then 

click the Next button. Shortcuts can be created for the current user (the user installing GCLAS) or for all users (if the 

user has sufficient rights to do so). 

The installation progress will update and a window similar to that above will be displayed. Click the Next button.
Getting Started with GCLAS 7

If the installation was successful, a window similar to that above will be displayed. Click the Done button to close the 

window. Optionally, an XML install script can be created by left-clicking the Generate an automatic installation 

script button. If, for example, the name autoinstall.xml is given for the install script, it can be copied into the same 

directory as the GCLAS installer on another machine, and then an identical install can be done without having to step 

through the prompt windows by issuing the command java -jar gclas_install_1.05e.jar autoinstall.xml. 

If installation is done on a computer running the Unix operating system, a symbolic link to the gclas file in the 

bin directory of the GCLAS installation should be established in the user’s path. For more information, see the 

unix_readme.txt file that is created in the gclas directory during installation on a Unix system.

A current version of GCLAS can be installed over an existing version. If that is done, the installer will present 

a warning indicating that the install directory already exists and requesting that the user verify that they wish to overwrite the existing files. Because more than one version of GCLAS can be installed on a computer at the same time, it 

is not necessary to overwrite older versions of GCLAS unless desired.

Getting Started with GCLAS

Starting the Program on a Computer Running the Windows Operating System

Installation of GCLAS on a computer running the Windows operating system by default will add “USGS” to 

the list of programs that you run from the Start menu. To start GCLAS,

• go to the Start menu and select Programs. 

• drag down to USGS and select GCLAS 1.05e from the menu that pops up to the right. 
8 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

A DOS window may open as GCLAS starts up. The GCLAS interface will appear shortly after that. You will 

probably want to maximize the GCLAS window when working with GCLAS. 

Note: If the GCLAS window appears coarse or fuzzy, check the screen resolution (also called “screen area”) to 

ensure that it is set to at least 1024 by 768 pixels. GCLAS requires a resolution of at least 1024 by 768 pixels for its 

display.

Starting the Program on a Computer Running the UNIX Operating System

With a standard installation of GCLAS on a UNIX machine, you should be able to start the program by typing 

the command gclas.

Importing Data for Analysis — A Short Example

Data can be imported into GCLAS from any local or networked file system. For purposes of getting started, 

however, a practice data set comes as part of the GCLAS installation. The following steps outline how to import one 

of the practice data sets:

1. From the File menu, select Import (or use the keyboard shortcut shift-i). This will open a file browser window. 

2. Using the Look In pick list at the top of file browser window, navigate to the data subdirectory of the GCLAS 

installation. In most PC-Windows installations, this will be on a local hard drive (probably C:\) in Program 

Files\USGS\gclas\data. With a standard UNIX installation, the practice data set can be found in the directory 

/usr/opt/wrdapp/gclas. 

3. After you have located the data subdirectory, select the file big.darby.sed.98 (a card-image file containing sedimentconcentration data) and left-click the Import button to load the concentration data into GCLAS. 
Getting Started with GCLAS 9

4. Repeat the above process and select and load a streamflow unit-values file (big.darby.bcard.u.98; the concentration 

file and streamflow unit-values file must be from the same water year). Note: It is also possible to load daily values 

of streamflow in the daily-values card-image format. 

5. Locate the folder and file-display tree in the left-hand panel at the top of the GCLAS window. Expand the tree by 

double left-clicking the folder icon that has a station number as its label or by single left-clicking the toggle icon 

to the left of the folder. You will see nodes (file names) for any sediment and streamflow data that have been loaded. 

6. Now, left-click the folder icon associated with the concentration file. The name of the concentration node should 

be highlighted. 

7. Click the right mouse button and choose the option to Create/Edit GCLAS year. 
10 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

8. A window will appear (as shown below), and the dialog box at the bottom of this window will explain how to proceed. Either right-click in the plain white area of the window then select Create/Edit GCLAS year or left-click 

the button labeled Create/Edit GCLAS year. 

9. The Param and Year tab in the window will become active, as shown below. left-click the concentration parameter 

that you intend to work with (it will be highlighted when selected) and select the water year and load3

 unit. After 

the parameter, water year, and load unit have been selected, left-click the Next button. 

3

The term “load” refers to the mass or volume of material that is transported in a stream without implicit consideration for the

rate of transport. The mass or volume rate of transport (for example tons per day) is actually a discharge. Because it is common to 

discuss the load for a given time period (for example the load for a day) and because it is also common to refer to streamflow as 

discharge, the term “load” will be use in this report and in GCLAS to refer to either the mass or mass rate of transport, and the term 

“discharge” will be used solely to refer to streamflow.
Getting Started with GCLAS 11

10. The Daily Discharge tab will become active as shown below. If no daily discharge data have been imported prior 

to this step, then no data-set names will appear in this tab. Loading of daily-values data is optional. Daily discharge 

data are not used for purposes other than display. If one or more daily discharge data sets have been imported, you 

can select one of the data sets and parameters and then left-click the Next button. Otherwise, left-click the Skip

button. 

11. The Discharge tab will become active as shown below. Select the data-set name and parameter for the unit streamflow data then left-click the Finish button. Once the Finish button has been selected, GCLAS will read the data 

sets and create the graphs and tables used during the GCLAS session. The time required to read the data sets and 

create the graphs and tables depends on the size of the data sets and on speed and memory capacity of your computer. Commonly, the time required ranges from about 5 to 30 seconds. 

You are now ready to explore more features of GCLAS.
12 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

Importing/Opening Data Files

Import Command

The Import command (from the File menu; see below) is used to import plain-text (ASCII) data (either in cardimage format or GCLAS tab-delimited “gcl” format) into GCLAS.

After you select Import on the menu shown above, an import window will pop up (shown below); from here, 

you can navigate to the directory containing the data that you wish to import. Make sure that the file type of the file 

that you wish to import has been selected from the pick list at the bottom of the import window (as in the example 

below) or else the file to be imported may not be displayed as a possible selection.

After a GCLAS year has been established (either by creating it or editing a GCLAS year that had previously 

been created), additional water-quality and (or) streamflow data can be imported and ultimately used as reference 

curves. References curves are discussed later in the section titled “Using Reference Curves.” Data imported after a 

GCLAS year has been established do not have to be for the same water year as the GCLAS year.

Streamflow Data

GCLAS can read streamflow time-series data in the USGS National Water Information System (NWIS) dailyvalues and unit-values card-image formats. (See Appendix 4 for a description of these formats.) There is one exception 
Importing/Opening Data Files 13

to the unit-values card-image format described in Appendix 4. If the number of readings per day for streamflow is 1440 

(corresponding to a 1-minute time interval), then a “Q” must be entered in column 31 of the first (and only the first) 

B-card image in the data set.

Water-Quality Data

GCLAS can read water-quality data in an ASCII-delimited “gcl” format and in the SEDCALC 2- and B-card 

image (SEDATA) format. (See Appendix 1 for description of SEDATA format.) The USGS Sediment Laboratory Environmental Data System (SLEDS) can output data in the 2- and B-card image format for entry into GCLAS.

At present, GCLAS is not designed to facilitate direct entry of measured concentration data from the keyboard, 

so all measured data must either be output from a USGS database or assembled in another application (such as SEDCALC, a spreadsheet, or an editor) and then imported into GCLAS. Microsoft Excel spreadsheet templates (called 

input_template.xls and input_template2.xls) for constructing concentration data files are available and are included as 

part of the GCLAS installation (in the folder or directory named “data”). The templates differ only in the input formats 

used for dates and times. 

Figure 1. Sample Excel-based input template for creating GCLAS gcl input files.

Figure 1 shows part of a simple Excel-based input template, with line numbers on the left and letters designating 

columns on the top. Lines that begin with the “#” symbol in figure 1 are ignored by GCLAS with the exceptions of the 

station number, name, and separator, which are required entries. The station-number field is intended to contain an 8- 

or 15-digit station identifier. Station numbers are also present in other input-file formats, thereby facilitating the proper 

linkage of data from different files. The contents of the name field appears in the GCLAS file tree panel (discussed 

later) in association with the data contained in the file. Finally, the separator entry must be set to “tab” or “comma” to 

indicate the character that is used to delimit columns of data.

The keyword entries on line 12 of figure 1 identify the contents of data in the columns below. Figure 1 shows a 

small subset of the valid keyword entries. (Appendix 2 (p. 45) includes a complete list of keywords, formats/codes, 

and domains, where applicable.) Below each keyword entry is a format or code. The format or code dictates the format 

and (or) domain of the data that follow below in the column. The data must conform exactly to the indicated format 

and (or) domain for GCLAS to successfully read and interpret the data. 
14 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

To use either spreadsheet template included with the GCLAS installation, do the following:

• Open the spreadsheet template in Excel. It is recommended that you make a copy of the original template 

in case you accidentally overwrite the template. Depending on your version of Excel and security settings, 

Excel may provide a security warning similar to that shown below:

It is recommended that you enable macros. It is not essential that macros be enabled to use the templates, but 

enabling macros will make saving your input data easier.

