Using the transport relation window to aid estimation

In order to compute accurate loads, you'll want to ensure that the constituent time series is 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 provides you with a transport plot--a plot of concentration as a function of streamflow for the measured concentration 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 working graph panel. The crosshair display facilitates estimation of missing values by allowing you to consider ancillary factors and cues (such as measured recession characteristics) and at the same time see how well alternative estimates fit with previously observed transport characteristics.

The current version of GCLAS displays a single transport curve showing all non-estimated concentrations (unadjusted) over the entire range of flows. If the concentration and streamflow data files being worked contain more than one water year of data, then the transport curve will show points for all years over the multiyear range of flows. (The overview graph, working graph, and tabular data panel will reflect only the water year being actively worked, however.) Other display options (such as partial years and rising or falling limbs of the hydrograph) are planned for future releases.

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.

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

• The transport-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 basically the same as those in the curve label panel, and they correspond to the same basic pick-list functions available by right clicking on the curve name. (See Using the curve label panel in Adding and editing concentration)

• 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 mouse click on the table brings up the Report option, which allows you to write data displayed in the table to an rdb file.)

Until additional functionality is available in future releases of GCLAS, your main use of the window will be as a visual reference, to see how an estimated data point will fit with the trend of measured data for the water year(s) loaded into GCLAS for a particular station.