Computing loads

At any time during the record-working process, you can compute daily, monthly, or annual loads in GCLAS, literally at the press of a button. Load computations are performed by application of the mid-interval method to concentration data interpolated to the same temporal frequency as the unit streamflow data. If desired, you can easily recompute to test the effects of alternative analysis strategies on computed loads.

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") data in the load-computation algorithm and consequently should not be used to compute loads of constituents that have an appreciable amount of censored values.

To compute loads:

• Make sure that you have added all the estimated points and applied all the cross-section coefficients that you wish at this point.
• Left click on the Compute Loads tab in the lower left panel of the main GCLAS window.
• Left click on the Options tab in the lower right panel. The following pick-list options are available:
  • Interpolation mode (linear is default and recommended; log-transformed linear is provided only for the sake of backward compatibility with SEDCALC files)
  • Number of months of data displayed in the loads table (without having to scroll)
  • Start and End boxes to set the range of dates for computing load (reset changes the range to the entire water year).
• Left click compute if you're satisfied with the options. Daily load data will be displayed in detail in the left panel.
• Left click on the Summary tab in the right-hand panel to see a monthly summary of the computed loads or to compute loads for other ranges of time:
  • To compute loads for the entire water year, left click the button with the home icon.
  • To compute loads for the current view in the working graph, left click on the button with the graph icon.
  • To compute loads for a specific range of date/time specified in the Options view, left click on the button with the parallel bars icon.
• If you wish, save the daily loads and/or daily mean concentrations in daily values card-image format so that eventually then can be imported into the NWIA database. (See Exporting data.)