• Fill in the header data in column B. Fill in creation date (mm/dd/yyyy format preferred), creator, station 

number, and file name in their respective rows, and choose between tab or comma delimited on the separator 

pick list. Note that the cells with red triangles in the corner will display instructions when you “mouse over” 

then (pause the cursor over them). 

• Fill in the body of the spreadsheet. Fill in date and time (columns A and B in fig. 1) in the format specified 

on line 13. Enter the sample representation and sample collector using the pick-list options given. (Mouse-over 

instructions in the column headings list the options.) Enter numerical concentration values for each sample in 

the column labeled “p80154Value,” where 80154 is the five-digit NWIS parameter code for suspended-sediment concentration. NWIS parameter codes for parameters other than suspended sediment also can be used. 

In addition to the standard NWIS parameter codes, generic parameter codes can be used within GCLAS 

(table 1).

If macros were enabled, once you have entered your data, you can save a copy of the Excel spreadsheet as well 

as a tab-delimited or comma-separated variable file (depending on the separator type specified in the header area of 

the Excel file) by left-clicking the Create gcl file button. The files that are created are named using the value contained 

in the name cell (cell B9 in fig. 1) as a prefix and “.xls” (for the Excel file) and “.gcl” (for the comma- or tab-delimited 

Table 1. Generic parameter codes that can be used within GCLAS.

Parameter 

code Description

99900 Generic concentration, mg/L (milligrams per 

liter)

99991 Generic concentration, mg/L (micrograms per 

liter)

99992 Generic discharge, t/d (short tons per day)

99993 Generic discharge, lb/d (pounds per day)

99994 Generic discharge, kg/d (kilograms per day)

99995 Generic discharge, Mg/d (megagrams per day)
Importing/Opening Data Files 15

file) as the suffixes. If macros were not enabled for the input templates, once you have entered your data in Excel, leftclick on File in menu bar and then left-click on the Save as option. A file window will open with a pick list titled “Save 

as type” at the bottom. Choose Text (tab delimited) or CSV (comma delimited) depending on the separator type that 

you entered in the header area of the Excel template file. Enter a name for the file (use the same file name that you 

specified in cell B9 of the Excel file), and then left-click on the Save button4. Unless you placed the file name in quotes 

(for example, “filename.gcl”), Excel will append an extension of “.txt” or “.csv” to the file, depending on the format 

in which the file was saved. The extension of the newly saved tab- or comma-delimited file (not the Excel file) should 

be renamed to “.gcl” if the file was saved with another extension. (Note: Some versions of Excel occasionally omit 

end-of-row delimiters on rows where there is no value in the last column. The omission does not occur in all cases, but 

GCLAS may not read the data properly if the delimiters are omitted. To avoid this problem, make sure that the last 

column of data is one that contains an entry for most rows.)

Open Command

The Open command (from the File menu) is used to open a previously created GCLAS project file. A GCLAS 

project file, which has an extension of “.gpf”, is a special file format that GCLAS creates (using the Save As option 

on the GCLAS File menu); this file can contain all input data, coefficient information, and computed loads associated 

with a GCLAS session.

Once you have opened a GCLAS project file, you must select the data node corresponding to the concentration 

parameter from the file-tree panel (in the upper left corner of the GCLAS display). Select the node by left-clicking the 

toggles in the file-tree panel until the concentration node is visible, then left-click the concentration node, causing the 

node to be highlighted as shown in the example below:

After the concentration node has been selected, click the right mouse button (with the cursor over the node) and 

choose the option to Create/Edit GCLAS year (example shown below) by left-clicking the option.

4

It is also recommended that the file be saved in Excel format to facilitate future addition of or changes to data.
16 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

A new window will appear (example shown below) positioned to a tab labeled Edit/create. left-click the row 

corresponding to the water year that you wish to edit or view, then left-click the Edit GCLAS year button. Once that 

is done, the graph and tabular views of the selected data will be displayed, and the project data can be edited or viewed.

Overview of GCLAS Window and Panel Interface

Once data have been imported/opened in GCLAS and the GCLAS year has been created, you'll see a multipanel 

display showing the data in graphical and tabular formats. As a new user of GCLAS, you'll be confronted by two challenges: (1) learning the functions of all parts of the main GCLAS window and (2) learning to manipulate the various 

panels within the window, which differ slightly from other windows-type interfaces you may be familiar with. This 

section tackles both challenges in turn. Read this section carefully while looking back frequently at the initial layout 

of the main window. (Do this before you resize or reposition panels.) This will help prevent the attendant frustration 

of searching for missing panels hidden behind other panels. Also, maximize the GCLAS window to fit the whole monitor screen; this will minimize the need for resizing panels.
Overview of GCLAS Window and Panel Interface 17

Organization of the GCLAS Display

Initially, seven panels are displayed in the main window. In addition, a window labeled “Ref. curves (Transport)” is minimized and shows as a small rectangle in the lower left corner of the main window.

Figure 2. Schematic of GCLAS main window showing panel arrangement.

The upper third of the main window (fig. 2) contains two panels:

• At the left is the file tree and time-series overview panel. Three views of this panel are available by left-clicking 

on the icon tabs at the panel's right side. The folder and file view (top tab) shows the files that you've loaded 

into GCLAS and the folders that they're stored in, and it allows you to pick and choose the data to display and 

work on. The graph view (middle tab) shows an overview graph of your time-series data. The information 

view (bottom tab), when fully operational, will provide miscellaneous information about the GCLAS year 

being worked. 

• At the right is the information panel, which presents startup information at the beginning and then shows information about specific data points when you're actually working with your data. 

The middle third of the main window contains three panels:

• At the left is the working-graph panel. This panel is where estimated concentration data can be edited directly 

from a graph display by using the mouse to add and remove data points, shift curves, and so on. 

• Two vertically stacked panels are at the right of the working-graph panel. The top one is the curve-label panel, 

which displays a color-coded list showing the relation between points and curves in the graph and the timeseries data represented, plus information about attributes of the data being displayed and which elements of 

the display can or cannot be manipulated. 

• Immediately below the curve-label panel is the tabular-data panel, which displays the combined streamflow 

and concentration data in tabbed tables. Changes made to the tabular-data display are immediately reflected 

in the working graph and vice versa. 

File tree and time-series

overview panel Information panel

Working-graph panel

Curve-label panel

Tabular-data panel

Coefficient and load panels
18 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

An alternative configuration of the preceding three panels is available by left-clicking the panel orientation button in the upper right corner of the working-graph panel. Clicking this button changes the orientation of the working-graph and tabular-data panels from side-by-side to vertically stacked. The many tools and functions available in 

these panels are discussed in the section titled “Adding and Editing Water-Quality Data” on page 19.

The bottom third of the main window, which is used for computing and applying cross-section coefficients and 

computing loads, contains two panels whose functions change, depending on which of the tabbed folder views (Calculate Coefficients, Apply Coefficients, or Compute Loads) has been selected. Details about this panel are given in 

the sections titled “Analyzing and Applying Cross-Section Coefficients” and “Computing Loads.” 

Transport-Relation Window

Figure 3. Transport-relation window.

When maximized, the transport-relation window (fig. 3) shows a scatterplot of concentration as a function of 

streamflow for all non-estimated concentration data in the input data set that can be used to help estimate and fill in 

periods with missing data. Double left-click anywhere on the minimized form of this window (a small rectangle initially in the lower left corner of the GCLAS main window) to maximize it. To minimize it again, left-click the small 

square with an arrow pointing to it (upper right corner of the maximized window). Details about use of this window 

are given in the section titled “Using the Transport-Relation Window to Aid Estimation” on page 27.

Working with GCLAS Panels, Tabs, and Buttons

The GCLAS windows (main window and transport-relation window) work similarly to windows on a PC or 

UNIX machine. You can, for example, drag them around on your computer screen, and you can minimize them by leftclicking on a small box in the upper right corner of the frame. Panels, however, behave differently. You cannot drag 

them around the screen like you can windows, but you can resize them in two ways:

• Left-click any edge of the frame of the panel and drag that edge to expand or contract the panel by as much as 

you wish, up to the panel's horizontal or vertical limit. You will know when the cursor is over a draggable edge 

because it changes to a horizontal, vertical, or slanted double-headed arrow. The orientation of the doubleheaded arrow indicates the directions in which the edge can be dragged. 
Adding and Editing Water-Quality Data 19

• Left-click the small arrows on the frame to maximize the panel within its section of the main window (outward-facing arrow) or return the panel to its former size (inward-facing arrow). 

