Analyzing and applying cross-section coefficients

Construction of cross-section coefficient relations can be complex. GCLAS provides 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.

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 (cross-section) 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 on the symbol in the working graph or the corresponding row in the data table.
3. Select the other sample(s) by holding the control key while left clicking (or holding the shift key and left clicking to select a range of samples).
4. Now look at the lower left panel in the main window. Left click on the Calculate coefficients tab if it has not already been selected.
5. Left click on the Get button to bring the selected samples into this panel.
6. Left click on 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.
   
   

7. Left click on 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 shows several entries in the holding area (the upper portion of the panel).
   
   

8. Repeat the above procedure for as many more samples 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 scrolling arrows (which will appear whenever undisplayed rows of data are in the holding area) or do both.

• If you forget which original sample values were used to construct the coefficient data, just 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 erroneously placed in the holding area, right click on the row of interest in the holding area and then left click on the remove option.

• To view how the coefficients in the holding area relate to flow and time, left click on the Graphs tab in the left-hand panel to see a display as shown in the illustration below. 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 on the erroneous row in the holding area, (c) left click on the left-arrow button (<-) to bring the data back into the editing area, (d) correct the data and send it back to the holding area with a left click on the right-arrow button (->).
  
  

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 panel below the holding area by means of the Mv Down button.

   • Combine (average) similar coefficients by means of the Merge button; the merged data will be moved as a single row into the Coefficient relations panel below the holding area. Note that the start time will be the earliest date and time among the original coefficients and the end time will be the latest; the flow (Q cfs) will be the average flow of the entries being merged.

     
     Note: To delete erroneously moved or merged data in the Coefficient relations panel, right click on the row of interest and then left click on the remove option. To remind yourself which original coefficients made up a merged coefficient, left click on the merged coefficient row, and the original data rows will be highlighted in the holding area.

Hand-entering 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 on the Calculate coefficients tab if it hasn't already been selected.
• Left click on the New button.
• Select either Point or Single Vertical in the Coefficient types box.
• Modify data in the five boxes at the bottom of the panel, or enter new data overtop the existing data.
• Press the right arrow button (->) to move the new coefficient to the holding area at the right; then see step 9 above.

Applying coefficients as a function of streamflow

Use the following steps if you wish to adjust concentration data using a coefficient relation that varies with flow over the entire GCLAS year (water year):

1. Left click on the Apply Coefficients tab in the lower left panel after you've moved a coefficient (or multiple coefficients) down into the Coefficient relations panel. The Coefficient relations panel will change somewhat in appearance after the Apply Coefficients tab is selected but it will remain approximately in the same place.
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 you wish to work with) and then left click on the New QC button. The panel labeled Q's influence 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 on the coefficient entry in the Coefficient relations panel (causing it to be highlighted, see example below) and then left click on 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 as clicking to add estimated concentrations in the working graph panel.) You can adjust the coefficient in the same way as a concentration data point, 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 on the field that you wish to modify). The figure below shows an example of the graph display after adding several coefficients.

   
   

6. To preview how the new coefficients 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 on the Show button in either the graph-display panel or the Application of coefficient relations panel. The coefficient curve in the working graph panel will respond accordingly.
7. If you like what you see and wish to apply the revised coefficients to the concentration data, left click on Apply in the graph-display panel. If you want the 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 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 displays the coefficient-relation icon and information describing the applied relation (as shown below). 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 coefficient relation information to your liking.

   
   

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 left click on 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 on the coefficient entry and then left click on 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

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 on the Apply Coefficients tab in the lower left panel after you've placed a coefficient (or multiple coefficients) in the Coefficient relations panel. The Coefficient relations panel will change somewhat but will remain in the same place; the other two panels will change substantially.
2. Left click on either the Point or the Single Vertical tab, depending on which type of coefficient you wish to work with.
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 show, a straight-line curve representing the default coefficient of 1.00 will display in the working graph panel to the left.

To select and apply a previously calculated coefficient:

4. In the Coefficient relations panel, left click on the row of data that contains the desired coefficent and then left click on 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. To refresh the graph display and see the change(s), you may need to type control-l (or resize the panel slightly by dragging a border).
5. Use the tabular date and time display to adjust the time range of the coefficient. (See the quick reference section on special functions for editing dates and times.) (Note: To set a "ballpark" range that you can later modify, left click on the range button in the working graph panel and drag the mouse within the working graph to approximate the range you want.) To apply the coefficient at a single point in time, you can set the beginning date to the time 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 change you made will affect the coefficient curve displayed in the working graph and the overview graph, then left click on Apply if you're ready to apply that coefficient to the data. If you want the coefficients applied to estimated points, be sure that their representation type is set to that of the coefficient type being applied before you apply the coefficient relation.
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.

To create a new coefficient relation (using coefficients not previously calculated):

9. Left click on the New QC button in the Application of coefficient relations panel. A new horizontal curve, default coefficient of 1.00, will display in the 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 on 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 year-long coefficient curve displayed in the working graph and the overview graph, then left click on Apply if you're ready to apply that coefficient to the data. If you want the coefficients applied to estimated points, be sure that their representation type is set to that of the coefficient type being applied before you apply the coefficient relation.
12. 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.
13. Repeat steps 9-12 for any additional new coefficient relations.

To link coefficient relations by time:

14. In the Application of coefficient relations panel, left click on the icon for the first of two coefficient-time relations you wish to link, then left click on 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 on 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 on the left will change, displaying (a) a graph on top showing the coefficient-relation as a function of time over the linking period and (b) two graphs on the bottom showing the coefficients relations at the beginning (left) and end (right) of linking period. (The slider tool allows you to change the flow for which the coefficient relation is displayed. The graphs represent the bounding and time-varying coefficients applicable for the flow indicated in the box below the label "Q:". Since 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 flow rate 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 techinques described in Applying coefficients as a function of time. The only difference is that coefficient relations that vary as a function of flow are linked by time instead of coefficient relations that do not vary as a function of flow. 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.