If a panel disappears when being resized, it most likely is hidden behind another panel. If that happens, uncover 

the hidden panel by sequentially resizing panels that normally are adjacent to it. Once you get the hang of the panel 

arrangement, you'll find that it's convenient to hide unused panels by sliding panels of current interest in front, thereby 

maximizing your active working space.

Tabs are another important feature of certain GCLAS panels. They look similar to index tabs in a three-ring 

notebook or on manila folders. You can use tabs to locate and display different views of a multipart panel. 

Buttons, which are used to execute common functions, are included at the top or side of some of the panels, and 

they work much like buttons do in other windowed software.

Adding and Editing Water-Quality Data

Analyzing and editing water-quality data primarily involves the panels in the upper two-thirds of the main 

GCLAS window (fig. 2). Data shown in most graphs and tables are dynamically linked so that modifications to data 

in one panel are automatically reflected in the other panels. For example, if an estimated concentration value is modified in the tabular-data panel, its position in the working graph is automatically updated, and vice versa. The curvelabel panel also is synchronized with the working-graph and tabular-data panels, helping you distinguish between 

curves and showing what data manipulations are enabled or disabled.

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

On the top left panel is a tab with a graph icon . left-click on this tab and you will see an overview graph 

showing a streamflow curve (in blue) and a concentration curve (in red) for the GCLAS year. When you see the overview graph, move the cursor into the white graph area and press and hold the left mouse button; then drag the mouse 

to create a box that spans at least 15 days on the graph (fig. 4). When you release the mouse button, the working graph 

will be zoomed in, and a box showing the extent of the zoomed view will be displayed (fig 4). Repeat this procedure 

if you wish to see a different part of the GCLAS year in the working graph

Figure 4. Time-series overview panel.
20 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

Note the two buttons at the bottom right of the overview panel (fig. 4). The one on the right, with the box-andaxis icon , lets you zoom the overview graph to the currently defined zoom box. The one on the left, with the home 

icon , takes you back to the default water-year view.

Figure 5. Working-graph panel.

Note the shape of the symbols in the working graph:

• A rectangle means that the data point is for a sample whose concentration is representative of the mean concentration in the cross section (for example, a sample collected by integrating over the width and depth of the 

stream). 

• An X means that the data point is an estimated value. 

• A triangle means that the data point is from a sample collected at a point or single vertical. 

The zoom features operate within the working graph in a fashion similar to that of the overview panel. If you 

move your cursor into the working graph, then press and hold the left mouse button and drag to create a box, the working graph will be zoomed to include the area bounded by the box, and the overview graph will update to display a box 

showing the extent of this zoom. Additionally, a button on the toolbar immediately above the working graph with a <<

symbol will become enabled. left-click on the << (back) button to return to the previous zoom view. Now, left-click on 

the >> (forward) button to return to the newer zoom view. GCLAS allows you to go back to multiple previous zoom 

views and forward again.

If you wish to pan the GCLAS curve from the current zoom view, use the arrow buttons on the toolbar 

 to shift the working-graph view vertically or horizontally. The arrow keys on the keyboard can also be 

used to pan the current zoom view.

If you wish to go back to the default water-year view, use the button at the extreme left of the toolbar, with the 

home icon .

If you wish to rescale the y-axes of the curves to fill the entire working-graph frame, use the maximize scale 

toolbar button . The individual y-axes (corresponding to different parameter or units) cannot be scaled independently of one another.
Adding and Editing Water-Quality Data 21

Adding/Editing Estimated Values in the Working-Graph Panel

To add estimated values in the working-graph panel, position the cursor to the desired location within the graph 

and then, while holding down the shift and control keys, click the left mouse button. The x and y coordinates of the 

cursor are tracked continuously in the working graph and displayed in the lower left corner of the panel. (See fig. 5.) 

The coordinate information is particularly useful when you're graphically adding estimated values to help ensure that 

estimates are added at or near the desired concentration and time coordinates. If after adding an estimated data point 

you determine that it is not at the intended concentration or time coordinate, you can modify the point in two ways:

• Remove it. Click on the point with the left mouse button to select it, then click on the point with the right mouse 

button to bring up a small two-item menu and select Remove Pt(s). 

• Modify its location. Left-click on the point and drag it vertically (up or down) in the working graph or edit the 

time or concentration in the tabular-data panel. Time coordinates of a point cannot be edited by dragging; however, they can be edited in the tabular-data panel. To edit time or concentration values of estimated data in the 

tabular-data panel, you must double left-click in the cell to begin editing and press the Enter key to register 

the edit.

Extra care should be used when adding estimated values at concentrations near zero because negative concentrations 

can result if the mouse is slightly out of position when its button is clicked to register the value. GCLAS does not prevent entry of negative values, nor does it give any warning of their presence.

Left-click a data point in the working-graph panel to find and highlight the corresponding data-point entry in 

the tabular-data panel and vice versa. This feature can be useful when two points of interest plot very close to each 

other, too close to effectively use the mouse to select both; you can select one of the points on the graph, then use the 

table to select the other point.

The text that appears to the right of the button bar (fig. 5) contains hints for use. The phrase “shift cntrl click: 

add pt” is intended to remind the user that an estimated value can be added by holding down the shift and control keys 

on the keyboard while left-clicking in the working graph. Similarly, the phrase “rect-zoom” is intended to be a reminder 

that you can zoom in the graph windows by holding down the left mouse button and dragging to enclose the intended 

zoom extent within the rectangle that is drawn as the mouse is moved.

Setting the Default Representation Type of Estimated Values

When estimated values are added, they are assigned a representation type of “cross section,” “single vertical,” 

or “point.” The representation type is used to determine which, if any, cross-section coefficients can be applied to the 

value. Samples with a representation type of “cross section” are assumed to be representative of the mean concentration 

of that constituent within the stream cross section. As a consequence, cross-section coefficients (other than 1.0) are 

never applied to samples with a representation type of “cross section.” Samples with a representation type of “single 

vertical” or “point” are not assumed to be representative of the mean concentration of that constituent within the stream 

cross section. Sample concentrations with these representation types can be modified by application of coefficients of 

the identical type. A single data set can contain samples of one, two, or three representation types. 
22 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

By default, GCLAS assigns a representation type of “cross section” to newly estimated values; however, the 

default representation can be changed for the duration of a GCLAS session by choosing a different representation from 

the Options menu shown below:

Left-click the radio button next to a representation type to change the default representation type. The change 

in default representation type will affect only those estimated values that are added subsequently within the current 

GCLAS session; the representation type always defaults to Cross Section at the start of a GCLAS session. Any estimated values that were added before the change in default representation type will retain the representation type 

assigned at the time they were added. If you wish to change the representation type of an estimated value that already 

has been added, you must follow the instructions given below for editing data in the tabular-data panel.

Editing Data in the Tabular-Data Panel

The tabular-data panel (fig. 6) displays data in a tabbed-folder format with different types of data and data from 

different sites organized in separate tabbed tables.

Figure 6. Tabular-data panel.

One of these tables has a tab with the concentration file name followed by the parameter code for the constituent 

of interest (for example, hellbranch.sed.03_80154 as shown in fig. 6). This table—referred to as the “GCLAS waterquality table” hereafter—contains both concentration data and streamflow data (machine interpolated, if necessary), 

and it is editable. The GCLAS water-quality table is divided into three or more sections that are organized under spanner headings. For example, the spanner headings shown in figure 6 are labeled Sample, interp:00060 (for interpolated 

streamflow), and 80154 (the parameter code for suspended-sediment concentration). Under each spanner heading is 

one or more columns containing data or metadata. Metadata may be important for some analyses, but it can be a distraction for others. Consequently, GCLAS was designed so that you can toggle between detailed and less detailed 

views of the data by left-clicking on spanner and (or) column headings. For example, after left-clicking the 80154 spanner heading shown in figure 6, the spanner heading expands to show all of the columns contained within it (fig.7), and 

the name on the spanner heading changes to reflect the text description corresponding to parameter code 80154. For 

additional data-viewing flexibility, you can reorder columns by dragging a column heading to another position within 
Adding and Editing Water-Quality Data 23

the same spanner heading. You can also use the scroll bars to navigate through the table and the slider tool (near 

the upper right corner of the GCLAS water-quality table) to adjust the spacing between rows for easier viewing.

Figure 7. Tabular-data panel showing expanded spanner heading.

When a constituent such as sediment is selected for working a record, subcolumns for cross-section coefficients 

and the adjusted concentrations that result from the application of the coefficients (the last two columns shown in fig. 7) 

are added to the table, and the curve that is plotted will reflect the coefficient-adjusted concentrations.

The other tabbed table contains streamflow data as contained in the original card-image file, and its tab label 

reflects the name of that data file; this table is for reference only and is not editable. To switch between tables, leftclick on the appropriate tab.

The GCLAS water-quality table contains a wealth of ancillary information (metadata) associated with each data 

value. Some of these metadata may have been placed in the table as default entries when external files were read in and 

the GCLAS year was created. Most of these entries, however, can be changed to match your knowledge of actual conditions or can be set to accurately represent added data. Some of the columns in the GCLAS water-quality table are 

self-explanatory, but others, especially those that have pick-list options, require some description.

Under the Sample spanner heading: 

• Representation (4 options). Sample-representation type includes cross section, point, single vertical, and 

unspecified. 

• Hydro Condition (7 options). Hydrologic condition includes choices for stable flow at various flow levels or 

for rising or falling stage. 

• Collector (4 options). Hydrologist, observer, automatic, unspecified. 

• Hydro event (12 options). Hydrologic event choices, including hurricane, flood, storm, routine sample, and 

others. 

• Method (7 options). Sample-collection method includes equal discharge increment (EDI), equal width increment (EWI), pumped, single vertical, grab, unspecified, and none. 

• QA Type (12 options). Quality-assurance type includes replicate, duplicate, composite, spike, and others. 

Under the 80154 (or comparably named concentration parameter) spanner heading: 

• Remark. The remark field is not currently implemented. 

• Usable (check box). This column allows you to stipulate that a value should not be used (by unchecking it). 

Unused values will continue to be displayed in the graphs and tables but will be ignored for all other purposes. 

• Status (5 options). The status field shows information about the quality-assurance status of the datum, consisting of the following options: awaiting review, presumed OK, accepted, rejected, and not reported 
24 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

• Type (2 options). The type field shows information about the source of the measurement with options of field 

or lab. 

• QA Type (12 options). Same options as under Sample spanner heading.

Data in the GCLAS water-quality table can be manipulated in three ways:

• Numerical data can be changed by double left-clicking on the table cell to enable editing. Position the cursor 

with a single left click, then delete, backspace over, or type in new numbers. Double left-click to highlight all 

data in the cell to delete or type over everything. Then press the Enter key to apply the change.

• Pick-list data can be changed by double left-clicking on the pick-list table cell, left-clicking on the desired 

entry from the pick list, and then left-clicking in any other table cell on the same line in the table and under 

the same spanner heading as the cell being edited. Alternatively, a pick-list selection can be registered by pressing the Enter key while holding down the Shift key.

• Date and Time data can be changed in a fashion similar to other numerical data; however, certain special editing characteristics are associated with these fields. Date and time editing functions are described in detail in 

Appendix 3 (p. 48). 

• Check boxes can be checked or unchecked by left-clicking twice and then pressing Enter.

As you change concentration or discharge values in the table, the curves and symbols in the working graph and 

the overview graph will reflect the changes accordingly.

Using the Curve-Label Panel

The curve-label panel (fig. 8) shows information about what data are being displayed and which elements of the 

display can or cannot be manipulated. It also is used to change settings that enable or disable certain editing features. 

Features of the curve-label panel are described below.

Figure 8. Curve-label panel.

Curve text label:

• Color coding of curve labels corresponds to that of the curves themselves. 

• Line through label name indicates that the corresponding data set is not displayed on the graph. 

• Order of curve labels in the list indicates and controls the order in which curves are plotted; the curve listed 

first is plotted on top. Reordering curve labels changes the plotting order. This can be done by left-clicking on 

a label and dragging it. (The cursor will change to a different symbol while the curve label is being dragged.) 

Symbols on icons to the left of the label:

• Circle and slash means that the curve will not respond to manipulation with the mouse. Absence of the 

circle and slash means that mouse manipulation is enabled. 
Adding and Editing Water-Quality Data 25

• Red (“active”) dot means that the curve is the active curve. The coordinates that are tracked in the working graph are those of the active curve.

• I-beam symbol means that the curve is editable. Absence of I-beam means that the curve cannot be edited. 

• Point symbol (an open circle in the lower right corner) means that symbols are displayed on the working 

graph. 

• Line symbol (a forward slash in the upper right corner) means that lines (curves) are displayed on the 

working graph. 

• Carets indicate whether a curve can be moved or has been moved . A slash through the caret indicates that the curve has been moved but cannot presently be moved. 

Pop-up menu accessed by right-clicking curve label text (fig. 9):

Figure 9. Curve label pop-up menu.

• Can Mouse enables or disables “mousing” (data-point manipulation with the mouse) for the curve of interest. 

For example, you might wish to disable mousing of a streamflow curve so that you can better manipulate a 

concentration curve if the two curves are close together. 

• Can Move enables or disables curve movement with the mouse. When enabled, the curve can be moved by 

pressing the control key and simultaneously left-clicking on a point on the curve and dragging with the mouse. 

(The middle mouse button also works on some UNIX machines.) 

• Reset Move restores the curve to its original position (and thus serves as an undo for a move). 

• Can Edit allows a curve/data set to be edited. 

• Hide Curve removes a previously displayed curve from the working and overview graphs. 

• Show Curve displays a previously undisplayed curve on the working and overview graphs. 

• Delete Curve eliminates the entry in the curve label list (so you'll need to recreate the curve from the file tree 

if you wish to bring it back). 

• Draw Lines plots a line between the points, colored to correspond to the color of the curve label. 

• Draw Symbols plots the measured data points as triangles or rectangles and estimated data points as X’s. 
26 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

• Curve Properties — this feature is not yet available. 

Grayed-out entries in the pop-up menu cannot be selected.

Using Reference Curves

Water-quality and (or) streamflow data that have been imported during a GCLAS session can be used as reference curves. Reference curves are time series that are used for comparative purposes. For example, turbidity time series 

are sometimes used to help estimate the shape of a sediment-concentration time series during periods when concentration data are missing or undersampled. Once a GCLAS year has been established, other time series that have been 

imported during the GCLAS session can be used as a reference curve by left-clicking on the corresponding node for 

the time series in the file-tree panel and then left-clicking on the Create Curve/s button as shown below.

The parameter and water year to be used for the reference curve must be selected in the window that pops up. As shown 

in the example below, left-click on the Create Curves button to finish creating the reference curve. The water year of 

the reference curve does not have to be the same as the GCLAS year. Irrespective of the water year chosen, the reference curve will always be plotted on the same timescale (ignoring the difference in years) as the GCLAS year. After 

the Create Curves button has been clicked, the reference curve will be displayed in the overview and working-graph 

panels. In addition, the reference curve will become the active curve. In general, you will want your primary concentration time series to be the active curve. In that case, double left-click on the entry in the curve-label panel for the 

primary concentration time series to make it the active curve. The active curve can be identified by a red dot in the 

upper right-hand corner of the icon that appears to the left of the curve label in the curve-label panel.
Using the Transport-Relation Window to Aid Estimation 27

Using the Transport-Relation Window to Aid Estimation

To compute accurate loads, the constituent time series must be drawn accurately. Most commonly, you'll need 

to estimate data for periods when measured data are lacking. Developing those estimates requires knowledge of the 

stream hydrology and of the transport characteristics of the constituent of interest.

The transport-relation window (fig. 3) shows a transport plot—a plot of concentration as a function of streamflow for data in the data set. GCLAS displays crosshairs in the transport-relation window that intersect at coordinates 

that are a function of the position of the cursor in the working-graph panel. Specifically, the streamflow (x) coordinate 

is set to the streamflow that is coincident in time with the position of the cursor in the working-graph panel, and the 

concentration (y) coordinate is set to the concentration value corresponding to the position of the cursor in the workinggraph panel. The crosshair display facilitates estimation of missing values by allowing you to consider ancillary factors 

and cues (such as observed recession characteristics) and at the same time see how well alternative estimates fit with 

previously observed transport characteristics.

GCLAS displays a single transport curve showing only unadjusted measured (not estimated) concentrations in 

the input data set. The fact that concentration data in the transport-relation window are not adjusted (that is, they do no 

reflect application of any coefficient relations) has important implications for its use. If the majority of concentration 

values in the data set are derived from samples collected at a single point or vertical, then it is best to use the transportrelation window for estimation before applying coefficient relations. If instead, the majority of concentration values in 

the data set are derived from samples collect by means of depth- and width-integrating techniques (such as EWI or 

EDI; see Edwards and Glysson, 1999), then coefficient relations should be applied before using the transport-relation 

window for estimation. 

If the input concentration and streamflow data files contain more than one water year of data, then the transport 

curve will show measured concentrations for all years over the multiyear range of flows. (However, with the exception 

of reference curves and reference-curve data, the overview graph, working graph, and tabular-data panel will reflect 

only the water year being actively worked.) 

The panel that contains the transport curve has basically the same layout as the working-graph panel. The buttons have the identical functions, and the display of coordinates shows the value of flow and concentration at the intersection of the crosshairs if the cursor is in the working graph or of the cursor if the cursor is in the transport-curve graph.

You'll see two other dynamically linked panels in this window:

• The transport-curve curve-label panel looks like the working-graph curve-label panel, but the labels describe 

the data shown on the transport curve and the range of values to which they apply. The icon symbols are the 

same as those in the curve-label panel, and an identical pop-up menu appears by right-clicking on the curve 

name. 

• The tabular transport-data panel lists the numerical data that are represented graphically in the transport 

curve. These data can be exported for statistical analysis outside GCLAS. (A right click on the table brings up 

the Report option, which allows you to write data displayed in the table to an rdb file.) 
28 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

Analyzing and Applying Cross-Section Coefficients

In essence, cross-section coefficients are used to correct for systematic bias in concentrations measured at a single point or vertical as compared to the true mean concentrations in the cross section. Cross-section coefficients commonly are determined from concentrations for one or more samples collected at a single point or vertical and one or 

more samples that are integrated over the width and depth of the cross section. Coefficients should be determined only 

from sets of samples that are collected close in time to each other and at streamflows that not appreciably different 

from one another. In the simplest case, the coefficient is computed by dividing the concentration obtained from a depthand width-integrated sample by the concentration obtained from a sample collected at a point or single vertical. After 

cross-section coefficients have been determined from sample sets collected from a representative sampling of seasons 

and streamflows, the analyst can view the coefficients as a whole to look for trends with respect to time and (or) streamflow. More detail about the computation of cross-section coefficients and their subsequent analysis can be found in 

Porterfield (1972).

Construction of cross-section coefficient relations can be complex. GCLAS includes a variety of tools to aid in 

(a) computing the cross-section coefficients, (b) assessing trends in the coefficients, and (c) visualizing and applying 

coefficient relations. In addition, GCLAS can track, store, and apply cross-section coefficients that apply to both single-vertical and point samples concurrently. Consequently, separate cross-section coefficient relations can be determined and applied, for example, in those instances where samples are collected by an automatic sampler and at a single 

vertical by an observer or technician. 

Selecting Samples and Calculating Sample-Based Coefficients

1. Using the working graph in combination with the tabular-data panel, locate a depth- and width-integrated (crosssection) sample and any point sample(s) or single-vertical sample(s) that you wish to relate to it. As with any calculation of cross-section coefficients, the samples to be related should have been collected relatively close together 

in time and at approximately the same flow. 

2. Select one of these samples by left-clicking either the symbol in the working graph or the corresponding row in the 

data table. 

3. Select the other sample(s) by holding down the control key while left-clicking (or holding the shift key and leftclicking to select a range of samples). 

4. Now look at the lower left panel in the main window. If the Calculate Coefficients tab is not already selected (as 

indicated by a darkening of the tab relative to the others), then left-click the tab to select it. 

5. Left-click the Get button to bring the selected samples into this panel. 
Analyzing and Applying Cross-Section Coefficients 29

6. Left-click the Calc. button to calculate the coefficient. The white boxes in the lower part of the panel will show the 

results and indicate the coefficient type (point or single vertical) as shown in the example below (fig. 10).

Figure 10. Get Coeffs. tab of the Calculate Coefficients panel.

7. Left-click the right-arrow button (->) to move the computed coefficient and supporting data into the holding area 

in the upper part of the adjacent panel. The illustration below (fig. 11) shows the entry above after it has been moved 

to the holding area (the upper part of the panel). 

Figure 11. Coefficient holding area (top) and coefficient relation area (bottom) of the Calculate Coefficients panel.
30 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

8. Repeat the above procedure for as many more sample sets as you wish to work with for the current GCLAS year. 

Notes:

• If you can see only one row of data when you're placing more than one coefficient computation in the holding 

area, either enlarge the holding-area panel slightly by dragging down the bottom border or use the scroll bar 

(which will appear whenever undisplayed rows of data are in the holding area) or do both. 

• If you wish to inspect the original sample values used to construct the coefficient data, left-click on the row of 

interest in the holding area and use the left-arrow button (<-) in the lower left panel to display the original sample data there. 

• To delete a coefficient placed in the holding area, right-click the row of interest in the holding area and then 

left-click the remove option in the pop-up menu. 

• To view how the coefficients in the holding area related to flow and time, left-click on the Graphs tab in the 

left-hand panel to see a display (fig. 12). This is a good way to spot errors as well as trends in the coefficients. 

If you need to correct an error, (a) left-click on the Get Coeffs. tab, (b) left-click the erroneous row in the holding area, (c) left-click the left-arrow button (<-) to bring the data back into the editing area, (d) correct the data, 

recalculate, and then send it back to the holding area with a left-click on the right-arrow button (->). The curvelabel panels on the Graphs tab (fig. 12) work in a fashion similar to that of the curve-label panels discussed 

earlier. In particular, it may be useful to turn off drawing of the lines (by right-clicking on the Coeff. entry and 

unchecking the Draw Lines box on the pop-up menu) to help visualize trends in coefficients.

Figure 12. Graphs tab of the Calculate Coefficients panel.
Analyzing and Applying Cross-Section Coefficients 31

9. After you've calculated all your coefficients for the GCLAS year and have moved them to the holding area, you 

have two choices before beginning to apply them to the record: 

• Move coefficients individually into the coefficient-relations area below the holding area by means of the Mv 

Down button. Coefficients that are moved into the coefficient-relations area also will appear in the coefficientrelations panel (located on the Apply Coefficients tab), where they can be used to create coefficient relations.

• Combine (average) similar coefficients by means of the Merge button; the merged data will be moved as a 

single row into the coefficient-relations area below the holding area. Note that the start time will be the earliest 

date and time among the coefficients merged, and the end time will be the latest; the streamflow will be the 

rounded average flow of the entries being merged, and the coefficient will be their average. 

Direct Entry of Coefficients

If you already know what coefficients you want to apply and don't need to calculate them in GCLAS, do the following:

• Left-click the Calculate coefficients tab if it hasn't already been selected. 

• Left-click the New button. 

• Select either Point or Single Vertical in the Coefficient types box. 

• Enter coefficient data in the five boxes at the bottom of the panel. (See fig. 10.) 

• Press the right-arrow button (->) to move the new coefficient to the holding area at the right; then see step 9 in 

the section titled “Selecting Samples and Calculating Sample-Based Coefficients.” 

Applying Coefficients as a Function of Streamflow

Use the following steps if you wish to adjust concentration data using a coefficient relation that varies as a function of streamflow:

1. Left-click the Apply Coefficients tab in the lower left panel after you've moved one or more coefficients down into 

the coefficient-relations area. The coefficients that were moved in the coefficient-relations area will be listed in the 

coefficient-relations panel. 

2. Left-click either the Point or the Single Vertical tab in the Application of coefficient relations panel (depending on 

which type of coefficient you wish to work with), then left-click on the New QC button (to create a new relation 

between streamflow and concentration). Immediately after clicking the New QC button, the panel labeled Q's influ-
32 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

ence on Coeff.s will change to look something like that shown below. 

3. The coefficient defaults to 1.00 for the entire year for both point and single-vertical samples (provided that this is 

the first time you've worked on this concentration file). 

4. To modify the default relation by adding coefficients that you have calculated, left-click the coefficient entry in the 

coefficient-relations panel (causing it to be highlighted; see example below), then left-click the Add button to add 

the entry into the graph and flow versus coefficient table shown in the left panel. 

5. To further modify the relation with coefficients that are not in the coefficient-relations panel, enter points directly 

on the graph by holding the shift and control keys and left-clicking the mouse. (This is exactly the same method 

used to add estimated concentrations in the working-graph panel.) You can adjust the coefficient in the same way 

as a concentration data point in the working graph, by either dragging with the mouse, removing the point, or editing the tabular representation to the right of the coefficient versus flow graph (left-click the field that you wish to 

modify). Figure 13 shows an example of the graph display after adding several coefficients. Note that, for the example shown in figure 13, a coefficient of 1.00 is applied at streamflows less than or equal to 140 ft3

/s, and a coefficient 
Analyzing and Applying Cross-Section Coefficients 33

of 1.54 is applied at streamflows greater than or equal to 4,380 ft3/s.

Figure 13. Panel showing cross-section coefficient as a function of streamflow.

6. To preview how the new coefficient relation will be applied, (a) make sure that curve for the point or single-vertical 

coefficient curves is set to be shown in the working-graph panel and (b) left-click the Show button in either the 

Apply Coefficients tab or the Application of coefficient relations panel. The coefficient curve in the working-graph 

panel (fig. 14) will change to reflect the constructed coefficient relation; however, the concentration curve will 

remain unchanged. 

Figure 14. Working-graph panel showing streamflow (red), concentration (dark blue), and cross-section coefficient 

(light blue) time series.
34 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

7. If the coefficient curve is acceptable and you wish to apply the coefficient relation to the concentration data, leftclick Apply in the Q’s influence on Coeff.s panel. If you want coefficients applied to estimated points, you must 

change their representation type to that of the coefficient type being applied. By default, estimated points are 

assumed to have a representation type of “cross section,” and so coefficients are not applied. The representation 

type is assigned at the time that an estimated value is added. The default representation type can be changed for the 

duration of a GCLAS session; however, that change affects only those estimated values that are added during the 

GCLAS session after the default representation type is changed. 

8. After a coefficient relation has been applied, make sure that the panel labeled Application of coefficient relations 

(fig. 15) displays the coefficient-relation icon and information describing the applied relation. 

Note that the identifier shown below the coefficient-relation icon is the same identifier shown in the identification 

field on the Apply coefficients tab (fig.13). If you don't see the entry, it may be necessary to expand the panel by 

dragging the bottom border down. Use the slider tool to expand or condense the rows containing coefficientrelation information to your liking. 

Figure 15. Application of coefficient relations panel showing a coefficient relation that varies as a function of 

streamflow.

9. If you applied coefficients to single-vertical concentrations and now wish to work with point samples (or vice 

versa), follow the preceding procedure, but first left-click the Point tab in the Application of coefficient relations 

panel. 

10. To create a new relation beginning with a coefficient entry in the coefficient-relations panel, left-click the coefficient entry and then left-click the New button to add the entry into the graph and table shown in the left panel; then 

follow steps 5 through 8 above.

Applying Coefficients as a Function of Time

When coefficients are applied as a function of time, GCLAS determines coefficients from relations specified at 

a beginning and ending time and then interpolates linearly (as a function of time) to determine coefficients at points in 

between. The following three steps are the same as for applying a coefficient as a function of flow. The steps after that 

differ somewhat because you create separate coefficient relations that vary with time, each of which applies over all 

ranges of flow.

1. Left-click the Apply Coefficients tab in the lower left panel after you've moved one or more coefficients down into 

the coefficient-relations area. The coefficients that were moved in the coefficient-relations area will be listed in the 

coefficient-relations panel. 

2. Left-click on either the Point or the Single Vertical tab in the Application of coefficient relations panel, depending 

on which type of coefficient relation you wish to work with. 
Analyzing and Applying Cross-Section Coefficients 35

3. A default coefficient of 1.00 is used for both point and single-vertical samples (provided that this is the first time 

you've worked on this concentration file). If the coefficient curve has been set to be shown, a straight-line curve 

representing the default coefficient of 1.00 will display in the working-graph panel. 

Selecting and Applying a Previously Calculated Coefficient

4. In the coefficient-relations panel, left-click the row of data that contains the desired coefficient, then left-click the 

New button in that panel. The relation should appear (as a straight line equal to the selected coefficient) on the graph 

to the left. 

5. Use the Start: and End: boxes (see fig. 13) to set the time range of the coefficient. (See “Appendix 3 — Date and 

Time Editing Functions” to learn about special functions for editing dates and times.) (Note: To set an approximate 

time range that you can later modify, left-click the range button in the working-graph panel and then leftclick in the working graph, dragging the cursor from the desired start time to the desired end time.) To apply the 

coefficient at a single point in time, you can set the beginning date and time that you want and then left-click on 

the take start button to make the ending date and time the same as the beginning date and time. 

6. Left-click Show to see how the changes made will affect the coefficient curve displayed in the working graph and 

the overview graph, then left-click Apply to apply the coefficient relation to the data. 

7. Once you've applied the coefficient for the chosen time (or range of time), an entry for that coefficient and time 

will appear in the Application of coefficient relations panel. 

8. Repeat the procedure with any additional previously calculated coefficients. 

Creating and Applying a New Ad Hoc Coefficient Relation

9. Left-click the New QC button in the Application of coefficient relations panel. A new horizontal curve, default 

coefficient of 1.00, will display in the Q’s influence on Coeff.s panel on the left, with a time range equal to the 

GCLAS year being worked. 

10. To change the coefficient from the default of 1.00, hold the shift and control keys and left-click the mouse to enter 

a new point. You can adjust the coefficient by either dragging with the mouse, removing the point, or editing the 

tabular representation to the right of the coefficient-versus-streamflow graph (left-click the coefficient field); you 

can ignore the entry for flow because, unless you change the curve from a horizontal line, the coefficient will apply 

over the full range of flows. 

11. Left-click Show to see how the change you made will affect the coefficient curve displayed in the working graph 

and the overview graph, then left-click Apply to apply the coefficient relation to the data. 

12. Once you've applied the coefficient for the chosen time (or time range), an entry for that coefficient and time(s) will 

appear in the Application of coefficient relations panel. 

13. Repeat steps 9–12 for any additional new coefficient relations. 
36 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

Linking Coefficient Relations by Time

14. In the Application of coefficient relations panel, left-click the icon for the first of two coefficient-time relations you 

wish to link, then left-click the second one while holding the control key. The Link by Time button should become 

active as shown in the example below. 

15. Left-click the Link by Time button. Within the Application of coefficient relations panel, a new icon indicating 

the linkage will appear between the two linked coefficient relations, as shown below. 

As illustrated below, the panel to the left of the Application of coefficient relations panel will change, displaying 

(a) a graph on top showing the coefficient-relation as a function of time over the linked period and (b) two graphs on 

the bottom showing the coefficients relations at the beginning (left) and end (right) of linked period. (The slider tool 

 allows you to change the flow for which the coefficient-versus-time relation is displayed. The graphs represent 

the bounding and time-varying coefficients applicable for the flow indicated in the box below the label “Q:”. Because, 

in this example, the bounding-coefficient relations are both applied as a constant over the full range of flows, moving 

the slider will not affect the top graph but will cause the vertical lines on the bottom graphs to move left or right as the 
Computing Loads 37

flow value of application is decreased or increased, respectively.)

16. Repeat steps 14 and 15 for any other pairs of coefficient relations that you wish to link. 

Applying Coefficients as a Function of Streamflow and Time

Constructing coefficient relations that vary with streamflow and time is just a special case of the techniques 

described in “Applying Coefficients as a Function of Time” (p. 34). The only difference is that the coefficient relations 

that vary as a function of time are not constant but instead vary as a function of streamflow. For any given point in time, 

GCLAS determines its corresponding streamflow (by interpolation, if necessary) from the streamflow time series and 

then computes coefficients for that streamflow from both streamflow-varying coefficient relations that bracket the 

point in time. GCLAS then determines the coefficient that should be applied at that time by linear interpolation (as a 

function of time) between the coefficients determined from the bracketing relations. Familiarize yourself with the techniques described in “Applying Coefficients as a Function of Streamflow” and “Applying Coefficients as a Function of 

Time,” then combine these techniques as necessary to get the desired effect on your data.

Computing Loads

At any time during the record-working process, you can compute daily, monthly, and annual loads in GCLAS, 

literally at the press of a button. If desired, you can easily recompute to test the effects of alternative analysis strategies

on computed loads. Load computations are performed by application of the mid-interval method (Porterfield, 1972) to 

concentration data interpolated (if necessary) to the same temporal frequency as the streamflow time series. Although 

concentration data do not have to be collected as frequently as streamflow, it is assumed implicitly that the constituentconcentration time series used by GCLAS adequately represents the true time-varying concentration. Generally, this 

requires that concentration data (or an appropriate surrogate from which concentration can be estimated) are collected 

relatively frequently.

GCLAS has the potential to compute loads for any constituent that is transported in water at measurable concentrations. At present, GCLAS contains no provision to explicitly handle censored (“less than” or “greater than”) data 
38 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

in the load-computation algorithm; consequently, it should not be used to compute loads of constituents that have an 

appreciable amount of censored values. GCLAS assigns censored values their censoring level when plotting or using 

the values to compute loads. 

To compute loads:

• Make sure that you have added all the estimated points and applied all the cross-section coefficient relations 

that you wish at this point. 

• Left-click the Compute Loads tab in the lower panel of the main GCLAS window. 

Figure 16. Options tab on the load-computation panel. 

• Left-click the Options tab in the lower right panel (fig. 16). The following pick-list options are available: 

• Interpolation mode (linear is the default and is recommended; log-transformed linear is provided only for 

the sake of backward compatibility with SEDCALC files (Koltun and others, 1994)) 

• Number of months of data displayed in the loads table (without having to scroll) 

• The timespan for load computation is specified by entering date and time values in the Start and End boxes 

(reset time changes the timespan to the entire water year). 

• Left-click compute if you're satisfied with the options. Daily load data will be displayed in the left panel. 

(Note: If the timespan for load computation includes partial days at the beginning or end of the time period, 

mean concentrations and loads for those partial days will be computed and displayed in the loads table on the 

Compute Loads tab. The partial-day values will also be included in monthly and annual summary values.) If 

compute w/UV is selected, in addition to displaying loads in the left panel, unit values of concentration and 

load will be written to files in the SEDATA card-image format. (See “Appendix 1 — SEDATA 2- and B-CardImage Formats” for a description of unit-values card-image format.) Selecting the compute w/UV button 
Saving Your Work 39

causes two windows to pop up in which the file names and locations of the concentration and load card-image 

output files must be specified.

Figure 17. Summary tab on the load-computation panel.

• Left-click the Summary tab (fig. 17) in the right-hand panel to see a monthly summary of the streamflow (in 

cfs-days), mean concentration (in the concentration parameter’s base units), and computed loads (in the load 

units selected when creating the GCLAS year). In addition, you can compute loads for other time ranges by 

left-clicking the following buttons: 

 to compute loads for the entire water year. 

 to compute loads for the current view in the working graph. 

 to compute loads for time range specified on the Options tab. 

Saving Your Work

The Save feature allows you to save an in-progress GCLAS session so that it can be resumed later. GCLAS does 

not automatically save sessions, so use the Save feature periodically as insurance against the consequences of a power 

failure or computer malfunction.

To save a GCLAS session that is in progress:

• Left-click File in the menu bar in the upper left corner of the main window, then left-click the Save option in 

the menu that pops up. 

• Enter a valid file name in the File name field. The extension “.gpf” (where gpf stands for GCLAS project file) 

automatically will be appended when the session is saved. 

• Left-click Save to save the file. 

• Repeat this procedure as often as desired to overwrite previous saves. 
40 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

To save a GCLAS session in a different project file (if, for example, you're experimenting with multiple analytical options), use the Save as command in the File menu (or use the keyboard shortcut shift-a).

Note: To reopen a GCLAS project file or open a different GCLAS project file, you'll need to exit GCLAS and 

restart it.

Exporting Data and Tables

Information can be exported from GCLAS in several forms, including GCLAS gcl files (delimited text files that 

contain data from the water-quality table), card-image files of computed concentrations or loads, and tables of computed values. Some of the export formats can also be read back into GCLAS by means of the Import command on the 

File menu (see page 12).

Exporting GCLAS gcl Files

• Start at the tabular-data panel. If you wish to export only some of the columns in the tabular data, make sure 

that only those columns are visible. 

• Right-click anywhere in the body of the table. A small menu will pop up with Reports being one of the menu 

options. left-click Reports, and a rdb report options window will pop up. The options on both tabs of the window are shown in figure 18. 

Figure 18. Tab views of the rdb report options window.

• Select the desired options from the pick lists grouped under the Output Choices and Formats tabs in the dialog box. Generally, you should use the defaults that are displayed, but you may want to change the following: 
Exporting Data and Tables 41

• Rows — choose either all or selected rows 

• Delimiter — choose tab, comma, or an exclamation point to delimit columns

• Date — choose from the following formats: yyyy mm d, yyyy/mm/d, mm/d/y hh:mm:ss, or julian

• Time — if the date format chosen above does contain a time field, choose hh mm ss or hh/mm/ss

• Left-click on export. The Export file window will appear; use it to name and save your exported file. The 

extension “.gcl” will be appended to the file name specified.

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

• Start at the computed loads table in the bottom left panel. Right-click anywhere in the body of the table to bring 

up the Reports command box (fig. 19), select cardExports, and then select the desired option to the right. 

Figure 19. Load table showing card-image export options.

The Export file window will appear; use it to name and save your card-image file. (Note: Daily loads and daily 

mean concentrations for days where the specified computation period or available data represent less than 23 hours 

will not be written to card images even though they appear in the GCLAS loading table.) A description of the dailyvalues card image format can be found in “Appendix 4 — Unit- and Daily-Values Card-Image Formats.”
42 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

Exporting Streamflow, Concentration and Load Data in Table Format

Start at the computed loads table in the bottom left panel. Right-click anywhere in the body of the table to bring 

up the Reports command box (fig. 20), and select Print Daily Load Report. 

Figure 20. Load table showing daily-load report option.

• The Export file window will appear; use it to name and save your daily load report. The daily load report is a 

text file that can be viewed or printed with any application suitable for viewing and (or) printing ASCII text 

(for example, Wordpad or Emacs). A small part of a daily load report is shown in figure 21.

Figure 21. Sample of daily-load report output.

Acknowledgments

The authors thank Tom McKallip, a former USGS employee who developed much of the code for GCLAS. We 

also thank Barry Hill (USGS, Hawaii), Denis O’Halloran (USGS, California), and Michael Roark (USGS, New Mexico), who provided technical reviews and suggestions to improve this report.
References Cited 43

References Cited

Edwards, T.K., and Glysson, D.G., 1999, Field methods for measurement of fluvial sediment: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 3, chap. C2, 80 p.

Koltun, G.F., Gray, J.R., and McElhone, T.J., 1994, User's manual for SEDCALC, a computer program for computation of suspended-sediment discharge: U.S. Geological Survey Open-File Report 94–459, 46 p.

Porterfield, George, 1972. Computation of fluvial-sediment discharge. U.S. Geological Survey Techniques of WaterResources Investigations, book 3, chap. C3, 66 p.

U.S. Geological Survey, 2003, User’s manual for the National Water Information System of the U. S. Geological Survey—Automated Data Processing System (ADAPS) U.S. Geological Survey Open-File Report 03–123, version 

4.3, 407 p.
44 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

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

SEDATA 2-card format

Column Description

 1 Enter a 2. The 2-card must preceded the B-cards.

 2 - 16 Station identification number (left justified)

17 - 28 Blank

29 - 33 Parameter code.

34 - 38 Statistic code.

39 - 80 Blank.

SEDATA B-card format

Column Description

 1 Enter a B. There will be one B-card for each unit value.

 2 - 16 Station identification number (left justified).

17 - 20 Calendar year. Four-digit number representing the calendar year

in which the observation was made.

21 - 22 Month. Two-digit number representing the month on which the

observation was made.

23 - 24 Day. Two-digit number representing the day on which the 

observation was made.

25 - 30 Time of the observation coded in columns 39-44.

Columns 25-26, hour (24-hour system)

27-28, minute

29-30, second

31 - 35 Enter 1440.

36 Remark code.

37 - 38 Blank.

39 - 44 Unit value for date and time listed in columns 17-30.
Appendix 2 — Keywords, Format Codes, and Value Domains for GCL Files 45

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

Files

Table 2-1. Time keywords and permissible format codes. 

[HH, hour; mm, minute; ss, second; MM, month; 

d or dd, day; yyyy, year]

Keyword Permissible format(s)

SampTime yyyy/MM/d

MM/d/yyyy HH:mm:ss

SampTime_Year yyyy

SampTime_Month MM

SampTime_Day dd

SampTime_Hour HH

SampTime_Min mm

SampTime_Sec ss

SampTime_Time HH:mm

Table 2-2. Sample metadata keywords, format codes, and value domains. 

Keyword

Format code

name code id

SampRepresentation Cross Section xSec I

Point pt. P

Single vertical sVrt S

Unspecified unsp U

SampHydroCond Not determined notDet A

Stable low stage lStage 4

Falling stage fStage 5

Stable high stage hStage 6

Peak stage pStage 7

Rising stage rStage 8

Stable, normal stage nStage 9

SampCollector Hydrologist hydr H

Observer obsr O

Automatic auto A

Unspecified unsp U
46 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

SampHydroEvt Spring breakup sprBr A

Under ice cover iceCov B

Glacial lake outbreak lakeBr C

Mudflow mudflw D

Tidal action tidal E

Dambreak damBr H

Storm strm J

Drought drght 1

Spill spill 2

Regulated flow rgltd 3

Snowmelt snMlt 4

Earthquake quake 5

Hurricane hurr 6

Flood fld 7

Volcanic action vlAct 8

Routine Sample rSamp 9

SampMethod Equal discharge increment EDI Q

Equal width increment EWI W

Grab Grab G

Pumped Pump P

Single Vertical sVrt S

None NA N

Unspecified Unsp U

SampQAType Other QA other B

Spike solution sSol 8

Spike 1 1

Blank blnk 2

Reference ref 3

Blind blnd 4

Duplicate dup 5

Replicate repl 7

Composite (time) Composite (time) H

Reference material Reference Material 6

Not determined noDet A

Table 2-2. Sample metadata keywords, format codes, and value domains.—Continued

Keyword

Format code

name code id
Appendix 2 — Keywords, Format Codes, and Value Domains for GCL Files 47

Table 2-3. Parameter keywords, format codes, and value domains. 

[XXXXX represents the five-digit National Water Information System parameter code]

Keyword

Format code

val name code id bol

pXXXXXValue real number1

1

Parameter values may be preceded by an E, <, or > to indicate that it is an estimate, the true value is less 

than the indicated value, or the true value is greater than the indicated value, respectively. Values preceded 

by a < or > are treated in GCLAS identically to uncoded values.

pXXXXXCoeff real number

pXXXXXAdjusted real number

pXXXXXStatus_Code Awaiting review await I

Presumed Ok Ok S

Accepted Accpt R

Rejected rjct Q

Not reported notR A

pXXXXXType_Code field Field F

Lab Lab L

pXXXXXQAType_Code Not determined noDet A

Other QA other B

Composite (time) tComp H

Spike 1 1

Blank blnk 2

Reference ref 3

Blind blnd 4

Duplicate dup 5

Reference Material refMat 6

Replicate repl 7

Spike solution sSol 8

Regular reg 9

pXXXXXUsable TRUE

FALSE
48 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

Appendix 3 — Date and Time Editing Functions

Table 3-1. Date-editing functions. 

Key Date Function

Home key Positions the cursor in the first position of the field.

End key Positions the cursor in the last position of the field.

Space There is no effect of pressing this key in the month and day fields. On pressing this 

key in the year field, it is changed to the default current year. Date-field separator 

characters are not deleted on pressing this key. 

Backspace On pressing this key in the month and day fields, it changes to some valid month and 

day, respectively. On pressing this key in the year field, it is changed to the current 

year. Date-field separator characters are not deleted on pressing this key. 

Delete On pressing this key in the month and day fields, it changes to some valid month and 

day, respectively. On pressing this key in the year field, it is changed to the current 

year. Date-field separator characters are not deleted on pressing this key. 

Left-Arrow key Moves the cursor to the left by one character, skipping separators.

Right-Arrow key Moves the cursor to the right by one character, skipping separators.

Up-Arrow Key Increments the part (day, month, or year) on which the cursor is positioned. The 

increment is cyclic, and it updates its super field. For example, if the mask is 

dd/mm/yyyy, the cursor is positioned on mm, and the month displayed is 12 and you 

press the Up-arrow key, then the month changes to 01 and the year is incremented 

by 1.

Down-Arrow Key Decrements the part (day, month or year) on which the cursor is positioned. The 

decrement is cyclic, and it updates its super field. For example, if the mask is 

dd/mm/yyyy, the cursor is positioned on mm, and the month displayed is 01 and you 

press the Down-arrow key, then the month changes to 12 and the year is 

decremented by 1.

Character Key [A-Z, a-z] Does nothing. Causes bell to ring on computer indicating invalid entry.

Digit Keys [0-9] Displays the digit at its cursor position, and the cursor position is incremented by 1, 

skipping over separators where they occur. Each field is checked for validity as it is 

typed. If the field is not valid, then the digit is ignored. For example, if the day field 

contains the value “11” and the cursor is positioned in front of the first 1, then typing 

an 8 results in the day field changing to “08” because “08” is the only valid day-field 

entry that yields a valid result. If a 2 were typed instead of an 8, then the first digit in 

the day field would be replaced by a 2 (because “21” is a valid day in any month), 

and the cursor is repositioned following it.
Appendix 3 — Date and Time Editing Functions 49

Table 3-2. Time-editing functions. 

Key Time functions

Home key Positions the cursor in the first position of the field.

End key Positions the cursor in the last position of the field.

Delete key Text selection — All the selected characters are deleted except for the separators.

No selection — The character at the current cursor position is deleted.

Backspace key Text selection — All the selected characters are deleted except for the separators. 

No selection — The character before the current cursor position is deleted.

Space Key Text selection — All the selected characters are deleted except the separators.

No selection — Part (hour, minute, or second) of the time at which the cursor is 

positioned is deleted. If the cursor is positioned on the separator, then the part 

preceding it is cleared.

Left-Arrow key Moves the cursor to the left by one character, skipping separators.

Right-Arrow key Moves the cursor to the right by one character, skipping separators.

Up-Arrow Key Increments the part (hour, minute, or second) on which the cursor is positioned. The 

increment is cyclic, and it updates its super field. For example, if the mask is 

hh:mm:ss, the cursor is positioned on mm, and the minute displayed is 59 and you 

press the Up-arrow key, then the minute changes to 00, and the hour is incremented 

by 1.

Down-Arrow Key Decrements the part (hour, minute or second) on which the cursor is positioned. The 

decrement is cyclic and it updates its super field. for example, if the mask is 

hh:mm:ss, the cursor is positioned on mm, and the minute displayed is 00 and you 

press the Down-arrow key then the minute changes to 59, and the hour is 

decremented by 1.

Character Key [A-Z, a-z] Does nothing.

Digit Keys [0-9] Text selection —All the selected characters are deleted except the separators, the 

digit at the current cursor position is displayed, and the cursor position is incremented 

by 1, skipping over separators where they occur.

No selection — Displays the digit at the current cursor position, and the cursor 

position is incremented by 1, skipping over separators where they occur. Each field is 

checked for validity as it is typed. If the field is not valid, then the digit is ignored. For 

example, if the hour field contains the value “15” and the cursor is positioned in front 

of the 1, then typing a 2 results in an invalid field because the hour field is interpreted 

as “25” (and so the 2 is ignored). In this case, if you wish to replace the “15” with an 

hour value of (for example) “22,” then select the entire hour field (so that it is 

highlighted) before typing.

Separator key When the user presses the separator key (“:”) and the cursor is not in the first column 

of a field, then the cursor is moved to the position following the separator. It the 

cursor is in the first column of a field, then the separator key does nothing.
50 User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)

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

Unit-values (2-card) card-image format

Column Description

 1 Enter a 2. The 2-card must preceded the B- or 3-cards.

 2 - 16 Station identification number (left justified).

17 - 28 Blank.

29 - 33 Parameter code.

34 - 38 Statistic code.

39 - 80 Blank.

Unit-values (B-card) card-image format

Column Description

 1 Enter a B. There will be one B-card for each set of up to 6 unit values.

 2 - 16 Station identification number (left justified).

17 - 20 Calendar year. Four-digit number representing the calendar year in 

which the observation was made.

21 - 22 Month. Two-digit number representing the month on which the

observation was made.

23 - 24 Day. Two-digit number representing the day on which the 

observation was made.

25 - 30 Time of the observation coded in columns 39-45. 

Columns 25-26, hour (24-hour system)

27-28, minute

29-30, second

31 - 35 Readings per day. Right justify, and number evenly divisible 

into 2880. If the number of readings per day for streamflow is 1440

(corresponding to a 1-minute time interval), then a “Q” must be entered in column

31 of the first (and only the first) B-card image in the data set.

36 - 38 Blank.

39 - 80 Unit value for six consecutive intervals of time. Each value is in 

a seven-column field (39-45, 46-52, and so on).
Appendix 4 — Unit- and Daily-Values Card-Image Formats 51

Daily-values (3-Card) card-image format

Column Description

 1 Enter a 3. There will be one 3-card for each set of up to 8 daily values.

 2 - 16 Station identification number.

17 - 20 Calendar year. Four-digit number representing actual calendar year

of data on the card.

21 - 22 Month. Two-digit number representing the month. 

For example, March is punched as 03, November as 11.

23 - 24 Card number. A two-digit number representing the fraction of the

month that the data were collected. 

This number is coded as follows:

Card no. Days

 01 1 - 8

 02 9 - 16

 03 17 - 24

 04 25 - 31

25 - 80 Daily values. Eight seven-column fields in which the daily values 

are entered for the designated days. The value should include 

significant digits to the right of the decimal point where needed.

Whole numbers need no decimal point. Blank fields are interpreted

as “no data available.”
G.F. Koltun, Michael Eberle, J.R. Gray, and G.D. Glysson—User’s Manual for the Graphical Constituent Loading Analysis System (GCLAS)—

Techniques and Methods 4-C1

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